Claudine P. Torfs

Polymorphisms in genes involved in folate metabolism as maternal risk factors for Down syndrome

Down syndrome is a complex genetic and metabolic disorder attributed to the presence of three copies of chromosome 21. The extra chromosome derives from the mother in 93% of cases and is due to abnormal chromosome segregation during meiosis (nondisjunction). Except for advanced age at conception, maternal risk factors for meiotic nondisjunction are not well established. A recent preliminary study suggested that abnormal folate metabolism and the 677C-->T polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene may be maternal risk factors for Down syndrome. The present study was undertaken with a larger sample size to determine whether the MTHFR 677C-->T polymorphism was associated with increased risk of having a child with Down syndrome. Methionine synthase reductase (MTRR) is another enzyme essential for normal folate metabolism. A common polymorphism in this gene was recently associated with increased risk of neural tube defects and might also contribute to increased risk for Down syndrome. The frequencies of the MTHFR 677C-->T and MTRR 66A-->G mutations were evaluated in DNA samples from 157 mothers of children with Down syndrome and 144 control mothers. Odds ratios were calculated for each genotype separately and for potential gene-gene interactions. The results are consistent with the preliminary observation that the MTHFR 677C-->T polymorphism is more prevalent among mothers of children with Down syndrome than among control mothers, with an odds ratio of 1.91 (95% confidence interval [CI] 1.19-3.05). In addition, the homozygous MTRR 66A-->G polymorphism was independently associated with a 2. 57-fold increase in estimated risk (95% CI 1.33-4.99). The combined presence of both polymorphisms was associated with a greater risk of Down syndrome than was the presence of either alone, with an odds ratio of 4.08 (95% CI 1.94-8.56). The two polymorphisms appear to act without a multiplicative interaction.

Maternal medications and environmental exposures as risk factors for gastroschisis

In a case-control study of gastroschisis, we evaluated the risks associated with mothers first-trimester use of medications and with hobby or occupational exposures for 110 cases and 220 controls without a birth defect. Mothers of cases and controls were age-matched. For hobby or occupational exposures, we found significantly elevated risks for high levels of solvents (odds ratio (OR) = 3.8; 95% confidence interval (CI) = 1.6-9.2) and for colorants (OR = 2.3; 95% CI = 1.3-4.0). For medications, we found significantly elevated risks for two strong cyclooxygenase inhibitors, aspirin (OR = 4.7; 95% CI = 1.2-18.1) and ibuprofen (OR = 4.0; 95% CI = 1.0-16.0), but not for acetaminophen, a weak cyclooxygenase inhibitor. Periconceptional exposure to X rays was also associated with gastroschisis (OR = 2.5; 95% CI = 1.2-5.5), but exposure to antibiotics, antinauseants, sulfonamides, or oral contraceptives was not. We also found elevated risks for two decongestants, pseudoephedrine (OR = 2.1; 95% CI = 0.8-5.5) and phenylpropanolamine (OR = 10.0; 95% CI = 1.2-85.6). For the group of all decongestants, including also oxymetazoline and ephedrine, the risk was significantly elevated (OR = 2.4; 95% CI = 1.0-5.4). Controlling in multivariate analyses for several demographic and pregnancy variables associated with gastroschisis in a previous analysis [Torfs et al. (1994) Teratology 50: 44-53] did not substantially change the level or direction of the associations. Most of these associations are for vasoactive substances, which supports a vascular hypothesis for the pathogenesis of gastroschisis.

Anomalies in Down syndrome individuals in a large population-based registry

In a population of close to 2.5 million infants born from 1983 to 1993 registered in the California Birth Defects Monitoring Program, we compared the prevalence of structural birth defects among 2,894 infants with Down syndrome (DS) with that of infants without DS. Among 61 defects uniformly ascertained in affected and unaffected infants, 45 were significantly more common in DS, with atrioventricular canal (risk ratio = 1,009), duodenal atresia (risk ratio = 265), and annular pancreas (risk ratio = 430) being the most common. Most defects of blastogenesis and most midline defects were either nonsignificantly associated or not observed in infants with DS. Theories on the pathogenesis of defects in trisomies must account for the lack of and for the presence of specific defects.

