MedGen

Type 2 diabetes mellitus is distinct from maturity-onset diabetes of the young (see 606391) in that it is polygenic, characterized by gene-gene and gene-environment interactions with onset in adulthood, usually at age 40 to 60 but occasionally in adolescence if a person is obese. The pedigrees are rarely multigenerational. The penetrance is variable, possibly 10 to 40% (Fajans et al., 2001). Persons with type 2 diabetes usually have an obese body habitus and manifestations of the so-called metabolic syndrome (see 605552), which is characterized by diabetes, insulin resistance, hypertension, and hypertriglyceridemia. Genetic Heterogeneity of Susceptibility to Type 2 Diabetes Susceptibility to T2D1 (601283) is conferred by variation in the calpain-10 gene (CAPN10; 605286) on chromosome 2q37. The T2D2 locus (601407) on chromosome 12q was found in a Finnish population. The T2D3 locus (603694) maps to chromosome 20. The T2D4 locus (608036) maps to chromosome 5q34-q35. Susceptibility to T2D5 (616087) is conferred by variation in the TBC1D4 gene (612465) on chromosome 13q22. A mutation has been observed in hepatocyte nuclear factor-4-alpha (HNF4A; 600281.0004) in a French family with NIDDM of late onset. Mutations in the NEUROD1 gene (601724) on chromosome 2q32 were found to cause type 2 diabetes mellitus in 2 families. Mutation in the GLUT2 glucose transporter was associated with NIDDM in 1 patient (138160.0001). Mutation in the MAPK8IP1 gene, which encodes the islet-brain-1 protein, was found in a family with type 2 diabetes in individuals in 4 successive generations (604641.0001). Polymorphism in the KCNJ11 gene (600937.0014) confers susceptibility. In French white families, Vionnet et al. (2000) found evidence for a susceptibility locus for type 2 diabetes on 3q27-qter. They confirmed the diabetes susceptibility locus on 1q21-q24 reported by Elbein et al. (1999) in whites and by Hanson et al. (1998) in Pima Indians. A mutation in the GPD2 gene (138430.0001) on chromosome 2q24.1, encoding mitochondrial glycerophosphate dehydrogenase, was found in a patient with type 2 diabetes mellitus and in his glucose-intolerant half sister. Mutations in the PAX4 gene (167413) have been identified in patients with type 2 diabetes. Triggs-Raine et al. (2002) stated that in the Oji-Cree, a gly319-to-ser change in HNF1-alpha (142410.0008) behaves as a susceptibility allele for type 2 diabetes. Mutation in the HNF1B gene (189907.0007) was found in 2 Japanese patients with typical late-onset type 2 diabetes. Mutations in the IRS1 gene (147545) have been found in patients with type 2 diabetes. A missense mutation in the AKT2 gene (164731.0001) caused autosomal dominant type 2 diabetes in 1 family. A (single-nucleotide polymorphism) SNP in the 3-prime untranslated region of the resistin gene (605565.0001) was associated with susceptibility to diabetes and to insulin resistance-related hypertension in Chinese subjects. Susceptibility to insulin resistance has been associated with polymorphism in the TCF1 (142410.0011), PPP1R3A (600917.0001), PTPN1 (176885.0001), ENPP1 (173335.0006), IRS1 (147545.0002), and EPHX2 (132811.0001) genes. The K121Q polymorphism of ENPP1 (173335.0006) is associated with susceptibility to type 2 diabetes; a haplotype defined by 3 SNPs of this gene, including K121Q, is associated with obesity, glucose intolerance, and type 2 diabetes. A SNP in the promoter region of the hepatic lipase gene (151670.0004) predicts conversion from impaired glucose tolerance to type 2 diabetes. Variants of transcription factor 7-like-2 (TCF7L2; 602228.0001), located on 10q, have also been found to confer risk of type 2 diabetes. A common sequence variant, rs10811661, on chromosome 9p21 near the CDKN2A (600160) and CDKN2B (600431) genes has been associated with risk of type 2 diabetes. Variation in the PPARG gene (601487) has been associated with risk of type 2 diabetes. A promoter polymorphism in the IL6 gene (147620) is associated with susceptibility to NIDDM. Variation in the KCNJ15 gene (602106) has been associated with T2D in lean Asians. Variation in the SLC30A8 gene (611145) has been associated with susceptibility to T2D. Variation in the HMGA1 gene (600701.0001) is associated with an increased risk of type 2 diabetes. Mutation in the MTNR1B gene (600804) is associated with susceptibility to type 2 diabetes. Protection Against Type 2 Diabetes Mellitus Protein-truncating variants in the SLC30A8 (611145) have been associated with a reduced risk for T2D. [from OMIM]

