Focal Dermal Hypoplasia

Description: Focal dermal hypoplasia is an example of an X-linked inherited condition. Women have two X chromosomes, and men have an X and a Y chromosome. As with all genetic conditions it may have arisen spontaneously through mutation. I think that you are confusing gene with chromosome. The genes lie on the chromosome, in this case on the X chromosome. In all X-linked inherited conditions the clinical risk and severity of diseases is different for each sex. A female has 2 X chromosomes, and so may only have the offending gene on one of them (heterozygous), or on both X chromosomes (homozygous). If she only has the gene on one chromosome, then she will pass it to some, but not all of her children. If she has the gene on both chromosomes, then she will pass it to all her male children, and all her female children will carry the gene. Men only have one X chromosome, so if they inherit the gene they will display the full range of symptoms of an X-linked genetic disorder. In all X-linked inherited disorders there is no male to male transmission. This is because a man must pass his Y chromosome to his sons, so he can never contribute his X chromosome. That must come from the mother. On the other hand, a man always contributes his one X chromosome to all his daughters. Focal dermal hypoplasia is an example of a so-called X-linked dominant characterstic in which the gene is lethal in males. The disorder only occurs in women who are heterozygous for the mutant gene, an affected mother transmits the characteristic to half of her daughters, and an increased frequency of miscarriage occurs in affected women, the aborted foetuses representing affected males. As far as I am aware, there is, as yet no way of detecting the gene, and consequently no means of prevention.