The elevated risk was greater if the parent had received a diagnosis before or during pregnancy rather than after birth. A substance use disorder diagnosis registered before birth was associated with more than twice the risk of intellectual disability in the baby, regardless of which parent had the diagnosis. The correlation was weaker but still statistically significant after adjustment of socioeconomic factors and psychiatric comorbidity in the parents.

“Since it was an observational study, we can draw no conclusions about the underlying mechanism, but we suspect that both genetic and environmental factors, including harmful effects of substance abuse on foetal development, may play a part,” says Dr Khemiri. “We hope that the results will contribute to the preventative efforts, as well as to the improved diagnosis of children with an intellectual disability and to timely intervention directed both to the child as well as parents in need of substance use disorder treatment.”

Alcohol is a major risk factor

Intellectual disability was observed to be much more likely in alcohol-related problems during pregnancy, where the risk was five and three times higher depending on whether it was the mother or father who had the alcohol use disorder diagnosis.

The study was financed by several bodies, primarily Region Stockholm, Systembolaget (the Swedish government alcohol retail monopoly) and the Fredrik and Ingrid Thuring Foundation. Co-author and KI researcher Henrik Larsson has received research grants from Shire/Takeda and fees from Medice, Shire/Takeda and Evolan Pharma AB, although unconnected to this present study. All other researchers report no conflicts of interest.

Publication

“Parental substance use disorder and risk of intellectual disability in offspring in Sweden: a national register study”, Lotfi Khemiri, Ralf Kuja-Halkola, Henrik Larsson, Agnieszka Butwicka, Magnus Tideman, Brian M. D’Onofrio, Antti Latvala, Paul Lichtenstein, eClinicalMedicine, online 30 August 2023, doi: 10.1016/j.eclinm.2023.102170.