SLC26A4-related sensorineural hearing loss (SLC26A4-SNHL), characterized by inner ear malformations also associated with vestibular dysfunction, comprises two phenotypes: (1) nonsyndromic SLC26A4-SNHL (also referred to as DFNB4 or nonsyndromic enlargement of the vestibular aqueduct [NSEVA]) and (2) Pendred syndrome (PDS) that includes thyroid involvement (typically identified more frequently in countries without universal salt iodization programs). The time of onset and type of presentation of the SNHL vary (such that some newborns pass their newborn hearing screening); however, by age three years most children have bilateral and severe-to-profound hearing loss. Manifestations of vestibular dysfunction (such as head-tilting, vomiting, and/or delayed ambulation or clumsiness in a child who previously walked well) can precede or accompany the fluctuations in hearing typical of this disorder. Thyroid enlargement (goiter) occurs gradually and is typically evident in the second decade, especially if iodine is not routinely included in the diet.

Maternally inherited diabetes-deafness syndrome (MIDD) is a mitochondrial disorder characterized by onset of sensorineural hearing loss and diabetes in adulthood. Some patients may have additional features observed in mitochondrial disorders, including pigmentary retinopathy, ptosis, cardiomyopathy, myopathy, renal problems, and neuropsychiatric symptoms (Ballinger et al., 1992; Reardon et al., 1992; Guillausseau et al., 2001). The association of diabetes and deafness is observed with Wolfram syndrome (see 222300), Rogers syndrome (249270), and Herrmann syndrome (172500), but all 3 of these disorders have other clinical manifestations.

Any autosomal recessive nonsyndromic deafness in which the cause of the disease is a mutation in the GRXCR1 gene.

Usher syndrome type II (USH2) is characterized by the following: Congenital, bilateral sensorineural hearing loss that is mild to moderate in the low frequencies and severe to profound in the higher frequencies. Intact or variable vestibular responses. Retinitis pigmentosa (RP); progressive, bilateral, symmetric retinal degeneration that begins with night blindness and constricted visual fields (tunnel vision) and eventually includes decreased central visual acuity; the rate and degree of vision loss vary within and among families.

Episodic ataxia is a genetically heterogeneous neurologic condition characterized by spells of incoordination and imbalance, often associated with progressive ataxia. Episodic ataxia type 2 is the most common form of EA (Jen et al., 2007). For a discussion of genetic heterogeneity of episodic ataxia, see EA1 (160120).

Autosomal recessive deafness-70 (DFNB70) is a neurologic disorder with a variable disease course. All individuals present with isolated congenital sensorineural hearing loss in infancy that appears to be stable for the first decades of life. Affected members of 1 family with longer follow-up developed a neurodegenerative disease in their forties, including ataxia with loss of ambulation, optic atrophy, dystonia or spasticity, and cognitive decline with psychiatric features. The later onset of additional symptoms in this family suggests that others with DFNB70 may be at risk of developing multisystem disease in mid-to-late adulthood. These reports indicate that there is a phenotypic spectrum of PNPT1-related disease manifestations (Von Ameln et al., 2012; Eaton et al., 2018).

A genetic condition inherited in an autosomal recessive caused by mutation(s) in the CDH23 gene, encoding cadherin-23, characterized by progressive sensorineural hearing loss. Mutation(s) in the CDH23 gene may also cause Usher syndrome 1D.

Autosomal dominant deafness-11 is a nonsyndromic form of progressive neurosensory hearing loss with postlingual onset. Some affected individuals have mild vestibular symptoms (summary by Sun et al., 2011).

Usher syndrome type I (USH1) is characterized by congenital, bilateral, profound sensorineural hearing loss, vestibular areflexia, and adolescent-onset retinitis pigmentosa (RP). Unless fitted with a cochlear implant, individuals do not typically develop speech. RP, a progressive, bilateral, symmetric degeneration of rod and cone functions of the retina, develops in adolescence, resulting in progressively constricted visual fields and impaired visual acuity.

