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Genetics of hearing loss Chapter 146/147 Bobby Tajudeen • 1 child in every 1000 born will have congenital hearing impairment • At least 50% of congenital hearing impairment has a genetic origin Classification • Causality – Genetic (hereditary) – Environmental (nonhereditary) – Multifactorial • Time of onset – Congenital (at birth) – Acquired (late-onset) • Age of onset – Prelingual (before speech development) – Postlingual (after speech development) • Clinical Presentation – Nonsyndromic (hearing loss only symptom) – Syndromic (hearing loss and other symptoms) • Anatomic Defect – CHL/SNHL/Mixed • Severity • Frequency loss • Ears affected • Prognosis – stable vs. progressive Genetics AD AS X-Linked Mitochondrial • Most common type of genetic hearing loss is transmitted in what fashion? a. b. c. d. AR AD X-linked Mitochondrial Autosomal Recessive Nonsyndromic Hearing Loss • Usually prelingual and severe to profound across all frequencies • Connexin 26 mutation most common – GJB2 gene – integral for gap junction formation and mechanosensry transduction Autosomal Dominant Nonsyndromic Hearing Loss • Onset generally postlingual, progressive, and milder with characteristic audioprofiles • DFNA2 – high frequency hearing loss • DFNA8/12/13 – midfrequency hearing loss • DFNA6/14/38 – low frequency hearing loss X-linked Nonsyndromic Hearing loss • Accounts for less than 2% of nonsyndromic hearing loss • DFN3 most common – mutation in POU3F4 – Congenital stapes fixation – Widening of lateral IAC – Dilation of vestibule – Mixed HL – Stapedectomy gusher Mitochondrial Nonsyndromic Hearing Loss • 1555 A-to-G mtDNA mutation best characterized • Associated with aminoglycoside ototoxicity • Mild high frequency loss that progresses • Presbycusis may have mitochondrial basis due to mtDNA mutation accumulation Syndromic Hearing loss • Less common than nonsyndromic forms • Cosegregate with other features What is the structure? • A patient with Pendreds is most likely to to benefit from: a. b. c. d. Synthroid Thyroidectomy Amplification Steroid Burst Pendred Syndrome • • • • • • Most common form of hereditary syndromic SNHL Autosomal recessive Affected individuals also have goiter Congenital severe-profound HL, bilateral Mutation in SLC26A4 gene Pendrin anion transporter involved in chloride and iodine transport • Goiter in 2nd decade, usually euthyroid • Perchlorate discharge test • Radiographs always show temporal bone anomaly either dilated vestibular aqueducts or Mondini dysplasia • A patient with hearing loss is diagnosed with Jervell-Lange Nielsen syndrome. Why did his brother die at a young age? a. b. c. d. Neurologic disease Cardiac disease Renal disease Thyroid disease Jervell and Lange-Nielsen Syndrome • Autosomal recessive • Characterized by congenital deafness, prolonged Q-T, syncopal attacks • KVLQT1 and KCNE1 genes important for potassium channels expressed in heart and inner ear • Congenital, bilateral, severe to profound SNHL • Prolonged QT can leads to ventricuar arrhythmias, syncopal attacks, and death • Beta blockers reduce mortality from 71% to 6% • A patient has progressive hearing loss and blurry vision. Ophthalmologic evaluation reveals interstitial keratitis. What syndrome does the patient have? a. b. c. d. Usher’s Cogan’s Waardenburg syndrome Jervell-Lange Neilson syndrome • Two brothers developed congenital deafblindness with vestibular dysfunction. Which type of Ushers syndrome do they most likely have? a. b. c. d. Type 1 Type 2 Type 3 Type 4 Usher syndromes • Autosomal recessive • SNHL, retinitis pigmentosa, and often vestibular dysfunction • Cause of 50% of deaf-blindness • Three variants: – Type 1 – severe to profound congenital HL, vestibular dysfunction, retinitis pigmentosa develops in childhood – Type 2 – mod to severe HL, no vestibular dysfunction, retinal degeneration in 3rd-4th decade – Type 3 – progressive hearing loss, variable vestibular dysfunction, variable onset of retinitis pigmentosa • Which form of Waardenburg syndrome is not associated with dystopia canthorum? a. b. c. d. Type 1 Type 2 Type 3 Type 4 • Which form of Waardenburg syndrome is associated with Hirschsprung disease? a. b. c. d. Type 1 Type 2 Type 3 Type 4 Waardenburg syndrome • Autosomal dominant (except type 4) • SNHL, pigmentary abnormalities (heterochromic iridis, white forelock, patchy skin depigmentation), craniofacial abnormalities (dystopia canthorum, synophrys, broad nasal root) • Four types – Type 1 – presence of dystopia canthorum – Type 2 – no dystopia canthorum – Type 3 – skeletal abnormalities – Type 4 – associated with Hirschsprung disease • A patient is diagnosed with Alport syndrome. How are they likely to present? a. b. c. d. Congenital hearing loss that is progressive Congenital hearing loss that is stable Adolescent onset hearing loss that is progressive Adolescent onset hearing loss that is stable Alport Syndrome • X-linked syndrome of Type IV collagen • Hematuric nephritis, hearing impairment, ocular changes • Diagnostic criteria: three of following – – – – Positive family history of hematuria Progressive high-tone SNHL Typical eye lesion (anterior lenticonus or macular flecks) Histologic changes of glomerular basement membrane of the kidney • Hearing loss is symmetric, high-frequency that can be detected in late childhood and progresses to involve all frequencies • Ultimately progress to end-stage renal disease • What type of hearing loss does this patient likely to have? a. b. c. d. SNHL Progressive SNHL Mixed hearing loss Mild “cookie bite” SNHL Treacher Collins • Autosomal dominant • Abnormalities of craniofacial development – Maldevelopment of the mandible and maxilla – Abnormal canthi placement – Downsloping palpebral fissures – Ocular colobomas – Choanal atresia • Typically normal intelligence • Otologic symptoms findings – – – – – – Auricular deformities Atresia/stenosis of EAC Malformed ossicles (CHL) Preauricular fistulas Malformed ossicles Bony plate replacement of TM – Widened aqueduct – Abberrant facial nerve – Mondini malformation