Abstract: Objective To investigate the gene mutation in a pedigree with pachyonychia congenita typeⅡ(PC-Ⅱ)and to explore the relationship between the mutation and clinical manifestations.Methods The exon1of K17 gene of genomic DNA from peripheral blood was amplified by PCR,and the PCR products were sequenced by automated sequencing system.Results In all the 3 patients of the pedigree with PC-Ⅱ(2 patients presented as delayed-onset PC at 4 and 15-16 years of age respectively),the codon 92(AAT)of K17 gene was mutated as AGT,which caused missense mutation(N92S) in the 1 A domain of keratin 17,but the 2 unaffected members of the pedigree and50unrelated controls had no such mutation.Conclusions Mutation of N92S in the1A domain of keratin 17 exists in this pedigree with PC-Ⅱ.Our results indicate that mutation in the1A domain of keratin 17 can present as delayed-onset pachyonychia congenita.Therefore,the site and type of keratin mutation are not the sole determinant of the age of onset for PC-Ⅱ,there may be other genetic and/or environmental factors that determine the age of onset of PC-Ⅱ.

Key words: Nail diseases, Skin diseases, genetic, Keratin, Mutation