Mouse genetic models of cleft lip with or without cleft palate

Nonsyndromic cleft lip and palate (CLP) is among the most common human birth defects. Transmission patterns suggest that the causes are "multifactorial" combinations of genetic and nongenetic factors, mostly distinct from those causing cleft secondary palate (CP). The major etiological factors are largely unknown, and the embryological mechanisms are not well understood. In contrast to CP or neural tube defects (NTD), CLP is uncommon in mouse mutants. Fourteen known mutants or strains express CLP, often as part of a severe syndrome, whereas nonsyndromic CLP is found in two conditional mutants and in two multifactorial models based on a hypomorphic variant with an epigenetic factor. This pattern suggests that human nonsyndromic CLP is likely caused by regulatory and hypomorphic gene variants, and may also involve epigenetics. The developmental pathogenic mechanism varies among mutants and includes deficiencies of growth of the medial, lateral or maxillary facial prominences, defects in the fusion process itself, and shifted midline position of the medial prominences. Several CLP mutants also have NTD, suggesting potential genetic overlap of the traits in humans. The mutants may reflect two interacting sets of genetic signaling pathways: Bmp4, Bmpr1a, Sp8, and Wnt9b may be in one set, and Tcfap2a and Sox11 may be in another. Combining the results of chromosomal linkage studies of unidentified human CLP genes with insights from the mouse models, the following previously unexamined genes are identified as strong candidate genes for causative roles in human nonsyndromic CLP: BMP4, BMPR1B, TFAP2A, SOX4, WNT9B, WNT3, and SP8.     

Genetic variation in transforming growth factor alpha: possible association of BamHI polymorphism with bilateral sporadic cleft lip and palate

Non-syndromic cleft lip with or without cleft palate (CL/P) is one of the most common birth defects affecting 1/1000 Caucasians. Genetic factors are thought to contribute to the development of this disorder. A significant association between two restriction fragment length polymorphisms, the TGF TaqI 2.7-kb allele and the TGF BamHI 40-kb allele, at the transforming growth factor alpha (TGF) locus and the occurrence of clefting has previously been reported. A total of 98 Caucasian patients of Alsacian ancestry was recruited from our registry of congenital malformations. These patients had isolated CL/P but no other anomalies. In addition 57 patients with cleft palate, but without cleft lip, were studied. A control group comprised 99 unrelated healthy Caucasians of the same Alsacian ancestry. TaqI and BamHI identify two-allele polymorphisms. The TGFA Taq and BamHI alleles showed no significant association with the presence of clefting, the only exception being that the BamHI 10.0-kb allele was significantly more frequent in patients with bilateral CL/P.     

Cleft lip with or without cleft palate: associations with transforming growth factor alpha and retinoic acid receptor loci.

The first association study of cleft lip with or without cleft palate (CL/P), with candidate genes, found an association with the transforming growth-factor alpha (TGFA) locus. This finding has since been replicated, in whole or in part, in three independent studies. Here we extend our original analysis of the TGFA TaqI RFLP to two other TGFA RFLPs and seven other RFLPs at five candidate genes in 117 nonsyndromic cases of CL/P and 113 controls. The other candidate genes were the retinoic acid receptor (RARA), the bcl-2 oncogene, and the homeobox genes 2F, 2G, and EN2. Significant associations with the TGFA TaqI and BamHI RFLPs were confirmed, although associations of clefting with previously reported haplotypes did not reach significance. Of particular interest, in view of the known teratogenic role of retinoic acid, was a significant association with the RARA PstI RFLP (P = .016; not corrected for multiple testing). The effect on risk of the A2 allele appears to be additive, and although the A2A2 homozygote only has an odds ratio of about 2 and recurrence risk to first-degree relatives (lambda 1) of 1.06, because it is so common it may account for as much as a third of the attributable risk of clefting. There is no evidence of interaction between the TGFA and RARA polymorphisms on risk, and jointly they appear to account for almost half the attributable risk of clefting.     

Transforming growth factor-alpha (TGFA): genomic structure, boundary sequences, and mutation analysis in nonsyndromic cleft lip/palate and cleft palate only.

Transforming growth factor-alpha (TGFA) has been proposed as a candidate gene in the etiology of nonsyndromic cleft lip with or without cleft palate (NS-CL/P) and of nonsyndromic cleft palate only (NS-CPO). Biologic support for a role of TGFA arises from its presence at high levels in the epithelial tissue of the medial edge of the palatal shelves at the time of shelf fusion in mice. Genetic support for the role of TGFA in clefting comes from the reported association of TGFA alleles with human NS-CPO and NS-CL/P. In this study we report the sequence and structure of human genomic TGFA and the search for causal TGFA mutations in 250 individuals with NS-CL/P or NS-CPO by conformational analysis of the coding sequence, splice junctions, and a portion of the 3' untranslated region strongly homologous between human and mouse. We confirm that human TGFA is composed of six exons and here report several new sequence substitutions and their frequencies. Five variants in conserved segments may represent rare causes for clefting in humans and provide support for the role of TGFA in facial morphogenesis.     

