Deborah Koontz

Genetic Studies of a Cluster of Acute Lymphoblastic Leukemia Cases in Churchill County, Nevada

Objective In a study to identify exposures associated with 15 cases of childhood leukemia, we found levels of tungsten, arsenic, and dichlorodiphenyldichloroethylene in participants to be higher than mean values reported in the National Report on Human Exposure to Environmental Chemicals. Because case and comparison families had similar levels of these contaminants, we conducted genetic studies to identify gene polymorphisms that might have made case children more susceptible than comparison children to effects of the exposures. Design We compared case with comparison children to determine whether differences existed in the frequency of polymorphic genes, including genes that code for enzymes in the folate and purine pathways. We also included discovery of polymorphic forms of genes that code for enzymes that are inhibited by tungsten: xanthine dehydrogenase, sulfite oxidase (SUOX gene), and aldehyde oxidase. Participants Eleven case children were age- and sex-matched with 42 community comparison children for genetic analyses. Twenty parents of case children also contributed to the analyses. Results One bilalleleic gene locus in SUOX was significantly associated with either case or comparison status, depending on which alleles the child carried (without adjusting for multiple comparisons). Conclusions Although genetic studies did not provide evidence that a common agent or genetic susceptibility factor caused the leukemias, the association between a SUOX gene locus and disease status in the presence of high tungsten and arsenic levels warrants further investigation. Relevance Although analyses of community clusters of cancer have rarely identified causes, these findings have generated hypotheses to be tested in subsequent studies.

Prothrombin G20210A mutation is associated with young-onset stroke: the genetics of early-onset stroke study and meta-analysis.

Background and Purpose— Although the prothrombin G20210A mutation has been implicated as a risk factor for venous thrombosis, its role in arterial ischemic stroke is unclear, particularly among young adults. To address this issue, we examined the association between prothrombin G20210A and ischemic stroke in a white case–control population and additionally performed a meta-analysis. Methods— From the population-based Genetics of Early Onset Stroke (GEOS) study, we identified 397 individuals of European ancestry aged 15 to 49 years with first-ever ischemic stroke and 426 matched controls. Logistic regression was used to calculate odds ratios (ORs) in the entire population and for subgroups stratified by sex, age, oral contraceptive use, migraine, and smoking status. A meta-analysis of 17 case–control studies (n=2305 cases <55 years) was also performed with and without GEOS data. Results— Within GEOS, the association of the prothrombin G20210A mutation with ischemic stroke did not achieve statistical significance (OR=2.5; 95% confidence interval [CI]=0.9–6.5; P=0.07). However, among adults aged 15 to 42 years (younger than median age), cases were significantly more likely than controls to have the mutation (OR=5.9; 95% CI=1.2–28.1; P=0.03), whereas adults aged 42 to 49 years were not (OR=1.4; 95% CI=0.4–5.1; P=0.94). In our meta-analysis, the mutation was associated with significantly increased stroke risk in adults ⩽55 years (OR=1.4; 95% CI=1.1–1.9; P=0.02), with significance increasing with addition of the GEOS results (OR=1.5; 95% CI=1.1–2.0; P=0.005). Conclusions— The prothrombin G20210A mutation is associated with ischemic stroke in young adults and may have an even stronger association among those with earlier onset strokes. Our finding of a stronger association in the younger young adult population requires replication.

Evaluation of DNA extraction methods for the detection of Cytomegalovirus in dried blood spots

