A deletion involving the connexin 30 gene in nonsyndromic hearing impairment.
BACKGROUND
Inherited hearing impairment affects about 1 in 2000 newborns. Up to 50 percent of all patients with autosomal recessive nonsyndromic prelingual deafness in different populations have mutations in the gene encoding the gap-junction protein connexin 26 (GJB2) at locus DFNB1 on chromosome 13q12. However, a large fraction (10 to 42 percent) of patients with GJB2 mutations have only one mutant allele; the accompanying mutation has not been identified. DFNB1-linked familial cases with no mutation in GJB2 have also been reported.


METHODS
We evaluated 33 unrelated probands with nonsyndromic prelingual deafness who had only one GJB2 mutant allele. Nine subjects had evidence of linkage to DFNB1. We used haplotype analysis for markers on 13q12 to search for mutations other than the one involving GJB2.


RESULTS
We identified a 342-kb deletion in the gene encoding connexin 30 (GJB6), a protein that is reported to be expressed with connexin 26 in the inner ear. The deletion extended distally to GJB2, which remained intact. The break-point junction of the deletion was isolated and sequenced, and a specific diagnostic test was developed for this common mutation. Twenty-two of the 33 subjects were heterozygous for both the GJB6 and GJB2 mutations, including all 9 with evidence of linkage to DFNB1. Two subjects were homozygous for the GJB6 mutation.


CONCLUSIONS
A 342-kb deletion in GJB6 is the second most frequent mutation causing prelingual deafness in the Spanish population. Our data suggest that mutations in the complex locus DFNB1, which contains two genes (GJB2 and GJB6), can result in a monogenic or a digenic pattern of inheritance of prelingual deafness.
del Castillo
Ignacio
I
Unidad de Genética Molecular, Hospital Ramón y Cajal, Madrid, Spain.
Villamar
Manuela
M
Moreno-Pelayo
Miguel A
MA
del Castillo
Francisco J
FJ
Alvarez
Araceli
A
Tellería
Dolores
D
Menéndez
Ibis
I
Moreno
Felipe
F
D001483:Base Sequence; D015139:Blotting, Southern; D002882:Chromosomes, Human, Pair 13; D000072259:Connexin 26; D000075302:Connexin 30; D017630:Connexins / Q000235:genetics*; D004252:DNA Mutational Analysis; D005808:Genes, Recessive; D005838:Genotype; D006319:Hearing Loss, Sensorineural / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D017384:Sequence Deletion
D000075302:Connexin 30; D017630:Connexins; C000607042:GJB2 protein, human; C491020:GJB6 protein, human; D000072259:Connexin 26