Any autosomal recessive nonsyndromic deafness in which the cause of the disease is a mutation in the TMC1 gene.

DFNB48 is an autosomal recessive form of deafness. Affected individuals have prelingual onset of severe to profound sensorineural hearing loss affecting all frequencies (summary by Riazuddin et al., 2012).

Any autosomal recessive nonsyndromic deafness in which the cause of the disease is a mutation in the MYO7A gene.

Hyperostosis cranialis interna (HCIN) is a bone disorder characterized by endosteal hyperostosis and osteosclerosis of the calvaria and the skull base. The progressive bone overgrowth causes entrapment and dysfunction of cranial nerves I, II, V, VII, and VIII (Waterval et al., 2010).

Any autosomal recessive nonsyndromic deafness in which the cause of the disease is a mutation in the MYO6 gene.

POLG-related disorders comprise a continuum of overlapping phenotypes that were clinically defined before the molecular basis was known. POLG-related disorders can therefore be considered an overlapping spectrum of disease presenting from early childhood to late adulthood. The age of onset broadly correlates with the clinical phenotype. In individuals with early-onset disease (prior to age 12 years), liver involvement, feeding difficulties, seizures, hypotonia, and muscle weakness are the most common clinical features. This group has the worst prognosis. In the juvenile/adult-onset form (age 12-40 years), disease is typically characterized by peripheral neuropathy, ataxia, seizures, stroke-like episodes, and, in individuals with longer survival, progressive external ophthalmoplegia (PEO). This group generally has a better prognosis than the early-onset group. Late-onset disease (after age 40 years) is characterized by ptosis and PEO, with additional features such as peripheral neuropathy, ataxia, and muscle weakness. This group overall has the best prognosis.

Any autosomal dominant nonsyndromic deafness in which the cause of the disease is a mutation in the CCDC50 gene.

Usher syndrome type I (USH1) is characterized by congenital, bilateral, profound sensorineural hearing loss, vestibular areflexia, and adolescent-onset retinitis pigmentosa (RP). Unless fitted with a cochlear implant, individuals do not typically develop speech. RP, a progressive, bilateral, symmetric degeneration of rod and cone functions of the retina, develops in adolescence, resulting in progressively constricted visual fields and impaired visual acuity.

Autosomal recessive deafness-67 (DFNB67) is characterized by congenital bilateral severe to profound sensorineural deafness, with or without vestibular dysfunction (Shabbir et al., 2006; Kalay et al., 2006; Lerat et al., 2019).

Any autosomal dominant nonsyndromic deafness in which the cause of the disease is a mutation in the SLC17A8 gene.

An autosomal dominant nonsyndromic deafness that has material basis in variation in the chromosome region 14q11.2-q12.

An autosomal recessive nonsyndromic deafness that has material basis in variation in the chromosome region 4q12-q13.2.

An autosomal recessive nonsyndromic deafness that has material basis in variation in the chromosome region 2p25.1-p24.3.

Usher syndrome type I (USH1) is characterized by congenital, bilateral, profound sensorineural hearing loss, vestibular areflexia, and adolescent-onset retinitis pigmentosa (RP). Unless fitted with a cochlear implant, individuals do not typically develop speech. RP, a progressive, bilateral, symmetric degeneration of rod and cone functions of the retina, develops in adolescence, resulting in progressively constricted visual fields and impaired visual acuity.

This form of autosomal recessive deafness is sensorineural and nonsyndromic, and shows prelingual onset (summary by Charizopoulou et al., 2011).

Any autosomal recessive nonsyndromic deafness in which the cause of the disease is a mutation in the LRTOMT gene.

