The effects of CMIP (rs6564903) and ATP2C2 (rs11860694) on nonword-repetition performance were modeled as additive effects within a regression framework in the R package. This regression model included all available SLIC children with genotype and nonword-repetition data (n = 503). Group means were calculated for each SNP in isolation (“Single SNP” entries) and in combinations of genotypes (3 × 3 grid) across risk SNPs. Note that individuals carrying combinations of risk alleles performed significantly worse than those carrying risk variants at a single locus. Nonword-repetition scores are age adjusted and standardized against normal population controls with a mean of 100 and a SD of 15.