PORCN mutations and variants identified in patients with focal dermal hypoplasia through diagnostic gene sequencing

Focal dermal hypoplasia (FDH) is an X-linked dominant disorder caused by mutations in the gene PORCN, which encodes a protein required for the secretion and signaling of Wnt proteins. While deletions are responsible for a small percentage of FDH-causing mutations, the vast majority of mutations are single-nucleotide substitutions or small deletions or insertions that can be identified by sequence analysis. In 2007, we implemented a PORCN gene sequencing test for individuals with a clinical diagnosis of FDH. To date, we have detected 12 novel PORCN mutations and 6 previously reported mutations in 53 such unrelated patients. The pathogenic PORCN mutations included nine nonsense mutations, three missense mutations, one small deletion, two small duplications, and three splice-site mutations. Of these mutations, two were found in affected men and were mosaic; one of these was found in three other affected women. The remaining 16 mutations were found only in women. All the mutations detected in women were presumed heterozygous. In addition to the disease-causing mutations, eight nucleotide variants of unknown significance were identified. Further characterization of these variants suggests that four of them are pathogenic mutations. These findings add to the heterogeneity of mutations in the PORCN gene that cause FDH.