The authors ascertained 46 families with multiple incidences of autism
(41 with two and five with three autistic probands). Classical segregation
analyses revealed a maximum likelihood estimate of the segregation ratio of
p = 0.19 +/- 0.07. This is not significantly less than 0.25, the expected
value for autosomal recessive inheritance. However, it is significantly
less than 0.50, the expected value for autosomal dominant inheritance. The
polygenic threshold model was tested and rejected over a full range of
values of heritability and ascertainment probability for these families.
These results are most consistent with the hypothesis of autosomal
recessive inheritance in this subset of 46 families with multiple
incidences of autism.