Genetics · MU Sofia

32. Hereditary Hearing Loss (Non-Syndromic and Syndromic)

Explains hereditary hearing loss as sensorineural deafness caused by genetic mutations, separating non-syndromic forms, which are isolated, from syndromic forms that involve other organ systems. Covers inheritance patterns and the connexin-based DFNB1 locus, the pathophysiology of gap-junction defects, and clinical features, diagnosis and management. A classification table, a table of major syndromes with genes and features, a table linking organ systems to syndromic deafness, and a comparison table of the two groups are included.

Inside: 14 sections · 6 labelled pictures · 4 tables · 14 flashcards · 5 min

Topic 32 of 65 in the MU Sofia syllabus for Genetics (Medicine, Year 3). The free AceMed note covers it in 11 sections, about 422 words (5 min of reading), with 14 flashcards.

In this note

  1. Hereditary Hearing Loss (Non-Syndromic and Syndromic)
  2. Classification of Hereditary Hearing Loss
  3. I. HEREDITARY NON-SYNDROMIC HEARING LOSS (NSHL)
  4. Pathophysiology
  5. Clinical Features
  6. Diagnosis
  7. Management
  8. II. HEREDITARY SYNDROMIC HEARING LOSS (SHL)
  9. Major Syndromic Forms
  10. Clinical Clues by System
  11. Comparison Table – Non-Syndromic vs Syndromic Hearing Loss

Hereditary Hearing Loss (Non-Syndromic and Syndromic)

Hereditary hearing loss (HHL) refers to congenital or early-onset sensorineural hearing impairment caused by genetic mutations affecting the inner ear structures, hair cell function, or auditory nerve. It can occur either as an isolated defect (non-syndromic) or as part of a multisystem disorder (syndromic). Approximately 50–60% of congenital deafness is genetic in origin.

I. HEREDITARY NON-SYNDROMIC HEARING LOSS (NSHL)

Genetic and Molecular Basis

  • Inheritance patterns:
  • Autosomal recessive (AR): ~75–80% (congenital, severe–profound).
  • Autosomal dominant (AD): ~15–20% (progressive, post-lingual).
  • X-linked / mitochondrial: rare forms.
  • Most common locus: DFNB1 – caused by mutations in:
  • GJB2 gene (Connexin-26) and GJB6 (Connexin-30) on chromosome 13q11–12.
  • These encode gap-junction proteins essential for potassium ion recycling within the cochlear hair cells.

Pathophysiology

  1. 1. Connexin-26/30 gap-junction defects → impaired K⁺ ion homeostasis in the cochlea.
  1. 2. Disturbed endocochlear potential → defective hair-cell depolarization.
  2. 3. Leads to loss of cochlear hair cell function → sensorineural hearing loss.
  3. 4. No structural abnormalities elsewhere → isolated deafness (non-syndromic).

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