Summary
Clinical characteristics.
Permanent neonatal diabetes mellitus (PNDM) is characterized by the onset of hyperglycemia within the first six months of life (mean age: 7 weeks; range: birth to 26 weeks). The diabetes mellitus is associated with partial or complete insulin deficiency. Clinical manifestations at the time of diagnosis include intrauterine growth restriction, hyperglycemia, glycosuria, osmotic polyuria, severe dehydration, and failure to thrive. Therapy with insulin corrects the hyperglycemia and results in dramatic catch-up growth. The course of PNDM varies by genotype.
Diagnosis/testing.
Persistent hyperglycemia (plasma glucose concentration >150-200 mg/dL) in infants younger than age six months establishes the diagnosis of PNDM. Molecular testing is recommended: identification of pathogenic variant(s) in ABCC8 or KCNJ11 can guide treatment.
Management.
Treatment of manifestations: Start rehydration and intravenous insulin infusion promptly after diagnosis. When the infant is stable and tolerating oral feedings begin subcutaneous insulin therapy. Children with pathogenic variants in ABCC8 or KCNJ11 can be treated with oral sulfonylureas; all others require long-term insulin therapy. High caloric intake is necessary for appropriate weight gain. Pancreatic enzyme replacement therapy is required for those with exocrine pancreatic insufficiency.
Prevention of secondary complications: Aggressive treatment and frequent monitoring of blood glucose concentrations to avoid acute complications such as diabetic ketoacidosis and hypoglycemia and reduce the long-term complications of diabetes mellitus.
Surveillance: Lifelong monitoring of blood glucose concentrations at least four times a day; periodic developmental evaluations. After age ten years, annual screening for chronic complications of diabetes mellitus including urinalysis for microalbuminuria and ophthalmologic examination for retinopathy.
Agents/circumstances to avoid: In general, avoid rapid-acting insulin preparations (lispro and aspart) as well as short-acting (regular) insulin preparations (except as a continuous intravenous or subcutaneous infusion) as they may cause severe hypoglycemia in young children.
Genetic counseling.
The mode of inheritance of PNDM is autosomal dominant for mutation of KCNJ11, autosomal dominant or autosomal recessive for mutation of ABCC8 and INS, and autosomal recessive for mutation of GCK and PDX1.
Individuals with autosomal dominant PNDM may have an affected parent or may have a de novo pathogenic variant. Each child of an individual with autosomal dominant PNDM has a 50% chance of inheriting the pathogenic variant.
The parents of a child with autosomal recessive PNDM are obligate heterozygotes and therefore carry one pathogenic variant. Heterozygotes for pathogenic variants in GCK and PDX1 have a mild form of diabetes mellitus known as GCK-familial monogenic diabetes (formerly known as MODY2) and PDX1-familial monogenic diabetes (formerly known as MODY4). At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier (or of having familial monogenic diabetes), and a 25% chance of being unaffected and not a carrier.
Prenatal diagnosis for pregnancies at increased risk is possible if the pathogenic variant(s) in the family are known.
Diagnosis
Suggestive Findings
Permanent neonatal diabetes mellitus (PNDM) should be suspected in individuals with the following laboratory and radiographic features.
Laboratory features
Persistent hyperglycemia (plasma glucose concentration >150-200 mg/dL) in infants younger than age six months
Features typical of diabetes mellitus (e.g., glucosuria, ketonuria, hyperketonemia)
Low or undetectable plasma insulin and C-peptide relative to the hyperglycemia
Low fecal elastase and high stool fat in infants with pancreatic aplasia or hypoplasia
Note: Measurement of hemoglobin A1c is not suitable for diagnosing diabetes mellitus in infants younger than age six months because of the higher proportion of fetal hemoglobin compared to hemoglobin A.
Radiographic features
Pancreatic hypoplasia identified on ultrasound, CT, or MRI examination
Note: Visualization of the pancreas in neonates may be difficult; biochemical evidence of pancreatic insufficiency (e.g., low fecal elastase, high stool fat) may help with the diagnosis in these infants.
Establishing the Diagnosis
The diagnosis of PNDM is established in an infant with diabetes mellitus diagnosed in the first six months of life that does not resolve over time. Molecular testing is recommended: identification of pathogenic variant(s) in one of the genes listed in Table 1 can guide treatment (see Management).
Molecular genetic testing approaches can include serial single-gene testing, use of a multigene panel, and more comprehensive
genomic testing.
Serial single-gene testing
Individuals with one parent with diabetes mellitus:
Sequence analysis of KCNJ11 first.
If no KCNJ11 pathogenic variant is found, sequence analysis of ABCC8 and INS
Individuals whose parents both have diabetes mellitus: sequence analysis of GCK and PDX1
Individuals without a family history of diabetes mellitus:
Sequence analysis of ABCC8 and KCNJ11 first (as identification of pathogenic variants changes management)
If no pathogenic variants are identified, sequence analysis of GCK and INS
Individuals with pancreatic insufficiency or agenesis without extra-pancreatic abnormalities:
Note: Deletion/duplication analysis of GCK, INS,
PDX1, and PTF1A (and for genes associated with syndromic PNDM) should be considered when sequencing is negative, as homozygous deletions in these genes can be associated with permanent neonatal diabetes mellitus.
A multigene panel that includes ABCC8, GCK, INS, KCNJ11, and PDX1 and other genes of interest (see Differential Diagnosis) may also be considered. Notes: (1) The genes included in the panel and the diagnostic sensitivity of the testing used for each gene vary by laboratory and are likely to change over time. (2) Some multigene panels may include genes not associated with the condition discussed in this GeneReview; thus, clinicians need to determine which multigene panel is most likely to identify the genetic cause of the condition while limiting identification of variants of uncertain significance and pathogenic variants in genes that do not explain the underlying phenotype. (3) In some laboratories, panel options may include a custom laboratory-designed panel and/or custom phenotype-focused exome analysis that includes genes specified by the clinician. (4) Methods used in a panel may include sequence analysis, deletion/duplication analysis, and/or other non-sequencing-based tests.
For an introduction to multigene panels click here. More detailed information for clinicians ordering genetic tests can be found here.
More comprehensive genomic testing (when available) including exome sequencing and genome sequencing may be considered if serial single-gene testing (and/or use of a multigene panel that includes ABCC8, GCK, INS, KCNJ11, and PDX1) fails to confirm a diagnosis in an individual with features of PNDM. Such testing may provide or suggest a diagnosis not previously considered (e.g., mutation of a different gene or genes that results in a similar clinical presentation).
