Among siblings, the prevalence of autism is fifty times greater than in the general population. All these epidemiological studies support the arguments for a genetic origin of autism. The reports of twin studies are significant. Individual cases of monozygotic and dizygotic twins were published before 1977. However, I want to draw your attention to fragile-X syndrome.
Opinions differ over the interpretation of the association of fragile-X syndrome and autism.
Different authors suggest that fragile-X syndrome does not exist in autistic boys. Others assert that there is an association between fragile-X syndrome and autistic syndrome in both boys and girls. The last review by Fisch of 21 recent studies revealed a proportion of 6.4 fragile-X to 1,006 autistic males. The most recent methods of molecular diagnosis described Mandel's team enable us to obtain more accurate epidemiology data. We found a significant Chi Square for the locus DXS 287 in Xq22-23.