FMR1 and fragile X syndrome: On the one hand, incomplete silencing of FMR1 was associated with elevated autistic features as measured by ADOS-2 CSS, with 21% more of the 18 and under FM-only group expressing FM FMR1 mRNA meeting the ADOS-2 criteria for ASD (CSS ≥ 4), as compared to FM-only males with completely silenced FMR1. On the other hand, decreased levels of FMR1 mRNA were associated with decreased intellectual functioning in FXS males, with the relationships primarily driven by variability in the PM/FM mosaic subgroup.