For an introduction to comprehensive genomic testing click here. More detailed information for clinicians ordering genomic testing can be found here.
Table 1.
Molecular Genetic Testing Used in Permanent Neonatal Diabetes Mellitus
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Gene 1 | Proportion of Permanent Neonatal Diabetes Mellitus Attributed to Pathogenic Variants in Gene | Proportion of Pathogenic Variants 2 Detectable by Method |
---|
Sequence analysis 3 | Gene-targeted deletion/duplication analysis 4 |
---|
ABCC8
| 19% 5 | 100% | None reported 7 |
GCK
| 4% 8 | 100% | None reported 7 |
INS
| 20% 9 | >99% | 1 family 10 |
KCNJ11
| 30% 11 | 100% | None reported 7 |
PDX1
| <1% 12 | 100% | None reported 7 |
Unknown 13 | | NA |
- 1.
- 2.
- 3.
Sequence analysis detects variants that are benign, likely benign, of uncertain significance, likely pathogenic, or pathogenic. Variants may include small intragenic deletions/insertions and missense, nonsense, and splice site variants; typically, exon or whole-gene deletions/duplications are not detected. For issues to consider in interpretation of sequence analysis results, click here.
- 4.
Gene-targeted deletion/duplication analysis detects intragenic deletions or duplications. Methods used may include a range of techniques such as quantitative PCR, long-range PCR, multiplex ligation-dependent probe amplification (MLPA), and a gene-targeted microarray designed to detect single-exon deletions or duplications.
- 5.
- 6.
No data on detection rate of gene-targeted deletion/duplication analysis are available.
- 7.
No deletions or duplications involving ABCC8, GCK, KCNJ11, or PDX1 have been reported to cause permanent neonatal diabetes mellitus. Note that the KCNJ11 and ABCC8 defects are activating pathogenic variants and therefore must be missense. Duplication/deletion analysis would not identify ABCC8 and KCNJ11 defects.
- 8.
- 9.
- 10.
- 11.
- 12.
Attributed to inactivating pathogenic variants [Stoffers et al 1997a]. Note: Carrier parents have mild, adult-onset diabetes mellitus (PDX1-familial monogenic diabetes, previously known as MODY4).
- 13.
Clinical Characteristics
Clinical Description
Permanent neonatal diabetes mellitus (PNDM) is characterized by the onset of hyperglycemia within the first six months of life with a mean age at diagnosis of seven weeks (range: birth to 26 weeks) [Gloyn et al 2004b].
The diabetes mellitus is associated with partial or complete insulin deficiency.
Clinical manifestations at diagnosis include intrauterine growth restriction (IUGR; a reflection of insulin deficiency in utero), hyperglycemia, glycosuria, osmotic polyuria, severe dehydration, and failure to thrive.
Therapy with insulin corrects the hyperglycemia and results in dramatic catch-up growth.
Phenotype Correlations by Gene
The course of PNDM is highly variable depending on the genotype.
ABCC8 and KCNJ11. Most individuals with PNDM caused by pathogenic variants in ABCC8 and KCNJ11 are diagnosed before age three months, but a few present in childhood or early adult life. The majority of affected infants have low birth weight resulting from lower fetal insulin production. The typical presentation is symptomatic hyperglycemia, and in many individuals, ketoacidosis.
Although most individuals with pathogenic variants in KCNJ11 have isolated diabetes, 20% have associated neurologic features, called DEND syndrome (developmental delay, epilepsy, and neonatal diabetes mellitus) [Hattersley et al 2006]. A milder form, called intermediate DEND syndrome, presents with less severe developmental delay and without epilepsy. In individuals with KCNJ11 pathogenic variants, treatment with sulfonylureas corrects the hyperglycemia [Pearson et al 2006] and may reverse some of the neurologic manifestations [Hattersley & Ashcroft 2005, Slingerland et al 2006]. Neurologic manifestations might be prevented by early treatment with these agents [Greeley et al 2010] (see Management).
GCK. PNDM caused by biallelic GCK pathogenic variants is characterized by IUGR, insulin-requiring diabetes from the first day of life, and hyperglycemia in both parents.
INS. Individuals with PNDM caused by heterozygous INS pathogenic variants or biallelic deletions of INS present with diabetic ketoacidosis or marked hyperglycemia. Most newborns are small for gestational age [Støy et al 2007, Polak et al 2008]. The median age at diagnosis is nine weeks, but some children present after age six months [Edghill et al 2008].
PDX1. Pancreatic hypoplasia caused by biallelic PDX1 pathogenic variants results in a more severe insulin deficiency than in ABCC8, GCK, or KCNJ11-related neonatal diabetes as shown by a lower birth weight and a younger age at diagnosis. These individuals also have exocrine pancreatic insufficiency.
Genotype-Phenotype Correlations
ABCC8. For neonatal diabetes caused by pathogenic variants in ABCC8, genotype-phenotype correlations are less distinct [Edghill et al 2010]. Children with neonatal diabetes associated with dominant ABCC8 pathogenic variants may have a parent with the same ABCC8 variant and type 2 diabetes, suggesting that the severity of the phenotype and age of onset of diabetes is variable among individuals with ABCC8 pathogenic variants [Babenko et al 2006].
INS. The relationship between genotype and phenotype is beginning to emerge for NDM caused by pathogenic variants in INS. The diabetes mellitus in persons who are homozygous or compound heterozygous for pathogenic variants in INS can be permanent or transient. The variants c.-366_343del, c.3G>A, c.3G>T, c.184C>T, c.-370-?186+?del (a 646-bp deletion) and c.*59A>G appear to be associated with PNDM, whereas the variants c.-218A>C and c.-331C>A or c.-331C>G have been identified in persons with both PNDM and TNDM as well as persons with type 1b diabetes mellitus [Støy et al 2010].
KCNJ11. Clear genotype-phenotype correlations exist for those forms of PNDM associated with KCNJ11 pathogenic variants.
Genotype-phenotype studies correlate KCNJ11 pathogenic variants and phenotype with the extent of reduction in KATP channel ATP sensitivity.
Some KCNJ11 pathogenic variants are associated with transient neonatal diabetes mellitus (TNDM); others are associated with PNDM; and two variants, p.Val252Ala and p.Arg201His, are associated with both disorders [Colombo et al 2005, Girard et al 2006]. Furthermore, functional studies have shown some overlap between the magnitude of the KATP channel currents in TNDM- and PNDM-associated pathogenic variants [Girard et al 2006].
