Original reportA Case-Control Study of Nonsyndromic Oral Clefts in Maryland
Introduction
Oral clefts include cleft lip (CL), cleft lip and palate (CLP), and cleft palate (CP), and collectively they represent a common, nonlethal birth defect of complex and heterogeneous etiology (1). Because CL and CLP share similarities in both epidemiologic characteristics (e.g., sex ratio) and embryologic timing (the secondary palate forms later than the lip and primary palate), CL and CLP are typically grouped together into cleft lip with/without cleft palate (CL/P). Although the proportion of all oral cleft cases representing a recognized malformation syndrome varies, more infants born with CP have a recognizable syndrome as compared to infants with CL/P (2). In a recent California study, the highest proportion of nonisolated clefts was seen among CP infants (53%), and 14 and 32% of CL and CLP cases, respectively, had another malformation (3). When conducting population-based studies of oral clefts, it is a major challenge to distinguish isolated, nonsyndromic from syndromic or nonisolated forms of oral clefts, because both family history information and direct physical examination of affected individual(s) are needed (4).
A number of environmental factors have been examined as risk factors for oral clefts, including maternal smoking, exposure to antiepileptic drugs, antiemetic agents, vitamin use during the periconceptual period, maternal metabolic factors, alcohol consumption and exposure to agricultural chemicals (5). Maternal smoking, the best studied environmental risk factor, is associated with a slight increase in risk for both CL/P and CP (6).
Other environmental risk factors may also be important. In a population-based case-control study from Iowa, Manger et al. (7) showed a higher risk of isolated CL/P associated with increasing maternal alcohol consumption. Romitti et al. (8) showed similar results using an extended dataset from this same population. Christensen et al. (9); however, found that fewer case mothers reported drinking alcohol than did control mothers (59% vs. 65%) before the pregnancy. Shaw et al. (10) found that maternal prenatal vitamin supplements decreased the first occurrence of CL/P. Czeizel et al. (11) also showed a protective effect of folic acid in a Hungarian study and later suggested this effect may depend on dose (12). Clinical trial data to confirm this protective effect of vitamin supplementation are lacking, however.
There is also a strong genetic component to oral clefts. The ratio of risk in first degree relatives of cases as compared to the general population is as high as 30 (13). Different models of inheritance have been proposed, including single gene models with reduced penetrance, multifactorial models, and various combinations of both 14, 15. Multilocus or oligogenic models have also been suggested 16, 17, 18, but no one model can yet fully explain observed familial aggregation of oral clefts.
Ardinger et al. (19) was the first to use a case-control design to test candidate genes. They found a significant statistical association between case status and two of 12 markers in five genes, with an intronic Taq1 marker in the transforming growth factor alpha (TGFα) gene showing the strongest association. Similar studies, primarily in Caucasians, have shown differences in allele frequencies between cleft cases and controls, but not all were statistically significant. Mitchell (20) argued that heterogeneity in the proportion of bilateral clefts and cases with a positive family history across studies could explain some of this inconsistency. Lidral et al. (21) recently found a higher allele frequency in a population-based series of controls in Iowa, which reduced the association between oral clefts and this TGFα marker.
Other candidate genes also show association with oral clefts, including retinoic acid receptor A (RARA) 22, 23 and an anonymous marker on chromosome 4q (24). The Msh homeobox homolog 1 gene, MSX1, was reported to be associated with CP in cases from Iowa 21, 8, but no such association was seen in a Philippine population (25). In the Iowa case-control study, Lidral et al. (21) also found an association with TGFβ3 and risk of CL/P.
Two case-control studies have raised the possibility that gene-environment interaction may determine risk to oral clefts 26, 27. In particular, maternal smoking was shown to be a strong risk factor for CP in the presence of the rarer allele at the TaqI marker in TGFα, but not in its absence 26, 27. Other studies have failed to confirm this, however 28, 8, 9. Romitti et al. (8) did show evidence for similar gene-environment interaction when testing markers in TGFβ3 and MSX1 and exposure to maternal smoking on risk of CP, as well as apparent interactions between exposure to maternal alcohol consumption and these two loci on risk of CL/P.
