No abstract

Non-syndromic cleft lip/palate (NSCL/P) is a common congenital defect in Mexico. Periconceptional intake of folic acid (FA) may reduce the risk of this malformation. Although the 5,10-methylenetetrahydrofolate reductase (MTHFR) enzyme participates in folate metabolism, several studies failed to find any association between NSCL/P and the MTHFR C677T and A1298C polymorphisms. However, interactions among NSCL/P, MTHFR gene polymorphisms, and FA intake have not been explored in Mexican populations. This case-control study included 132 patients with NSCL/P and 370 controls from Mexico City. Maternal FA consumption during pregnancy was examined, as were the MTHFR C677T and A1298C polymorphisms and gene-FA interactions. Maternal FA intake during the periconceptional period was lower in cases (1.5%) than in controls (13%), with the risk of delivering a child with NSCL/P lower in mothers who consumed FA (OR = 0.29, 95% CI: 0.19-0.44). In addition, the risk of NSCL/P was lower in children with the TT than the CC genotype of MTHFR C677T (OR = 0.39, 95% CI: 0.23-0.68), after Bonferroni correction and exclusion of stratification. No evidence of gene-FA interaction was found. These results indicate that maternal FA intake and the TT genotype of the MTHFR C677T polymorphism in children independently reduced the risk of NSCL/P in our population.

Nonsyndromic cleft lip with or without cleft palate (NSCL/P) is a common craniofacial birth defect that has a complex etiology. Genome-wide association studies have recently identified new loci associated with NSCL/P, but these loci have not been analyzed in a Mexican Mestizo population. A complex etiology implies the presence of genetic interactions, but there is little available information regarding this in NSCL/P, and no signaling pathway has been clearly implicated in humans. Here, we analyzed the associations of 24 single nucleotide polymorphisms (SNPs) with NSCL/P in a Mexican Mestizo population (133 cases, 263 controls). The multifactorial dimensionality reduction method was used to examine gene-gene and gene-folic acid consumption interactions for the 24 SNPs analyzed in this study and for 2 additional SNPs that had previously been genotyped in the same study population. Six SNPs located in paired box 7, ventral anterior homeobox 1, sprouty RTK signaling antagonist 2, bone morphogenetic protein 4, and tropomyosin 1 genes were associated with higher risks of NSCL/P (P = 0.0001 to 0.04); 2 SNPs, 1 each in netrin 1 and V-maf avian musculoaponeurotic fibrosarcoma oncogene homolog B, were associated with a lower risk of NSCL/P (P = 0.013 to 0.03); and 2 SNPs, 1 each in ATP binding cassette subfamily A member 4 (ABCA4) and noggin, showed associations with NSCL/P that approached the threshold of significance (P = 0.056 to 0.07). In addition, 6 gene-gene interactions (P = 0.0001 to 0.001) and an ABCA4-folic acid consumption interaction (P < 0.0001) were identified. On the basis of these results, combined with those of previous association studies in the literature and biological characterizations of murine models, we propose an interaction network in which interferon regulatory factor 6 plays a central role in the etiology of NSCL/P.

The FKRP-related disorders include the limb-girdle muscular dystrophy type 2I (LGMD2I, MIM#607155) which has a clinical overlap with dystrophinopathies. Except for Brazil, LGMD2I has not been described in other Latin-American countries, despite that 1/64 Mexican-ancestry individuals carry the commonest European p.(Leu276Ile) pathogenic FKRP variant (rs28937900, 1000 Genomes Project Phase 3), suggesting an underdiagnosis. Sequencing of exon 4 of FKRP in 60 unrelated Mexican patients with presumptive diagnoses of dystrophinopathy without DMD gene deletions, or with a neuromuscular disorder of unknown etiology, revealed two patients (2/60, 3.3%): one of them with an unreported pathogenic genotype, p.[Leu276Ile];[Asn463Asp] and a Duchenne-like phenotype; and the other that stands as the third reported case bearing the severe genotype, p.[Asn463Asp];[Asn463Asp] leading to a congenital presentation (MIM#606612). We identified two patients heterozygous for the p.(Arg143Ser) and the novel p.(Arg48Pro) variants, respectively, which were absent in 200 control alleles. Protein modeling suggests that p.(Arg143Ser) is a tolerated change, while p.(Arg48Pro) induces a structural modification, although further molecular confirmation of dystrophinopathy was obtained in the p.(Arg48Pro) patient. Our results justify the inclusion of FKRP-related disorders in the differential diagnosis of Mexican neuromuscular patients. The commonly reported heterozygous FKRP genotypes deserve attention to avoid LGMD2I molecular misdiagnosis.