Schizophrenia is highly heritable, as shown by family, twin, and adoption studies. For example, for identical twins, if one twin develops schizophrenia, the other twin has about a 50% chance of also developing the disease. The risk of the general population developing the schizophrenia is about 0.3-0.7% worldwide. The search for “schizophrenia genes” has been elusive. Initial linkage studies looked at parts of the genome associated with schizophrenia, and many candidate genes were identified, including APOE, COMT, DAO, DRD1, DRD2, DRD4, DTNBP1, GABRB2, GRIN2B, HP, IL1B, MTHFR, PLXNA2, SLC6A4, TP53, and TPH1. However, some of these have later been questioned. Microdeletions and microduplications have been found to be three times more common in individuals with schizophrenia, compared to controls. Because these deletions and duplications are in genes that are overexpressed in pathways related to brain development, it is possible that the inheritance of multiple rare variants may contribute to the development of schizophrenia. Several genetic disorders feature schizophrenia as a clinical feature. The 22q11.2 Deletion Syndrome comprises many different syndromes, of which one of the most serious is DiGeorge syndrome. Children born with DiGeorge syndrome typically have heart defects, cleft palate, learning difficulties, and immune deficiency. Schizophrenia is a late manifestation, affecting around 30% of individuals. Microdeletions and duplications in chromosome 1, 2, 3, 7, 15 and 16 have also been associated with schizophrenia. In 2014, a genome-wide association study looked at the genomes of over 35,000 patients and 110,00 controls. The study identified 108 SNPs that were associated with schizophrenia, 83 of which had not been previously reported. As expected, many of these loci occurred in genes that are expressed in the brain. For example, the SNPs included a gene that encodes the dopamine D2 receptor, DRD2 (the target of antipsychotic drugs), and many genes involved in glutamine neurotransmitter pathways and synaptic plasticity (e.g., GRM3, GRIN2A, SRR, GRIA1). More surprisingly, however, associations were also enriched among genes expressed in tissues with important immune functions. In 2016, a study based on nearly 65,000 people investigated the association between schizophrenia and variation in the Major Histocompatibility Complex (MHC) locus—a region on chromosome 6 that is important for immune function. The study focused on the C4 gene (complement component 4) that exists as two distinct genes: C4A and C4B, which encode particularly structurally diverse alleles. The study found that the alleles which promoted greater expression of C4A in the brain were associated with a greater risk of schizophrenia. By using mice models, the study showed that C4 is involved in the elimination of synapses during brain maturation. In humans, “synaptic pruning” is most active during late adolescence, which coincides with the typical onset of symptoms of schizophrenia. It is therefore possible that the inheritance of specific C4A alleles could lead to “run away” synaptic pruning, increasing the risk of schizophrenia. Further research may even determine C4 as a potential therapeutic target. [from Medical Genetics Summaries]

