63.1 Classification

• Only 5 to 10% deaf children have deaf parents

• Congenital: sensorineural, conductive, or mixed; isolated or part of syndrome; 1:1000 children born with SNHL (50% of these profound)

Genetic: usually SNHL, usually from single gene disorders

– Single gene disorders

– Syndromic

Perinatal/intrauterine causes

Congenital disorders causing deafness to develop in childhood

• Acquired: hearing normal at birth

Meningitis (bacterial): commonest cause of acquired SNHL seen in ~10% children infected; fast track for CI due to risk of cochlear ossification

Mumps, measles

Trauma

OME

63.2 Genetic Nonsyndromic Sensorineural Hearing Loss

• Autosomal or X-linked; 1:8 people carry a recessive gene for deafness; of hereditary deafness (1:4000 live births) 80% autosomal recessive, 15% auto dominant, 4% X-linked, 1% mitochondrial

• Connexin 26 most common type (50% non-syndromic autosomal recessive HL)

Mutation in GJB2 gene alter function of connexin-26 gap junction protein causing potassium intoxication of organ of Corti

Homozygous mutations usually cause non-progressive HL, heterozygous ones cause progressive HL

Genetic testing available

63.3 Syndromal

• Many are associated with congenital deafness and include:

Autosomal recessive:

– Pendred syndrome: SNHL and thyroid goitre ±vestibular disturbance; usually euthyroid, may be hypothyroid; associated with widened vestibular aqueduct and Mondini; most common cause of syndromic deafness (10% cases)

– Usher syndrome: SNHL and retinitis pigmentosa; some types have absent vestibular responses

– Jervell–Lange-Nielsen syndrome: SNHL and prolonged ECG QT interval that disturbs cardiac conduction and leads to fainting and sudden death; gene mapped to short arm chromosome 11; high incidence of consanguinity in parents