MedGen

Retinitis pigmentosa-46 (RP46) is characterized by night blindness, loss of peripheral vision, and reduced visual acuity. Funduscopic findings are typical of RP, including pale optic discs, attenuated retinal vessels, and intraretinal pigment deposits. Electroretinography shows substantial loss of rod and cone photoreceptor function (Hartong et al., 2008). For a discussion of genetic heterogeneity of retinitis pigmentosa, see 268000. [from OMIM]

The PTEN hamartoma tumor syndrome (PHTS) includes Cowden syndrome (CS), Bannayan-Riley-Ruvalcaba syndrome (BRRS), PTEN-related Proteus syndrome (PS), and PTEN-related Proteus-like syndrome. CS is a multiple hamartoma syndrome with a high risk for benign and malignant tumors of the thyroid, breast, kidney, and endometrium. Affected individuals usually have macrocephaly, trichilemmomas, and papillomatous papules, and present by the late 20s. The lifetime risk of developing breast cancer is 85%, with an average age of diagnosis between 38 and 46 years. The lifetime risk for thyroid cancer (usually follicular, rarely papillary, but never medullary thyroid cancer) is approximately 35%. The lifetime risk for renal cell cancer (predominantly of papillary histology) is 34%. The risk for endometrial cancer may approach 28%. BRRS is a congenital disorder characterized by macrocephaly, intestinal hamartomatous polyposis, lipomas, and pigmented macules of the glans penis. PS is a complex, highly variable disorder involving congenital malformations and hamartomatous overgrowth of multiple tissues, as well as connective tissue nevi, epidermal nevi, and hyperostoses. Proteus-like syndrome is undefined but refers to individuals with significant clinical features of PS who do not meet the diagnostic criteria for PS. [from GeneReviews]

P450scc deficiency is a rare disorder that can present as acute adrenal insufficiency in infancy or childhood. ACTH and plasma renin activity are grossly elevated and adrenal steroids are inappropriately low or absent; the 46,XY patients have female external genitalia, sometimes with clitoromegaly. The phenotypic spectrum ranges from prematurity, complete underandrogenization, and severe early-onset adrenal failure to term birth with clitoromegaly and later-onset adrenal failure (summary by Kim et al., 2008). Although hormonal and phenotypic features can resemble those of congenital lipoid adrenal hyperplasia (lipoid CAH; 201710), no patient with P450scc deficiency has been described with the massive adrenal enlargement typical of lipoid CAH (summary by Sahakitrungruang et al., 2011). [from OMIM]

Swyer syndrome is a condition that affects sex development. Sex development usually follows a particular path based on an individual's chromosomes; however, in Swyer syndrome, sex development is not typical for the affected individual's chromosomal pattern.

Chromosomes contain the genetic instructions for how the body develops and functions. People usually have 46 chromosomes in each cell. Two of the 46 chromosomes, known as X and Y, are called sex chromosomes because they help determine whether a person will develop male or female reproductive structures. Girls and women typically have two X chromosomes (46,XX karyotype), while boys and men typically have one X chromosome and one Y chromosome (46,XY karyotype). In Swyer syndrome, individuals have one X chromosome and one Y chromosome in each cell, which is the pattern typically found in boys and men; however, they have female reproductive structures.

Because they appear female on the outside, babies with Swyer syndrome are usually raised as girls and develop a female gender identity, which is a person's sense of their gender (girl, boy, a combination, or neither). Swyer syndrome may be identified before birth, at birth, or later when a child does not go through puberty as usual. Because they do not have functional ovaries that produce hormones, affected individuals often begin hormone replacement therapy during early adolescence to start puberty, causing the breasts and uterus to grow, and eventually leading to menstruation. Hormone replacement therapy is also important for bone health and helps reduce the risk of low bone density (osteopenia) and fragile bones (osteoporosis). Women with Swyer syndrome do not produce eggs (ova), but if they have a uterus, they may be able to become pregnant with a donated egg or embryo.

People with Swyer syndrome have female external genitalia and some female internal reproductive structures. These individuals usually have a uterus and fallopian tubes, but their gonads (ovaries or testes) are not functional. Instead, the gonads are small and underdeveloped and contain little gonadal tissue. These structures are called  streak gonads. The streak gonadal tissue is at risk of developing cancer that is often hard-to-detect, so it is usually removed surgically. Swyer syndrome is also called 46,XY complete gonadal dysgenesis; the medical term “dysgenesis” means "abnormal development." [from MedlinePlus Genetics]