Familial exudative vitreoretinopathy (FEVR) is an inherited disorder characterized by the incomplete development of the retinal vasculature. Its clinical appearance varies considerably, even within families, with severely affected patients often registered as blind during infancy, whereas mildly affected patients with few or no visual problems may have such a small area of avascularity in their peripheral retina that it is visible only by fluorescein angiography. It is believed that this peripheral avascularity is the primary anomaly in FEVR and results from defective retinal angiogenesis. The sight-threatening features of the FEVR phenotype are considered secondary to retinal avascularity and develop because of the resulting retinal ischemia; they include the development of hyperpermeable blood vessels, neovascularization, vitreoretinal traction, retinal folds, and retinal detachments (summary by Poulter et al., 2010). In 31 Chinese pedigrees clinically diagnosed with FEVR, Rao et al. (2017) analyzed 6 FEVR-associated genes and identified mutations in 12 of the probands, including 5 (16.1%) in LRP5, 3 (9.7%) in NDP, 2 (6.5%) in FZD4, and 1 (3.2%) in TSPAN12. In addition, a mutation in the KIF11 gene (148760) was identified in a patient who also exhibited microcephaly (MCLMR; 152950). The authors noted that their detection rate did not exceed 50%, suggesting that other FEVR-associated genes remained to be discovered. Genetic Heterogeneity of Familial Exudative Vitreoretinopathy Also see EVR2 (305390), caused by mutation in the NDP gene (300658) on chromosome Xp11; EVR3 (605750), mapped to 11p13-p12; EVR4 (601813), caused by mutations in the LRP5 gene (603506) on 11q13.4; EVR5 (613310), caused by mutation in the TSPAN12 gene (613138) on 7q31; EVR6 (616468), caused by mutation in the ZNF408 gene (616454) on 11p11; and EVR7 (617572), caused by mutation in the CTNNB1 gene (116806) on chromosome 3p22. [from OMIM]

Miscarriage, the commonest complication of pregnancy, is the spontaneous loss of a pregnancy before the fetus has reached viability. The term therefore includes all pregnancy losses from the time of conception until 24 weeks of gestation. Recurrent miscarriage, defined as 3 or more consecutive pregnancy losses, affects about 1% of couples; when defined as 2 or more losses, the scale of the problem increases to 5% of all couples trying to conceive (summary by Rai and Regan, 2006). Pregnancy losses have traditionally been designated 'spontaneous abortions' if they occur before 20 weeks gestation and 'stillbirths' if they occur after 20 weeks. Subtypes of spontaneous abortions can be further distinguished on the basis of embryonic development and include anembryonic loss in the first 5 weeks after conception (so-called 'blighted ovum'), embryonic loss from 6 to 9 weeks' gestation, and fetal loss from 10 weeks' gestation through the remainder of the pregnancy. These distinctions are important because the causes of pregnancy loss vary over gestational ages, with anembryonic losses being more likely to be associated with chromosomal abnormalities, for example. Possible etiologies for RPRGL include uterine anatomic abnormalities, cytogenetic abnormalities in the parents or fetus, single gene disorders, thrombophilic conditions, and immunologic or endocrine factors as well as environmental or infectious agents (summary by Warren and Silver, 2008). Genetic Heterogeneity of Recurrent Pregnancy Loss Susceptibility to RPRGL2 (614390) is conferred by mutation in the coagulation factor II gene (176930) on chromosome 11p11; RPRGL3 (614391) by mutation in the ANXA5 gene (131230) on chromosome 4q27; and RPRGL4 (see 270960) by mutation in the SYCP3 gene (604759) on chromosome 12q23. Genetic variation in the conceptus itself that results in decreased viability of the embryo or fetus is discussed in the respective gene and/or phenotype entry (see, e.g., MTHFR, 607093.0004; NLRP7, 609661; hydatidiform mole, 231090). [from OMIM]

The pathogenesis of HIV infection and the progression from infection to AIDS vary significantly between exposed individuals. Infection occurs after the virus, which has macrophage (M)- and T lymphocyte (T)-tropic strains and more than 12 subtypes, survives an array of nonspecific, nongenetic environmental and host factors. [from OMIM]

