High prevalence of Rett syndrome in a small area.

Five cases of Rett syndrome were revealed in a population of 2,269 girls 4-14 years of age and born in 1973-83. This gives a prevalence of 22.03 per 10,000 girls in this small rural area situated around the city of Crema in northern Italy. Family history of these families did not reveal any inbreeding among these families. This unusual concentration of patients with this syndrome is apparently the first example of a strong geographical concentration of Rett syndrome.