The PTEN hamartoma tumor syndrome (PHTS) includes Cowden syndrome (CS), Bannayan-Riley-Ruvalcaba syndrome (BRRS), PTEN-related Proteus syndrome (PS), and PTEN-related Proteus-like syndrome. CS is a multiple hamartoma syndrome with a high risk for benign and malignant tumors of the thyroid, breast, kidney, and endometrium. Affected individuals usually have macrocephaly, trichilemmomas, and papillomatous papules, and present by the late 20s. The lifetime risk of developing breast cancer is 85%, with an average age of diagnosis between 38 and 46 years. The lifetime risk for thyroid cancer (usually follicular, rarely papillary, but never medullary thyroid cancer) is approximately 35%. The lifetime risk for renal cell cancer (predominantly of papillary histology) is 34%. The risk for endometrial cancer may approach 28%. BRRS is a congenital disorder characterized by macrocephaly, intestinal hamartomatous polyposis, lipomas, and pigmented macules of the glans penis. PS is a complex, highly variable disorder involving congenital malformations and hamartomatous overgrowth of multiple tissues, as well as connective tissue nevi, epidermal nevi, and hyperostoses. Proteus-like syndrome is undefined but refers to individuals with significant clinical features of PS who do not meet the diagnostic criteria for PS. [from GeneReviews]

The PTEN hamartoma tumor syndrome (PHTS) includes Cowden syndrome (CS), Bannayan-Riley-Ruvalcaba syndrome (BRRS), PTEN-related Proteus syndrome (PS), and PTEN-related Proteus-like syndrome. CS is a multiple hamartoma syndrome with a high risk for benign and malignant tumors of the thyroid, breast, kidney, and endometrium. Affected individuals usually have macrocephaly, trichilemmomas, and papillomatous papules, and present by the late 20s. The lifetime risk of developing breast cancer is 85%, with an average age of diagnosis between 38 and 46 years. The lifetime risk for thyroid cancer (usually follicular, rarely papillary, but never medullary thyroid cancer) is approximately 35%. The lifetime risk for renal cell cancer (predominantly of papillary histology) is 34%. The risk for endometrial cancer may approach 28%. BRRS is a congenital disorder characterized by macrocephaly, intestinal hamartomatous polyposis, lipomas, and pigmented macules of the glans penis. PS is a complex, highly variable disorder involving congenital malformations and hamartomatous overgrowth of multiple tissues, as well as connective tissue nevi, epidermal nevi, and hyperostoses. Proteus-like syndrome is undefined but refers to individuals with significant clinical features of PS who do not meet the diagnostic criteria for PS. [from GeneReviews]

Nonsyndromic 46,XX testicular disorders/differences of sex development (DSD) are characterized by: the presence of a 46,XX karyotype; external genitalia ranging from typical male to ambiguous; two testicles; azoospermia; absence of müllerian structures; and absence of other syndromic features, such as congenital anomalies outside of the genitourinary system, learning disorders / cognitive impairment, or behavioral issues. Approximately 85% of individuals with nonsyndromic 46,XX testicular DSD present after puberty with normal pubic hair and normal penile size but small testes, gynecomastia, and sterility resulting from azoospermia. Approximately 15% of individuals with nonsyndromic 46,XX testicular DSD present at birth with ambiguous genitalia. Gender role and gender identity are reported as male. If untreated, males with 46,XX testicular DSD experience the consequences of testosterone deficiency. [from GeneReviews]

CHMP2B frontotemporal dementia (CHMP2B-FTD) has been described in a single family from Denmark, in one individual with familial FTD from Belgium, and in one individual with FTD and no family history. It typically starts between ages 46 and 65 years with subtle personality changes and slowly progressive behavioral changes, dysexecutive syndrome, dyscalculia, and language disturbances. Disinhibition or loss of initiative is the most common presenting symptom. The disease progresses over a few years into profound dementia with extrapyramidal symptoms and mutism. Several individuals have developed an asymmetric akinetic rigid syndrome with arm and gait dystonia and pyramidal signs that may be related to treatment with neuroleptic drugs. Symptoms and disease course are highly variable. Disease duration may be as short as three years or longer than 20 years. [from GeneReviews]

GRIN2D-related developmental and epileptic encephalopathy (GRIN2D-related DEE) is characterized by mild-to-profound developmental delay or intellectual disability, epilepsy, abnormal muscle tone (hypotonia and spasticity), movement disorders (dystonia, dyskinesia, chorea), autism spectrum disorder, and cortical visual impairment. Additional findings can include sleep disorders and feeding difficulties. To date 22 individuals with GRIN2D-related DEE have been reported. [from GeneReviews]

Autosomal recessive spastic paraplegia-46 (SPG46) is a neurodegenerative disorder characterized by onset in childhood of slowly progressive spastic paraplegia and cerebellar signs. Some patients have cognitive impairment, cataracts, and cerebral, cerebellar, and corpus callosum atrophy on brain imaging (summary by Boukhris et al., 2010 and Martin et al., 2013). For a discussion of genetic heterogeneity of autosomal recessive spastic paraplegia, see SPG5A (270800). [from OMIM]

Nonsyndromic 46,XX testicular disorders/differences of sex development (DSD) are characterized by: the presence of a 46,XX karyotype; external genitalia ranging from typical male to ambiguous; two testicles; azoospermia; absence of müllerian structures; and absence of other syndromic features, such as congenital anomalies outside of the genitourinary system, learning disorders / cognitive impairment, or behavioral issues. Approximately 85% of individuals with nonsyndromic 46,XX testicular DSD present after puberty with normal pubic hair and normal penile size but small testes, gynecomastia, and sterility resulting from azoospermia. Approximately 15% of individuals with nonsyndromic 46,XX testicular DSD present at birth with ambiguous genitalia. Gender role and gender identity are reported as male. If untreated, males with 46,XX testicular DSD experience the consequences of testosterone deficiency. [from GeneReviews]

