How common is fragile x syndrome in us?

Depends on your dfn. Significant impairment (iq<70) in FAS is felt to represent 1/3600 of the population, mostly male. A lesser form of involvement with lesser alterations in this gene (add, behavior issues) may affect 1/130-250 female & 1/250-800 males. See: www.Ncbi.Nlm.Nih.Gov/pmc/articles/pmc2888470/?Tool=pmcentrez.

Related Questions

My son was recently tested for fragile x syndrome. How rare or common is fragile x?

1 in 4000-6000 male. Fragile x syndrome is the most common inherited form of intellectual disability, affecting 1 per 4000-6000 male. Read more...