What Is Fragile X Syndrome?
Reviewed: Dr. Gromatzky
6. Heritability
The mutation responsible for fragile X occurs on the X chromosome. Because women normally have two X chromosomes, they have a 50% chance of giving the mutation to each child. Men have only one X chromosome, so they have a 100% chance of passing it to their daughters and a 0% chance of passing it to their sons.
If a person’s FMR1 gene has the full mutation responsible for fragile X, a child will inherit the same mutation. A lesser form of the mutation also is inherited as-is, causing the associated syndromes of FXTAS and FXPOI. However, when inherited from the mother, the mutation can expand into its full form and cause fragile X.
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