The location of the KCNJ11 pathogenic variant appears to predict the severity of the disease (isolated diabetes mellitus, intermediate DEND syndrome, DEND syndrome), however, there are some exceptions. Pathogenic variants in residues that lie within the putative ATP-binding site (Arg50, Ile192, Leu164, Arg201, Phe333) or are located at the interfaces between Kir6.2 subunits (Phe35, Cys42, and Gu332) or between Kir6.2 and SUR1 (Gly53) are associated with isolated diabetes mellitus. See Molecular Genetics, KCNJ11, Normal gene product for a discussion of Kir6.2 and ABCC8, Normal gene product for Sur1.
The severity of PNDM along the spectrum of isolated diabetes mellitus, intermediate DEND syndrome, and DEND syndrome correlates with the genotype [Proks et al 2004]. KCNJ11 variants that cause additional neurologic features occur at codons for amino acid residues that lie at some distance from the ATP-binding site (Gln52, Gly53, Val59, Cys166, and Ile296) [Hattersley & Ashcroft 2005].
Penetrance
Reduced penetrance has been seen in PNDM caused by pathogenic variants in KCNJ11 and ABCC8 [Flanagan et al 2007].
Nomenclature
Some individuals with "neonatal" diabetes mellitus may not be diagnosed until age three to six months, therefore it has been suggested that the term "diabetes mellitus of infancy" or "congenital diabetes" should replace the designation "neonatal diabetes mellitus" [Massa et al 2005, Greeley et al 2011].
Differential Diagnosis
Permanent neonatal diabetes mellitus (PNDM) vs transient neonatal diabetes mellitus (TNDM). When diabetes mellitus is diagnosed in the neonatal period, it is difficult to determine if it is likely to be transient or permanent.
6q24-related TNDM is defined as transient neonatal diabetes mellitus caused by overexpression of the imprinted genes at 6q24 (PLAGL1 and HYMAI). The cardinal features are: severe intrauterine growth restriction (IUGR), hyperglycemia that begins in the neonatal period in a term infant and resolves by age 18 months, dehydration, and absence of ketoacidosis. Macroglossia and umbilical hernia are often present. In the subset of children with ZFP57 pathogenic variants, other manifestations can include structural brain abnormalities, developmental delay, and congenital heart disease. Diabetes mellitus usually starts within the first week of life and lasts on average three months but can last more than a year. Although insulin is usually required initially, the need for insulin gradually declines over time. Intermittent episodes of hyperglycemia may occur in childhood, particularly during intercurrent illnesses. Recurrence in adolescence is more akin to type 2 diabetes mellitus. Relapse in women during pregnancy is associated with gestational diabetes mellitus.
The two most common causes of transient neonatal diabetes are 6q24-related TNDM and pathogenic variants in ABCC8 or KCNJ11. In 50 children presenting with neonatal diabetes, Metz et al [2002] failed to demonstrate clear clinical indicators to differentiate 6q24-related TNDM from other causes. However, the clinical presentation may be slightly different: neonates with 6q24-related TNDM have more severe IUGR, present earlier, remit earlier, and relapse later than KATP-related TNMD. The presence of other distinguishing features of 6q24-related TNDM may guide the approach to genetic testing, such macroglossia (seen in 1/3 of individuals) and umbilical hernia [Rubio-Cabezas et al 2014].
For infants presenting in the first two weeks of life, it is reasonable to test for 6q24-related aberrations first, followed by testing for KCNJ11 and ABCC8 pathogenic variants.
For infants presenting from the third week of life onward, it may be more appropriate to test for KCNJ11 and ABCC8 pathogenic variants first, followed by testing for 6q24-related aberrations.
In infants presenting between age six and 12 months or later who are antibody negative or have a family history consistent with autosomal dominant inheritance, evaluation for pathogenic variants in INS should be considered first.
For infants with associated extra-pancreatic features or consanguineous parents, other genetic analysis may be appropriate.
Syndromic causes of permanent neonatal diabetes mellitus
GATA4-related PNDM. Heterozygous inactivating pathogenic variants in
GATA4 are associated with pancreatic agenesis or pancreatic hypoplasia leading to PNDM and congenital heart defects [
D'Amato et al 2010,
Shaw-Smith et al 2014]. GATA4 is a zinc finger transcription factor closely related to GATA6. The diabetes phenotype in individual carrying pathogenic variants is quite variable, ranging from TNDM, PNDM and diabetes presenting later in life. The severity of the exocrine insufficiency is also variable. Extrapancreatic manifestations include cardiac abnormalities and neurodevelopmental delays. Inheritance is autosomal dominant, but in most reported individuals the pathogenic variants have arisen
de novo.
GATA6-related PNDM (OMIM
600001). Heterozygous inactivating pathogenic variants in
GATA6 are the most common cause of pancreatic agenesis [Lango
Allen et al 2011]. Extrapancreatic features are common and include structural heart defects, biliary tract and gut anomalies, and other endocrine abnormalities. The diabetic phenotype in those with pathogenic variants in
GATA6 is broad, ranging from PNDM with exocrine insufficiency to transient episodes of hyperglycemia. In the largest published series of
GATA6-PNDM, the median age at diagnosis of diabetes was two days and the median birth weight was 1588 grams. Individuals with heterozygous pathogenic variants in
GATA6 have also been diagnosed with diabetes at an older age [Lango
Allen et al 2011,
De Franco et al 2013]. Inheritance is autosomal dominant, but in most reported individuals the pathogenic variants have arisen
de novo.
PTF1A-related PNDM (OMIM
609069). Homozygous inactivating pathogenic variants in
PTF1A cause pancreatic agenesis leading to PNDM associated with cerebellar agenesis and severe neurologic dysfunction [
Sellick et al 2004].
PTF1A encodes a basic helix-loop-helix protein of 48 kd. The protein plays a role in determining whether cells allocated to the pancreatic buds continue toward pancreatic organogenesis or revert back to duodenal fates [
Kawaguchi et al 2002]. Infants with
PTF1A-related PNDM present with severe IUGR, and very low circulating insulin and C-peptide in the presence of severe hyperglycemia. Neurologic features include flexion contractures of extremities and absence of the cerebellum demonstrated on brain imaging [
Sellick et al 2004]. A recent report described an individual with
PTF1A-related PNDM without neurologic manifestations [
Houghton et al 2016]. Exocrine pancreatic dysfunction may be present as well. Inheritance is autosomal recessive.