Ethnicity, sex, and the incidence of congenital heart defects: a report from the National Down Syndrome Project

Purpose: The population-based National Down Syndrome Project combined epidemiological and molecular methods to study congenital heart defects in Down syndrome.Methods: Between 2000 and 2004, six sites collected DNA, clinical, and epidemiological information on parents and infants. We used logistic regression to examine factors associated with the most common Down syndrome-associated heart defects.Results: Of 1469 eligible infants, major cardiac defects were present in 44%; atrioventricular septal defect (39%), secundum atrial septal defect (42%), ventricular septal defect (43%), and tetralogy of Fallot (6%). Atrioventricular septal defects showed the most significant sex and ethnic differences with twice as many affected females (odds ratio, 1.93; 95% confidence interval, 1.40–2.67) and, compared with whites, twice as many blacks (odds ratio, 2.06; 95% confidence interval, 1.32–3.21) and half as many Hispanics (odds ratio, 0.48; 95% confidence interval, 0.30–0.77). No associations were found with origin of the nondisjunction error or with the presence of gastrointestinal defects.Conclusions: Sex and ethnic differences exist for atrioventricular septal defects in Down syndrome. Identification of genetic and environmental risk factors associated with these differences is essential to our understanding of the etiology of congenital heart defects.

Hypospadias in California: Trends and Descriptive Epidemiology

Background The occurrence of hypospadias has been reported to be increasing. The objectives of this study were to extend the literature on the descriptive epidemiology of hypospadias and to determine whether its birth prevalence increased in California in recent years. We used actively ascertained, population-based data for which detailed clinical descriptions permitted careful phenotypic classifications. Methods We examined registry data on 5838 male live births and stillbirths that occurred in California from 1984 through 1997. To reduce pathogenic heterogeneity, cases were classified as mild, severe, or not otherwise specified based on the anatomic position of the urethral opening. We also classified cases as isolated or nonisolated based on the presence and type of accompanying malformations. We used multivariable Poisson regression analysis to examine time trends and risk factors. Results There was no evidence for an increase in prevalence of any of the case groups between 1989 and 1997. The adjusted relative risk (RR) for change in prevalence per year of isolated severe cases was 0.99 (95% confidence interval = 0.96–1.03). Adjusted RRs indicated increased risks for specific types of hypospadias with maternal non-Hispanic white race–ethnicity, higher education, older age, and nulliparity. Delivery before 37 weeks and multiple births tended either not to be associated with risk or to be associated with reduced risk. Lower birthweight was associated with increased risk for all case groups. Conclusions This study suggests that hypospadias prevalence has not been increasing in California in recent years. Differences by phenotype suggest that examining certain phenotypes separately could help to understand hypospadias etiology.

Association between mothers' nutrient intake and their offspring's risk of gastroschisis

The young age of mothers of infants with gastroschisis, a congenital defect of the abdominal wall, suggested that deficient nutrition, with maternal-fetal competition for nutrients, could be a risk factor for gastroschisis. This population-based hypothesis-generating study consisted of 55 cases of gastroschisis and 182 matched controls. We assessed maternal nutrient intake during the trimester before conception with a self-reported food-frequency questionnaire and screened 38 nutrients to identify those most likely to be associated with gastroschisis. We used statistical classification trees to empirically generate cutpoints that determined the low and high levels of nutrient intakes corresponding to the risk of gastroschisis; cutpoints for most nutrients were similar to the corresponding recommended daily dietary allowances (RDAs). In univariate analysis, low intake of several nutrients emerged as the leading risk factors: carotenoids, e.g., alpha-carotene (odds ratio (OR) = 4.6; 95% confidence interval (CI) = 2.2-9.5), beta-carotene (OR = 3.1; 95% CI = 1.6-6.0); amino-acid compounds, e.g., total glutathione (OR = 3.5; 95% CI = 1.7-7.2); vitamin C (OR = 2.2; 95% CI = 1.5-7.8); vitamin E (OR = 2.3; 95% CI = 1.2-4.4); and minerals, fiber, and the fruit-and-vegetable group (OR = 3.1; 95% CI = 1.5-6.2). High intake of nitrosamines (OR = 2.4; 95% CI = 1.3-4.5) was also a good candidate. Many nutrient values were correlated and, in multivariate analysis, those most associated with gastroschisis were low alpha-carotene (OR = 4.3; 95% CI = 1.9-9.8), low total glutathione (OR = 3.3; 95% CI = 1.4-7.6), and high nitrosamines (OR = 2.6; 95% CI = 1.3-5.4). Adjusting for variables associated with gastroschisis in previous analyses of this population did not substantially alter those risks. These results suggest that maternal dietary inadequacy may be a risk factor for gastroschisis, and the three nutrients that emerged from the nutrient screening appear to be the best candidates to examine in further epidemiological analyses or biological studies.

