On the other hand, the median age at diagnosis of bladder carcinoma in 4 cases with Costello syndrome was 13.5 years, although bladder carcinoma most frequently occurs in the elderly.14 If epidermal nevus patients have the mosaic HRAS mutation not only in epidermal nevi but also in other tissues, they may be at risk of developing neoplasms similar to those found in Costello syndrome. Here, HRAS is linked to wooly hair nevus.