Immune dysregulation, polyendocrinopathy, and enteropathy, X-linked (IPEX) syndrome is characterized by the development of overwhelming systemic autoimmunity in the first year of life resulting in the commonly observed triad of watery diarrhea, eczematous dermatitis, and endocrinopathy seen most commonly as insulin-dependent diabetes mellitus. The majority of affected males have other autoimmune phenomena including Coombs-positive anemia, autoimmune thrombocytopenia, autoimmune neutropenia, and tubular nephropathy. Typically, serum concentration of immunoglobulin E (IgE) is elevated. The majority of affected males die within the first year of life of either metabolic derangements or sepsis.
FOXP3 is currently the only gene in which mutation is known to cause IPEX syndrome. Inheritance is X-linked.
Wolcott-Rallison syndrome (OMIM
226980) is characterized by infantile-onset diabetes mellitus and exocrine pancreatic dysfunction (25%) as well as the extra-pancreatic manifestations of epiphyseal dysplasia (90%), developmental delay (80%), acute liver failure (75%), osteopenia (50%), and hypothyroidism (25%). In addition, older individuals with Wolcott-Rallison syndrome may develop chronic kidney dysfunction [
Senée et al 2004]. The prognosis is poor.
EIF2AK3, the gene encoding eukaryotic translation initiation factor 2-alpha kinase 3, is the only gene in which pathogenic variants are known to cause Wolcott-Rallison syndrome.
Durocher et al [2006] observed that the severity of the manifestations and age of presentation in individuals with the same pathogenic variant may vary and concluded that no simple relationship exists between the clinical manifestation and
EIF2AK3 pathogenic variants in Wolcott-Rallison syndrome. This is the most common cause of PNDM in consanguineous families [
Rubio-Cabezas et al 2009]. Inheritance is autosomal recessive.
A syndrome of neonatal diabetes mellitus with congenital hypothyroidism (OMIM
610199) has been associated with mutation of
GLIS3.
GLIS3 encodes zinc finger protein GLIS3 (also known as GLI similar protein 3), a transcription factor expressed in the pancreas from early developmental stages. GLIS3 plays a role in the transcriptional regulation of neurogenin-3 and insulin [
Kim et al 2012,
ZeRuth et al 2013]. In addition to neonatal diabetes and congenital hypothyroidism, the syndrome can present with congenital glaucoma, hepatic fibrosis, polycystic kidneys, and dysmorphic facial features [
Senée et al 2006]. Inheritance is autosomal recessive and partial gene deletions are the most common type of pathogenic variant [
Dimitri et al 2011].
A syndrome of neonatal diabetes mellitus with pancreatic hypoplasia, intestinal atresia, and gall bladder hypoplasia (OMIM
615710) has been associated with pathogenic variants in
RFX6. RFX6 is a transcription factor required for the differentiation of four of the five islet cell types and for the production of insulin. RFX6 acts downstream of the pro-endocrine factor neurogenin-3. Pancreatic exocrine function is normal [
Smith et al 2010]. Inheritance is autosomal recessive.
A syndrome of neonatal diabetes mellitus, cerebellar hypoplasia, sensorineural deafness, and visual impairment has been associated with pathogenic variants in
NEUROD1 (OMIM
601724), encoding neurogenic differentiation factor 1, a transcription factor that plays an important role in the development of the endocrine pancreas. Pancreatic exocrine function is normal [
Rubio-Cabezas et al 2010]. Inheritance is autosomal recessive.
A
syndrome of congenital malabsorptive diarrhea and neonatal diabetes mellitus (OMIM
610370) has been associated with pathogenic variants in
NEUROG3, encoding neurogenin-3, a basic helix loop helix transcription factor essential in the development of enteroendocrine, Paneth, goblet, and enterocyte cells in the intestine and pancreatic endocrine cells [
Pinney et al 2011]. Diabetes may also present later in childhood [
Wang et al 2006]. Pancreatic exocrine function may also be affected. Inheritance is autosomal recessive.
A syndrome of neonatal diabetes mellitus and renal abnormalities (OMIM
137920) has been associated with pathogenic variants in
HNF1B. HNF1 beta is a key regulator of a transcriptional network that controls the specification, growth and differentiation of the embryonic pancreas. The diabetes phenotype in individuals heterozygous for a single pathogenic variant in
HNF1B manifests more frequently later in life (renal cysts and diabetes syndrome – RCAD, or
MODY5). The neonatal presentation due to biallelic pathogenic variants in
HNF1B is characterized by evidence of severe insulin deficiency (low birth weight, diabetes ketoacidosis) and pancreatic exocrine insufficiency due to hypoplastic pancreas. Other manifestations include genital tract malformations, hyperuricemia and gout, as well as abnormal liver function. The inheritance is autosomal recessive but penetrance is incomplete [
Yorifuji et al 2004,
Edghill et al 2006,
Haldorsen et al 2008,
Tjora et al 2013].
A
syndrome of neonatal diabetes with brain malformations, microcephaly, and microphthalmia has been associated with pathogenic variants in
PAX6 (OMIM
607108). PAX6 is a transcription factor involved in eye and brain development that also plays a role in pituitary development and in ß-cell differentiation and function. In heterozygous individuals, diabetes presents later in life, however in individuals with biallelic pathogenic variants, the diabetes manifests in the neonatal period. The central nervous system (CNS) phenotype includes microcephaly and panhypopituitarism. The ocular phenotype includes aniridia, keratopathy, optic nerve defects, cataracts, microphthalmia and anophthalmia [
Yasuda et al 2002,
Solomon et al 2009].
Wolfram syndrome – diabetes mellitus with optic atrophy, diabetes insipidus, and/or deafness. The associated gene,
WFS1, encodes an endoplasmic reticulum (ER) membrane-embedded protein involved in regulating ER stress. The earliest and most consistent phenotypic characteristic in individuals with Wolfram syndrome is diabetes, which is usually diagnosed during childhood, but it can also present in the first year of life. The inheritance is autosomal recessive [
Rigoli et al 2011,
Rohayem et al 2011]. See
WFS1 Spectrum Disorder.
A syndrome of neonatal diabetes mellitus, deafness, and thiamine-responsive megaloblastic anemia caused by pathogenic variants in
SLC19A2.
SLC19A2 encodes a thiamine transporter. Also known as Rogers syndrome, this syndrome can also be associated with neurologic deficits, visual disturbances, and cardiac abnormalities. The diabetes phenotype can manifests in the first six months of life or later. The inheritance is autosomal recessive [
Shaw-Smith et al 2012]. See
Thiamine-Responsive Megaloblastic Anemia Syndrome.
A
syndrome of neonatal diabetes mellitus, developmental delays, sacral agenesis and imperforated anus caused by pathogenic variants in
MNX1. Other manifestations include IUGR, hypoplastic lungs. Inheritance is autosomal recessive [
Flanagan et al 2014].
