Non-syndromic mental retardation is not expressed in RAC1 gene polymorphisms

We investigated whether non-syndromic mental retardation (NSMR) is associated with RAC1 gene polymorphisms, using a case-control association study. A group of Han children of northwestern China were evaluated for three common single nucleotide polymorphisms (SNPs) in the gene (rs1647224, rs836488, rs702482). Pairwise linkage disequilibrium (LD) analysis revealed that the three SNPs were in linkage disequilibrium (all D'>0.5). The case-control analysis showed that there were no significant differences in either allele or genotype frequencies at any of the SNPs between 66 NSMR and 239 controls nor between 99 Border and 239 controls. Using haplotype analysis we found the haplotype G-C-A was associated with NSMR (chi(2)=4.13, P=0.042). However, this association was no longer significant after multiple test correction. In conclusion, our negative results suggested that variants of RAC1 gene did not influence the occurrence of NSMR in Chinese children. Therefore we propose that there may be a compensatory mechanism which works to compensate the effect of mutation in the RAC1 gene on NSMR.