How is Fragile X passed on in families?
Carriers of Fragile X
With each pregnancy, female premutation carriers have a 50% chance of passing on the Fragile X gene change either as a premutation or a full mutation to a child of either sex. The chance of a female premutation carrier having a child with Fragile X syndrome depends on how many CGG repeats she carries. For each pregnancy, females with the full mutation have a 50% chance of having a child with Fragile X syndrome.
Male carriers of the Fragile X premutation will pass the premutation on to all of their daughters, but none of their sons.
Diagram source: Women’s Health and the Fragile X premutation, Espinel & Sherman, Emory University, Georgia, USA, 2015.