Mosaicism in women with focal dermal hypoplasia

This report from Germany and France describes four women with focal dermal hypoplasia (FDH), a genetic condition affecting the skin, skeleton, teeth and eyes. FDH is caused by a mutant (abnormal) gene called PORCN, found on the X chromosome. Male embryos with the mutant gene do not usually survive. Females are more complicated. Firstly, they have two X chromosomes, but for FDH to show up it only needs the mutant gene to be present on one of...