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Congenital Hearing Loss

return to: Otology - Neurotology 

For more information about genetic testing for hearing loss at the University of Iowa
and the 'audiogene' see: http://www.healthcare.uiowa.edu/labs/morl/
return to: Otology - Neurotology
Pediatric Otolaryngology

PREVALENCE* Sensorineural hearing loss (SNHL) is the most common sensory deficit in the world.

  • The prevalence of permanent childhood hearing loss is 1.2 to 1.7 per 1000 live births in the United States.
  • 20-30% of children with congenital SNHL have profound hearing loss.
  • Congenital hearing loss has the potential to negatively impact educational attainment, future employment, future income, use of healthcare systems, and life expectancy. For a child with congenital severe-to-profound SNHL, the total lifetime cost of hearing loss exceeds $1 million (U.S.).
  • Early identification of children with hearing loss is vital for proper care leading to appropriate development. Early identification improves speech and language and decreases the expected lifetime cost of SNHL.
  • The establishment of universal newborn hearing screening programs has significantly improved early detection of congenital hearing loss, offering not only benefit to the affected children and their families but also long term public health cost savings.
     
    ASSESSMENT
     
          Hearing Loss Severity:
  • Normal hearing            < 20 dB
  • Mild                            20-40 dB
  • Moderate                    41-55 dB
  • Moderately Severe       56-70 dB
  • Severe                        71-90 dB
  • Profound                     > 90 dB

      Hearing loss frequency:

  • Low frequency             < 500 Hz
  • Middle frequency         501-2000 Hz
  • High frequency            > 2000 Hz
     
    ETIOLOGY
  • Greater than 50% of congenital SNHL is due to genetic factors. The remainder is due to environmental factors.
  • Genetic Factors of SNHL:
    • Approximately 2/3 of genetic SNHL are non-syndromic forms in which hearing loss is the only manifestation. The remaining 1/3 are syndromic forms in which hearing loss segregates with other phenotypes. Some examples of syndromic SNHL include: Pendred syndrome, Usher syndrome, Waardenburg syndrome, Branchio-Oto-Renal syndrome and Vohwinkel syndrome.
    • Pendred syndrome is the most common form of syndromic hereditary SNHL. The majority of affected children have mutations in a gene called SLC26A4 on chromosome 7q31.
    • Approximately 80% of congenital non-syndromic SNHL cases follow an autosomal recessive pattern of inheritance. 15% are autosomal dominant, while x-linked and mitochondrial inheritance account for < 1% of cases.
    • While mutations in over 100 different genes may lead to hearing loss, mutations in a single gene, GJB2, account for up to ½ of autosomal recessive non-syndromic hearing loss in many countries.
    • Genetic testing is becoming available for an expanding number of genes involved in hereditary hearing loss.
  • Environmental factors of SNHL:
    • Infectious causes of SNHL in newborns are classically grouped as the TORCH infections (toxoplasmosis, others, rubella, CMV, HSV).
    • Infectious causes can be divided into congenital infections and acquired infections.
    • Congenital infections include: CMV, lymphocytic choriomeningitis virus, rubella virus, Toxoplasma gondii, Treponema pallidum.
    • Acquired infections include: Borrelia burgdorferi, Epstein-Barr virus, Haemophilus influenza, Lassa virus, measles virus, mumps virus, Neisseria meningitidis, non-polio enteroviruses, Plasmodium falciparum, Streptococcus pneumonia, varicella zoster virus
    • In developed countries, congenital CMV infection is the most frequent cause of acquired hearing loss in neonates.
    • Other environmental factors include: ototoxic agents (e.g. aminoglycoside antibiotics, cisplatin chemotherapeutic agent), prematurity, asphyxiation/anoxia, sepsis, craniofacial anomalies, low birth weight, Rh incompatibility, extracorporeal membrane oxygenation, and noise. 
       
      TREATMENT
  • Current habilitation options for children with hearing loss include hearing aids and cochlear implants, with cochlear implants being the foremost treatment for children with severe-to-profound SNHL.
  • In the future, gene-based therapies will become available to provide further treatment options for hereditary hearing loss.
     
    REFERENCES/SUGGESTED READING
     
    1. Hildebrand et al. Advances in molecular and cellular therapies for hearing loss. Mol Ther. 2008 Feb;16(2):224-36.
    2. Kral and O’Donoghue. Profound deafness in childhood. N Engl J Med. 2010 Oct 7;363(15):1438-50.
    3. Papsin and Gordon. Cochlear implants for children with severe-to-profound hearing loss. N Engl J Med. 2007 Dec 6;357(23):2380-7.
    4. Smith et al. Sensorineural hearing loss in children. Lancet. 2005 Mar 5-11;365(9462):879-90.
    5. Deafness and Hereditary Hearing Loss Overview (GeneReviews)
    6. Hereditary Hearing Loss Homepage
    7. Molecular Otolaryngology & Renal Research Laboratory