Risk Factors For Orofacial Clefts Research Articles

Epidemiologic Characteristics, Time Trend, and Seasonality of Orofacial Clefts in São Paulo State, Brazil. 2008-2019.

To characterize the epidemiology, identify trends in prevalence, seasonality, and risk factors for orofacial clefts (OFC), selecting the São Paulo state (SPS) population database. A population-based study to estimate the OFC prevalence trends in recent years, stratified by maternal age and SPS geographical clusters. All live births (LB) with OFC in SPS from 2008-2019. 5342 cases of OFC among 7 301 636 LB. Not applicable. OFC prevalence trends, annual percent change (APC) with a 95% confidence interval, and seasonality. We found an OFC prevalence of 7.3/10 000LB in SPS, Brazil. Among all the cases, the majority were male (57.1%), Caucasian (65.4%), 77.8% born at term, 75.8% weight >2500 g, 97.1% singleton, and 63.9% of births were by cesarean section. From 2008-2019, SPS presented a stationary OFC prevalence trend; in São Paulo city, the highest APC was observed (0.05%); the maternal age group with the highest OFC prevalence rate was ≥35 years (9.2/10 000LB). We identified the existence of seasonal variation based on the conception date in the final months of the year, corresponding to the spring season (P < .001). OFC had a stationary prevalence trend in recent years, with the highest prevalence in the Central North Cluster and ≥35 years maternal age group. Seasonality was observed in the spring season, and congenital malformation of lips was the most common associated pathology. This population-based study is the first to summarize the current epidemiology of OFC in SPS.

Elevated concentrations of chromium in maternal serum, umbilical cord serum, and cord tissue are associated with an increased risk for orofacial clefts

Chromium (Cr) exposure during gestation causes malformations in animal experiments. In this multicenter case–control study, we initially involved 130 orofacial clefts (OFCs) and 260 controls to assess the association between Cr concentration and risk for OFCs. Then, umbilical cord serum (49 vs. 119) and cord tissue (84 vs. 142) were used to validate the association between Cr and OFCs. We found that maternal serum Cr concentrations in OFC cases were significantly higher than those in controls. Compared with the lowest tertile of maternal serum Cr concentration, the highest tertile of Cr increased the risk for OFCs [OR = 2.14 (1.14–4.05)]. In the validation cohort of umbilical cord serum and tissue, higher concentrations of Cr were associated with increased risks for OFCs in a dose-dependent manner (all Ps for trends <0.05). Cr concentrations in maternal serum and cord serum showed a positive correlation. The Cr concentration in cord serum was inversely correlated with egg and milk consumption frequencies, and the Cr concentration in cord tissue was positively associated with indoor coal burning. In conclusion, prenatal Cr exposure is a risk factor for OFCs, and indoor coal burning during pregnancy may be one of the sources of Cr exposure.

The effect of maternal smoking and alcohol consumption on lip morphology.

To determine whether maternal smoking and/or alcohol consumption has an influence on lip morphology. Maternal smoking is a known risk factor for orofacial clefts; however, its influence on normal lip variation is unknown. Recent research regarding normal lip morphology has been contradictory. Retrospective cohort study. A total of 4747 children from the Avon Longitudinal Study of Parents and Children (ALSPAC) who each had 3D facial scans carried out at 15 years of age were included in the study. Each of the participants was automatically categorised regarding predetermined lip morphological traits. Questionnaires completed by their mothers identified smoking and alcohol habits during pregnancy. Logistic regression analyses were applied to determine the effect of maternal smoking and alcohol consumption on lip morphology. Maternal smoking has significant effects on upper and lower lip contours, Cupid's bow, lower lip-chin shape and lower lip tone (all P < 0.05). There was also an indication of a potential epigenetic effect of smoking pre-pregnancy on upper lip contour (P = 0.0573). Alcohol consumption is significantly associated with philtrum shape, particularly when >6 units of alcohol are consumed per week (P = 0.0149, 32 weeks). Overall results suggest a deeply grooved philtrum is more likely if alcohol is consumed. Investigating the combined effect of smoking and alcohol consumption, lower lip contour (P = 0.00923) and lower lip-chin shape (P = 0.0171) are statistically significant, with lower lip contour more likely to be narrow in the midline, and lower lip-chin shape more likely to be an angular concavity. Maternal smoking influences a number of lip traits, including a possible epigenetic effect on upper lip contour. Maternal alcohol consumption, particularly at a high level, influences philtrum shape. Maternal smoking and alcohol consumption have a combined effect on lower lip contour and lower lip-chin shape.