The Heidelberg histologic classification of renal cell tumors subdivides renal cell tumors into benign and malignant parenchymal neoplasms and, where possible, limits each subcategory to the most common documented genetic abnormalities (Kovacs et al., 1997). Malignant tumors are subclassified into common or conventional renal cell carcinoma (clear cell); papillary renal cell carcinoma; chromophobe renal cell carcinoma; collecting duct carcinoma, with medullary carcinoma of the kidney; and unclassified renal cell carcinoma. The common or conventional type accounts for about 75% of renal cell neoplasms and is characterized genetically by a highly specific deletion of chromosome 3p. Papillary renal cell carcinoma (see 605074) accounts for about 10% of renal cell tumors. Chromophobe renal cell carcinoma accounts for approximately 5% of renal cell neoplasms. Genetically, chromophobe RCC is characterized by a combination of loss of heterozygosity of chromosomes 1, 2, 6, 10, 13, 17, and 21 and hypodiploid DNA content. Collecting duct carcinoma accounts for about 1% of renal cell carcinoma. Renal cell carcinoma occurs nearly twice as often in men as in women; incidence in the United States is equivalent among whites and blacks. Cigarette smoking doubles the likelihood of renal cell carcinoma and contributes to as many as one-third of cases. Obesity is also a risk factor, particularly in women. Other risk factors include hypertension, unopposed estrogen therapy, and occupational exposure to petroleum products, heavy metals, or asbestos (summary by Motzer et al., 1996). Genetic Heterogeneity of Renal Cell Carcinoma Germline mutation resulting in nonpapillary renal cell carcinoma of the clear cell and chromophobe type occurs in the HNF1A gene (142410) and the HNF1B gene (189907). Somatic mutations in renal cell carcinomas occur in the VHL gene (608537), the TRC8 gene (603046), the OGG1 gene (601982), the ARMET gene (601916), the FLCN gene (607273), and the BAP1 gene (603089). See also RCCX1 (300854) for a discussion of renal cell carcinoma associated with translocations of chromosome Xp11.2 involving the TFE3 gene (314310). For a discussion of papillary renal cell carcinoma, see RCCP1 (605074). Occurrence of Renal Cell Carcinoma in Other Disorders Von Hippel-Lindau syndrome (193300) is a familial multicancer syndrome in which there is a susceptibility to a variety of neoplasms, including renal cell carcinoma of clear cell histology and renal cysts. A syndrome of predisposition to uterine leiomyomas and papillary renal cell carcinoma has been reported (150800). Medullary carcinoma of the kidney is believed to arise from the collecting ducts of the renal medulla and is associated with sickle cell trait (603903) (Kovacs et al., 1997). Renal cell carcinoma occurs in patients with the Birt-Hogg-Dube syndrome (135150). Bertolotto et al. (2011) identified a missense mutation in the MITF (156845) gene that increases the risk of renal cell carcinoma with or without malignant melanoma (CMM8; 614456). [from OMIM]

Hepatocellular carcinoma is the major histologic type of malignant primary liver neoplasm. It is the fifth most common cancer and the third most common cause of death from cancer worldwide. The major risk factors for HCC are chronic hepatitis B virus (HBV) infection, chronic hepatitis C virus (HCV) infection, prolonged dietary aflatoxin exposure, alcoholic cirrhosis, and cirrhosis due to other causes. Hepatoblastomas comprise 1 to 2% of all malignant neoplasms of childhood, most often occurring in children under 3 years of age. Hepatoblastomas are thought to be derived from undifferentiated hepatocytes (Taniguchi et al., 2002). [from OMIM]

MPPH (megalencephaly-postaxial polydactyly-polymicrogyria-hydrocephalus) syndrome is a developmental brain disorder characterized by megalencephaly (brain overgrowth) with the cortical malformation bilateral perisylvian polymicrogyria (BPP). At birth the occipital frontal circumference (OFC) ranges from normal to 6 standard deviations (SD) above the mean for age, sex, and gestational age; in older individuals the range is from 3 to 10 SD above the mean. A variable degree of ventriculomegaly is seen in almost all children with MPPH syndrome; nearly 50% of individuals have frank hydrocephalus. Neurologic problems associated with BPP include oromotor dysfunction (100%), epilepsy (50%), and mild-to-severe intellectual disability (100%). Postaxial hexadactyly occurs in 50% of individuals with MPPH syndrome. [from GeneReviews]

