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Genetic counseling: Hearing loss - Unknown Cause

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Hearing loss - Unknown Cause

IntroductionEdit

  • What have you been told about coming to genetics today?
  • What information have you been given already?
  • Have you done any research on your own? What have you found out?
  • What concerns or questions would you like to have answered today?
  • Outline session

Medical HistoryEdit

  • Complete intake
  • How was his hearing loss first found?
  • Eye problems?
  • Development
    • Age first walked? Sat up?
  • EKG?
  • CT scan
  • Kidney problems?
  • Infections?
  • Neurological problems? Seizures?
  • Birthmarks? Rashes?

Family HistoryEdit

  • Complete pedigree
  • Anyone with deafness? Hearing loss?
  • Eye problems?
  • White forelock?
  • Mental retardation?
  • Kidney problems?

Genetics of Hearing lossEdit

  • 1/2000 to 1/1000 children born with profound hearing loss
  • 50% hearing loss has a genetic cause
    • 1/3 related to syndrome
    • 2/3 nonsyndromic
    • 76% recessive genes
    • 20% dominant genes
    • 4% X-linked genes
  • Hearing loss increases with age
    • Impact of genetics and environment
  • Empiric Risks (if no diagnosis can be established)
    • Hearing parents with one deaf child
      • 18% risk of deafness in future children
    • offspring of deaf person and hearing person
      • 10% risk of deafness
    • deaf couple without AD hearing loss
      • 15% risk of deafness in children
    • child of hearing sib of deaf proband and deaf person
      • 1/200 risk for deafness

ManagementEdit

  • Frequent audiologic evaluations to document stability or progression of hearing loss
  • Determine appropriate habilitation option
    • Hearing aids
    • Cochlear implants
  • Educational intervention

Common causes of Genetic hearing lossEdit

Syndromic Hearing lossEdit

(Accounts for 30% prelingual deafness)

  • Autosomal Recessive
    • Usher Syndrome
      • Congenital sensorineural hearing loss
      • Type 1
  • Severe to profound hearing loss
  • Abnormal vestibular function
  • Delayed walking and sitting
      • Type 2
  • mild to severe hearing loss
  • normal vestibular function
      • Type 3
  • Progressive hearing loss
  • Progressive deterioration of vestibular function
  • Retinitis Pigmentosa
  • Apparent after first decade of life
  • Electroretinography can identify abnormalities in photoreceptor function in children as young as 2 - 4
    • Pendred Syndrome
      • Most common type of AR syndromic hearing loss
      • Congenital severe to profound SNHL
  • Abnormality of bony labyrinth that can be diagnosed with CT scan
      • Euthyroid goiter
  • Develops in puberty to adulthood
      • located at 7q22-q13
      • mutations in this gene can also cause nonsyndromic deafness
    • Jervell and Lange-Nielsen syndrome
      • Congenital deafness
      • Prolongation of QT wave on ultrasound
  • Can be detected by EKG
  • Syncopal episodes can cause sudden death
      • Caused by mutations in two different genes
  • Genetic testing not recommended in evaluation of deaf children
  • Recommended for those at high risk
    • Refsum disease
      • Severe progressive SNHL
      • Retinitis Pigmentosa
      • Caused by faulty phytanic acid metabolism
      • Can be controlled with dietary modification
      • Diagnosed by serum concentration of phytanic acid
  • Autosomal Dominant
    • Waardenburg syndrome
      • Variable degrees of SNHL
      • Pigmentary abnormalities of the skin, hair, and eyes
      • Type 1 - lateral displacement of inner canthus (PAX3 gene - clinical testing)
      • Type 2 - no displacement of inner canthus (MITF gene - research testing)
      • Type 3 - upper limb abnormalities (PAX3 gene - clinical testing)
      • Type 4 - Hirschprung disease (EDNRB, EDN3, SOX10 genes - research testing)
    • Branchiootorenal Syndrome
      • Conductive, sensorineural, and mixed hearing loss
      • Brachial cleft cysts or fistula
      • External ear malformation (prearicular pits)
      • Renal anomalies
      • 20-30% have mutation in EYA1 (locus 8q13) - testing available
    • Stickler Syndrome
      • Progressive SNHL
      • Cleft palate
      • Spondyloepiphyseal dysplasia causing osteoarthritis
      • Genetic causes:
  • STL1(COL2A1)
  • STL2 (COL11A2)
  • STL3 (COL11A1)
      • STL1 and STL3 are associated with severe myopia
      • Clinical testing available
    • Neurofibromatosis type II
      • Bilateral vestibular schwannomas causing hearing loss
  • Generally begins in 3rd decade
  • Hearing loss is generally unilateral and gradual
  • MRI to diagnose
      • Other tumors are associated
      • Molecular testing available
  • X-linked
    • Alport syndrome
      • Progressive sensorineural hearing loss (variable severity)
  • Generally begins after 10 years of age
      • Progressive renal disease
      • Ophthalmologic findings
      • 85% X-linked, AR and AD forms also identified
    • DFN1 (Xq22)
      • Progressive, postlingual hearing loss
      • Visual disability
      • Dystonia
      • Fractures
      • Mental retardation
  • Mitochondrial syndromes

Nonsyndromic Hearing LossEdit

(70% hereditary hearing loss)

  • Autosomal Recessive
    • 50% families DFNB1
    • 50% other multiple loci
      • many different genes - many in only one family
  • Autosomal Dominant
    • Many different genes
    • No one gene causes majority of cases
  • X-linked
    • DFN3 (Xq21.1)
      • Mixed hearing loss
      • Stapedial fixation
      • Gene called POU3F4
    • Multiple other genes
  • Mitochondrial
    • Multiple genes
    • Low penetrance
    • Possible environmental factors

Psychosocial IssuesEdit

  • Deaf child born to hearing parents
  • How did you feel when you first found out?
  • How have your feelings changed?
  • How have other family members reacted?
  • Have you been in contact with any other families?
  • Have you been in contact with any support groups?
  • What are your biggest concerns at the moment?

ResourcesEdit

  • American Society for Deaf Children
PO Box 3355
Gettysburg, PA 17325
Phone: 800-942-ASDC (parent hotline)
Email: ASDC1@aol.com
Web: www.deafchildren.org
  • National Association of the Deaf
814 Thayer
Silver Spring, MD 20910
Phone: 301-587-1788
Email: NADinfo@nad.org
Web: www.nad.org

NotesEdit

The information in this outline was last updated in 2002.



This material has been imported fom the wikibook "Genetic counseling"[ http://en.wikibooks.org/wiki/Genetic_counseling] under the GNU Free Documentation License.

Heckert GNU white Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License."

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