MedGen

Homocystinuria caused by cystathionine ß-synthase (CBS) deficiency is characterized by involvement of the eye (ectopia lentis and/or severe myopia), skeletal system (excessive height, long limbs, scolioisis, and pectus excavatum), vascular system (thromboembolism), and CNS (developmental delay/intellectual disability). All four ? or only one ? of the systems can be involved; expressivity is variable for all of the clinical signs. It is not unusual for a previously asymptomatic individual to present in adult years with only a thromboembolic event that is often cerebrovascular. Two phenotypic variants are recognized, B6-responsive homocystinuria and B6-non-responsive homocystinuria. B6-responsive homocystinuria is usually milder than the non-responsive variant. Thromboembolism is the major cause of early death and morbidity. IQ in individuals with untreated homocystinuria ranges widely, from 10 to 138. In B6-responsive individuals the mean IQ is 79 versus 57 for those who are B6-non-responsive. Other features that may occur include: seizures, psychiatric problems, extrapyramidal signs (e.g., dystonia), hypopigmentation of the skin and hair, malar flush, livedo reticularis, and pancreatitis. [from GeneReviews]

Any autosomal recessive nonsyndromic deafness in which the cause of the disease is a mutation in the TPRN gene. [from MONDO]

Spastic paraplegia-79B (SPG79B) is an autosomal recessive progressive neurologic disorder characterized by onset of spastic paraplegia and optic atrophy in the first decade of life. Additional features are variable, but may include peripheral neuropathy, cerebellar ataxia, and cognitive impairment (summary by Rydning et al., 2017). For a discussion of genetic heterogeneity of autosomal recessive spastic paraplegia, see SPG5A (270800). [from OMIM]

Present in 30% to 79% of the cases. [from HPO]

Developmental and epileptic encephalopathy-79 (DEE79) is a severe neurologic disorder characterized by onset of refractory seizures in the first months of life. Affected individuals have severely impaired psychomotor development and may show hypotonia or spasticity. Brain imaging may show hypomyelination, cerebral atrophy, and thinning of the corpus callosum (summary by Butler et al., 2018 and Hernandez et al., 2019). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350. [from OMIM]

Immunodeficiency-79 (IMD79) is an autosomal recessive disorder characterized by childhood onset of recurrent and recalcitrant skin warts due to uncontrolled viral infection with human papillomavirus (HPV). Some patients may also have recurrent respiratory infections beginning in childhood, but the phenotype overall is mild compared to other primary immunodeficiencies. Patients may not come to attention until adulthood. Laboratory studies show absence of the CD4 antigen on T cells, monocytes, and dendritic cells, with variable secondary abnormalities in B cells and NK cells due to lack of CD4+ T cells (summary by Lisco et al., 2021). [from OMIM]

Spermatogenic failure-79 (SPGF79) is characterized by male infertility due to an abnormal acrosome reaction and impaired membrane potential after capacitation. Some patients exhibit asthenoteratozoospermia, with defective acrosome formation and mitochondrial sheath assembly, and reduced progressive motility (Lv et al., 2022; Liu et al., 2022). For a general phenotypic description and discussion of genetic heterogeneity of spermatogenic failure, see SPGF1 (258150). [from OMIM]

Autosomal dominant deafness-79 (DFNA79) is a nonsyndromic form of progressive sensorineural hearing loss with age of onset ranging from 20 years to 65 years. Affected females appear to have milder hearing loss than males (Lu et al., 2020). [from OMIM]

Auriculocondylar syndrome-1 (ARCND1) is an autosomal dominant disorder of the first and second pharyngeal arches and is characterized by malformed ears (question mark ears), prominent cheeks, microstomia, abnormal temporomandibular joint, and mandibular condyle hypoplasia (summary by Masotti et al., 2008). Genetic Heterogeneity of Auriculocondylar Syndrome See also ARCND2A (614669), caused by heterozygous mutation in the PLCB4 gene (600810) on chromosome 20p12.3-p12.2; ARCND2B (620458), caused by biallelic mutation in the PLCB4 gene; ARCND3 (615706), caused by mutation in the EDN1 gene (131240) on chromosome 6p24; and ARCND4 (620457), caused by mutation the HDAC9 gene (606543) on chromosome 7p21. See also 612798 for isolated question mark ears. Reviews Kokitsu-Nakata et al. (2012) tabulated clinical findings in 24 reported cases of auriculocondylar syndrome. The most common clinical signs observed were ear constriction (100%), abnormal temporomandibular joint (100%), mandibular condyle abnormality (93%), malocclusion (93%), round face (78%), microstomia (78%), micrognathia (78%), prominent cheeks (74%), hearing loss (56%), abnormal palate (55%), and crowded teeth (50%). The authors noted that the phenotype was highly variable in severity, even within families. Liu et al. (2021) reviewed 19 published cases of ARCND1 and tabulated the common features, including micrognathia (79%), auricular malformation (68%), microstomia (67%), prominent cheeks (63%), mandibular hypoplasia (58%), and round face (58%). Asymmetry of mandibular and auricular malformations was present in 4 patients, and the lesions were either more severe on the right or only the right side was affected, suggesting a predilection for right-sided deformities. The authors also noted that severe cases mostly occurred in female patients. Prenatal findings were available in 3 patients, and all showed polyhydramnios, with 2 having micrognathia evident on ultrasonography. The authors suggested that severe micrognathia and mandibular hypoplasia accompanied by polyhydramnios might be prenatal indicators of ARCND. Using a standardized questionnaire sent to referring physicians, Vegas et al. (2022) collected clinical data on 39 patients from 27 families with auriculocondylar syndrome and mutation in the GNAI3, PLCB4, or EDN1 genes. PLCB4 was the most common gene associated with ARCND, being mutated in 16 (59%) of the 27 families. Incomplete penetrance and/or variable expression was observed within families. [from OMIM]

Autosomal recessive intellectual developmental disorder-79 (MRT79) is characterized by global developmental delay apparent from infancy. Affected individuals have mildly delayed walking with an ataxic gait and severely impaired intellectual development with poor or absent speech. Additional features may include postnatal microcephaly and dysmorphic features (Van Bergen et al., 2022). [from OMIM]

The spectrum of MECP2-related phenotypes in females ranges from classic Rett syndrome to variant Rett syndrome with a broader clinical phenotype (either milder or more severe than classic Rett syndrome) to mild learning disabilities; the spectrum in males ranges from severe neonatal encephalopathy to pyramidal signs, parkinsonism, and macroorchidism (PPM-X) syndrome to severe syndromic/nonsyndromic intellectual disability. Females: Classic Rett syndrome, a progressive neurodevelopmental disorder primarily affecting girls, is characterized by apparently normal psychomotor development during the first six to 18 months of life, followed by a short period of developmental stagnation, then rapid regression in language and motor skills, followed by long-term stability. During the phase of rapid regression, repetitive, stereotypic hand movements replace purposeful hand use. Additional findings include fits of screaming and inconsolable crying, autistic features, panic-like attacks, bruxism, episodic apnea and/or hyperpnea, gait ataxia and apraxia, tremors, seizures, and acquired microcephaly. Males: Severe neonatal-onset encephalopathy, the most common phenotype in affected males, is characterized by a relentless clinical course that follows a metabolic-degenerative type of pattern, abnormal tone, involuntary movements, severe seizures, and breathing abnormalities. Death often occurs before age two years. [from GeneReviews]