If a male child is found to have a FGD1 gene mutation for Aarskog syndrome, is his mother then always found to be a carrier?
There is always the chance for a new gene change or mutation in a boy with Aarskog syndrome, although it is rare. There has also been one reported case of two fraternal twin brothers with the same FGD1 gene mutation and a genetic diagnosis of Aarskog syndrome. The mother had genetic testing on her blood and was not found to have the FGD1 gene mutation. This finding suggests that some of the mother's sex cells (eggs) have the mutation, but not all. Because of this, it was unable to be detected through a blood draw. The term for this is called "germline mosaicism." The recurrence risk for future pregnancies is therefore not as high, but higher than the general population.
Pilozzi-Edmonds L, et al. Fraternal twins with Aarskog-Scott syndrome due to maternal germline mosaicism. Am J Med Genet A. 2011 Aug;155A(8):1987-90. doi: 10.1002/ajmg.a.34094. Epub 2011 Jul 7.