A case control study on the risk factors of non-syndromic orofacial clefts

Background: Orofacial clefts (OFCs) are the most common craniofacial malformation of the new born in the world. In India OFCs are the 3rd most common congenital anomaly following anencephaly and club foot. Objectives were to study the association of family history, medications during pregnancy, passive smoking with non-syndromic OFC, and to determine the pattern of OFCs in the study population.Methods: This is a hospital-based, matched case-control study conducted in a tertiary care centre, Thrissur, Kerala. We interviewed 30 mothers of children affected by non-syndromic OFCs. Mothers were asked about their sociodemographic details and other suspected risk factors using a semi structured questionnaire.Results: In our study unilateral left sided cleft lip was found to be more prevalent 62%. Those who had a family history of OFCs was found to have a significantly higher risk of OFC (OR 26.333). Medications for diabetes mellitus, hypertension, thyroid dysfunction, bronchial asthma, analgesics and non-steroidal anti-inflammatory drugs (NSAIDs) during first trimester of pregnancy posed a higher risk for OFCs (OR 7.222). Maternal age at pregnancy greater than or equal to 30 was also found to be a significant risk factor.Conclusions: In our study we found out that family history is a risk factor for OFCs. We conclude that exposure of the mother to passive smoking should be avoided during pregnancy and family members should be made aware of the health hazards of passive smoking. Medications should only be taken after consulting a doctor preferably an obstetrician. Self-medication during pregnancy should be strictly avoided.

Concentrations of organochlorine pesticides in placental tissue are not associated with risk for fetal orofacial clefts

Previous epidemiological studies have shown that prenatal exposure to organochlorine pesticides (OCPs) entails a variety of adverse impacts on fetal health, but it is not yet known whether it is associated with risk for orofacial clefts (OFCs). This study of 103 fetuses or newborns with a diagnosis of OFCs (cases) and 103 healthy newborns without malformations (controls) examined whether prenatal exposure to OCPs, as indicated by their concentrations in placental tissue, is a risk factor for OFCs. No differences were found in the median concentrations of OCPs between cases and controls, with exception of o,p’-dichlorodiphenyldichloroethylene, o,p’-dichlorodiphenyldichloroethane, and total o,p’-dichlorodiphenyltrichloroethane (DDTs), whose concentrations were higher in controls than in cases (Ps < 0.05). Although higher concentrations of placental δhexachlorocyclohexane and isodrin were found to be associated with decreased risk for OFCs in logistic regression, no association was observed in the Bayesian kernel machine regression, a novel statistical model in analyzing exposure mixtures. Women who reported periconceptional folic acid supplementation had lower placental concentrations of DDTs than women who did not. In conclusion, no association between levels of OCPs in placental tissue and risk for OFCs was observed in this population. Supplementation with folic acid may help decrease the levels of DDTs in placental tissue, but further studies are needed to confirm this unexpected finding.

