In a sample of 5049 pairs of individuals from high-risk pedigrees, no evidence could be found for a uterine or socialization maternal effect on IQ or on the incidence of mental retardation. The observed excess of affected males and higher risk for children of affected females are fully consistent with all of three multifactorial threshold models.
Key Words mental retardation - IQ - maternal effects - threshold model
This work was supported by Grants GM 17173 from the U.S. National Institutes of Health and 72/515, 72/516 from the Brazil 
Fundação de Amparo à Pesquisa do Estado de São Paulo
. This work is designated PGL paper 108.