Cognitive, language and social-cognitive skills of individuals with fragile X syndrome with and without autism

Background It is not known whether those with co‐morbid fragile X syndrome (FXS) and autism represent a distinct subtype of FXS; whether the especially severe cognitive delays seen in studies of young children with co‐morbid FXS and autism compared with those with only FXS continue into adolescence and young adulthood; and whether autism in those with FXS is ‘true autism’, i.e. reflects the same underlying problems as idiopathic autism. Method We compared the non‐verbal IQ of adolescents and young adults with co‐morbid FXS and autism (n = 10) with those with only FXS (n = 44). We then created a subsample of those with FXS only, matched on non‐verbal IQ, mental age and gender (n = 21) to the subsample of those with co‐morbid FXS and autism. We compared the two groups on measures of expressive language, receptive language (lexical, grammatical morphology and syntactic patterns), and a theory of mind task. Results Those with co‐morbid FXS and autism had lower non‐verbal IQs than those with only FXS. The participants with co‐morbid FXS and autism did not perform as well as the cognitive ability‐ and gender‐matched participants with only FXS on the three measures of receptive language or the theory of mind task; there were no differences on the expressive language measure. Conclusions Our findings support the notion that those with co‐morbid FXS and autism represent a distinct subtype of FXS, with more impairment in receptive language and theory of mind even when controlling for their lower non‐verbal IQ relative to those with only FXS. The greater cognitive impairments observed in those with co‐morbid FXS and autism continues into adolescence and young adulthood; and the autism seen in those with FXS appears to be the same as idiopathic autism.