Levels of uranium and thorium in maternal scalp hair and risk of orofacial clefts in offspring

Uranium and thorium are common radioactive elements that exist in the environment. However, few environmental epidemiological studies have focused on their possible effects on congenital malformations. Here, we explored the association between uranium and thorium concentrations in maternal scalp hair grown from 3 months before to 3 months after conception, namely during the periconceptional period and the risk of orofacial clefts (OFCs) in offspring. Our study included 153 women whose pregnancies were affected by OFCs (cases) and 601 women who delivered infants without birth defects (controls) from four provinces in China. Face-to-face interviews were used to collect sociodemographic characteristics with a structured questionnaire. Concentrations of uranium and thorium in maternal scalp hair grown during the periconceptional period were detected using inductively coupled plasma-mass spectrometry. The risk of OFCs in association with higher concentrations of the two radioactive elements was estimated using odds ratios (ORs) and 95% confidence intervals (CIs) while adjusting for potential confounding factors. The levels of uranium and thorium in maternal hair were in agreement with the published literature. After adjusting for several confounders, the ORs of thorium in the highest, upper, and lower quartile versus the lowest quartile were 2.63 (95% CI, 1.41–4.92), 1.98 (95% CI, 1.03–3.79), and 2.73 (95% CI, 1.46–5.12), respectively. No association was found between levels of uranium and the risk of OFCs. Maternal periconceptional exposure to thorium may be a risk factor for OFCs in offspring.

Common polymorphism in the glycine N-methyltransferase gene as a novel risk factor for cleft lip with or without cleft palate

The objective of this study was to identify new environmental and genetic risk factors for orofacial clefts that arise during early foetal development. In this retrospective, case–control, mother–child pair study, 172 orofacial clefts cases and 199 healthy controls, and their respective mothers, were genotyped for common variants in relevant genes obtained by text and database mining using STRING 10.0. Exposure to environmental risk factors was evaluated using questionnaires. Variant glycine N-methyltransferase (odds ratio (OR) 2.1, 95% confidence interval (95% CI) 1.0–4.4) and dihydrofolate reductase (OR 2.4, 95% CI 1.3–4.5) genotypes were identified as risk factors for cleft lip with or without cleft palate formation. Furthermore, synergy was detected between variant glycine N-methyltransferase and dihydrofolate reductase genotypes in promoting cleft lip with or without cleft palate formation (OR 7, 95% CI 2–23). This study is novel in finding that common glycine N-methyltransferase variant genotypes increase the risk of cleft lip with or without cleft palate.

Proportion of Orofacial Clefts Attributable to Recognized Risk Factors.

Estimate the population attributable fraction (PAF) for a set of recognized risk factors for orofacial clefts. We used data from the National Birth Defects Prevention Study. For recognized risk factors for which data were available, we estimated crude population attributable fractions (cPAFs) to account for potential confounding, average-adjusted population attributable fractions (aaPAFs). We assessed 11 modifiable and 3 nonmodifiable parental/maternal risk factors. The aaPAF for individual risk factors and the total aaPAF for the set of risk factors were calculated using a method described by Eide and Geffler. Population-based case-control study in 10 US states. Two thousand seven hundred seventy-nine cases with isolated cleft lip with or without cleft palate (CL±P), 1310 cases with isolated cleft palate (CP), and 11 692 controls with estimated dates of delivery between October 1, 1997, and December 31, 2011. Crude population attributable fraction and aaPAF. The proportion of CL±P and CP cases attributable to the full set of examined risk factors was 50% and 43%, respectively. The modifiable factor with the largest aaPAF was smoking during the month before pregnancy or the first month of pregnancy (4.0% for CL±P and 3.4% for CP). Among nonmodifiable factors, the factor with the largest aaPAF for CL±P was male sex (27%) and for CP it was female sex (16%). Our results may inform research and prevention efforts. A large proportion of orofacial cleft risk is attributable to nonmodifiable factors; it is important to better understand the mechanisms involved for these factors.

Maternal occupational cadmium exposure and nonsyndromic orofacial clefts.

