Parental migration and risks of intellectual disability and autism

Background: Intellectual disability and autism are overlapping heterogeneous neurodevelopmental conditions with early onset. The prevalence of diagnosed autism has increased in recent decades. In addition, children with migrant parents have been shown to have a higher prevalence of autism with intellectual disability. However, there is limited evidence on time trends in the prevalence of intellectual disability and the association between parental migration and intellectual disability. The primary aim of this thesis was to describe the time trends and risks of intellectual disability, with and without autism, overall and in relation to parental migration.

Methods: In study IV, we described the time trends in the prevalence of intellectual disability diagnosed by age 10, using a cohort that included 1,096,800 children born in Sweden from 2001 to 2011. The other three studies focused on intellectual disability, with and without autism. In study I, a systematic review, and study II, a cohort study including 670,098 children aged 0 to 17 who resided in Stockholm at any time from 2001 to 2011, we described the risks in relation to parental migration status and migration-related factors. Study III explored age at first recorded diagnosis by parental migration status, using a cohort including 1,769,499 children born in Sweden from 2001 to 2017.

Results: The prevalence of mild, moderate, and other/unspecific intellectual disability diagnoses at age 10 increased in Sweden between 2011 and 2021, particularly in the later years, regardless of co-occurring autism. This trend remained unchanged after adjustment or stratification by birth weight, gestational age, or parental age, migration status, and education.

Children with two migrant parents had higher risks of intellectual disability, both with and without autism, compared with children with two Swedish-born parents. The association was more pronounced if the parents had migrated from low- and middle-income countries and for reasons other than work or study. Additionally, among children with two migrant parents, being born either before or more than four years after maternal migration was associated with a lower risk of intellectual disability with autism, but not intellectual disability without autism. Furthermore, these children, particularly those with parents from low-income countries, were diagnosed with mild intellectual disability at younger ages compared with those with at least one Swedish-born parent, regardless of co- occurring autism.

Conclusions: The recorded prevalence of mild and moderate intellectual disability has increased during the last decade in Sweden. This increase does not appear to be explained by concurrent changes in the distribution of sociodemographic or perinatal factors over time, such as an increase in the number of children born preterm, with low birth weight, to migrant parents, or to older mothers, nor by shifts in the levels of parental education. Instead, this increase may reflect changes in diagnostic practices over time.

Children with migrant parents are more frequently diagnosed with intellectual disability, with and without autism, compared with their peers with Swedish-born parents. Our findings further indicate that the underlying factors linking parental migration to the risk of intellectual disability may vary depending on the co- occurrence of autism and the severity of the condition, at least in part. For intellectual disability overall, factors related to parental origin in low- and middle-income countries appear to play a role. In cases of intellectual disability with autism, environmental factors acting during pregnancy and associated with adverse migration-related circumstances may contribute. For mild intellectual disability, disparities in diagnostic practices between children with migrant parents from low-income countries and those with native-born parents may account for part of the observed associations.

List of scientific papers

I. Morinaga M, Rai D, Hollander AC, Petros N, Dalman C, Magnusson C. Migration or ethnic minority status and risk of autism spectrum disorders and intellectual disability: systematic review. Eur J Public Health. 2021;31(2):304-12. https://doi.org/10.1093/eurpub/ckaa108

II. Morinaga M, Hollander AC, Heuvelman H, Lundberg M, Dalman C, Rai D, Magnusson C. Migration and risk of intellectual disability with and without autism: A population-based cohort study. Acta Psychiatr Scand. 2021;144(5):487-500. https://doi.org/10.1111/acps.13350

III. Morinaga M, Magnusson C, Hollander AC, Ahlqvist VH, Lundberg M. Age at diagnosis of autism and intellectual disability in children with migrant parents: a nationwide population-based study. [Manuscript]

IV. Morinaga M, Ahlqvist VH, Lundberg M, Hollander AC, Rai D, Magnusson C. Changes in the prevalence of intellectual disability among 10-year-old children in Sweden during 2011 through 2021: a total population study. J Neurodev Disord. 2024;16(1):58. https://doi.org/10.1186/s11689-024-09576-3