A Twin Study of Autism in Denmark, Finland, Iceland, Norway and Sweden

TLDR

The study screened Nordic twin registries for autism in same‑sexed twins under 25, identifying 21 pairs (11 monozygotic, 10 dizygotic) and one identical triplet set for detailed examination. Autism concordance was 91 % in monozygotic pairs and 0 % in dizygotic pairs, with similar patterns for cognitive disorder (91 % vs 30 %); discordant pairs often showed perinatal stress in the autistic twin, supporting both hereditary and perinatal contributions.

Abstract

The Nordic countries were screened for the occurrence of cases of autism with a same-sexed twin under age 25 years. Twenty-one pairs (11 monozygotic and 10 dizygotic) of twins and one set of identical triplets were found and extensively examined. The concordance for autism by pair was 91% in the monoygotic and 0% in the dizygotic pairs. The corresponding concordances for cognitive disorder were 91% and 30%, respectively. In most of the pairs discordant for autism, the autistic twin had more perinatal stress. The results lend support for the notion that autism sometimes has a hereditary component and that perinatal stress is involved in some cases.