On the twin risk in autism

Area of Science:

• Childhood psychiatric disorders
• Genetics and epigenetics
• Epidemiology

Background:

• Autism spectrum disorder (ASD) is a complex childhood psychiatric disorder with strong genetic influences.
• Family and twin studies suggest a significant genetic component in ASD etiology.
• Recent studies proposed twinning as a potential risk factor for ASD development.

Purpose of the Study:

• To investigate the hypothesis that the twinning process is an independent risk factor for autism.
• To re-evaluate the interpretation of twin studies in autism research.
• To determine if an increased rate of autism exists in twin births.

Main Methods:

• Conducted an epidemiological study in Western Australia, identifying children diagnosed with autism, Asperger syndrome, or PDD-NOS between 1980-1995.
• Compared the observed rate of autism in twin births to the general twin birth rate.
• Analyzed data to explain the proportion of twins in affected-sibling-pair studies.

Main Results:

• Identified 14 twin births among 465 children diagnosed with autism or related disorders.
• The observed twin birth rate among children with autism (30.0/1,000) was not substantially higher than the general twin rate (26.3/1,000).
• The higher proportion of twins in previous studies is attributable to higher concordance rates in monozygotic twins and family size distributions.

Conclusions:

• The findings do not support twinning as a significant risk factor in the etiology of autism.
• The observed excess of twins in affected-sibling-pair studies can be explained by genetic factors and study design, not the twinning process itself.
• Results align with similar epidemiological studies conducted in California and Sweden.