Cigarette smoking is a well-studied risk factor for orofacial clefts (OFCs). Little is known about which constituents in cigarette smoke contribute to this teratogenicity in humans. One constituent, cadmium, has been associated with OFCs in animal studies; in humans, the role of maternal cadmium exposure on OFCs, independent of cigarette smoke, is unclear. In particular, the relation between maternal occupational cadmium exposure and OFCs is largely unexplored. Using data from a large, population-based case-control study, we compared expert rater assessed maternal occupational cadmium exposure from self-reported occupational histories during the period 1 month before through 3 months after conception between OFC cases (n = 1,185) and unaffected controls (n = 2,832). Multivariable logistic regression analyses were used to estimate adjusted odds ratios (aORs) and 95% confidence intervals for any (yes/no) and cumulative (no, low, high exposure) occupational cadmium exposures and all OFCs, cleft lip ± cleft palate (CL/P) and cleft palate (CP). Overall, 45 mothers (cases = 13, controls = 32) were rated as having occupational cadmium exposure. Comparing all OFCs to controls, we observed inverse, nonsignificant aORs for any or low exposure, and positive, nonsignificant aORs for high exposure. Where data were available, aORs for CL/P and CP tended to parallel those for all OFCs. To our knowledge, this is the first study to specifically examine maternal occupational cadmium exposure and OFCs, using expert rater exposure assessment. The small numbers of exposed mothers observed, however, led to imprecise estimates. Continued research using more detailed occupational exposure assessment and increased sample sizes is recommended.

Risk factors for orofacial clefts in India: A case-control study.

BackgroundOrofacial clefts (OFC) are linked with several genetic and environmental factors. The aim of this study was to explore the association of potential risk factors with OFCs in India.MethodsThis was a hospital‐based, matched case–control (1:4 ratio; matching done for parity) study conducted in Hyderabad, Bengaluru, and Delhi‐National Capital Region. Cases (nonsyndromic clefts) were recruited from treatment centers, while controls (live births) were recruited from maternity centers. Information on exposures was collected during personal interviews. Exposures of interest included folic acid supplementation during the peri‐conceptional period, consanguineous marriage, exposure to drugs, infections during pregnancy, family history of OFC, and dietary factors.ResultsA total of 785 participants were included in the study: 157 cases and 628 controls. A family history of cleft lip/palate (adjusted odds ratio [AOR], 15.48; 95% confidence interval [CI], 4.36–54.96; p value = 0.001), exclusive vegetarianism (AOR, 4.47; 95% CI, 1.83–10.98; p value = 0.001), and delayed first conception (AOR, 2.55, 95% CI, 1.25–5.21, p = 0.01) were found to be strongly associated with higher risk of OFCs. Supplementation with folic acid during first 3 months of pregnancy was not found to be protective against OFCs (AOR, 1.24; 95% CI, 0.59–2.58; p value = 0.56).ConclusionOur study confirmed the importance of family history as a risk factor for OFC. Our study did not show an association with folic acid supplementation but was underpowered to detect small effects. Our finding of higher risk among vegetarians requires replication. Birth Defects Research 109:1284–1291, 2017. © 2017 Wiley Periodicals, Inc.

Distinct DNA methylation profiles in subtypes of orofacial cleft

BackgroundEpigenetic data could help identify risk factors for orofacial clefts, either by revealing a causal role for epigenetic mechanisms in causing clefts or by capturing information about causal genetic or environmental factors. Given the evidence that different subtypes of orofacial cleft have distinct aetiologies, we explored whether children with different cleft subtypes showed distinct epigenetic profiles.MethodsIn whole-blood samples from 150 children from the Cleft Collective cohort study, we measured DNA methylation at over 450,000 sites on the genome. We then carried out epigenome-wide association studies (EWAS) to test the association between methylation at each site and cleft subtype (cleft lip only (CLO) n = 50; cleft palate only (CPO) n = 50; cleft lip and palate (CLP) n = 50). We also compared methylation in the blood to methylation in the lip or palate tissue using genome-wide data from the same 150 children and conducted an EWAS of CLO compared to CLP in lip tissue.ResultsWe found four genomic regions in blood differentially methylated in CLO compared to CLP, 17 in CPO compared to CLP and 294 in CPO compared to CLO. Several regions mapped to genes that have previously been implicated in the development of orofacial clefts (for example, TBX1, COL11A2, HOXA2, PDGFRA), and over 250 associations were novel. Methylation in blood correlated with that in lip/palate at some regions. There were 14 regions differentially methylated in the lip tissue from children with CLO and CLP, with one region (near KIAA0415) showing up in both the blood and lip EWAS.ConclusionsOur finding of distinct methylation profiles in different orofacial cleft (OFC) subtypes represents a promising first step in exploring the potential role of epigenetic modifications in the aetiology of OFCs and/or as clinically useful biomarkers of OFC subtypes.

