Migration and autism spectrum disorder: Population-based study

Department of Public Health Sciences, Karolinska Institutet, Norrbacka, Stockholm, Sweden.
The British journal of psychiatry: the journal of mental science (Impact Factor: 7.99). 02/2012; 201(2):109-15. DOI: 10.1192/bjp.bp.111.095125
Source: PubMed


Migration has been implicated as a risk factor for autism, but evidence is limited and inconsistent.
To investigate the relationship between parental migration status and risk of autism spectrum disorder, taking into consideration the importance of region of origin, timing of migration and possible discrepancies in associations between autism subtypes.
Record-linkage study within the total child population of Stockholm County between 2001 and 2007. Individuals with high- and low-functioning autism were defined as having autism spectrum disorder with and without comorbid intellectual disability, and ascertained via health and habilitation service registers.
In total, 4952 individuals with autism spectrum disorder were identified, comprising 2855 children with high-functioning autism and 2097 children with low-functioning autism. Children of migrant parents were at increased risk of low-functioning autism (odds ratio (OR) = 1.5, 95% CI 1.3-1.7); this risk was highest when parents migrated from regions with a low human development index, and peaked when migration occurred around pregnancy (OR = 2.3, 95% CI 1.7-3.0). A decreased risk of high-functioning autism was observed in children of migrant parents, regardless of area of origin or timing of migration. Parental age, income or obstetric complications did not fully explain any of these associations.
Environmental factors associated with migration may contribute to the development of autism presenting with comorbid intellectual disability, especially when acting in utero. High- and low-functioning autism may have partly different aetiologies, and should be studied separately.

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Available from: Anna Goodman, Aug 02, 2014
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    • "After exclusion of observations with missing covariate data, the final sample consisted of 2,371,403 persons, with 24,414 identified ASD cases. The Stockholm Youth Cohort is a register-based study with continuous enrollment comprising all individuals who were ever resident in Stockholm County as children (Idring et al., 2012; Magnusson et al., 2012). All data are derived from linkages to national registers held by Statistics Sweden and the National Board of Health and Welfare, as well as regional registers held by the Stockholm County Council. "
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    • "Many previous studies conducted in Europe have shown that immigrant mothers born outside Europe have an increased risk of having a child with childhood autism [9-11] or other ASD [12], but there are also studies reporting a non-significant association [13,14]. In one study maternal immigration was associated only with ASD with intellectual disability [15]. Outside Europe, an Australian study showed that immigrant mothers had an increased risk of having a child with ASD [16]. "
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    ABSTRACT: Studying second-generation immigrants can help in identifying genetic or environmental risk factors for childhood autism. Most previous studies have focused on maternal region of birth and showed inconsistent results. No previous study has been conducted in Finland. The study was a nested case--control study based on a national birth cohort. Children born in 1987--2005 and diagnosed with childhood autism by the year 2007 were identified from the Finnish Hospital Discharge Register. Controls were selected from the Finnish Medical Birth Register. Information on maternal and paternal country of birth and mother tongue was collected from the Finnish Central Population Register. There were 1132 cases and 4515 matched controls. The statistical test used was conditional logistic regression analysis. Compared with children with two Finnish parents, the risk of childhood autism was increased for those whose parents are both immigrants (adjusted odds ratio [aOR] 1.8, 95% confidence interval [CI] 1.2--2.7) and for those with only an immigrant mother (aOR 1.8, 95% CI 1.2--2.7), but not for those with only an immigrant father. The risk was increased for those with a mother born in the former Soviet Union or Yugoslavia and for those with a mother or a father born in Asia. Specific parental countries of birth associated with an increased risk were the former Soviet Union, the former Yugoslavia and Vietnam. In Finland, children who are born to immigrant mothers with or without an immigrant partner, have an increased risk of childhood autism. The risk varies with immigrant parents' region of birth. The findings may help in identifying possible risk factors, which can be examined in future studies.
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    • "Since 1999, the Child and Adolescent Mental Health Services (CAMH) in Stockholm County, Sweden has used a client database (Pastill) with clinical patient information for all individuals attending CAMHS in the greater Stockholm area, which includes the capital of Sweden and surrounding suburban areas. Complete and valid data, including sociodemographic data, referral reason, treatment provided, and diagnostic assessment are available from 2001 to 2010 for 92,000 individuals (Lundh et al. 2012; Magnusson et al. 2012) based on one or more clinical contacts at 19 in-and outpatient clinics. Diagnoses according to the Diagnostic and Statistical Manual of Mental Disorders—fourth edition (APA 1994) and the International Classification of Diseases and Related Health Problems-tenth edition (WHO 1992) are assigned based on clinical contacts with psychiatrists, psychologists , and social workers. "
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