Autosomal dominant tubulointerstitial kidney disease – MUC1 (ADTKD-MUC1) is characterized by slowly progressive tubulointerstitial disease that leads to end-stage renal disease (ESRD) and the need for dialysis or kidney transplantation. The rate of loss of kidney function for individuals is variable within and between families, with a median age of onset of end-stage renal disease (ESRD) of 46 years (range: ages 20-70 years). There are no other systemic manifestations. [from GeneReviews]

Mosaic variegated aneuploidy (MVA) syndrome is a rare disorder in which some cells in the body have an abnormal number of chromosomes instead of the usual 46 chromosomes, a situation known as aneuploidy. Most commonly, cells have an extra chromosome, which is called trisomy, or are missing a chromosome, which is known as monosomy. In MVA syndrome, some cells are aneuploid and others have the normal number of chromosomes, which is a phenomenon known as mosaicism. Typically, at least one-quarter of cells in affected individuals have an abnormal number of chromosomes. Because the additional or missing chromosomes vary among the abnormal cells, the aneuploidy is described as variegated.

In MVA syndrome, growth before birth is slow (intrauterine growth restriction). After birth, affected individuals continue to grow at a slow rate and are shorter than average. In addition, they typically have an unusually small head size (microcephaly). Another common feature of MVA syndrome is an increased risk of developing cancer in childhood. Cancers that occur most frequently in affected individuals include a cancer of muscle tissue called rhabdomyosarcoma, a form of kidney cancer known as Wilms tumor, and a cancer of the blood-forming tissue known as leukemia.

There are at least three types of MVA syndrome, each with a different genetic cause. Type 1 is the most common and displays the classic signs and symptoms described above. Type 2 appears to have slightly different signs and symptoms than type 1, although the small number of affected individuals makes it difficult to define its characteristic features. Individuals with MVA syndrome type 2 grow slowly before and after birth; however, their head size is typically normal. Some people with MVA syndrome type 2 have unusually short arms. Individuals with MVA syndrome type 2 do not seem to have an increased risk of cancer. Another form of MVA syndrome is characterized by a high risk of developing Wilms tumor. Individuals with this form may also have other signs and symptoms typical of MVA syndrome type 1.

Less commonly, people with MVA syndrome have eye abnormalities or distinctive facial features, such as a broad nasal bridge and low-set ears. Some affected individuals have brain abnormalities, the most common of which is called Dandy-Walker malformation. Intellectual disability, seizures, and other health problems can also occur in people with MVA syndrome. [from MedlinePlus Genetics]

Juvenile-onset cataract-46 with or without arrhythmic cardiomyopathy (CTRCT46) is characterized by onset of cataract in the first decades of life, associated with variable onset of a severe form of arrhythmic cardiomyopathy, with mild impairment of left ventricular systolic function but severe ventricular arrhythmias resulting in sudden cardiac death. Affected individuals are descendants of the Hutterite founder population (Abdelfatah et al., 2019). [from OMIM]

Any non-syndromic X-linked intellectual disability in which the cause of the disease is a mutation in the ARHGEF6 gene. [from MONDO]

Any autosomal recessive non-syndromic intellectual disability in which the cause of the disease is a mutation in the NDST1 gene. [from MONDO]

Spermatogenic failure-46 (SPGF46) is characterized by male infertility due to asthenoteratozoospermia. Sperm of affected men exhibit multiple morphologic abnormalities of the flagella (MMAF), including flagella that are absent, short, coiled, angulated, and/or of irregular caliber. Ultrastructural analysis shows disorganization of axonemal and periaxonemal structures (Liu et al., 2020). For a discussion of genetic heterogeneity of spermatogenic failure, see SPGF1 (258150). [from OMIM]

A rare genetic combined T and B cell immunodeficiency characterised by life-threatening infections due to disrupted transferrin receptor 1 endocytosis, resulting in defective cellular iron transport and impaired T and B cell function. Patients present with early-onset chronic diarrhoea, severe recurrent infections and failure to thrive. Laboratory studies reveal hypo or agammaglobulinaemia, normal lymphocyte counts but decreased numbers of memory B cells, intermittent neutropenia and thrombocytopenia, and mild anaemia (resistant to iron supplementation) with low mean corpuscular volume. [from SNOMEDCT_US]

Palmoplantar keratoderma-XX sex reversal-predisposition to squamous cell carcinoma syndrome is characterised by sex reversal in males with a 46, XX (SRY-negative) karyotype, palmoplantar hyperkeratosis and a predisposition to squamous cell carcinoma. To date, five cases (four of whom were brothers) have been described. The aetiology is unknown. [from ORDO]

A rare autosomal dominant cerebellar ataxia with characteristics of slowly progressive late-onset cerebellar ataxia variably combined with sensory axonal neuropathy. Patients may present gait and limb ataxia, dysarthria, abnormal oculomotor function and distal sensory impairment. Cerebellar atrophy is typically mild or absent. [from SNOMEDCT_US]