Somatic FGFR3 and PIK3CA mutations are present in familial seborrhoeic keratoses

Seborrhoeic keratosis (SK) represents one of the most common benign skin tumours. Familial occurrence of multiple SKs has been reported, but the genetic basis of these SKs has not been investigated so far. We present a German family with at least seven affected members in two generations and occurrence of high numbers of SKs at an unusually young age, suggesting a hereditary background.

Because FGFR3 and PIK3CA mutations have been reported to be involved in the pathogenesis of sporadic SK, we analysed five SKs of an affected family member for hotspot mutations of these genes.

A SNaPshot multiplex assay was used for analysis of 11 previously described FGFR3 hotspot mutations. In addition, exon 9 of PIK3CA was directly sequenced and the H1047R hotspot mutation in exon 20 was analysed by a SNaPshot assay.

FGFR3 mutations were present in three of five SKs. One SK with a FGFR3 mutation additionally showed a hotspot PIK3CA mutation. None of these mutations was present in the germline.

The results show that this case of familial SK reveals the same mutational spectrum as sporadic SK. Because FGFR3 and PIK3CA germline mutations can be excluded as an underlying genetic basis, alternative mechanisms have to contribute to familial SK such as inherited susceptibility factors predisposing to the acquisition of somatic FGFR3 and PIK3CA mutations in skin, or increased exposure of the family members to yet unknown environmental risk factors causing these mutations.