This study aims to identify potential variants in the TP63–IRF6 pathway and GREM1 for the etiology of non-syndromic orofacial cleft (NSOFC) among the Vietnamese population. By collecting 527 case–parent trios and 527 control samples, we conducted a stratified analysis based on different NSOFC phenotypes, using allelic, dominant, recessive and over-dominant models for case–control analyses, and family-based association tests for case–parent trios. Haplotype and linkage disequilibrium analyses were also conducted. IRF6 rs2235375 showed a significant association with an increased risk for non-syndromic cleft lip and palate (NSCLP) and cleft lip with or without cleft palate (NSCL/P) in the G allele, with p_allele values of 0.0018 and 0.0003, respectively. Due to the recessive model (p = 0.0011) for the NSCL/P group, the reduced frequency of the GG genotype of rs2235375 was associated with a protective effect against NSCL/P. Additionally, offspring who inherited the G allele at rs2235375 had a 1.34-fold increased risk of NSCL/P compared to the C allele holders. IRF6 rs846810 and a G-G haplotype at rs2235375–rs846810 of IRF6 impacted NSCL/P, with p-values of 0.0015 and 0.0003, respectively. In conclusion, our study provided additional evidence for the association of IRF6 rs2235375 with NSCLP and NSCL/P. We also identified IRF6 rs846810 as a novel marker associated with NSCL/P, and haplotypes G-G and C-A at rs2235375–rs846810 of IRF6 associated with NSOFC.

Background: Non-syndromic orofacial clefts (NSOFCs) are one of the common congenital malformations in Vietnam, with 1.4 per 1000 live births, with notable sex differences in occurrence. This case–control study aims to investigate potential sex-specific interactions of WNT3 and NOG polymorphisms across NSOFC subtypes in a Vietnamese population. Methods: A total of 720 participants were separated into 4 groups with a male/female ratio of 1:1 (160 individuals with cleft lip and palate (NSCLP), 160 with cleft lip only (NSCLO), 160 with cleft palate only (NSCPO), 240 healthy controls). Two single-nucleotide polymorphisms (SNPs), rs3809857 and rs227731, were genotyped by using the StepOnePlus Real-Time PCR System. Results: The most significant findings were found in the male NSCLO group under a recessive model of WNT3 rs3809857 after applying Bonferroni correction, as a five-fold protective factor with OR = 0.18 (95% confidence interval: 0.05–0.64, p = 0.0033). Additionally, the weak or moderate protective association between rs3809857 and male NSCLP was found with p < 0.05 under the dominant model. However, there were no significant findings in the female NSOFC subtypes associated with WNT3. Conversely, NOG rs227731 results showed a weak increased risk in female NSCLO and NSCPO with p < 0.05. Conclusion: this study identified the critical role of WNT3 rs3809857 in reducing NSCLO risk in males. These findings support the potential influence of sex as a modifying factor in the genetic susceptibility to non-syndromic orofacial clefts.