A syndrome of neonatal diabetes mellitus, developmental delays, hypotonia, short stature and deafness caused by pathogenic variants in
NKX2-2. Other manifestations include IUGR, cortical blindness, and impaired visual tracking. Inheritance is autosomal recessive [
Flanagan et al 2014].
A syndrome of neonatal diabetes, microcephaly, lissencephaly, and epileptic encephalopathy caused by pathogenic variants in
IER3IP1.
IERI31P1 encodes a highly conserved protein with marked expression in beta cells in cerebral cortex but which function is not well known. Inheritance is autosomal recessive [
Shalev et al 2014].
Testing strategy for syndromic permanent neonatal diabetes mellitus. Individuals with PNDM and:
Pancreatic exocrine insufficiency or agenesis and cardiac abnormalities should be tested for pathogenic variants in GATA4 and GATA6;
Enteropathy and dermatitis should be tested for pathogenic variants in
FOXP3 (
IPEX syndrome);
Cerebellar involvement should be tested for pathogenic variants in PTF1A;
Congenital hypothyroidism should be tested for pathogenic variants in GLIS3;
Cerebellar hypoplasia, sensorineural deafness, and visual impairment should be tested for pathogenic variants in NEUROD1;
Pancreatic hypoplasia, intestinal atresia, and gall bladder hypoplasia should be tested for pathogenic variants in RFX6;
Congenital malabsorptive diarrhea should be tested for pathogenic variants in NEUROG3;
Skeletal abnormalities and liver dysfunction should be tested for pathogenic variants in EIF2AK3 (WRS - Wolcott-Rallison syndrome);
Megaloblastic anemia and deafness should be tested for pathogenic variants in
SLC19A2 (
TRMA; thiamine-responsive megaloblastic anemia);
Renal and genital abnormalities should be tested for pathogenic variants in HNF1B;
Brain malformations, microcephaly and microphthalmia should be tested for pathogenic variants in PAX6;
Optic atrophy, diabetes insipidus and deafness should be tested for pathogenic variants in
WFS1 (
Wolfram syndrome).
Management
Evaluations Following Initial Diagnosis
To establish the extent of disease and needs in an individual diagnosed with neonatal diabetes mellitus as a result of pathogenic variants in ABCC8 or KCNJ11, a complete neurologic evaluation should be performed.
To establish the extent of disease in an individual with suspected or confirmed pathogenic variants in PDX1, imaging of the pancreas and evaluation of pancreatic exocrine function (stool elastase, serum concentrations of fat-soluble vitamins) should be performed.
Consultation with a clinical geneticist and/or genetic counselor should be obtained early in the evaluation of PNDM.
Treatment of Manifestations
Initial treatment. Rehydration and intravenous insulin infusion should be started promptly after diagnosis, particularly in infants with ketoacidosis.
Long-term medical management. An appropriate regimen of subcutaneous insulin administration should be established when the infant is stable and tolerating oral feedings. Few data on the most appropriate insulin preparations for young infants are available.
Intermediate-acting insulin preparations (neutral protamine Hagedorn [NPH]) tend to have a shorter duration of action in infants, possibly because of smaller dose size or higher subcutaneous blood flow.
The longer-acting preparations with no significant peak-of-action effect such as Lantus® (glargine) or Levemir® (detemir) may work better in small infants.
In individuals with very low insulin requirements, diluted insulin (5 or 10 U/mL) may be more appropriate if used with caution.
Some centers recommend the use of continuous subcutaneous insulin infusion for young infants [
Polak & Cave 2007] as a safer, more physiologic, and more accurate way of administering insulin.
Caution:
In general, rapid-acting (lispro and aspart) and short-acting (regular) preparations (except when used as a continuous intravenous or subcutaneous infusion) should be avoided as they may cause severe hypoglycemic events.
Extreme caution should be observed when using a diluted insulin preparation in order to avoid dose errors.
Identification of a KCNJ11 or ABCC8 pathogenic variant is important for clinical management since most individuals with these pathogenic variants can be treated with oral sulfonylureas. Children with pathogenic variants in KCNJ11 or ABCC8 can be transitioned to therapy with oral sulfonylureas; high doses are usually required (0.4-1.0 mg/kg/day of glibenclamide). Transfer protocols are available at www.diabetesgenes.org. Treatment with sulfonylureas is associated with improved glycemic control [Hattersley & Ashcroft 2005, Pearson et al 2006, Thurber et al 2015, Babiker et al 2016].
Long-term insulin therapy is required for all other causes of PNDM, although mild beneficial effect of oral sulfonylureas in persons with GCK pathogenic variants has been reported [Turkkahraman et al 2008, Hussain 2010].
High caloric intake should be maintained to achieve weight gain.
Pancreatic enzyme replacement therapy is required in persons with exocrine pancreatic insufficiency.
Prevention of Secondary Complications
Aggressive treatment and frequent monitoring of blood glucose concentrations is essential to avoid acute complications such as diabetic ketoacidosis and hypoglycemia.
Long-term complications of diabetes mellitus can be significantly reduced by maintaining blood glucose concentrations in the appropriate range. The American Diabetes Association recommends the following glycemic goals across all pediatric age-groups [American Diabetes Association 2016a]:
Surveillance
Lifelong monitoring (≥4x/day) of blood glucose concentrations is indicated to achieve the goals of therapy.
Children with PNDM, particularly those with a pathogenic variant in KCNJ11 or ABCC8, should undergo periodic developmental evaluations.
Yearly screening for chronic complications associated with diabetes mellitus should be started after age ten years and should include the following:
Agents/Circumstances to Avoid
In general, rapid-acting insulin preparations (lispro and aspart) as well as short-acting (regular) insulin preparations should be avoided (except when used as a continuous intravenous or subcutaneous infusion) as they may cause severe hypoglycemic events in young children.
Evaluation of Relatives at Risk
See Genetic Counseling for issues related to testing of at-risk relatives for genetic counseling purposes.
Pregnancy Management
The management of pregnant women with PNDM should conform to the guidelines for treatment of other forms of diabetes during gestation [American Diabetes Association 2016b]. Glycemic control during gestation is not only important to prevent complications in the mother, but also to prevent fetal overgrowth (due to fetal hyperinsulinemia triggered by the excess of maternal glucose crossing the placenta) and associated complications. Referral to a maternal-fetal medicine specialist should be considered. In addition, high resolution ultrasonography and fetal echocardiography should be offered during pregnancy to screen for congenital anomalies in the fetus.
