The syndrome can hit both boys and girls, despite being caused by a defect in the X chromosome. This defect is already present before birth, but it often takes some time before symptoms are recognized and diagnosed.

Each of us has 23 pairs of chromosomes: the most important pair are the so-called sex chromosomes. There are therefore two types of sex chromosomes, X and Y: females have two X chromosomes, while males have one X and one Y.

An error on an X chromosome is enough to create this disease condition: therefore we call it an X linked dominant inheritance.