Simplex and Multiplex Classification
Family type was classified as simplex, multiplex, or unknown. Simplex families had one known affected individual among the first- to third-degree relatives (cousins only) and included affected monozygotic twins. Multiplex families had at least two first- to third-degree relatives (cousins only) with a validated, clinical ASD diagnosis. All other situations, including instances where a family history of autism was not assessed explicitly, were coded as unknown.