BACKGROUND Dried blood spots (DBS) are collected universally from newborns and may be valuable for the diagnosis of congenital Cytomegalovirus (CMV) infection. The reported analytical sensitivity for DBS testing compared to urine or saliva varies greatly across CMV studies. The purpose of this study was to directly compare the performance of various DNA extraction methods for identification of CMV in DBS including those used most often in CMV studies. STUDY DESIGN Whatman(®) Grade 903 filter paper cards were spotted with blood samples from 25 organ transplant recipients who had confirmed CMV viremia. Six DNA extraction methods were compared for relative yield of viral and cellular DNA: 2 manual solution-based methods (Gentra Puregene, thermal shock), 2 manual silica column-based methods (QIAamp DNA Mini, QIAamp DNA Investigator), and 2 automated methods (M48 MagAttract Mini, QIAcube Investigator). DBS extractions were performed in triplicate followed by real-time quantitative PCR (qPCR). RESULTS For extraction of both viral and cellular DNA, two methods (QIAamp DNA Investigator and thermal shock) consistently gave the highest yields, and two methods (M48 MagAttract Mini and QIAamp DNA Mini) consistently gave the lowest yields. There was an average 3-fold difference in DNA yield between the highest and lowest yield methods. CONCLUSION The choice of DNA extraction method is a major factor in the ability to detect low levels of CMV in DBS and can largely account for the wide range of DBS sensitivities reported in studies to date.

Folate-related gene variants in Irish families affected by neural tube defects

Periconceptional folic acid use can often prevent neural tube defects (NTDs). Variants of genes involved in folate metabolism in mothers and children have been associated with occurrence of NTDs. We identified Irish families with individuals affected by neural tube defects. In these families, we observed that neural tube defects and birth defects overall occurred at a higher rate in the maternal lineage compared with the paternal lineage. The goal of this study was to look for evidence for genetic effects that could explain the discrepancy in the occurrence of these birth defects in the maternal vs. paternal lineage. We genotyped blood samples from 322 individuals from NTD-affected Irish families, identified through their membership in spina bifida associations. We looked for differences in distribution in maternal vs. paternal lineages of five genetic polymorphisms: the DHFR 19 bp deletion, MTHFD1 1958G>A, MTHFR 1298A>C, MTHFR 677C>T, and SLC19A1 80A>G. In addition to looking at genotypes individually, we determined the number of genotypes associated with decreased folate metabolism in each relative (“risk genotypes”) and compared the distribution of these genotypes in maternal vs. paternal relatives. Overall, maternal relatives had a higher number of genotypes associated with lower folate metabolism than paternal relatives (p = 0.017). We expected that relatives would share the same risk genotype as the individuals with NTDs and/or their mothers. However, we observed that maternal relatives had an over-abundance of any risk genotype, rather than one specific genotype. The observed genetic effects suggest an epigenetic mechanism in which decreased folate metabolism results in epigenetic alterations related to the increased rate of NTDs and other birth defects seen in the maternal lineage. Future studies on the etiology of NTDs and other birth defects could benefit from including multigenerational extended families, in order to explore potential epigenetic mechanisms.

Evaluation of mailed pediatric buccal cytobrushes for use in a case‐control study of birth defects

BACKGROUND Buccal cell collection is a convenient DNA collection method; however, little attention has been given to the quality of DNA obtained from pediatric populations. The purpose of this study was to determine the effect of a modified cytobrush collection method on the yield and quality of infant buccal DNA collected as part of a population-based case-control study of birth defects. METHODS Cytobrushes were collected from infants, mothers, and fathers using a standard collection method in 1997 to 2003 and a modified protocol that allows air-drying of the cytobrushes after collection from 2003 to the present. Yield and quality of DNA from 1057 cytobrushes was assessed by quantitative PCR and short tandem repeat (STR) genotyping, respectively. RESULTS Air-dried cytobrushes from infants had higher median DNA yields (1300 ng) and STR completion rates (99.5%) than standard collection method cytobrushes (60 ng and 59.5%, respectively). A subset of DNA aliquots was genotyped for six single nucleotide polymorphisms (SNPs). Aliquots from both collection methods that passed the quality protocol (DNA concentration >1 ng/μl, and successful amplification of ≥1 STR) had high genotype completion rates (99-100%). The median DNA yield following whole genome amplification was more than twofold higher for air-dried than standard collection specimens (p < 0.001). CONCLUSION Yield and quality of buccal DNA collected from infants are improved by using a method that incorporates air-drying; however, DNA collected by both methods is suitable for genotyping if stringent quality control procedures are instituted. These findings may be helpful for future epidemiologic studies of birth defects and other adverse pediatric outcomes.

Maternal smoking, xenobiotic metabolizing enzyme gene variants, and gastroschisis risk.