Maternal risk factors and major associated defects in infants with down syndrome

More than 50% of infants with Down syndrome have associated defects that cause considerable morbidity and mortality. We evaluated the hypothesis that the trisomic genome interacts with environmental factors to increase the risk for specific associated defects. We evaluated risk factors present during early pregnancy in a multiracial population of 687 infants with Down syndrome. Mothers cigarette smoking was associated with the grouped cardiac defects [odds ratio (OR)=2.0; 95% confidence interval (CI) = 1.2-3.2]. When adjusted for other cardiac defects and maternal race, the following specific defects were associated with smoking: atrioventricular canal (OR = 2.3; 95% CI = 1.2-4.5), tetralogy of Fallot (OR = 4.6; 95% CI = 1.2-17.0), and atrial septal defects without ventricular septal defect (OR = 2.2; 95% CI = 1.1-4.3). Hirschsprung disease was associated with mothers daily consumption of more than three cups of coffee (OR = 6.02; 95% CI = 1.2-29.7) and with mothers fever (OR = 3.4; 95% CI = 0.7-16.4), but the number of cases was small. Use of alcohol was not associated with any defect. Mothers race, age, parity, income, or education did not confound the associations. Results suggest that environmental factors can modify the occurrence of associated anomalies in the embryo with Down syndrome.

Variation in folate pathway genes contributes to risk of congenital heart defects among individuals with Down syndrome

Cardiac abnormalities are one of the most common congenital defects observed in individuals with Down syndrome. Considerable research has implicated both folate deficiency and genetic variation in folate pathway genes with birth defects, including both congenital heart defects (CHD) and Down syndrome (DS). Here, we test variation in folate pathway genes for a role in the major DS‐associated CHD atrioventricular septal defect (AVSD). In a group of 121 case families (mother, father, and proband with DS and AVSD) and 122 control families (mother, father, and proband with DS and no CHD), tag SNPs were genotyped in and around five folate pathway genes: 5,10‐methylenetetrahyrdofolate reductase (MTHFR), methionine synthase (MTR), methionine synthase reductase (MTRR), cystathionine β‐synthase (CBS), and the reduced folate carrier (SLC19A1, RFC1). SLC19A1 was found to be associated with AVSD using a multilocus allele‐sharing test. Individual SNP tests also showed nominally significant associations with odds ratios of between 1.34 and 3.78, depending on the SNP and genetic model. Interestingly, all marginally significant SNPs in SLC19A1 are in strong linkage disequilibrium (r2≥0.8) with the nonsynonymous coding SNP rs1051266 (c.80A>G), which has previously been associated with nonsyndromic cases of CHD. In addition to SLC19A1, the known functional polymorphism MTHFR c.1298A was over‐transmitted to cases with AVSD (P=0.05) and under‐transmitted to controls (P=0.02). We conclude, therefore, that disruption of the folate pathway contributes to the incidence of AVSD among individuals with DS. Genet. Epidemiol. 34: 603–612, 2010.

A low prepregnancy body mass index is a risk factor for an offspring with gastroschisis

A mothers prepregnancy obesity has been suggested as a risk factor for having offspring with an abdominal wall defect. We evaluated this hypothesis among 104 cases of gastroschisis--a severe birth defect of the abdominal wall most prevalent in infants of young women--and 220 controls with no defect. Using Quetelets index (QI = weight in kg/height in m2) as a measure of body mass, we found a higher risk of gastroschisis (odds ratio (OR) = 3.2; 95% confidence interval (CI) = 1.4-7.3) for underweight mothers (QI<18.1 kg/m2) and a lower risk (OR = 0.2; 0.05-0.9) for overweight mothers (QI>28.3 kg/m2) as compared with mothers of normal weight. As QI was correlated to height, with the correlation varying according to mothers ethnicity and age, we adjusted for these factors in the analysis; the adjusted values approximated the unadjusted values. Evaluation of QI as a continuous variable showed that, for every unit increase in QI, the risk for gastroschisis decreased by about 11%. Sociodemographic, pregnancy, and nutrient factors did not confound the association. These results suggest that low prepregnancy body mass rather than obesity is a risk factor for gastroschisis.

Congenital gastrointestinal defects in Down syndrome: a report from the Atlanta and National Down Syndrome Projects

We report Down syndrome (DS)‐associated congenital gastrointestinal (GI) defects identified during a 15 year, population‐based study of the etiology and phenotypic consequences of trisomy 21. Between 1989 and 2004, six sites collected DNA, clinical and epidemiological information on live‐born infants with standard trisomy 21 and their parents. We used chi‐squared test and logistic regression to explore relationships between congenital GI defects and infant sex, race, maternal age, origin of the extra chromosome 21, and presence of a congenital heart defect. Congenital GI defects were present in 6.7% of 1892 eligible infants in this large, ethnically diverse, population‐based study of DS. Defects included esophageal atresia/tracheoesophageal fistula (0.4%), pyloric stenosis (0.3%), duodenal stenosis/atresia (3.9%), Hirschsprung disease (0.8%), and anal stenosis/atresia (1.0%). We found no statistically significant associations between these defects and the factors examined. Although not significant, esophageal atresia was observed more often in infants of younger mothers and Hispanics, Hirschsprung disease was more frequent in males and in infants of younger mothers and blacks, and anal stenosis/atresia was found more often among females and Asians.