PREFERENTIAL SITES IN KERATIN-10 THAT ARE MUTATED IN EPIDERMOLYTIC HYPERKERATOSIS

Epidermolytic hyperkeratosis (EH) is a rare autosomal dominant skin di sease. Recent studies in our laboratory established genetic linkage to the type II keratin gene locus on chromosome 12q in one family with E H and identified a single amino acid mutation in keratin 1 that is res ponsible for the disease. Other point mutations in the keratin 1 or ke ratin 10 genes have now been reported in other patients with EH. We ha ve examined a series of probands with EH in order to develop a catalog of mutations in keratin 10. Using direct sequencing of PCR-amplified genomic DNA, we have identified mutations in six families, in which fi ve mutations occur in the beginning of the 1A rod domain of keratin 10 -namely, two Arg10 to His, one Arg10 to Cys, an Asn8 to His, and a Tyr 14 to Asp. This region contains highly conserved residues among all ke ratins. An additional mutation (Leu103 to Gln) was found in the conser ved region late in the 2B rod domain in keratin 10. We developed sever al allele-specific assays to assess the frequency of these mutations i n the general population. No evidence was found for the presence of su ch changes in unaffected individuals. In vitro functional assays perfo rmed with peptides corresponding to the 1A mutations in these families show severely diminished capacity to disaggregate preformed keratin i ntermediate filaments, in comparison with a wild-type control peptide. Results from this work support the hypothesis that the beginning of t he 1A rod domain segment in keratin 10 contains preferential sites for disease-causing mutation in EH. This should be of considerable use wh en developing prenatal diagnostic tests and biologically based therapi es for this disease.