X-chromosomal nonletal mutation

X-linked mutations can be lethal or non-lethal for male embryos.

Phenotypes underlying an X-linked non-lethal mutation occur in diffuse and full expression only in males, whereas carriers exhibit cutaneous mosaicism, predominantly in the form of Blaschko lines but also in other mosaic patterns.

In the case of X-linked lethal mutations, only female embryos can survive, as they can build up a functional mosaic via the so-called Lyon effect.

Examples of diseases caused by an X-linked non-lethal mutation are:

anhidrotic ectodermal dysplasia of the Christ-Siemens-Touraine type and X-linked hypertrichosis (hypertrichosis in checkerboard patterns).

1. Happle R (2016) The categories of cutaneous mosaicism: a proposed classification. Am J Med Genet A 170A: 452-459
2. Moog U et al (2020) Diseases caused by genetic mosaicism. Dtsch Ärztebl Int 117: 119-125