FMR1 and fragile X syndrome: Evidence that higher rates of ASD-related characteristics were present in the misclassified PM carriers and in their children with FXS could suggest the presence of additional etiologic factors in this subgroup of families, such as differences in genetic background, including variation in ASD risk genes known to interact with FMR1 (Belmonte and Bourgeron, 2006; Darnell et al., 2011; Hagerman et al., 2011; Steinberg and Webber, 2013).