Overall prevalence is between 1 to 2 1000 newborns and approximately 8 per 1000 in infants with risk factors for deafness.
Associated with delayed language, learning and speech development in early life and low educational and occupational performance in adulthood.
Congenital deafness is hearing loss present at birth, affecting approximately 1-2 per 1000 newborns.
The three major causes are genetic factors (50%), structural abnormalities of the temporal bones (30-40%), and congenital cytomegalovirus infection (5-20%).
Genetic causes account for the majority of cases in developed countries.
Approximately 70% of genetic hearing loss is nonsyndromic (isolated hearing loss), while 30% is syndromic (associated with other abnormalities).
Most genetic cases follow an autosomal recessive inheritance pattern (~80%), with autosomal dominant (~15%) and X-linked (~5%) being less common.
Bialleilic pathogenic variants in OTOF, the gene encoding otoferlin accounts for 1 to 3% of cases of congenital genetic deafness.
Otoferlin functions a a calcium sensor expressed in the inner hair cells and regulates synaptic transmission between sensory inner hair cells and the cochlear nerve.
The OTOF gene (otoferlin) encodes a calcium-sensing protein essential for synaptic vesicle fusion and neurotransmitter release at the ribbon synapses of inner hair cells in the cochlea.
Biallelic pathogenic variants in OTOF cause autosomal recessive nonsyndromic hearing loss (DFNB9), accounting for 1-3% of congenital genetic deafness and representing the leading cause of auditory neuropathy spectrum disorder (ANSD).
OTOF functions as a Ca²⁺ sensor that tethers glutamatergic synaptic vesicles to the plasma membrane and triggers their fusion and pool replenishment at ribbon synapses—processes essential for sound localization and speech comprehension.
Otoferlin contains six C2 calcium-binding domains (C2A-F), a transmembrane domain, and two Fer domains.
Without functional otoferlin, synaptic transmission from inner hair cells to cochlear nerve fibers fails despite intact hair cell structure, leading to impaired signal transmission to the auditory nerve.
The most common genetic cause is mutations in the GJB2 gene (connexin 26), which accounts for about half of all severe-to-profound autosomal recessive nonsyndromic hearing loss (designated DFNB1).
Other important genes include STRC (most common cause of moderate autosomal recessive hearing loss), GJB6 (connexin 30), and various genes associated with syndromic forms.
Common syndromic forms include:
Pendred syndrome rare-disease (SLC26A4 mutations): thyroid dysfunction, enlarged vestibular aqueduct
Usher syndrome: progressive vision loss (retinitis pigmentosa).
Waardenburg syndrome: pigmentary abnormalities
Alport syndrome: kidney disease, ocular abnormalities
Jervell and Lange-Nielsen syndrome:cardiac QT prolongation
Congenital CMV infection is the most common infectious cause, responsible for 5-20% of cases.
Other infectious causes include congenital syphilis and rubella.
Structural abnormalities of the temporal bones account for 30-40% of cases, many of which have underlying genetic etiologies such as branchiootorenal syndrome and CHARGE syndrome.
Hearing loss is significantly more common in high-risk populations, occurring in 1.2-7.5% of NICU infants.
Risk factors include prematurity (especially 24-31 weeks gestation), low birth weight (750-1500g), hyperbilirubinemia, sepsis, meningitis, ototoxic medication exposure, and prolonged ventilation.
The American College of Medical Genetics recommends comprehensive etiologic evaluation including:
Newborn hearing screening
Genetic testing: Starting with GJB2/GJB6 testing or comprehensive gene panels with >100 genes associated with hearing loss.
CMV testing: Particularly important in the neonatal period
Temporal bone imaging (CT or MRI): To identify structural abnormalities
Clinical genetics evaluation: To assess for syndromic features
Comprehensive genetic testing using next-generation sequencing panels can identify a definite cause in up to 86% of congenitally deaf children.
Early detection through newborn hearing screening and prompt intervention are critical, as they prevent delays in speech and language development and have long-lasting beneficial effects on social, emotional development, and quality of life.
Identifying the underlying etiology of neonatal hearing loss guides therapeutic decision-making, genetic counseling, and family planning.
Clinical Phenotypes
Typical Phenotype (90% of cases):
Most patients present with prelingual, severe-to-profound bilateral hearing loss:m75% showed profound hearing loss, 21.9% severe, and 3.1% mild hearing loss.
Atypical Phenotypes (10-15% of cases):
lSome patients display mild-to-moderate, progressive, or temperature-sensitive hearing loss.
The phenotypic presentation depends on specific genotypes—non-truncating variants located in and immediately downstream of the C2E calcium-binding domain are more likely to produce atypical phenotypes.
Diagnostic Features:
There is preserved otoacoustic emissions (OAEs) initially, indicating normal outer hair cell function
Absent or abnormal auditory brainstem responses (ABRs), indicating impaired neural transmission
Severe speech discrimination difficulties even with mild hearing thresholds in some cases.
Standard newborn hearing screening using OAE testing may initially miss OTOF-related deafness.
Genotype-Phenotype Correlations
Truncating mutations (nonsense, frameshift, splice-site) and the p.Arg1939Gln variant are clearly associated with severe-to-profound phenotypes.
Approximately half of patients with one or more non-truncating (missense) mutations show mild-to-moderate hearing loss.
Specific variants like p.His513Arg, p.Ile1573Thr, and p.Glu1910Lys demonstrate true auditory neuropathy characteristics.
Patients with loss-of-function/loss-of-function genotypes have significantly worse hearing (average thresholds 88.5-95.6 dB) compared to those with missense/missense or loss-of-function/missense genotypes (70.9-76.0 dB).
Some patients show progressive hearing loss, particularly during adolescence, with annual mid-frequency threshold deterioration of 0.87-1.87 dB/year depending on genotype.
Treatment and Management
Patients with OTOF mutations are excellent candidates for cochlear implantation because the auditory nerve and central pathways remain intact.
Approximately 85-90% achieved hearing levels of 20-39 dB with the implant and Categories of Auditory Performance (CAP) scale level 6 or better.
Cochlear implants bypass the dysfunctional synapse and directly stimulate the auditory nerve.
Hearing Aids are generally not beneficial due to the etiology of auditory synaptopathy.
A systematic review of 32 individuals found that none derived benefit in speech perception from hearing aids.
Gene therapy: Two landmark clinical trials demonstrate that AAV-based gene therapy can restore hearing in OTOF-related deafness:
Three participants achieved normal hearing sensitivity
These gene therapy results represent a paradigm shift, as they enable natural acoustic hearing and potentially eliminate the need for cochlear implants in many patients.