Clinical characteristics: 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).

Diagnosis/testing: The diagnosis of a TBC1D24-related disorder is established in an individual with suggestive findings biallelic TBC1D24 pathogenic variants when the mode of inheritance is autosomal recessive (i.e., DOORS syndrome, FIME, PME, EPRPDC, DEE, and DFNB), and in an individual with suggestive findings and a heterozygous TBC1D24 pathogenic variant when the mode of inheritance is autosomal dominant (DFNA).

Management: Treatment of manifestations: Hearing aids or cochlear implants as needed for hearing loss; early educational intervention and physical, occupational, and speech therapy for developmental delay; symptomatic pharmacologic management for seizures; standard treatment for tremors, dystonic attacks, or other neurologic manifestations; routine management of visual impairment and renal, cardiac, dental, orthopedic, and endocrine issues.

Surveillance: Neurologic evaluations with EEGs depending on seizure frequency and/or progression; annual audiologic evaluations to assess for possible progression of hearing loss and/or the efficacy of hearing aids; annual dental evaluations; annual endocrine evaluations.

Agents/circumstances to avoid: Excessive ambient noise, which may exacerbate hearing loss in individuals with a heterozygous TBC1D24 pathogenic variant that causes autosomal dominant hearing loss (DFNA).

Evaluation of relatives at risk: Molecular genetic testing for the familial TBC1D24 pathogenic variant(s) in older and younger sibs of a proband is appropriate in order to identify as early as possible those who would benefit from early treatment of seizures and/or hearing loss.

Genetic counseling: Most TBC1D24-related disorders are inherited in an autosomal recessive manner (DOORS syndrome, FIME, PME, EPRPDC, and DEE [including EIMFS]). TBC1D24-related nonsyndromic hearing loss can be inherited in an autosomal recessive (DFNB) or autosomal dominant (DFNA) manner.

Autosomal recessive inheritance: If both parents are known to be heterozygous for a TBC1D24 pathogenic variant, each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being heterozygous, and a 25% chance of inheriting neither of the familial TBC1D24 pathogenic variants. Heterozygotes (carriers) are typically asymptomatic. Carrier testing for at-risk relatives requires prior identification of the TBC1D24 pathogenic variants in the family.

Once the TBC1D24 pathogenic variant(s) have been identified in an affected family member, prenatal and preimplantation genetic testing are possible.