Stuart W. Tinker

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.

New insights into human nondisjunction of chromosome 21 in oocytes.

Nondisjunction of chromosome 21 is the leading cause of Down syndrome. Two risk factors for maternal nondisjunction of chromosome 21 are increased maternal age and altered recombination. In order to provide further insight on mechanisms underlying nondisjunction, we examined the association between these two well established risk factors for chromosome 21 nondisjunction. In our approach, short tandem repeat markers along chromosome 21 were genotyped in DNA collected from individuals with free trisomy 21 and their parents. This information was used to determine the origin of the nondisjunction error and the maternal recombination profile. We analyzed 615 maternal meiosis I and 253 maternal meiosis II cases stratified by maternal age. The examination of meiosis II errors, the first of its type, suggests that the presence of a single exchange within the pericentromeric region of 21q interacts with maternal age-related risk factors. This observation could be explained in two general ways: 1) a pericentromeric exchange initiates or exacerbates the susceptibility to maternal age risk factors or 2) a pericentromeric exchange protects the bivalent against age-related risk factors allowing proper segregation of homologues at meiosis I, but not segregation of sisters at meiosis II. In contrast, analysis of maternal meiosis I errors indicates that a single telomeric exchange imposes the same risk for nondisjunction, irrespective of the age of the oocyte. Our results emphasize the fact that human nondisjunction is a multifactorial trait that must be dissected into its component parts to identify specific associated risk factors.

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.

The National Down Syndrome Project: Design and Implementation

Objective. The National Down Syndrome Project (NDSP), based at Emory University in Atlanta, Georgia, represents a multi-site, population-based, case-control study with two major aims: (1) to identify molecular and epidemiological factors contributing to chromosome nondisjunction and the consequent packaging of an extra chromosome into an egg or sperm, and (2) to identify risk factors for Down syndrome-associated birth defects. Methods. The six national sites represent approximately 11% of U.S. births. Cases were newborns with Down syndrome (trisomy 21), and controls were infants without major birth defects randomly selected from the same birth populations. Biological samples were collected from case infants and their parents, and genetic markers were typed to determine the parental origin of chromosome 21 nondisjunction. Each site interviewed parents of case and control infants addressing pregnancy, medical and family history, occupation, and exposures. Sites collected medical information on case infants. Results. The NDSP enrolled 907 infants as cases and 977 infants as controls (participation rates: 60.7% for cases; 56.9% for controls). Participation rates varied widely by site as did important demographic factors such as maternal age, race, and education. Nondisjunction during oogenesis accounted for 93.2% of the cases. Errors in spermatogenesis were found in 4.1%, and 2.7% were post-zygotic errors. Conclusions. This exceptional compilation of questionnaire, clinical, and molecular data makes the NDSP a unique resource for ongoing studies of the etiology and phenotypic consequences of trisomy 21. The combined approach increases study power by defining subgroups of cases by the origin of nondisjunction. This report describes the design and successful implementation of the NDSP.

Free the Data: One Laboratory's Approach to Knowledge-Based Genomic Variant Classification and Preparation for EMR Integration of Genomic Data

Current technology allows clinical laboratories to rapidly translate research discoveries from small patient cohorts into clinical genetic tests; therefore, a potentially large proportion of sequence variants identified in individuals with clinical features of a genetic disorder remain unpublished. Without a mechanism for clinical laboratories to share data, interpretation of sequence variants may be inconsistent. We describe here the two components of Emory Genetics Laboratorys (EGL) in‐house developed data management system. The first is a highly curated variant database with a data structure designed to facilitate sharing of information about variants identified at EGL with curated databases. This system also tracks changes in variant classifications, creating a record of previous cases in need of updated reports when a classification is changed. The second component, EmVClass, is a Web‐based interface that allows any user to view the inventory of variants classified at EGL. These software tools provide a solution to two pressing issues faced by clinical genetics laboratories: how to manage a large variant inventory with evolving variant classifications that need to be communicated to healthcare providers and how to make that inventory of variants freely available to the community.

Fragile X-associated primary ovarian insufficiency: evidence for additional genetic contributions to severity

The fragile X mental retardation gene (FMR1) contains a CGG repeat sequence in its 5′ untranslated region that can become unstable and expand in length from generation to generation. Alleles with expanded repeats in the range of ∼55–199, termed premutation alleles, are associated with an increased risk for fragile‐X‐associated primary ovarian insufficiency (FXPOI). However, not all women who carry the premutation develop FXPOI. To determine if additional genes could explain variability in onset and severity, we used a random‐effects Cox proportional hazards model to analyze age at menopause on 680 women from 225 families who have a history of fragile X syndrome and 321 women from 219 families from the general population. We tested for the presence of a residual additive genetic effect after adjustment for FMR1 repeat length, race, smoking, body mass index, and method of ascertainment. Results showed significant familial aggregation of age at menopause with an estimated additive genetic variance of 0.55–0.96 depending on the parameterization of FMR1 repeat size and definition of age at menopause (P‐values ranging between 0.0002 and 0.0027). This is the first study to analyze familial aggregation of FXPOI. This result is important for proper counseling of women who carry FMR1 premutation alleles and for guidance of future studies to identify additional genes that influence ovarian insufficiency. Genet. Epidemiol. 2008.

