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.     

Evaluating eight newly identified susceptibility loci for nonsyndromic cleft lip with or without cleft palate in a Mesoamerican population

Background: Nonsyndromic cleft lip with or without cleft palate (NSCL/P) is among the most frequently occurring congenital malformations worldwide. The number of genetic loci identified as being involved in NSCL/P etiology was recently increased by a large genome‐wide meta‐analysis of European and Asian samples. This meta‐analysis confirmed all six previously recognized genetic susceptibility loci and identified six novel ones. Methods: To investigate which of these 12 loci contribute to NSCL/P risk in an independent sample of distinct ethnicity, we performed a case–control association analysis in a sample of the Mesoamerican population. A total of 153 individuals with NSCL/P (cases) and 337 unaffected controls were included. Top single‐nucleotide polymorphisms (SNPs) at 8 of the 12 loci (1p22.1, 1p36, 2p21, 3p11.1, 8q21.3, 13q31.1, 15q22, and 20q12) were analyzed using mass spectroscopy and restriction‐length‐fragment polymorphism analyses. In a previous study, we had analyzed the remaining four NSCL/P susceptibility regions (IRF6, 8q24, 10q25, and 17q22) in the same sample. Results: Single‐marker association analyses applying allelic, dominant, and recessive models revealed nominal significant associations for four of the eight loci, with two additional loci showing at least a trend of association in the hypothesized direction. Conclusion: In combination with results from our previous study using the same sample, our data suggest that the majority of the known NSCL/P susceptibility regions identified to date also confer risk for this malformation in the Mesoamerican population. Birth Defects Research (Part A) 100:43–47, 2014. © 2013 Wiley Periodicals, Inc.     

Maternal vitamin B-6 and folate status and risk of oral cleft birth defects in the Philippines

BACKGROUND: Vitamin deficiencies induce oral clefts in animal experiments, but the role of specific nutrients in human oral clefts is uncertain. METHODS: Associations between maternal vitamin B-6 and folate status and risk of nonsyndromic cleft lip, with or without cleft palate (CL/P), were examined in case-control studies at two sites in the Philippines--Negros Occidental and Davao. Cases were mothers of affected children and control mothers were those who had no children with oral clefts. RESULTS: The risk of having a CL/P-affected child increased with increasing tertile of vitamin B-6 deficiency in both Negros Occidental and Davao (odds ratios [ORs] and 95% confidence intervals [CIs] for sites combined = 1.0 [reference], OR, 2.94; 95% CI, 1.51-5.73; OR, 4.98; 95% CI, 2.56-9.67). Poor B-6 status had a stronger association with CL/P among mothers with lower versus higher plasma folate levels. Increasing tertiles of plasma folate were marginally associated with an increased risk of clefts in both sites combined (1.0 [reference]; OR, 1.58; 95% CI, 0.93-2.68; OR, 1.59; 95% CI, 0.94-2.70). Increasing tertiles of erythrocyte folate were associated with a decreased risk of CL/P in Negros Occidental (1.0 [reference]; OR, 0.34; 95% CI, 0.13-0.90; OR, 0.46; 95% CI, 0.20-1.09) and an increased risk in Davao (1.0 [reference]; OR, 1.23; 95% CI, 0.54-2.81; OR, 4.85; 95% CI, 2.24-10.50). The inconsistent associations between folate status and CL/P risk appeared to be a result of statistical interaction between folate, vitamin B-6, and case-control status that produced different results in study areas of higher versus lower prevalence of vitamin B-6 deficiency. CONCLUSIONS: Poor maternal vitamin B-6 status was consistently associated with an increased risk of CL/P at two sites in the Philippines. Folate-CL/P associations were inconsistent and may be related to the vitamin B-6 status or other characteristics of the populations under study.     

Wnt9b is the mutated gene involved in multifactorial nonsyndromic cleft lip with or without cleft palate in A/WySn mice, as confirmed by a genetic complementation test

BACKGROUND: Nonsyndromic cleft lip (CL) with or without cleft palate (CLP) is a common human birth defect with complex genetic etiology. One of the unidentified genes maps to chromosome 17q21. A mouse strain, A/WySn, has CLP with complex genetic etiology that models the human defect, and 1 of its causative genes, clf1, maps to a region homologous to human 17q21. Extensive studies of the candidate region pointed to a novel insertion of an IAP transposon 3' from the gene Wnt9b as the clf1 mutation. Independently a recessive knockout mutation of Wnt9b (Wnt9b-) was reported to cause a lethal syndrome that includes some CLP. METHODS: A standard genetic test of allelism between clf1 and the Wnt9b- mutation was done. A total of 83 F1 embryos at gestation day 14 (GD 14) from Wnt9b-/+ males crossed with A/WySn females, and 79 BC1 GD 14 embryos from F1 Wnt9b-/clf1 males back-crossed to A/WySn females were observed for CL. Embryo genotypes at clf1 and Wnt9b were obtained from DNA markers. Genotypes for a second unlinked modifier locus from A/WySn, clf2, were similarly obtained. RESULTS: The compound mutant embryos (Wnt9b-/clf1) had high frequencies of CL: 27% in the F1 and 63% in the BC1. The clf2 modifier gene was found to have 3 alleles segregating in this study and to strongly influence the penetrance of CL in the compound mutant. CONCLUSIONS: The noncomplementation of clf1 and Wnt9b- confirms that clf1 is a mutation of the Wnt9b gene. The homologous human WNT9B gene and 3' conserved noncoding region should be examined for a role in human nonsyndromic CLP.     

