Autism as a strongly genetic disorder: evidence from a British twin study

TLDR

Previous twin studies suggest autism is largely genetically determined, with conflicting evidence on broader cognitive or social traits, and obstetric hazards appear to be consequences of genetic abnormalities rather than independent causes. The study re‑examined the first British twin sample and recruited a second total‑population sample of autistic twins. In the combined sample, 60 % of monozygotic pairs and 92 % of pairs for broader cognitive or social abnormalities were concordant versus 10 % of dizygotic pairs, indicating strong genetic control and multiple loci, with few medical etiologies identified.

Abstract

Synopsis Two previous epidemiological studies of autistic twins suggested that autism was predominantly genetically determined, although the findings with regard to a broader phenotype of cognitive, and possibly social, abnormalities were contradictory. Obstetric and perinatal hazards were also invoked as environmentally determined aetiological factors. The first British twin sample has been re-examined and a second total population sample of autistic twins recruited. In the combined sample 60% of monozygotic (MZ) pairs were concordant for autism versus no dizygotic (DZ) pairs; 92% of MZ pairs were concordant for a broader spectrum of related cognitive or social abnormalities versus 10% of DZ pairs. The findings indicate that autism is under a high degree of genetic control and suggest the involvement of multiple genetic loci. Obstetric hazards usually appear to be consequences of genetically influenced abnormal development, rather than independent aetiological factors. Few new cases had possible medical aetiologies, refuting claims that recognized disorders are common aetiological influences.