Lack of maternal folic acid supplementation is associated with heart defects in Down syndrome: a report from the National Down Syndrome Project

BACKGROUND Maternal folic acid supplementation has been associated with a reduced risk for neural tube defects and may be associated with a reduced risk for congenital heart defects and other birth defects. Individuals with Down syndrome are at high risk for congenital heart defects and have been shown to have abnormal folate metabolism. METHODS As part of the population-based case-control National Down Syndrome Project, 1011 mothers of infants with Down syndrome reported their use of supplements containing folic acid. These data were used to determine whether a lack of periconceptional maternal folic acid supplementation is associated with congenital heart defects in Down syndrome. We used logistic regression to test the relationship between maternal folic acid supplementation and the frequency of specific heart defects correcting for maternal race or ethnicity, proband sex, maternal use of alcohol and cigarettes, and maternal age at conception. RESULTS Lack of maternal folic acid supplementation was more frequent among infants with Down syndrome and atrioventricular septal defects (odds ratio [OR], 1.69; 95% confidence interval [CI], 1.08-2.63; p = 0.011) or atrial septal defects (OR, 1.69; 95% CI, 1.11-2.58; p = 0.007) than among infants with Down syndrome and no heart defect. Preliminary evidence suggests that the patterns of association differ by race or ethnicity and sex of the proband. There was no statistically significant association with ventricular septal defects (OR, 1.26; 95% CI, 0.85-1.87; p = 0.124). CONCLUSIONS Our results suggest that lack of maternal folic acid supplementation is associated with septal defects in infants with Down syndrome. Birth Defects Research (Part A), 2011.

Detection of early FXTAS motor symptoms using the CATSYS computerised neuromotor test battery

Background: Carriers of the FMR1 premutation allele are at a significantly increased risk for a late-onset neurodegenerative disorder, fragile X-associated tremor/ataxia syndrome (FXTAS). This disorder is distinct from fragile X syndrome (FXS) in its molecular aetiology and clinical presentation. The primary features of FXTAS are late-onset intention tremor and gait ataxia. Associated features include parkinsonism, neuropsychological dysfunction, autonomic dysfunction and peripheral neuropathy. Aim: To investigate the usefulness of a quantitative neurological test battery implemented through the CATSYS instrument to identify preclinical symptoms of FXTAS. Methods: Both premutation carriers with 70–199 repeats (62 men) and their low-repeat allele carrier siblings (27 men), identified through families with an individual affected with FXS, were tested. Results: As expected, because of its sensitivity, use of the instrument allowed identification of tremor in 23% of men who had not self-reported tremor, and ataxia in 30% of men who had not self-reported ataxia. Among subjects with self-reported tremor and ataxia, we found significant concordance between measures of the CATSYS system and the self-report. Conclusion: Rates of these traits among premutation carriers and low-repeat allele carrier siblings could be identified, and are presented in this paper, along with the minimum estimates of age-related prevalence.

Preconception folic acid supplementation and risk for chromosome 21 nondisjunction: A report from the National Down Syndrome Project

Both a lack of maternal folic acid supplementation and the presence of genetic variants that reduce enzyme activity in folate pathway genes have been linked to meiotic nondisjunction of chromosome 21; however, the findings in this area of research have been inconsistent. To better understand these inconsistencies, we asked whether maternal use of a folic acid‐containing supplement before conception reduces risk for chromosome 21 nondisjunction. Using questionnaire data from the National Down Syndrome Project, a population‐based case–control study, we compared the use of folic acid‐containing supplements among mothers of infants with full trisomy 21 due to maternal nondisjunction (n = 702) and mothers of infants born with no major birth defects (n = 983). Using logistic regression, adjusting for maternal age, race/ethnicity, and infant age at maternal interview, we found no evidence of an association between lack of folic acid supplementation and maternal nondisjunction among all case mothers (OR = 1.16; 95% CI: 0.90–1.48). In analyses stratified by meiotic stage and maternal age (<35 or ≥35 years), we found an association among older mothers experiencing meiosis II nondisjunction errors (OR = 2.00; 95% CI: 1.08–3.71). These data suggest that lack of folic acid supplementation may be associated specifically with MII errors in the aging oocyte. If confirmed, these results could account for inconsistencies among previous studies, as each study sample may vary by maternal age structure and proportion of meiotic errors.

Investigation of factors associated with paternal nondisjunction of chromosome 21

Previous studies on relatively small samples of individuals with trisomy 21 caused by paternally derived errors have shown that: (1) advanced paternal age is not a risk factor for chromosome 21 nondisjunction (NDJ), (2) absence of recombination, but not the location of recombination is associated with paternal NDJ and (3) there is an excess of males among live‐births with paternally derived trisomy 21. An excess of males is also observed among all individuals with trisomy 21. Using 128 families that had a child with trisomy 21 due to a paternally derived error, we examined: paternal age, recombination and the male/female sex ratio. We genotyped STRs along 21q to identify the origin of the error and the location of recombination on the paternal chromosome. Results showed that 32% of paternal meiotic errors occurred in meiosis I (MI) and 68% in meiosis II (MII). We confirmed the lack of a paternal age association with either type of error (mean paternal age for controls, MI, and MII errors: 31.3 ± 6.6, 32.2 ± 6.3, 30.6 ± 6.5, respectively). However, contrary to previous findings, we did not find altered patterns of recombination among paternal MI or MII errors. We found an increased male/female sex ratio among paternal (1.28, 95% CI: 0.68–1.91) and maternal (1.16, 95% CI: 1.02–1.33) meiotic errors. While the sex ratio among individuals with paternal errors was not statistically significant, these findings suggest that selection against female fetuses with trisomy 21 may contribute to the excess of males observed among all individuals with trisomy 21.