Until recently, insulin was the mainstay of therapy of diabetes during pregnancy; however, emerging data support the safety and efficacy of glyburide in the treatment of diabetes during pregnancy [Moretti et al 2008]. Thus, in women with PNDM treated with glyburide before pregnancy, it is reasonable to continue this treatment if appropriate glycemic control can be achieved.
Therapies Under Investigation
Search ClinicalTrials.gov in the US and EU Clinical Trials Register in Europe for access to information on clinical studies for a wide range of diseases and conditions. Note: There may not be clinical trials for this disorder.
Genetic Counseling
Genetic counseling is the process of providing individuals and families with
information on the nature, mode(s) of inheritance, and implications of genetic disorders to help them
make informed medical and personal decisions. The following section deals with genetic
risk assessment and the use of family history and genetic testing to clarify genetic
status for family members; it is not meant to address all personal, cultural, or
ethical issues that may arise or to substitute for consultation with a genetics
professional. —ED.
Mode of Inheritance
The mode of inheritance of permanent neonatal diabetes mellitus (PNDM) varies by gene:
ABCC8 and INS. Autosomal dominant or autosomal recessive
GCK and PDX1. Autosomal recessive
KCNJ11. Autosomal dominant
Autosomal Dominant Inheritance ‒ Risk to Family Members
Table 2.
Autosomal Dominant PNDM – Risk to Parents of a Proband by Gene
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Gene | % of Probands with an Affected Parent | % of Probands with a De Novo Pathogenic Variant |
---|
ABCC8
| ~10% 1 | Most reported cases 2 |
INS
| 27% | 73% |
KCNJ11
| ~10% | 90% |
- 1.
A parent may have type 2 diabetes despite having the same ABCC8 pathogenic variant as their child with neonatal diabetes mellitus [Babenko et al 2006].
- 2.
Parents of a proband (see Table 2)
Recommendations for the evaluation of parents of a proband with an apparent de novo pathogenic variant in ABCC8, INS, or KCNJ11 include molecular genetic testing and clinical testing for diabetes mellitus (oral glucose tolerance testing).
If the pathogenic variant found in the proband cannot be detected in the leukocyte DNA of either parent, possible explanations include a
de novo pathogenic variant in the proband or germline mosaicism in a parent. Germline mosaicism for a pathogenic variant in
KCNJ11 has been reported [
Gloyn et al 2004a,
Edghill et al 2007]; the overall incidence of germline mosaicism is unknown.
Evaluation of parents may determine that one is affected but has escaped previous diagnosis because of failure by health care professionals to recognize the syndrome and/or a milder phenotypic presentation. Therefore, an apparently negative family history cannot be confirmed until appropriate evaluations have been performed.
Sibs of a proband. The risk to the sibs of the proband depends on the genetic status of the proband's parents.
If a parent of the proband is affected, the risk to the sibs is 50%.
When the parents are clinically unaffected, the risk to the sibs of a proband appears to be low.
If the ABCC8, INS, or KCNJ11 pathogenic variant found in the proband cannot be detected in the leukocyte DNA of either parent, the risk to sibs is slightly greater than that of the general population (though still <1%) because of the possibility of parental germline mosaicism.
Offspring of a proband. Each child of an individual with PNDM inherited in an autosomal dominant manner has a 50% chance of inheriting the ABCC8, INS, or KCNJ11 pathogenic variant.
Other family members. The risk to other family members depends on the status of the proband's parents: if a parent is affected, the parent's family members may be at risk.
Autosomal Recessive Inheritance ‒ Risk to Family Members
Parents of a proband
Sibs of a proband
At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being heterozygous, and a 25% chance of being unaffected and not heterozygous.
Heterozygotes for pathogenic variants in
GCK,
INS, or
PDX1 have a milder form of diabetes mellitus (e.g.,
GCK-familial monogenic diabetes, previously known as MODY2, or
PDX1-familial monogenic diabetes, previously known as MODY4). Heterozygotes for pathogenic variants in
ABCC8 have normal glucose tolerance. See
MODY Overview.
Offspring of a proband. The offspring of an individual with autosomal recessive neonatal diabetes mellitus are obligate heterozygotes for a pathogenic variant.
Other family members. Each sib of the proband's parents is at a 50% risk of being heterozygous for a PNDM-related pathogenic variant.
Heterozygote detection. Carrier testing for at-risk relatives requires prior identification of the PNDM-related pathogenic variants in the family.
Prenatal Testing and Preimplantation Genetic Testing
Once the PNDM-related pathogenic variant(s) have been identified in an affected family member, prenatal and preimplantation genetic testing for PNDM are possible.
Differences in perspective may exist among medical professionals and within families regarding the use of prenatal testing. While most centers consider use of prenatal testing to be a personal decision, discussion of these issues may be helpful.
Molecular Genetics
Information in the Molecular Genetics and OMIM tables may differ from that elsewhere in the GeneReview: tables may contain more recent information. —ED.
Table A.
Permanent Neonatal Diabetes Mellitus: Genes and Databases
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Data are compiled from the following standard references: gene from
HGNC;
chromosome locus from
OMIM;
protein from UniProt.
For a description of databases (Locus Specific, HGMD, ClinVar) to which links are provided, click
here.
Table B.
View in own window
138079 | GLUCOKINASE; GCK |
176730 | INSULIN; INS |
600509 | ATP-BINDING CASSETTE, SUBFAMILY C, MEMBER 8; ABCC8 |
600733 | PANCREAS/DUODENUM HOMEOBOX PROTEIN 1; PDX1 |
600937 | POTASSIUM CHANNEL, INWARDLY RECTIFYING, SUBFAMILY J, MEMBER 11; KCNJ11 |
606176 | DIABETES MELLITUS, PERMANENT NEONATAL, 1; PNDM1 |
ABCC8
Gene structure.
ABCC8 is located 4.5 kb centromeric to KCNJ11 on chromosome 11p15.1. The gene spans approximately 84 kb of genomic DNA and is made up of 39 exons. The shorter transcript variant NM_000352.4 is 4935 bp. For a detailed summary of gene and protein information, see Table A, Gene.
Pathogenic variants. More than 25 different ABCC8 variants have been associated with permanent neonatal diabetes (see Table 3). In addition, several other variants in compound heterozygotes have been associated with PNDM. (See Flanagan et al [2009] for variants in ABCC8 that cause both neonatal diabetes mellitus and persistent hyperinsulinemic hypoglycemia of infancy.)
Table 3.
