In ARSF three additional truncating variants were found among the 914 subjects with XLMR; only one could be evaluated and did not segregate with mental retardation. At least one additional truncating variant was found in each of ARSF, VSIG4 and ZNF183 in controls. In total, we found four truncating variants in ARSF in 1,122 XLMR-affected subjects and five in 1,346 controls. In both VSIG4 and ZNF183 one truncating variant was found in 1,122 cases and one in 1,653 and 1,391 controls, respectively. The results therefore suggest that none of these three genes is likely to be involved in mental retardation. No further USP9X truncating variants were found in cases or controls; consequently, the role of USP9X in XLMR remains uncertain.
