X-linked dominant chondrodysplasia punctata (CDPX2) caused by single gene mosaicism in a male

X-linked dominant chondrodysplasia punetata (CDPX2; Happle syndrome) is recognized almost exclusively in females, who display mosaic and asymmetric features, presumed to arise secondary to random X-inactivation. CDPX2 results from mutation of an X-linked gene coding for sterol-Δ⁸-Δ⁷ isomerase (emopamil binding protein). We describe a boy with clinical features of CDPX2 (including those presumed to arise usually secondary to functional mosaicism in females). Biochemical and molecular studies demonstrate that he is mosaic for a sterol-Δ⁸-Δ⁷ isomerase gene mutation. He is the first reported example of single gene mosaicism giving rise to CDPX2 in a male.