Maternal obesity is a risk factor for orofacial clefts: a meta-analysis

Orofacial clefts are the most prevalent birth defects that affect craniofacial structures and implicate genetic and environmental factors in their aetiology. Maternal metabolic state and nutrition have been related to these and other structural malformations, and studies of maternal obesity before pregnancy have shown controversial results about its association with the risk of orofacial clefts in their offspring. Our aim was to assess the combined effect of several single studies of maternal obesity on the risk of orofacial clefts using meta-analysis. We searched for these reports in the PubMed database, and selected 8 studies that met our criteria for eligibility. As a result of this analysis, and using maternal normal weight as a reference, we found that maternal obesity does increase the risk of orofacial clefts in their offspring (OR 1.18, 95% CI 1.11 to 1.26). When these clefts are considered separately, maternal obesity is associated with cleft lip with or without cleft palate (OR 1.13, 95% CI 1.04 to 1.23), and with cleft palate alone (OR 1.22, 95% CI 1.09 to 1.35). Our results support the relation between maternal obesity and orofacial clefts, and confirm two previous meta-analyses that considered fewer studies. However, the molecular mechanisms underlying this statistical evidence have not been fully elucidated.

Genetic risk factors for orofacial clefts in Central Africans and Southeast Asians.

Genome-wide association studies (GWAS) for orofacial clefts have identified several susceptibility regions, but have largely focused on non-Hispanic White populations in developed countries. We performed a targeted genome-wide study of single nucleotide polymorphisms (SNPs) in exons using the Illumina HumanExome+ array with custom fine mapping of 16 cleft susceptibility regions in three underserved populations: Congolese (87 case-mother, 210 control-mother pairs), Vietnamese (131 case-parent trios), and Filipinos (42 case-mother, 99 control-mother pairs). All cases were children with cleft lip with or without cleft palate. Families were recruited from local hospitals and parental exposures were collected using interviewer-administered questionnaires. We used logistic regression models for case-control analyses, family-based association tests for trios, and fixed-effect meta-analyses to determine individual SNP effects corrected for multiple testing. Of the 16 known susceptibility regions tested, SNPs in four regions reached statistical significance in one or more of these populations: 1q32.2 (IRF6), 10q25.3 (VAX1), and 17q22 (NOG). Due to different linkage disequilibrium patterns, significant SNPs in these regions differed between the Vietnamese and Filipino populations from the index SNP selected from previous GWAS studies. Among Africans, there were no significant associations identified for any of the susceptibility regions. rs10787738 near VAX1 (P = 4.98E-3) and rs7987165 (P = 6.1E-6) were significant in the meta-analysis of all three populations combined. These results confirm several known susceptibility regions and identify novel risk alleles in understudied populations.

Screening for maternal coeliac disease as a potential risk factor for orofacial clefts—a pilot study

There is increasing evidence that dietary folic acid deficiency in utero may increase the risk of developing the ‘cleft lip with or without cleft palate’ (CL±P) variant of orofacial cleft. Coeliac disease is a common cause of folic acid malabsorption, and in the majority of cases remains undiagnosed. This pilot study assessed the seroprevalence of undiagnosed coeliac disease in a cohort of mothers of infants with CL±P in the Hyderabad area of India. The seroprevalence of coeliac disease of 1.15% (95% confidence interval 0.37–2.66%) was little different from the expected figure based on published population studies, making a clinically significant association unlikely.

