AUTISM AS A STRONGLY GENETIC DISORDER - EVIDENCE FROM A BRITISH TWIN STUDY

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 wer e also invoked as environmentally determined aetiological factors. The first British twin sample has been re-examined and a second total pop ulation sample of autistic twins recruited. In the combined sample 60% of monozygotic (MZ) pairs were concordant for autism versus no dizygo tic (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 co ntrol and suggest the involvement of multiple genetic loci. Obstetric hazards usually appear to be consequences of genetically influenced ab normal development, rather than independent aetiological factors. Few new cases had possible medical aetiologies, refuting claims that recog nized disorders are common aetiological influences.