Pachyonychia congenita(PC),a rare autosomal dominant disorder characterized by hypertrophic nail dystrophy,is classified into two main clinical subtypes,PC-1 and PC-2.PC-1 is associated with mutations in the KRT6A or KRT16 genes,whereas PC-2 is linked to KRT6B or KRT17 mutations.Blood samples were collected from three generations of a new Chinese PC-1 family,including three PC patients and five unaffected family members.The coding regions of the KRT6A and KRT16 genes were amplified by PCR and analyzed by direct sequencing.A novel missense mutation p.Leu128Pro(c.383T>C)was identified in a highly conserved helix motif in domain 1A of KRT16.PolyPhen2 and SIFTS analysis rated the substitution as probably damaging;Swiss-Model analysis indicated that the structure of the mutant protein was not substantially different from the wild-type.The wider spectrum of KRT16 mutations suggests that changes in codons 125,127 and 132 are most commonly responsible for PC-1,and that proline substitution mutations at codons 127 or 128 may produce more severe disease.This study extends the KRT16 mutation spectrum and adds new information on the clinical and genetic diversity of PC.