Nuclear and mitochondrial genes mutated in nonsyndromic impaired hearing
ABSTRACT Half of the cases with congenital impaired hearing are hereditary (HIH). HIH may occur as part of a multisystem disease (syndromic HIH) or as disorder restricted to the ear and vestibular system (nonsyndromic HIH). Since nonsyndromic HIH is almost exclusively caused by cochlear defects, affected patients suffer from sensorineural hearing loss. One percent of the total human genes, i.e. 300-500, are estimated to cause syndromic and nonsyndromic HIH. Of these, approximately 120 genes have been cloned thus far, approximately 80 for syndromic HIH and 42 for nonsyndromic HIH. In the majority of the cases, HIH manifests before (prelingual), and rarely after (postlingual) development of speech. Prelingual, nonsyndromic HIH follows an autosomal recessive trait (75-80%), an autosomal dominant trait (10-20%), an X-chromosomal, recessive trait (1-5%), or is maternally inherited (0-20%). Postlingual nonsyndromic HIH usually follows an autosomal dominant trait. Of the 41 mutated genes that cause nonsyndromic HIH, 15 cause autosomal dominant HIH, 15 autosomal recessive HIH, 6 both autosomal dominant and recessive HIH, 2 X-linked HIH, and 3 maternally inherited HIH. Mutations in a single gene may not only cause autosomal dominant, nonsyndromic HIH, but also autosomal recessive, nonsyndromic HIH (GJB2, GJB6, MYO6, MYO7A, TECTA, TMC1), and even syndromic HIH (CDH23, COL11A2, DPP1, DSPP, GJB2, GJB3, GJB6, MYO7A, MYH9, PCDH15, POU3F4, SLC26A4, USH1C, WFS1). Different mutations in the same gene may cause variable phenotypes within a family and between families. Most cases of recessive HIH result from mutations in a single locus, but an increasing number of disorders is recognized, in which mutations in two different genes (GJB2/GJB6, TECTA/KCNQ4), or two different mutations in a single allele (GJB2) are involved. This overview focuses on recent advances in the genetic background of nonsyndromic HIH.
SourceAvailable from: uu.diva-portal.org
[Show abstract] [Hide abstract]
ABSTRACT: Mitochondrial 12S rRNA gene mutations account for non-syndromic hearing impairment (NSHI). The A1555G substitution is the most common mitochondrial DNA mutation and is associated with both aminoglycoside-induced HI and NSHI. Its frequency is variable among populations of different ethnic background. The purpose of the present survey was to determine the frequency of the A1555G mutation in the Iranian probands with NSHI. We have screened 152 unrelated Iranian probands with NSHI with childhood onset and 548 normal hearing controls for the occurrence of the A1555G mutation using PCR-RFLP method. Totally, 2 patients carrying the homoplasmic A1555G mutation were identified with a total frequency of 1.3% in Iran. Mutation A1555G had a variable frequency among subpopulations of different ethnic origins in Iran: Azeri Turkish (4.16%), Lure (0.0%), Fars (0.0%) and Bushehri (2.86%). The A1555G mutation was not found in any member of the controls. Our study shows that the frequency of the A1555G mutation in Azeri Turkish and Bushehri hearing impaired patients is compatible with that reported for Caucasian populations.