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Risks of Non-Affective Psychotic Disorder and Bipolar Disorder in Young People Diagnosed with Autism Spectrum Disorder. a Population-Based Study
Objectives: To test two hypotheses: (i) the risks of NAPD and BD in individuals with ASD are increased; (ii) these risks are higher than those of siblings not diagnosed with ASD.
Methods: Case-control study nested within the Stockholm Youth Cohort. This cohort comprises all individuals aged 0-17 years ever resident in Stockholm County during the period 2001-2011. Cases were cohort members ever diagnosed with ASD (N=9,062). The siblings were their full siblings never diagnosed with ASD. Each case was matched with 10 controls of the same sex, born in the same month and year. Since the cohort was followed until 31 December 2011, the oldest members had reached the age of 27.
A distinction was made between ASDs registered before 16 or 28 years of age and between ASDs with or without intellectual disability (ID). The information on the outcome (NAPD or BD) was obtained from Swedish Registers. Using conditional logistic regression analysis we computed Odds Ratios (ORs) for NAPD and BD, adjusted for age, sex, population density of place of birth, personal or parental history of migration, hearing impairment, parental age, parental income, parental educational level and parental history of psychiatric disorder
Results: The adjusted ORs of NAPD and BD for cases of ASD without ID, registered before 16 years, were 5.6 (95% CI: 3.3-8.5) and 5.8 (3.9-8.7), respectively; the adjusted ORs for cases of ASD with ID were 3.5 (2.0-6.0) and 1.8 (0.8-4.1). The adjusted ORs of NAPD and BD for cases of ASD without ID, registered before 28 years, were 12.3 (9.5-15.9) and 8.5 (6.5-11.2), respectively; for cases of ASD with ID, these values were 6.4 (4.2-9.8) and 2.0 (1.0-3.9), respectively. The ORs of NAPD and BD for the non-autistic full siblings of cases registered before 16 years, adjusted for hearing loss, were 1.8 (1.1-2.7) and 1.7 (1.1-2.6), respectively.
As for the impact of school leaving grades, the risks of NAPD and BD for individuals registered with ASD without ID before 28 years of age were higher among average-high performers than among low performers. For low performers the adjusted ORs for NAPD and BD were 11.1 (7.3-16.9) and 4.3 (2.7-6.6), respectively. For average-high performers the adjusted ORs were 18.3 (10.2-33.0) and 12.6 (7.4-21.4), respectively. The numbers of individuals with known school grades registered with ASD without ID before age 16 were small.
Conclusions: A diagnosis of ASD is associated with a substantially increased risk of NAPD and BD. This finding contributes to our understanding of these disorders and has implications for the management of ASD.