The strongest evidence of the association between AD and OCD or TD/CTD originates from a handful of family studies suggesting that the mothers of individuals with these disorders have elevated rates of AD. In a specialty clinic-based study,17 the mothers of 107 children and adolescents with OCD and/or TD/CTD were interviewed regarding their history of AD. Nearly 18% of the mothers reported at least one AD; this figure was higher for the mothers of children fulfilling likely criteria for PANDAS (Pediatric Autoimmune Neuropsychiatric Disorder Associated with Streptococcal Infection) (n=40; 25%), compared to the mothers of children with unlikely PANDAS (n=67; 13.4%). A longitudinal population-based study from Denmark examined the risk of TD (n=2,442) in the offspring of mothers with 31 different AD. A maternal history of AD was found in 110 cases, corresponding to an increased risk of TD of approximately 22%. The most common maternal AD were ulcerative colitis, rheumatoid arthritis, thyrotoxicosis, and multiple sclerosis, although power was limited to examine the risk for many of the individual AD.18 In two case-control family studies that analyzed the same Brazilian