Association of DVL2 and AXIN2 gene polymorphisms with cleft lip with or without cleft palate in a polish population

BACKGROUND: Nonsyndromic cleft lip with or without cleft palate (NSCL/P) is one of the most common congenital anomalies, with a complex and still not fully understood etiology. Given the important role of the Wnt/β‐catenin pathway during craniofacial development, we decided to test the hypothesis that common polymorphic variants of the genes encoding crucial components of this signaling pathway might contribute to the risk of NSCL/P in the Polish population. METHODS: A set of 19 single nucleotide polymorphisms (SNPs) in the APC, AXIN1, AXIN2, CTNNB1, DVL2, and GSK‐3β genes were analyzed using restriction fragment length polymorphism and high‐resolution melting curve methods in a group of 280 patients with NSCL/P and a properly matched control group (n = 330). RESULTS: Both single‐marker and haplotype analyses showed an association between SNPs in the DVL2 gene and the risk for NSCL/P. The strongest association was found under an overdominant model for the rs35594616 variant located in the exonic sequence of DVL2 (odds ratio [OR], 1.90; 95% confidence interval [CI], 1.37–2.62; p < 0.0001). Moreover, the gene‐gene interaction analysis revealed a significant epistatic interaction between DVL2 gene SNPs in the susceptibility to orofacial clefts. Borderline association with a decreased risk of NSCL/P was also observed for the AXIN2 rs3923087 variant (dominant model OR, 0.69; 95% CI, 0.50–0.95; p = 0.03). CONCLUSION: This study suggests that polymorphic variants of the Wnt/β‐catenin pathway genes have a role in the susceptibility to orofacial clefts. The DVL2 and AXIN2 genes might be candidate genes for this craniofacial anomaly in the Polish population. Birth Defects Research (Part A), 2012. © 2012 Wiley Periodicals, Inc.     

Association of bone morphogenetic protein 4 gene polymorphisms with nonsyndromic cleft lip with or without cleft palate in Chinese children

Nonsyndromic cleft lip with or without cleft palate (nsCL/P) is one of the most common congenital anomalies in humans. The pathogenesis of nsCL/P involves both genetic and environmental factors. On the basis of linkage data suggesting that 14q21-24 is one of the chromosomal regions that affects nsCL/P and data locating the BMP4 gene to 14q22-23, we performed a case-control study to evaluate whether BMP4 538T/C polymorphism, resulting in an amino acid change of Val/Ala (V152A) in the polypeptide, is associated with nsCL/P in a Chinese children population. Genotypes of 184 patients with nsCL/P and 205 controls were detected using a PCR-RFLP strategy. The results showed significant differences in the genotype and allele distribution of 538T/C polymorphisms of the BMP4 gene among the cases and controls. The 538C allele carriers were associated with a significantly increased risk of nsCL/P as compared with the noncarriers (odds ratio = 1.52; 95% confidence interval, 1.13-2.03; p = 0.005). Hence, our results support the hypothesis that this polymorphism contributes to risk of nsCL/P, which suggests that BMP4 538T/C polymorphisms could be used as genetic susceptibility markers of nsCL/P.     

Genetics of cleft lip and cleft palate in China.

During the past 10 years, 60 cases of cleft lip with or without cleft palate [CL(P)] were recorded among 45,072 newborns at Shanghai International Peace Maternity and Infant Hospital, China. The incidence was 1.33 per 1,000 births. The family histories of 163 CL(P) patients were analyzed. The incidences of CL(P) in the first-, second-, and third-degree relatives of CL(P) patients were 11/246 (4.47%), 10/1,032 (0.97%), and 6/1,727 (0.35%), respectively. Of the 163 probands, three had a history of consanguinity of the parents (1.8%), in contrast to 0.77% in the general population. These data are suggestive of multifactorial inheritance. The heritability of CL(P) in our study calculated by Falconer's formula was 77.6%.     

Familial recurrence-pattern analysis of cleft lip with or without cleft palate.

Cleft lip with or without cleft palate (CL/P) is a common congenital malformation with an incidence in European white populations of about 1/1,000. The familial clustering of CL/P has been extensively characterized, and epidemiological studies have proposed monogenic models (with reduced penetrance), multifactorial/threshold models, and mixed major-gene/multifactorial models to explain its inheritance. The recognition of an association between two RFLPs at the transforming growth factor alpha (TGFA) locus and CL/P supports a major-gene component to the etiology of CL/P. Risch has shown that the recurrence risk ratio lambda R (risk to relatives, vs. population prevalence) is a useful pointer to the mode of inheritance. Here we further develop the use of lambda R to analyze recurrence-risk data for CL/P. Recurrence risks for first-, second-, and third-degree relatives equate well with oligogenic models with as few as four loci. A monogenic/additive model is strongly rejected. The limited available twin data are also consistent with this model. A "major gene" interacting epistatically with an oligogenic background is shown to be a plausible alternative. Power calculations for a linkage study to map the CL/P major-risk locus suggest that a sample of 50 affected sib pairs will be adequate, but linkage to minor-risk loci will require very much larger samples.