Selected ABCC8 Pathogenic Variants
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Variants listed in the table have been provided by the authors. GeneReviews staff have not independently verified the classification of variants.
GeneReviews follows the standard naming conventions of the Human Genome Variation Society (varnomen.hgvs.org). See Quick Reference for an explanation of nomenclature.
For more information see Patch et al [2007], Figure 2 (full text) and Edghill et al [2010], Figures 2 and 3.
Normal gene product. The transcript variant NM_000352.4 encodes ATP-binding cassette sub-family C member 8 protein (SUR1) (NP_000343.2), which has 1581 amino acids. See KCNJ11, Normal gene product.
Abnormal gene product. Pathogenic variants in ABCC8 result in nonfunctional or dysfunctional KATP channels. The increased activity of KATP channels resulting from pathogenic variants in ABCC8 is caused by an increase in the magnesium-dependent stimulatory action of SUR1 on the pore [Babenko et al 2006, Masia et al 2007a], or by alteration in the inhibitory action of ATP on a mutated SUR1 channel [Proks et al 2006].
GCK
Gene structure.
GCK spans more than 45 kb of genomic DNA; the transcript variant NM_000162.3, which encodes the isoform expressed specifically in pancreatic islet beta cells, has ten exons. For a detailed summary of gene and protein information, see Table A, Gene.
Pathogenic variants. At least ten variants of GCK have been reported in association with PNDM (see Table 4). These are nonsense, missense, or frameshift variants.
Table 4.
Selected GCK Pathogenic Variants
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Variants listed in the table have been provided by the authors. GeneReviews staff have not independently verified the classification of variants.
GeneReviews follows the standard naming conventions of the Human Genome Variation Society (varnomen.hgvs.org). See Quick Reference for an explanation of nomenclature.
- 1.
Variant designation that does not conform to current naming conventions
Normal gene product. The isoform NP_000153.1, expressed specifically in pancreatic islet beta cells, has 465 amino acid residues. Glucokinase is a hexokinase that serves as the glucose sensor in pancreatic beta cells and appears to have a similar role in enteroendocrine cells, hepatocytes, and hypothalamic neurons. In beta cells, glucokinase controls the rate-limiting step of glucose metabolism and is responsible for glucose-stimulated insulin secretion [Matschinsky 2002].
Abnormal gene product. The reported pathogenic missense variants alter the kinetics of the enzyme: the glucose S0.5 is raised and the ATP Km is increased. The overall result for inactivating pathogenic variants is a decrease in the phosphorylating potential of the enzyme, which extrapolates to a marked reduction in beta-cell glucose usage and hyperglycemia. Splice site pathogenic variants are predicted to lead to the synthesis of an inactive protein.
INS
Gene structure. The INS transcript variant NM_000207.2 has three exons. Exon 2 encodes the signal peptide, the B chain, and part of the C peptide; exon 3 encodes the reminder of the C peptide and the A chain. For a detailed summary of gene and protein information, see Table A, Gene.
Pathogenic variants. More than 25 variants have been described in association with PNDM [Støy et al 2007, Polak et al 2008, Støy et al 2010]. See Table 5 and Genotype-Phenotype Correlations.
See Støy et al [2010] for variants in INS that cause diabetes mellitus.
Table 5.
Selected INS Pathogenic Variants
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DNA Nucleotide Change 1 | Predicted Protein Change | References | Reference Sequences |
---|
c.-366_343del 2, 3 | NA | Støy et al [2007], Polak et al [2008], Støy et al [2010] | NM_000207.2 4 NP_000198.1 |
c.-370-?186+?del 2, 3, 5, 6 |
c.-331C>A 2, 3, 7, 8 |
c.-331C>G 2, 3, 4, 9 |
c.-218A>C 2, 3, 7, 10 |
c.3G>A 2 | p.0? 11 |
c.3G>T 2 | p.0? 11 |
c.71C>A | p.Ala24Asp |
c.94G>A | p.Gly32Ser |
c.94G>C | p.Gly32Arg |
c.127T>G | p.Cys43Gly |
c.140G>T | p.Gly47Val |
c.143T>G | p.Phe48Cys |
c.184C>T 2 | p.Gln62Ter |
c.265C>T | p.Arg89Cys |
c.268G>T | p.Gly90Cys |
c.287G>A | p.Cys96Tyr |
c.323A>G | p.Tyr108Cys |
c.*59A>G 2, 12 | NA |
Variants listed in the table have been provided by the authors. GeneReviews staff have not independently verified the classification of variants.
GeneReviews follows the standard naming conventions of the Human Genome Variation Society (varnomen.hgvs.org). See Quick Reference for an explanation of nomenclature.
- 1.
Negative number indicates the number of base pairs preceding the A of the ATG start codon. An asterisk indicates a position in the 3’UTR; the number is the position relative to the first base past the stop codon.
- 2.
- 3.
- 4.
Reference sequences of the insulin preproprotein (or preproinsulin)
- 5.
Denotes an exon deletion starting at an unknown position in the promoter of coding DNA nucleotide -370 and ending at an unknown position in the intron 3’ of the coding DNA nucleotide 186 [Støy et al 2010]
- 6.
- 7.
- 8.
-94 relative to transcription initiation site
- 9.
-93 relative to transcription initiation site
- 10.
A+20 relative to transcription initiation site
- 11.
p.0? = effect unknown; probably no protein is produced
- 12.
59 nucleotides 3' of the termination codon (in the 3'UTR)
Normal gene product. The insulin preproprotein NP_000198.1 encoded by transcript NM_000207.2 has 110 amino acids. Insulin is synthesized by the pancreatic beta cells and consists of two dissimilar polypeptide chains, A and B, which are linked by two disulfide bonds. Chains A and B are derived from a 1-chain precursor, proinsulin. Proinsulin is converted to insulin by enzymatic removal of a segment that connects the amino end of the A chain to the carboxyl end of the B chain. This segment is called the C peptide.
Abnormal gene product. The diabetes-associated pathogenic variants lead to the synthesis of a structurally abnormal preproinsulin or proinsulin protein. The variants associated with PNDM disrupt proinsulin folding and/or disulfide bond formation. Some reported variants disrupt normal disulfide bonds (p.Cys43Gly and p.Cys96Tyr) or add an additional unpaired cysteine residue (p.Arg89Cys and p.Gly90Cys) at the A-chain C-peptide cleavage site. The variant p.Tyr108Cys may cause mispairing of cysteines in a critical region close to a disulfide bond [Støy et al 2007]. All of the pathogenic variants are likely to act in a dominant manner to disrupt insulin biosynthesis and induce endoplasmic reticulum (ER) stress. The exact mechanism by which these unpaired cysteines disrupt ER function remains unclear [Izumi et al 2003]. Three other pathogenic variants (p.Gly32Ser, p.Gly32Arg, and p.Gly47Val) are located in a residue that is invariant in both insulin and the insulin-like growth factors and must play an important structural role. It is believed that these glycine variants also act similarly to impair proinsulin folding and thereby induce ER stress via the unfolded protein response.