Tetrahydrobiopterin (BH4)-deficient hyperphenylalaninemia (HPA) comprises a genetically heterogeneous group of progressive neurologic disorders caused by autosomal recessive mutations in the genes encoding enzymes involved in the synthesis or regeneration of BH4. BH4 is a cofactor for phenylalanine hydroxylase (PAH; 612349), tyrosine hydroxylase (TH; 191290) and tryptophan hydroxylase (TPH1; 191060), the latter 2 of which are involved in neurotransmitter synthesis. The BH4-deficient HPAs are characterized phenotypically by hyperphenylalaninemia, depletion of the neurotransmitters dopamine and serotonin, and progressive cognitive and motor deficits (Dudesek et al., 2001). HPABH4A, caused by mutations in the PTS gene, represents the most common cause of BH4-deficient hyperphenylalaninemia (Dudesek et al., 2001). Other forms of BH4-deficient HPA include HPABH4B (233910), caused by mutation in the GCH1 gene (600225), HPABH4C (261630), caused by mutation in the QDPR gene (612676), and HPABH4D (264070), caused by mutation in the PCBD1 gene (126090). Niederwieser et al. (1982) noted that about 1 to 3% of patients with hyperphenylalaninemia have one of these BH4-deficient forms. These disorders are clinically and genetically distinct from classic phenylketonuria (PKU; 261600), caused by mutation in the PAH gene. Two additional disorders associated with BH4 deficiency and neurologic symptoms do not have overt hyperphenylalaninemia as a feature: dopa-responsive dystonia (612716), caused by mutation in the SPR gene (182125), and autosomal dominant dopa-responsive dystonia (DYT5; 128230), caused by mutation in the GCH1 gene. Patients with these disorders may develop hyperphenylalaninemia when stressed. [from OMIM]

Miscarriage, the commonest complication of pregnancy, is the spontaneous loss of a pregnancy before the fetus has reached viability. The term therefore includes all pregnancy losses from the time of conception until 24 weeks of gestation. Recurrent miscarriage, defined as 3 or more consecutive pregnancy losses, affects about 1% of couples; when defined as 2 or more losses, the scale of the problem increases to 5% of all couples trying to conceive (summary by Rai and Regan, 2006). Pregnancy losses have traditionally been designated 'spontaneous abortions' if they occur before 20 weeks' gestation and 'stillbirths' if they occur after 20 weeks. Subtypes of spontaneous abortions can be further distinguished on the basis of embryonic development and include anembryonic loss in the first 5 weeks after conception (so-called 'blighted ovum'), embryonic loss from 6 to 9 weeks' gestation, and fetal loss from 10 weeks' gestation through the remainder of the pregnancy. These distinctions are important because the causes of pregnancy loss vary over gestational ages, with anembryonic losses being more likely to be associated with chromosomal abnormalities, for example. Possible etiologies for recurrent pregnancy loss include uterine anatomic abnormalities, cytogenetic abnormalities in the parents or fetus, single gene disorders, thrombophilic conditions, and immunologic or endocrine factors as well as environmental or infectious agents (summary by Warren and Silver, 2008). [from OMIM]

The features of Ehlers-Danlos syndrome spondylodysplastic type 2 (EDSSPD2) include an aged appearance, developmental delay, short stature, craniofacial disproportion, generalized osteopenia, defective wound healing, hypermobile joints, hypotonic muscles, and loose but elastic skin (Okajima et al., 1999). For a discussion of genetic heterogeneity of the spondylodysplastic type of Ehlers-Danlos syndrome, see 130070. [from OMIM]

