Mutation of KCNQ4 has been reported to cause autosomal dominant non-syndromic
hearing loss (
DFNA2A) that usually presents as progressive
hearing loss starting from mild to moderate
hearing loss during childhood. Here, we identified a novel KCNQ4 mutation, c.1044_1051del8, in a family with autosomal recessive non-syndromic
hearing loss. The proband was homozygous for the mutation and was born to consanguineous parents; she showed severe
hearing loss that was either congenital or of early childhood onset. The proband had a sister who was heterozygous for the mutation but showed normal hearing. The mutation caused a frameshift that eliminated most of the cytoplasmic C-terminus, including the A-domain, which has an important role for
protein tetramerization, and the B-segment, which is a binding site for
calmodulin (CaM) that regulates channel function via Ca
ions. The fact that the heterozygote had normal hearing indicates that sufficient tetramerization and CaM binding sites were present to preserve a normal phenotype even when only half the
proteins contained an A-domain and B-segment. On the other hand, the severe
hearing loss in the homozygote suggests that complete loss of the A-domain and B-segment in the
protein caused loss of function due to the failure of tetramer formation and CaM binding. This family suggests that some KCNQ4 mutations can cause autosomal recessive
hearing loss with more severe phenotype in addition to autosomal dominant
hearing loss with milder phenotype. This genotype-phenotype correlation is analogous to that in KCNQ1 which causes autosomal dominant hereditary
long QT syndrome 1 with milder phenotype and the autosomal recessive
Jervell and Lange-Nielsen syndrome 1 with more severe phenotype due to deletion of the cytoplasmic C-terminus of the
potassium channel.