KCNJ11
Gene structure.
KCNJ11 is located 4.5 kb telomeric to ABCC8 on chromosome 11p15.1. The gene spans approximately 3.4 kb of genomic DNA and has a single exon. For a detailed summary of gene and protein information, see Table A, Gene.
Pathogenic variants. More than 20 different pathogenic variants in KCNJ11 have been reported in association with neonatal diabetes mellitus (see Table 6). The two common hot spots for recurrent mutation are at amino acid residues Val59 and Arg201 [Hattersley & Ashcroft 2005]. (See Flanagan et al [2009] for variants in KCNJ11 that cause both neonatal diabetes mellitus and persistent hyperinsulinemic hypoglycemia of infancy.)
Table 6.
View in own window
Variant Classification | DNA Nucleotide Change | Predicted Protein Change | Reference Sequences |
---|
Benign
| c.67G>A | p.Glu23Lys 1 |
NM_000525.3
NP_000516.3
|
Pathogenic
| c.103T>G | p.Phe35Val |
c.103T>C | p.Phe35Leu |
c.124T>C | p.Cys42Arg |
c.149G>C | p.Arg50Pro |
c.155A>G | p.Gln52Arg |
c.157G>C | p.Gly53Arg |
c.157G>A | p.Gly53Ser |
c.158G>A | p.Gly53Asp |
c.175G>A | p.Val59Met |
c.176T>G | p.Val59Gly |
c.497G>T | p.Cys166Phe |
c.497G>A | p.Cys166Tyr |
c.499A>C | p.Ile167Leu |
c.509A>G | p.Lys170Arg |
c.510G>C | p.Lys170Asn |
c.544A>G | p.Ile182Val |
c.602G>A | p.Arg201His |
c.601C>T | p.Arg201Cys |
c.602G>T | p.Arg201Leu |
c.755T>C | p.Val252Ala |
c.886A>C | p.Ile296Leu |
c.886A>G | p.Ile296Val |
c.964G>A | p.Glu322Lys |
c.989A>G | p.Tyr330Cys |
c.997T>A | p.Phe333Ile |
c.1001G>A | p.Gly334Asp |
Variants listed in the table have been provided by the authors. GeneReviews staff have not independently verified the classification of variants.
GeneReviews follows the standard naming conventions of the Human Genome Variation Society (varnomen.hgvs.org). See Quick Reference for an explanation of nomenclature.
- 1.
Normal gene product. The transcript variant NM_000525.3 encodes the 390-amino acid isoform known as Kir6.2 (NP_000516.3). KCNJ11 and ABCC8 encode the proteins ATP-sensitive inward rectifier potassium channel 11 (Kir6.2) and ATP-binding cassette sub-family C member 8 (SUR1), respectively; both are components of the beta-cell KATP channel. The KATP channel is a hetero-octameric complex with four Kir6.2 subunits forming the central pore, coupled to four SUR1 subunits. The KATP channels couple the energy state of the beta cell to membrane potential by sensing changes in intracellular phosphate potential (the ATP/ADP ratio). Following the uptake of glucose and its metabolism by glucokinase, there is an increase in the intracellular ATP/ADP ratio results in closure of the KATP channels, depolarization of the cell membrane, and subsequent opening of voltage-dependent Ca2+ channels. The resulting increase in cytosolic Ca2+ concentration triggers insulin release.
Abnormal gene product. Pathogenic variants in either ABCC8 or KCNJ11 result in nonfunctional or dysfunctional KATP channels. In either case, channels do not close, and thus glucose-stimulated insulin secretion does not happen. All pathogenic variants in KCNJ11 studied to date produce marked decrease in the ability of ATP to inhibit the KATP channel when expressed in heterologous systems. This reduction in ATP sensitivity means the channel opens more fully at physiologically relevant concentrations of ATP, leading to an increase in the KATP current and hyperpolarization of the beta-cell plasma membrane with subsequent suppression of Ca2+ influx and insulin secretion [Hattersley & Ashcroft 2005].
PDX1
Gene structure. The PDX1 transcript NM_000209.3 has 2573 bp and comprises two exons. For a detailed summary of gene and protein information, see Table A, Gene.
Pathogenic variants. At least four PDX1 variants have been described in association with pancreatic agenesis and PNDM:
A homozygous pathogenic missense variant p.Glu178Gly in the
PDX1 homeodomain associated with neonatal diabetes without exocrine insufficiency in two individuals [
Nicolino et al 2010]
Table 7.
Selected PDX1 Pathogenic Variants
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DNA Nucleotide Change | Predicted Protein Change | Reference Sequences |
---|
c.188_189delC | p.Pro63ArgfsTer60 |
NM_000209.3
NP_000200.1
|
c.492G>T | p.Glu164Asp |
c.532G>A | p.Glu178Lys |
c.533A>G | p.Glu178Gly |
Variants listed in the table have been provided by the authors. GeneReviews staff have not independently verified the classification of variants.
GeneReviews follows the standard naming conventions of the Human Genome Variation Society (varnomen.hgvs.org). See Quick Reference for an explanation of nomenclature.
Normal gene product. The pancreas/duodenum homeobox protein 1 or transcription factor insulin promoter factor 1 (PDX1) is a master regulator of pancreatic development and of the differentiation of progenitor cells into the beta-cell phenotype.
During embryogenesis in the mouse, pdx1 expression initiates on commitment of the foregut endoderm to a pancreatic fate. In the adult organism, pdx1 expression is limited to the beta cell and its importance in maintaining beta-cell phenotype is illustrated by multiple animal models. In mature beta cells, pdx1 regulates the expression of critical genes including insulin, glucokinase, and the glucose transporter Glut2 [Habener et al 2005].
Abnormal gene product. The single-nucleotide deletion c.188_189delC predicts the formation of a truncated, inactive protein (p.Pro63ArgfsTer60), whereas the mutated proteins p.Glu164Asp or p.Glu178Lys undergo increased degradation leading to a reduction in protein levels and ultimately to decreased transcriptional activity. The p.Glu178Gly variant reduces PDX1 transactivation.