Objectives: To a) replicate previous findings; b) identify new factors in the RRBI domain; c) examine their familiality among affected siblings; and, d) measure the association with broader autism phenotype (BAP) traits in their parents.
Methods: Our sample included 310 verbal subjects (age 5 to 22) who met DSM-IV criteria for autism. We factor analyzed the RRBI 'ever' items from the Autism Diagnostic Interview-Revised to replicate previous findings and then in a separate analysis we included the communication item, 'verbal rituals.' We examined the familial aggregation of factors and their association with BAP traits.
Results: The IS and RSMB two factor model was replicated in our sample. In the second factor analysis (RRBI + verbal rituals) we observed a four factor model: IS, ‘simple’ RSMB, ‘complex’ RSMB, and a fourth factor including symptoms associated with intense preoccupations (IP). IS and IP were each significantly familial (p < .001 for both), but only IP was significantly correlated with the BAP traits of rigidity (r = .39, p = .007) and aloofness (r = .39, p = .005) in fathers.
Conclusions: The results support previous evidence for the familiality of IS and identify IP as an additional strong candidate trait for genetic studies of autism.