STRC-related autosomal recessive hearing loss (STRC-HL) comprises both nonsyndromic sensorineural hearing loss and sensorineural hearing loss with decreased fertility in males who have biallelic contiguous gene deletions involving STRC and CATSPER2. The hearing loss is mild to moderate, congenital, bilateral, and symmetric. Mean pure tone hearing loss averages 40-50 decibels (dB) at the time of diagnosis; hearing loss is not severe to profound in children or young adults. Of note, while many newborns with STRC-HL will be identified by newborn hearing screening (NBHS), some newborns with STRC-HL will not because some screening methods may not detect milder hearing loss. Males with biallelic contiguous gene deletions involving STRC and CATSPER2 are at risk for CATSPER2-related male infertility due to morphologic sperm abnormalities that affect sperm motility. In contrast, females with contiguous gene deletions do not have related fertility issues.

GJB2-related autosomal recessive nonsyndromic hearing loss (GJB2-AR NSHL) is the most common genetic cause of congenital (present at birth) severe-to-profound non-progressive sensorineural hearing loss in many world populations. In countries where available, newborn hearing screening (NBHS) typically identifies severe-to-profound hearing loss. GJB2-AR NSHL can also be mild to moderate and is usually not progressive; however, it can progress. Congenital mild-to-moderate GJB2-AR NSHL is not detected by NBHS. GJB2-AR NSHL has no related systemic findings.

Any autosomal recessive nonsyndromic deafness in which the cause of the disease is a mutation in the GJB6 gene.

Any autosomal recessive nonsyndromic deafness in which the cause of the disease is a mutation in the LOXHD1 gene.

Any autosomal recessive nonsyndromic deafness in which the cause of the disease is a mutation in the PTPRQ gene.

Autosomal dominant deafness-4B is a form of nonsyndromic progressive sensorineural hearing loss with postlingual onset (summary by Wang et al., 2015)

Usher syndrome type I (USH1) is characterized by congenital, bilateral, profound sensorineural hearing loss, vestibular areflexia, and adolescent-onset retinitis pigmentosa (RP). Unless fitted with a cochlear implant, individuals do not typically develop speech. RP, a progressive, bilateral, symmetric degeneration of rod and cone functions of the retina, develops in adolescence, resulting in progressively constricted visual fields and impaired visual acuity.

Usher syndrome type I (USH1) is characterized by congenital, bilateral, profound sensorineural hearing loss, vestibular areflexia, and adolescent-onset retinitis pigmentosa (RP). Unless fitted with a cochlear implant, individuals do not typically develop speech. RP, a progressive, bilateral, symmetric degeneration of rod and cone functions of the retina, develops in adolescence, resulting in progressively constricted visual fields and impaired visual acuity.

Autosomal dominant deafness-56 is a form of nonsyndromic sensorineural hearing loss. Hearing impairment shows postlingual onset and is progressive (summary by Zhao et al., 2013).

An autosomal recessive nonsyndromic deafness that has material basis in variation in the chromosome region 1q43-q44.

TBC1D24-related disorders comprise a continuum of features that were originally described as distinct, recognized phenotypes: DOORS syndrome (deafness, onychodystrophy, osteodystrophy, mental retardation, and seizures), with profound sensorineural hearing loss, onychodystrophy, osteodystrophy, intellectual disability / developmental delay, and seizures; familial infantile myoclonic epilepsy (FIME), with early-onset myoclonic seizures, focal epilepsy, dysarthria, and mild-to-moderate intellectual disability; progressive myoclonus epilepsy (PME), with action myoclonus, tonic-clonic seizures, ataxia, and progressive neurologic decline; rolandic epilepsy with paroxysmal exercise-induced dystonia and writer's cramp (EPRPDC); developmental and epileptic encephalopathy (DEE), including epilepsy of infancy with migrating focal seizures (EIMFS); autosomal recessive nonsyndromic hearing loss (DFNB); and autosomal dominant nonsyndromic hearing loss (DFNA).

Any autosomal recessive nonsyndromic deafness in which the cause of the disease is a mutation in the GRXCR2 gene.

Any autosomal recessive nonsyndromic deafness in which the cause of the disease is a mutation in the CLIC5 gene.

Any autosomal dominant nonsyndromic deafness in which the cause of the disease is a mutation in the CRYM gene.