Whole-blood 3-hydroxyisovalerylcarnitine as a risk factor for orofacial clefts

Background/purposeIn mice, biotin deficiency is one of the most potent clefting factors. Increased 3-hydroxyisovalerylcarnitine (C5OH) is regarded as a biomarker of biotin deficiency. This retrospective study was undertaken to determine whether increased C5OH in newborns is associated with orofacial clefts. Materials and methodsSeventy newborns with non-syndromic cleft lip with or without cleft palate and 140 control newborns without congenital anomalies were investigated. Whole-blood C5OH concentrations were measured using tandem mass spectrometry. ResultsThe median (interquartile range, IQR) concentrations of C5OH in patients with clefts and controls were 0.16 (0.13–0.22)μmoll−1 and 0.17 (0.13–0.20)μmoll−1, respectively (p=0.90). The receiver operating characteristic analysis did not find out cut-off values for C5OH discriminating between cases and controls. ConclusionThere appears to be no association between biotin deficiency, as indexed by an increase of C5OH, and orofacial clefts in the investigated group of patients.

Lack of association of polymorphic variants of genes encoding zinc transporters with the risk of orofacial cleft-affected pregnancies.

Maternal zinc deficiency seems to be a risk factor for orofacial clefts in offspring. This study was undertaken to investigate the involvement of polymorphic variants of genes for zinc transporters in the susceptibility of clefting. PCRRFLP analysis was used to analyze single nucleotide polymorphisms of SLC30A1 (rs7526700, rs2278651, rs611386), SLC30A4 (rs2453531, rs8029246), SLC30A5 (rs351444, rs164393, rs6886492), SLC39A1 (rs10127484, rs11264736), and SLC39A3 (rs759071, rs4806874, rs10415622) in mothers of children with non-syndromic cleft lip with or without cleft palate (CL/P) and control mothers. The allele, genotype, and haplotype distribution was found to be similar among case and control mothers. Also, the gene-by-gene interaction analysis conducted using the Multifactor Dimensionality Reduction approach revealed no significant interactive genetic effect on having a child with a cleft. In conclusion, our results demonstrated that the analyzed polymorphic variants of genes for zinc transporters are not implicated in abnormal palatogenesis in the investigated group of women from the Polish population.

The search for risk factors that contribute to the etiology of non-syndromic cleft lip with or without cleft palate (CL/P) in the Polish population

Abstract Non-syndromic cleft lip with or without cleft palate (CL/P) has severe long-lasting adverse effects on both physical and psychological development. Although recent years have brought significant improvement in clinical treatment, our understanding of the etiology of this congenital anomaly is lagging. Many genes, genetic pathways, harmful exposures, as well as nutrient deficiencies have been implicated in abnormal palatogenesis. Extrapolating data regarding risk factors for CL/P from different populations is not always straightforward. This review gives an overview of knowledge about both environmental and genetic risk factors in the etiology of CL/P in the Polish population, which was originally presented in research papers by the author and collaborating investigators. The findings suggest a possible association between maternal consumption of α-tocopherol, retinol, zinc, citrulline, and dietary compounds contributing to methyl-group homeostasis and CL/P risk. Polymorphisms in BHMT1 and BHMT2 were significantly associated with decreased CL/P risk in the Polish population. Other interesting findings include associations of CL/P risk with polymorphisms in MTR, PCYT1A, ASS1, SLC 25A13, GSTM1, GSTT1, SUMO1 genes, and 8q24.21 loci. Reviewed research papers indicate interesting pathways and new candidate genes for further investigation, and partly confirm earlier findings according risk factors for orofacial clefts.

