Association between autism and dementia across generations: evidence from a family study of the Swedish population.

There is emerging evidence to suggest that autistic individuals are at an increased risk for cognitive decline or dementia. It is unknown whether this association is due to shared familial influences between autism and dementia. The main purpose of this study was, thus, to investigate the risk of dementia in relatives of autistic individuals. We conducted a family study based on linking Swedish registers. We identified all individuals born in Sweden from 1980-2013, followed until 2020, and clinical diagnoses of autism among these individuals. We linked these index individuals with their parents, grandparents, and aunts/uncles. The risk of dementia (including any type of dementia, Alzheimer's disease, and other types of dementia) in relatives of autistic individuals was estimated using Cox proportional hazards models. Analyses were then stratified by sex of the relatives and intellectual disability in autistic individuals. Relatives of autistic individuals were at an increased risk of dementia. The risk was strongest in parents (hazards ratio [HR] = 1.36, 95% confidence intervals = 1.25-1.49), and weaker in grandparents (HR = 1.08, 1.06-1.10) and aunts/uncles (HR = 1.15, 0.96-1.38). Furthermore, there were indications of a stronger association between autism in index individuals and dementia in mothers (HR = 1.51, 1.29-1.77) compared to dementia in fathers (HR = 1.30, 1.16-1.45). There was only a small difference in relatives of autistic individuals with and without intellectual disability. Our results provide evidence of familial co-aggregation between autism and different types of dementia, and a potential genetic link. Future research now needs to clarify the risk of dementia in autistic individuals.