Vol. 93 No.8 August　2000

Genetic Analysis of Hearing Impairment 

Shin-ichi Usami (Shinshu University)

   Recent progress in molecular genetics has revealed the genes responsible for hearing loss, enabling molecular diagnostic applications for individual affected patients. Our series of studies indicated that mutations of three genes are commonly found among the hearing impaired population in Japan, and thus much attention should be paid to the genetic background of these patients in the ENT clinic.
    Fitst, mutations in connexin 26 (GJB2), the gene responsible for DFNB1 and DFNA3, have recently been of particular interest because these mutations account for up to 50% of congenital deafness in European countries as well as in the United States. Our mutation screening study confirmed that GJB2 mutations are also an important cause of non‐syndromic recessive hearing loss in the Japanese population. However, our results indicate that different combinations of GJB2 mutations exist in the Japanese population.
   Secondly, PDS, the gene responsible for Pendred syndrome, also causes non‐syndromic hearing loss associated with an enlarged vestibular aqueduct (EVA), known as the most common form of inner ear abnormalities.
   Genetic analysis confirmed that mutations in PDS cause a broader phenotypic spectrum than previously believed, from typical Pendred syndrome to non‐syndromic hearing loss associated with EVA.
    Finally, the 1555A→G mitochondria mutation, the most prevalent mitochondrial mutation found in the hearing impaired population in Japan, was found in approximately 3% of the outpatients. The significance of the 1555A→G mutation among subjects with specific backgrounds, such as aminoglycoside‐induced hearing loss, is evident.

 Key words : hereditary, hearing loss, gene