Genetic Variants in the Mitochondrial Thymidylate Biosynthesis Pathway Increase Colorectal Cancer Risk.

We assess the contributions of genetic variants for the enzymes involved in capecitabine metabolism to colorectal cancer (CRC) development risk. In this case-control study, DNA samples were collected from 66 patients (King Abdulaziz University Hospital) and 65 controls (King Fahad General Hospital) between April and November 2022 to be used in PCR-RFLP. The chi-square (χ 2 ) test at a significance level of p ˂ 0.05 was used to estimate genotype and allele frequencies. The Lys27Gln variant of cytidine deaminase (CDA) showed a risk ratio (RR) of 1.47 for heterozygous (AC) carriers, with genotype distributions for patients (χ 2 = 1.97) and controls (χ 2 = 14.7). Homozygous (AA) Ala70Thr carriers demonstrated a three-fold higher risk, with genotype distributions for patients (χ 2 = 3.85) and controls (χ 2 = 4.23). Genotype distributions of the 5,10-methylenetetrahydrofolate reductase (MTHFR) C677T variant for patients were (χ 2 = 22.43) and for controls were (χ 2 = 0.07); for the MTHFR A1298C variant, they were (χ 2 = 54.44) for patients and (χ 2 = 4.58) for controls. Heterozygous (AC) carriers of the A1298C variant demonstrated highly significant protection against CRC development (RR = 0.2, p = 0.001), while a two-fold higher risk for CRC was estimated for homozygous genotype (CC) carriers. In conclusion, the heterozygous genotype of CDA Lys27Gln, the homozygous genotype of CDA Ala70Thr, and the homozygous genotype of MTHFR A1298C were associated with CRC development risk. The heterozygous genotype of MTHFR A1298C variant provided highly significant protection against CRC development. Further examinations using a larger population size are needed to reliably confirm our findings.