Optic atrophy-9 (OPA9) is characterized by onset of decreased visual acuity and optic disc pallor in the first decade of life, with severely reduced visual acuity and color vision deficits observed in the third decade. Although initially described as an autosomal recessive disease (Metodiev et al., 2014; Kelman et al., 2018; Gibson et al., 2020), autosomal dominant cases of OPA9 have also been reported (Charif et al., 2021). Mutation in the ACO2 gene also causes a neurodegenerative disorder, infantile cerebellar-retinal degeneration (ICRD; 614559), of which optic atrophy is a feature. Dominant and Recessive OPA9 From a cohort of approximately 1,000 patients with optic atrophy, Charif et al. (2021) identified 50 probands with dominant mutations in the ACO2 gene, and 11 patients with biallelic variants. There was no significant difference in distribution of mutation type, with two-thirds of all variants being missense mutations in both groups, and nonsense, frameshift, and splice site mutations comprising the remaining third. Age at onset of symptoms occurred during the first 2 decades, without significant difference between dominant and recessive cases. Visual acuity was significantly more affected in recessive cases than in dominant ones, with more than 60% of eyes from the recessive group having a visual acuity lower than 20/200, whereas more than 80% of eyes from the dominant group had a visual acuity above 20/200. Analysis of the optic disc as well as retinal nerve fiber layer thickness measurements indicated a preferential involvement of the temporal quadrant in both patient groups. Assessment of color vision revealed highly variable alterations, including protan, deutan, and tritan types of dyschromatopsia. Some patients had additional retinal changes, including macular microcysts as well as macular dystrophy in 1 case. Extraocular symptoms were observed in 6 (12%) of the dominant cases and in 3 (27%) of the recessive cases, including hearing impairment in 2 dominant cases, and late-onset cerebellar ataxia in 1 dominant case and in 1 recessive case. [from OMIM]

Sofosbuvir is an antiviral agent used in the treatment of chronic hepatitis C virus (HCV) infection. Sofosbuvir is FDA-approved to treat patients infected with HCV genotypes 1, 2, 3, and 4, as part of a combination antiviral treatment regimen. HCV genotype 1 is the most prevalent worldwide and HCV genotype 3 is the next most prevalent. Sofosbuvir may also be used as part of the treatment regimen of HCV genotypes 5 or 6. About 180 million people worldwide are infected with chronic hepatitis C, which is a major cause of chronic liver disease, cirrhosis, and liver cancer. Viral eradication is suboptimal with peginterferon plus ribavirin-based therapy, with only about half of patients with HCV genotype 1 infection achieving a sustained virological response (SVR) after 24 weeks. A SVR is defined as undetectable HCV RNA by the end of treatment or at a specific number of weeks after the initiation of treatment, e.g., undetectable HCV RNA at 12 weeks is annotated (SVR12). Direct-acting antivirals (DAAs), such as sofosbuvir, were developed to improve viral eradication rates. They target HCV-encoded proteins involved in viral replication and infection. Sofosbuvir, the first and thus far only DAA, targets NS5B polymerase, the viral enzyme required for HCV RNA replication. Sofosbuvir may be used in combination with peginterferon. The genetic variant rs12979860, located in the INFL4 gene, is a strong predictor of response to peginterferon-based therapies. The variant is a C to T change—individuals with the favorable "C/C" genotype have about a 2-fold higher likelihood of achieving SVR compared to individuals with CT or TT genotypes. (Note, because the association of rs12979860 with treatment response was reported several years before the discovery of IFNL4, the variant is commonly, but mistakenly, referred to as IL28B, which is the previous name for the IFNL3 gene.) For specific treatment regimens that include sofosbuvir, although the IFNL4 variant still influences treatment outcomes, the SVR remains relatively high for all IFNL4 genotypes. For example in the NEUTRINO study, which is referred to in the FDA-approved drug label for sofosbuvir, the SVR12 rate was 99% in individuals with baseline C/C alleles and 87% in individuals with baseline non-C/C alleles. The individuals in this study had HCV genotype 1 or 4 infection, and were receiving sofosbuvir plus peginterferon plus ribavirin therapy. The drug label for sofosbuvir also discusses viral resistance. In cell culture, the amino acid substitution S282T in the viral NS5B polymerase is associated with reduced susceptibility to sofosbuvir. During the ELECTRON trial, this substitution was transiently detected in one individual who relapsed during sofosbuvir monotherapy. However, the clinical significance of such substitutions remains unknown. [from Medical Genetics Summaries]

