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Objective The etiology of non-syndromic cleft lip with or without cleft palate (nsCL/P) is multifactorial, heterogeneous, and still not completely understood. The aim of the present study was to examine the associations between common and rare PAX7 nucleotide variants and the risk of this common congenital anomaly in a Polish population. Subjects and methods Eight top nsCL/P-associated PAX7 variants identified in our cleft genome-wide association study (GWAS) were selected for replication analysis in an independent group of patients and controls (n = 247 and n = 445, respectively). In addition, mutation screening of the PAX7 protein-coding region was conducted. Results Analysis of the pooled data from the GWAS and replication study confirmed that common PAX7 nucleotide variants are significantly associated with the increased risk of nsCL/P. The strongest individual variant was rs1339062 (c.586 + 15617T > C) with a p-value = 2.47E-05 (OR = 1.4, 95%CI: 1.20-1.64). Sequencing analysis identified a novel synonymous PAX7 substitution (c.87G > A, p.Val29Val) in a single patient with nsCLP. This transition located in the early exonic position was predicted to disrupt potential splice enhancer elements. Conclusion Our study confirmed that PAX7 is a strong candidate gene for nsCL/P. Nucleotide variants of this gene contribute to the etiology of nsCL/P in the homogenous Polish population.

Background. Non-syndromic cleft lip with or without cleft palate (NSCL/P) is a common developmental anomaly, which etiology is complex and not completely elucidated. Aim. The aim of the present study was to evaluate whether common polymorphisms in the distal-less homeobox gene 1 (DLX1) may contribute to the risk of orofacial clefts in the Polish population. Material and methods. Five single nucleotide variants were genotyped using high-resolution melting curve analysis in a group of 278 patients with NSCL/P and properly matched controls (n = 574). Results. Statistical analysis revealed that two variants located in the 3’ untranslated region of DLX1, rs788172 and rs788173, were associated with a decreased risk of NSCL/P (ptrend = 0.041 and ptrend = 0.025, respectively). The allelic frequencies for these polymorphisms were significantly lower in patients compared to healthy individuals (p = 0.040 and p = 0.024, respectively). However, all these results did not remain statistically significant after applying the Bonferroni correction for multiple comparisons. The results of single-marker analysis for DLX1 were confirmed by haplotype analysis. The best evidence of the haplotype association with the risk of NSCL/P was observed for the T-G-G haplotype consisting of rs1047889, rs788172 and rs788173 major alleles. This high risk haplotype was more frequent among cases than controls (p = 0.013, pcorrected = 0.026). Conclusions. We found evidence for the association between DLX1 gene variants and the risk of NSCL/P in the Polish population. To confirm our preliminary findings further, larger sample size studies are required.