The CRISPLD2 gene is involved in cleft lip and/or cleft palate in a Chinese population

BACKGROUND: Nonsyndromic cleft lip and/or cleft palate (NSCLP) are common congenital anomalies in humans, the etiologies of which are complex and associated with both genetic and environmental factors. Previous data suggested single nucleotide polymorphisms (SNPs) of rs1546124, rs4783099, and rs16974880 of the CRISPLD2 gene were associated with an increased risk of NSCLP; however, subsequent studies have yielded conflicting results. This study aims to evaluate the associations of the aforementioned polymorphisms with NSCLP in a Northwestern Chinese population. METHODS: Three CRISPLD2 SNPs were genotyped in a case‐control study (n = 907), including 444 NSCLP patients and 463 healthy individuals, using polymerase chain reaction–denaturing high‐performance liquid chromatography (PCR‐DHPLC). RESULTS: The genotype and allele frequencies of rs1546124 (odds ratio [OR], 2.30; 95% confidence interval [CI], 1.58–3.34; p = 1 × 10⁻⁵) and rs4783099 (OR, 0.73; 95% CI, 0.54–1.00; p = 0.05) were different in NSCLP patients compared with controls. Furthermore, the CC genotype at rs1546124 was associated with increased risk for cleft lip with or without cleft palate (CL/P; OR, 2.11; 95% CI, 1.41–3.15; p_correct = 1.5 × 10⁻⁴) and for cleft palate only (CPO; OR, 2.93; 95% CI, 1.69–5.07; p_correct = 5.4 × 10⁻⁴), whereas the T allele of rs4783099 was associated with decreased risk for CPO. Further gender stratification showed that the statistical association of these two loci is mainly in the male patients, and not in female patients. CONCLUSION: Our results suggest that the CRISPLD2 gene contributes to the etiology of NSCLP in the Northwestern Chinese population. SNP rs1546124 is significantly related to NSCLP, associated with both CL/P and CPO groups, and SNP rs4783099 is significantly associated with CPO. Birth Defects Research (Part A) 2011. © 2011 Wiley‐Liss, Inc.     

Segregation analysis of cleft lip with or without cleft palate in the First Nations (Amerindian) people of British Columbia and review of isolated cleft palate etiologies

BACKGROUND: The First Nations (Amerindian) population of British Columbia, Canada, has the highest reported birth prevalence in the world of cleft lip with or without cleft palate (CL/P) at nearly 3 per 1000 births. In addition, a substantial proportion of cleft palate only (CPO) cases in this population has been reported to be X‐linked. The aims of this study were to perform complex segregation analysis to investigate the mode of inheritance of CL/P in the First Nations people of British Columbia and to review the etiology of the CPO cases. METHODS: All First Nations children born in British Columbia between 1952 and 1971 with an orofacial cleft were included in the study. Multiple sources of ascertainment were used, so that nearly 100% of live births were identified and included during this time. No stillbirths were found but would likely have been ascertained. Extended pedigrees were constructed from these probands and examination of immediate family members, e.g., parents and siblings, was done wherever possible. Complex segregation analysis included all family members. In addition, a CPO case review was conducted. RESULTS: Complex segregation analysis supports the hypothesis that the most likely mode of inheritance of CL/P in this population is a mixed model; that is, an autosomal major gene with polygenic component. The review of 26 CPO cases showed that a substantial proportion are syndromic. Birth Defects Research (Part A), 2009. © 2009 Wiley‐Liss, Inc.     

Confirmation of the role of N-acetyltransferase 2 in teratogen-induced cleft palate using transgenics and knockouts

Previous work on Dilantin- and hydrocortisone-induced cleft palate and cleft lip with or without cleft palate using congenics for the N-acetyltransferase loci (Nat1 and Nat2 are closely linked) and recombinant inbred lines implicated the Nat1,2 region in susceptibility to teratogen-induced orofacial clefting. Since Nat1 does not differ between the two strains, Nat2 appeared to be responsible. We have now tested this conclusion using transgenics and knockouts. Transgenics for human NAT1 (equivalent to mouse Nat2) and knockouts for Nat2 were tested for susceptibility to Dilantin, hydrocortisone, and 6-aminonicotinamide-induced orofacial clefting. We found that Nat2 greatly influences teratogen-induced orofacial clefting on the A/J background but not on the C57BL/6J background. The magnitude and direction of the effects depended on which teratogen was used. The Nat2 knockout did not make C57BL/6J susceptible or A/J (already with very low activity) more susceptible but significantly decreased sporadic clefting in the A/J strain. We conclude that only the A/J strain, with several loci affecting orofacial clefting, is influenced by Nat2.