In the current study, the case-control design was used to examine both environmental and genetic risk factors for oral clefts, and to test for possible interactions. Individual effects of risk factors were compared among CP and CL/P in univariate analyses, and after adjustment for confounders. Where DNA was available on both parents, the case-parent trio design was also used to test these genetic markers for evidence of linkage disequilibrium.
Section snippets
Case Ascertainment
As described in (28), cases of oral clefts born between June, 1992 and December, 1998 were identified through treatment centers in Maryland, plus the Craniofacial Clinic of the Children's National Medical Center in Washington, DC (which treats many Maryland residents). Records of the Maryland Birth Defects Reporting and Information System (BDRIS) were also reviewed as a population-based ascertainment source, because oral clefts are included among the 12 sentinel defects reported to this
Smoking
Patterns and amount of maternal smoking around the time of conception and during the first trimester of pregnancy were examined as potential risk factors. Smoking exposure changed during pregnancy and varied slightly among groups. For example, 22% of mothers of CL/P cases reported smoking during the 3 months before pregnancy and 19% during the first trimester, but only 12% of these mothers reported continuous smoking during the second and third trimesters. In addition to ceasing, smoking
Discussion
In the current study, we compared infants with confirmed isolated, nonsyndromic oral clefts to unaffected controls to test a number of genetic and environmental risk factors using a case-control design. Although some debate remains about the use of unaffected infants versus malformed infants as controls in retrospective studies of birth defects 38, 39, 40, recall bias seems unlikely to lead to erroneous inferences except in extreme circumstances (41). Here we tested for effects of maternal
Selected Abbreviations and Acronyms
CL = cleft lip
CLP = cleft lip and palate
CP = cleft palate
CL/P = cleft lip with/without cleft palate
TGFα = transforming growth factor α
TGFβ3 = transforming growth factor β3
RARA = retinoic acid receptor A
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Cited by (97)
Maternal alcohol consumption and oral clefts: a meta-analysis
2019, British Journal of Oral and Maxillofacial SurgeryCitation Excerpt :For maternal drinking and CL/P, a formal test of heterogeneity was significant (χ2 = 25.01, df = 8, p = 0.002) and a random effects model was adopted. An overall OR of 1.00 (95% CI 0.87 to 1.15) was yielded ranging from 0.4311 to 1.66 (Fig. 2).19 Heterogeneity came solely from two studies.8,11
Maternal active smoking and risk of oral clefts: a meta-analysis
2016, Oral Surgery, Oral Medicine, Oral Pathology and Oral RadiologyCitation Excerpt :The maternal smoking period varied widely in the 29 studies included in the meta-analysis. Because oral clefts are reported to occur in the critical period around conception and through the first trimester,35,40,44,48 studies that limited the smoking period to 3 months before conception to the first trimester of pregnancy were collected.6,11,13,15,28,35,36,38-40,42-47 The results showed surprisingly lower ORs in all subgroups (for all CL ± P: OR = 1.277, 95% CI = 1.147-1.422; for isolated CL ± P: OR = 1.293, 95% CI = 1.129-2.479; for all CP: OR = 1.154, 95% CI = 1.101-1.427; for isolated CP: OR = 1.304, 95% CI = 1.085-1.567).
MSX1 gene polymorphisms in Mexican patients with non-syndromic cleft lip/palate
2016, International Journal of Pediatric OtorhinolaryngologyCitation Excerpt :Another haplotype, A-T (SNP1-SNP5) (P = 0.012), was related to protection in a single dose (Fig. 2). In view of mouse model [24] and linkage disequilibrium [25–27] findings, MSX1 has been identified as a strong candidate for CL/P because the gene is commonly deleted in cases of 4p-/Wolf-Hirschhorn syndrome, in which CL/P is a frequent feature [28]. However, MSX1 has also been studied in other ethnic groups, suggesting that only a small percentage of CL/P cases can be attributed to mutations in or variants of this gene [29–32].
Environmental tobacco smoke exposure and non-syndromic orofacial cleft: Systematic review and meta-analysis
2023, Tobacco Induced DiseasesMaternal Cigarette Smoking and Cleft Lip and Palate: A Systematic Review and Meta-Analysis
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