Molecular genetics of Meesmann's corneal dystrophy: ancestral and novel mutations in keratin 12 (K12) and complete sequence of the human KRT12 gene.

Recently, we identified the first mutations in corneal keratins K3 and K12 in families with Meesmann's corneal dystrophy (MCD). Here, we sequenced all regions of the human K12 gene, to enable mutation detection for all exons using genomic DNA as a template. The human K12 genomic sequence spans 5919 bp and consists of eight exons. A microsatellite dinucleotide repeat was identified within intron 3, which was highly polymorphic and which we developed for use in genotype analysis. In addition, two mutations in the helix initiation motif of K12 were found in families with MCD. A novel mutation was detected in an American kindred, 410T-->C, which predicts the amino acid substitution M129T. In a German family, mutation 428G-->C was identified, predicting amino acid change R135T. The latter mutation was identical to that which we identified in the original kindred described by Meesmann. Using the intragenic microsatellite polymorphism in K12 and additional flanking markers, we were able to show that this family shares a common haplotype with the original Meesmann kindred. These results strongly imply that R135T represents an ancestral mutation in the German population. Both mutations occur in the highly conserved helix initiation motif of the K12 polypeptide. A total of eight mutations have now been reported in the K12 gene.