Rett=congenital girl. Genetically, rett syndrome (rtt) is caused by mutations in the gene mecp2 (on x chromosome). Rtt is a neurodevelopmental disorder that almost exclusively affects females. The signs: small hands and feet , small head, repetitive hand movements, such as wringing/ putting hands into the mouth, stomach disorders, seizures, most can't talk and 50% don't walk. Rett is confused with:autism, angelman, cp.