Any autosomal recessive nonsyndromic deafness in which the cause of the disease is a mutation in the RIPOR2 gene.

Autosomal dominant deafness-66 is a form of nonsyndromic sensorineural hearing impairment with widely variable age at onset (Nyegaard et al., 2015).

Autosomal dominant deafness-70 (DFNA70) is a form of nonsyndromic sensorineural hearing loss. Hearing impairment shows postlingual onset and is slowly progressive (Gao et al., 2015).

Autosomal recessive deafness-57 (DFNB57) is characterized by symmetric bilateral moderate to severe hearing loss, represented by gently downward-sloping audiograms. The hearing loss may be mildly progressive (Guan et al., 2018).

Autosomal dominant deafness-74 (DFNA74) is characterized by nonsyndromic postlingual progressive hearing loss, with onset in the third decade of life in most affected individuals (Wang et al., 2018).

An atypical form of Usher syndrome, here designated type IV (USH4), is an autosomal recessive disorder characterized by late onset of retinitis pigmentosa and usually late-onset of progressive sensorineural hearing loss without vestibular involvement (summary by Khateb et al., 2018). For a discussion of genetic heterogeneity of Usher syndrome, see 276900.

DFNB99 is characterized by prelingual, severe to profound sensorineural hearing loss without vestibular dysfunction (Cheng et al., 2003).

DFNB113 is characterized by postlingual progressive hearing impairment (Booth et al., 2018).

DFNB100 is characterized by prelingual onset of profound sensorineural deafness without vestibular involvement (Yousaf et al., 2018).

DFNB94 is characterized by prelingual profound sensorineural hearing loss (Simon et al., 2015).

Usher syndrome type 1M (USH1M) is characterized by prelingual sensorineural hearing loss, vestibular dysfunction, and retinitis pigmentosa (Ahmed et al., 2018). For a general phenotypic description and discussion of genetic heterogeneity of Usher syndrome, see USH1 (276900).

Autosomal dominant deafness-76 (DFNA76) is characterized by progressive or nonprogressive hearing loss with variable age at onset. Hearing loss is more severe at higher frequencies in most patients (Schrauwen et al., 2019; Morgan et al., 2019; Diaz-Horta et al., 2019).

Tolchin-Le Caignec syndrome (TOLCAS) is a developmental disorder characterized by mildly to moderately impaired intellectual development and behavioral problems, such as autism, ADHD, labile mood, and aggressive episodes. Many patients have bony abnormalities, including osteochondroma, craniosynostosis, dysmorphic facies, arachnodactyly, and large head circumference. Rarely, additional congenital anomalies may also be observed. These additional features and the bony defects are highly variable (summary by Tolchin et al., 2020).

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).

Autosomal recessive deafness-117 (DFNB117) is characterized by nonsyndromic bilateral moderate-to-profound sensorineural deafness, with onset in early childhood (Vona et al., 2021).

DFNA81 is characterized by postlingual onset of slowly progressive sensorineural hearing loss (Li et al., 2018).

DFNB118 is characterized by congenital profound sensorineural hearing loss and cochlear aplasia (Bademci et al., 2020).

Any Usher syndrome in which the cause of the disease is a mutation in the CLRN1 gene.

Autosomal dominant deafness-86 (DFNA86) is characterized by late-onset progressive hearing loss through p53 (TP53; 191170)-mediated hair cell apoptosis (Zhang et al., 2020).

Autosomal recessive deafness-123 (DFNB123) is characterized by nonsyndromic bilateral severe to profound hearing impairment, with onset as early as the first decade of life (Schrauwen et al., 2023).

Autosomal recessive deafness-124 (DFNB124) is characterized by congenital nonsyndromic progressive sensorineural hearing loss (Redfield et al., 2024).

Autosomal recessive deafness-125 (DFNB125) is characterized by congenital nonsyndromic sensorineural hearing loss. Mild progression in the lower frequencies has been observed. Hearing loss results from a mechanism that alters the way the traveling sound wave propagates along the cochlea (Chen et al., 2021).