Polymorphic variants of genes related to arginine metabolism and the risk of orofacial clefts

Objective Maternal mid-pregnancy low levels of symmetric dimethylarginine and newborn low levels of citrulline are suspected to be risk factors for orofacial clefts. This study was undertaken to investigate the involvement of polymorphic variants of genes related to arginine metabolism in the susceptibility of clefting. Design PCR-RFLP and HRM analyses were used to analyze single nucleotide polymorphisms (SNPs) of ASS1, ASL, and SLC25A13 in 172 children with non-syndromic cleft lip with or without cleft palate (CL/P) and 188 controls without congenital anomalies. The differences in allele and genotype frequencies between cases and controls were determined using standard Chi-square and Fisher exact tests. The odds ratio (OR) and associated 95% confidence intervals (95% CI) for individuals with CL/P versus controls were also calculated. Associations between the investigated polymorphisms and the risk of being born with an orofacial cleft were tested using the nonparametric and genetic model-free Multifactor Dimensionality Reduction (MDR) approach. Results Analysis of five SNPs of the ASS1 gene revealed that the G allele of rs7860909 is associated with increased CL/P risk. Compared to individuals with the AA genotype, the G allele carriers had an OR of 1.768 (95% CI: 1.133–2.759; p = 0.012). For the remaining SNPs of all analysed genes, there was no overall evidence for cleft association considering the allele and genotype distribution. However, gene-by-gene interaction analysis conducted using the MDR approach revealed a significant interactive genetic effect of ASS1 (rs666174) and SLC25A13 (rs10252573) on the occurrence of clefting ( p = 0.002). Conclusion Our results demonstrate moderate evidence for the association of polymorphic variants of genes related to arginine metabolism with abnormal palatogenesis.

Orofacial Cleft Risk Is Increased with Maternal Smoking and Specific Detoxification-Gene Variants

Maternal smoking is a recognized risk factor for orofacial clefts. Maternal or fetal pharmacogenetic variants are plausible modulators of this risk. In this work, we studied 5,427 DNA samples, including 1,244 from subjects in Denmark and Iowa with facial clefting and 4,183 from parents, siblings, or unrelated population controls. We examined 25 single-nucleotide polymorphisms in 16 genes in pathways for detoxification of components of cigarette smoke, to look for evidence of gene-environment interactions. For genes identified as related to oral clefting, we studied gene-expression profiles in fetal development in the relevant tissues and time intervals. Maternal smoking was a significant risk factor for clefting and showed dosage effects, in both the Danish and Iowan data. Suggestive effects of variants in the fetal NAT2 and CYP1A1 genes were observed in both the Iowan and the Danish participants. In an expanded case set, NAT2 continued to show significant overtransmission of an allele to the fetus, with a final P value of .00003. There was an interaction between maternal smoking and fetal inheritance of a GSTT1-null deletion, seen in both the Danish (P=.03) and Iowan (P=.002) studies, with a Fisher's combined P value of <.001, which remained significant after correction for multiple comparisons. Gene-expression analysis demonstrated expression of GSTT1 in human embryonic craniofacial tissues during the relevant developmental interval. This study benefited from two large samples, involving independent populations, that provided substantial power and a framework for future studies that could identify a susceptible population for preventive health care.

Maternal Smoking, Genetic Variation of Glutathione S-Transferases, and Risk for Orofacial Clefts

Maternal smoking is a known risk factor for orofacial clefts. We investigated whether risk is greater among offspring who lack the genetic capacity to produce glutathione S-transferase enzymes relevant to detoxification of chemicals in cigarette smoke. Using a population-based case-control design, we genotyped 423 California infants with an isolated cleft and 294 nonmalformed controls for null variants of the glutathione S-transferases GSTT1 and GSTM1. If a mother smoked during pregnancy and her fetus was homozygous null for GSTT1, the risk of isolated cleft lip with or without cleft palate was tripled (odds ratio = 2.9; 95% confidence interval = 1.2-7.2). For fetuses who were homozygous null for GSTM1 and whose mothers smoked >/=20 cigarettes per day, we found nearly a 7-fold increased risk (6.8; 0.82-57). Combined absence of GSTM1 and GSTT1 enzymes among the offspring of smoking mothers was associated with a nearly 6-fold increased risk for cleft lip (6.3; 1.3-42). A similar increased risk for cleft palate was associated with absence of GSTM1, but not for absence of GSTT1. Maternal smoking during pregnancy increases risks for clefts among fetuses lacking enzymes involved in the detoxification of tobacco-derived chemicals.