Azoospermia, a condition in which there are no sperm present in the ejaculate, has historically been divided into 2 broad categories, obstructive (e.g., 277180) and nonobstructive. Among the genetically based, inherited nonobstructive causes are defects of spermatogenesis, which may interrupt the development of the sperm at various stages, either before (e.g., 415000) or during meiosis. SPGF4 is a form of azoospermia due to perturbations of meiosis. For a discussion of phenotypic and genetic heterogeneity of spermatogenic failure, see SPGF1 (258150). Recurrent Pregnancy Loss Miscarriage, the commonest complication of pregnancy, is the spontaneous loss of a pregnancy before the fetus has reached viability. The term therefore includes all pregnancy losses from the time of conception until 24 weeks' gestation. Recurrent miscarriage, defined as 3 or more consecutive pregnancy losses, affects about 1% of couples; when defined as 2 or more losses, the scale of the problem increases to 5% of all couples trying to conceive (summary by Rai and Regan, 2006). Pregnancy losses have traditionally been designated 'spontaneous abortions' if they occur before 20 weeks' gestation and 'stillbirths' if they occur after 20 weeks. Subtypes of spontaneous abortions can be further distinguished on the basis of embryonic development and include anembryonic loss in the first 5 weeks after conception (so-called 'blighted ovum'), embryonic loss from 6 to 9 weeks' gestation, and fetal loss from 10 weeks' gestation through the remainder of the pregnancy. These distinctions are important because the causes of pregnancy loss vary over gestational ages, with anembryonic losses being more likely to be associated with chromosomal abnormalities, for example. Possible etiologies for recurrent pregnancy loss include uterine anatomic abnormalities, cytogenetic abnormalities in the parents or fetus, single gene disorders, thrombophilic conditions, and immunologic or endocrine factors as well as environmental or infectious agents (summary by Warren and Silver, 2008). For a discussion of genetic heterogeneity of recurrent pregnancy loss, see RPRGL1 (614389). [from OMIM]

Miscarriage, the commonest complication of pregnancy, is the spontaneous loss of a pregnancy before the fetus has reached viability. The term therefore includes all pregnancy losses from the time of conception until 24 weeks of gestation. Recurrent miscarriage, defined as 3 or more consecutive pregnancy losses, affects about 1% of couples; when defined as 2 or more losses, the scale of the problem increases to 5% of all couples trying to conceive (summary by Rai and Regan, 2006). Pregnancy losses have traditionally been designated 'spontaneous abortions' if they occur before 20 weeks' gestation and 'stillbirths' if they occur after 20 weeks. Subtypes of spontaneous abortions can be further distinguished on the basis of embryonic development and include anembryonic loss in the first 5 weeks after conception (so-called 'blighted ovum'), embryonic loss from 6 to 9 weeks' gestation, and fetal loss from 10 weeks' gestation through the remainder of the pregnancy. These distinctions are important because the causes of pregnancy loss vary over gestational ages, with anembryonic losses being more likely to be associated with chromosomal abnormalities, for example. Possible etiologies for recurrent pregnancy loss include uterine anatomic abnormalities, cytogenetic abnormalities in the parents or fetus, single gene disorders, thrombophilic conditions, and immunologic or endocrine factors as well as environmental or infectious agents (summary by Warren and Silver, 2008). [from OMIM]

