Distribution of ACTN3 R577X, MTHFR C677T, MTHFR A1298C, and MTRR A66G Polymorphisms in 564 School-Aged Children in Beijing: A Cross-Sectional Study.

BACKGROUND: Beijing's 2024 school physical education reforms have substantially increased activity demands on children, yet population-level genotype data for Chinese schoolchildren remain scarce. OBJECTIVES: To characterize ACTN3 R577X, MTHFR C677T, MTHFR A1298C, and MTRR A66G polymorphisms in 564 Beijing schoolchildren; test Hardy-Weinberg equilibrium (HWE); compare allele frequencies with East Asian reference populations; and perform multi-locus cumulative allele analysis across all four loci. METHODS: Cross-sectional study of 564 primary and secondary school students (265 males, 299 females) in Beijing. Genotyping was performed by PCR and Sanger sequencing using saliva-derived DNA; the overall call rate was 100% (564/564). HWE was assessed using the exact test of Wigginton et al. Allele frequencies were compared with 1000 Genomes CHB (n=103) and gnomAD EAS (n≈2604) using chi-squared or Fisher's exact tests. Cumulative variant allele counts (0-8) were computed across all four loci. Linkage disequilibrium (LD) and haplotype frequencies were estimated using the EM algorithm. RESULTS: All four loci were in HWE (all p>0.05). Genotype frequencies were: ACTN3 R577X-RR 31.56%, RX 49.11%, XX 19.33%; MTHFR C677T-CC 18.62%, CT 46.99%, TT 34.40%; MTHFR A1298C-AA 71.81%, AC 26.42%, CC 1.77%; MTRR A66G-AA 56.21%, AG 35.82%, GG 7.98%. No significant sex differences were observed at any locus (all p>0.05). Allele frequencies were consistent with East Asian reference populations. Across all four loci, 87.23% of students carried ≥2 variant alleles; 29.26% carried ≥4. LD between MTHFR C677T and A1298C was moderate to strong (|D'|=0.97, r2=0.23). The double-mutant T-C haplotype was rare (frequency =0.002). CONCLUSIONS: This study provides genotype frequency data for exercise- and folate metabolism-related polymorphisms in a sample of Beijing schoolchildren. These descriptive frequency data establish a baseline for future genotype-phenotype association studies; however, the sample is limited to two schools in two districts of Beijing and does not represent the broader Chinese pediatric population. Studies incorporating fitness, biochemical, and dietary data are required before such genetic profiles can inform educational or clinical recommendations. Given the purely descriptive, cross-sectional nature of the study and the absence of phenotypic data, these genotype frequency data do not, on their own, provide a basis for individualized physical education programming or nutritional recommendations.