Children of migrant parents may be at greater risk of low-functioning autism spectrum disorder, but lower risk of high-functioning autism spectrum disorder

QUESTION Question: Is parental migration associated with an increased risk of autism spectrum disorder (ASD) among children, and does region of origin and timing of migration contribute to risk? People: 3918 cases (2269 high-functioning; 1649 have lowfunctioning) aged 17 and younger with ASD identified from the Stockholm Youth Cohort through data-linkage with health and service registries in Stockholm County. Diagnosis of ASD was made by specialist multiprofessional teams at paediatric or child mental health services. Controls (n=40 045) were randomly selected from the same cohort, with 10 controls being matched to each case by birth date and gender. Children who were residents of Stockholm County for less than four years, were adopted, had one parent born abroad, had missing data or were asylum seekers without a residence permit were excluded. Setting: Stockholm County, Sweden; 2001 to 2007. Risk factors: Parent and child migration status, as indicated by maternal birth outside of Sweden. This was determined by linkage with mandatory reporting registers containing information on: country of birth; date of immigration to Sweden; family income at birth (for children born abroad) or at the earliest measured point in childhood; pregnancy outcomes including birth weight for gestational age; gestational age; Apgar score at 5 min following birth. Other risk factors included geographical region of origin (according to the United Nations definition) and level of human development (as defined by the UNDP Human development Index) which were determined by the maternal country of birth. The maternal region of birth and timing of migration were analysed among migrant children only. All analyses were adjusted for maternal and paternal age at the child's birth and for the family disposable income at birth or in childhood. Outcomes: ASD; further subcategorised into: low-functioning ASD, defined as the presence of a recorded comorbid intellectual disability (IQ of 70 or less); high-functioning ASD, defined as the absence of a recorded comorbid intellectual disability. METHODS Design: Nested case-control study. Follow-up period: Up to 17 years (retrospectively assessed). MAIN RESULTS A total of 21% of cases and controls had both parents born outside of Sweden. Overall, children of migrant parents did not clearly differ in risk of ASD from children of parents born in Sweden (adjusted OR 0.9, 95% CI 0.9 to 1.0). Compared to children of Swedish-born parents, among children of migrant parents there was a trend towards increased risk of low-functioning ASD (adjusted OR 1.2, 95% CI 1.0 to 1.4) but a significantly lower risk of high functioning ASD (adjusted OR 0.5, 95% CI 0.4 to 0.6). Children of mothers who migrated in the year before the child's birth were at the highest odds of low-functioning ASD compared with children whose mothers migrated at least 15 years before the birth (adjusted OR 1.9, 95% CI 1.1 to 3.1) and compared to children of Swedish parents (adjusted OR 2.1, 95% CI 1.5 to 2.8). CONCLUSIONS In children of migrant parents, there may be a greater risk of ASD with intellectual disability but a decreased risk of ASD without intellectual disability compared with children of non-migrant parents.