Porokeratosis is a rare skin disorder characterized by one or more annular plaques with a surrounding raised horny border that spreads centrifugally. Variants of porokeratosis have been described that differ in morphologic shapes, distribution, and clinical course (Schamroth et al., 1997). However, as noted by Sybert (2010), several families with expression of more than one variant of porokeratosis among members, and several individuals expressing more than one variant, have been reported, suggesting that the distinctions among these variants may be artificial. Mutations in the MVK gene have been found to cause multiple types of porokeratosis, which have been described as porokeratosis of Mibelli, porokeratoma, genital porokeratosis, hyperkeratotic porokeratosis, and linear porokeratosis. The preferred title of this entry was formerly 'Porokeratosis 1, Mibelli Type; POROK1.' Genetic Heterogeneity of Porokeratosis Also see porokeratosis-2 (POROK2; 175850), mapped to chromosome 12q24; POROK3 (175900), caused by mutation in the MVK gene (251170) on chromosome 12q24; POROK4 (607728), mapped to chromosome 15q25-q26; POROK5 (612293), mapped to chromosome 1p31; POROK6 (612353), mapped to chromosome 1p31; POROK7 (614714), caused by mutation in the MVD gene (603236) on chromosome 16q24; POROK8 (616063), caused by mutation in the SLC17A9 gene (612107) on chromosome 20q13; and POROK9 (616631), caused by mutation in the FDPS gene (134629) on chromosome 1q22. A palmoplantar form of punctate porokeratosis has also been described (PPKP2; 175860). Genotype/Phenotype Correlations Zhang et al. (2015) screened 12 isoprenoid genes in 134 Chinese probands with porokeratosis and identified mutations in the MVK, MVD, PMVK, and FDPS genes in 113 patients. The authors noted that giant plaque-type porokeratosis ptychotropica with lesion diameters of at least 5 cm appeared to be uniquely associated with mutation in MVK; it was observed in 19 (50%) of 38 MVK probands, but not in patients with mutations in any of the other 3 genes or in the 21 probands in whom no mutation was found. MVK patients also showed the widest range in terms of the number and size of lesions, as well as presence of porokeratosis subtypes. In patients with MVD mutations, the age of onset ranged from 5 to 70 years, and lesion diameters were generally less than 2 cm. In addition, 6 of the 62 MVD probands exhibited solar facial porokeratosis, which was not seen in any other patients. Localized genital porokeratosis and porokeratoma appeared to be uniquely associated with mutation in the PMVK gene, whereas patients with mutations in the FDPS gene had more than 500 lesions, all with diameters of 1 cm or less. [from OMIM]

An autosomal dominant condition caused by mutation(s) in the SCN1A gene, encoding sodium channel protein type 1 subunit alpha. It is characterized by isolated febrile seizures, typically with onset between 3 months to 5 years, with spontaneous remission by 6 years of age. Mutation(s) in the SCN1A gene are also responsible for generalized epilepsy with febrile seizures plus, type 2; and Dravet syndrome. [from NCI]

The term frontonasal dysplasia was coined by Sedano et al. (1970) to describe a constellation of findings limited to the face and head. The disorder is defined as 2 or more of the following: (1) true ocular hypertelorism; (2) broadening of the nasal root; (3) median facial cleft affecting the nose and/or upper lip and palate; (4) unilateral or bilateral clefting of the alae nasi; (5) lack of formation of the nasal tip; (6) anterior cranium bifidum occultum (see 168500); and (7) a V-shaped or widow's peak frontal hairline (Sedano and Gorlin, 1988). Most reported cases are sporadic, but a few familial cases have been reported. Twigg et al. (2009) characterized frontonasal malformation (FNM) as a 'very heterogeneous group of disorders' and summarized clinical features. Also see acromelic frontonasal dysplasia (AFND; 603671), frontofacionasal dysplasia (FFND; 229400), oculoauriculofrontonasal syndrome (OAFNS; 601452), the acrofrontofacionasal dysostosis syndromes (201180, 239710), and craniofrontonasal syndrome (304110). Genetic Heterogeneity of Frontonasal Dysplasia Frontonasal dysplasia-2 (FND2; 613451) is caused by mutation in the ALX4 gene (605420) on chromosome 11p11. Frontonasal dysplasia-3 (FND3; 613456) is caused by mutation in the ALX1 gene (601527) on chromosome 12q21. [from OMIM]

Nocturnal enuresis, or nightly bedwetting in children more than 7 years of age, affects about 10% of 7-year-old children, with a wide range of frequencies between populations. The affliction is often linked to major social maladjustments and occupies considerable time in general medical practice. From the age of 7, there is a spontaneous cure rate of 15% per year, such that few remain affected after the age of 16 years. There are 2 types of nocturnal enuresis: type I, the primary form (PNE), with at least 3 nightly episodes in children older than 7 years, where the child has always had the disorder, and type II, or secondary type, where the child has been dry for at least 6 months but enuresis has recurred (summary by Eiberg et al., 1995). Genetic Heterogeneity of Nocturnal Enuresis ENUR1 has been mapped to chromosome 13q, and ENUR2 has been mapped to chromosome 12q. [from OMIM]

Obesity associated with an identifiable mutation in a single gene. [from NCI]