Maternal smoking during pregnancy is one proposed risk factor for gastroschisis, but reported associations have been modest, suggesting that differences in genetic susceptibility might play a role. We included 108 non‐Hispanic white and 62 Hispanic families who had infants with gastroschisis, and 1,147 non‐Hispanic white and 337 Hispanic families who had liveborn infants with no major structural birth defects (controls) in these analyses. DNA was extracted from buccal cells collected from infants and mothers, and information on periconceptional smoking history was obtained from maternal interviews, as part of the National Birth Defects Prevention Study. We analyzed five polymorphisms in three genes that code for enzymes involved in metabolism of some cigarette smoke constituents (CYP1A1, CYP1A2, and NAT2). Logistic regression models were used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) independently for maternal smoking and maternal and infant gene variants, and to assess joint associations of maternal smoking and maternal or infant gene variants with gastroschisis. In analyses adjusted for maternal age at delivery and stratified by maternal race‐ethnicity, we identified three suggestive associations among 30 potential associations with sufficient numbers to calculate ORs: CYP1A1*2A for non‐Hispanic white mothers who smoked periconceptionally (aOR = 0.38, 95% CI 0.15–0.98), and NAT2*6 for Hispanic non‐smoking mothers (aOR = 2.17, 95% CI 1.12–4.19) and their infants (aOR = 2.11, 95% CI 1.00–4.48). This analysis does not support the occurrence of effect modification between periconceptional maternal smoking and most of the xenobiotic metabolizing enzyme gene variants assessed.

MALDI-TOF-MS Assay to Detect the Hemizygous 22q11.2 Deletion in DNA from Dried Blood Spots

BACKGROUND A hemizygous deletion of 1.5-3 Mb in 22q11.2 causes a distinct clinical syndrome with variable congenital defects. Current diagnostic methods use fluorescent in situ hybridization (FISH) or comparative genomic hybridization by microarray to detect the deletion. Neither method is suitable for newborn screening (NBS), since they cannot be performed on dried blood spots (DBS). We developed a MALDI-TOF-MS assay that uses DBS to measure the hemizygous deletion of UFD1L, located within the 22q11.2 region. METHODS We used DBS from 54 affected patients, previously tested by FISH or microarray, and 100 cord blood samples to evaluate the performance of the MALDI-TOF-MS assay. With a single primer pair, a 97-base oligonucleotide within UFD1L was amplified, as was a sequence on chromosome 18 that differs by 2 nucleotides. A multiplexed, single-base extension reaction created allele-specific products for MALDI-TOF-MS detection. The products were spotted onto a silicon chip, and the height of the spectral peaks identified the relative amounts of target and reference gene. RESULTS The median ratio of the spectral peak for each UFD1L target:reference base was 0.96 and 0.99 for controls, compared with 0.35 and 0.53 for 22q11 deletion syndrome patients. There was 100% concordance between FISH/microarray and MALDI-TOF-MS in all patients with 22q11.2 deletion syndrome. CONCLUSIONS This method can be reliably performed with DBS and is suitable for high sample throughput. This assay may be considered for use in population-based NBS for 22q11.2 deletion.

A Pyrosequencing-Based Assay for the Rapid Detection of the 22q11.2 Deletion in DNA from Buccal and Dried Blood Spot Samples

The 22q11.2 deletion syndrome is one of the most common deletion syndromes in newborns. Some affected newborns may be diagnosed shortly after birth because of the presence of heart defects, palatal defects, or severe immune deficiencies. However, diagnosis is often delayed in patients presenting with other associated conditions that would benefit from early recognition and treatment, such as speech delays, learning difficulties, and schizophrenia. Fluorescence in situ hybridization (FISH) is the gold standard for deletion detection, but it is costly and time consuming and requires a whole blood specimen. Our goal was to develop a suitable assay for population-based screening of easily collectible specimens, such as buccal swabs and dried blood spots (DBS). We designed a pyrosequencing assay and validated it using DNA from FISH-confirmed 22q11 deletion syndrome patients and normal controls. We tested DBS from nine patients and paired buccal cell and venous blood specimens from 20 patients. Results were 100% concordant with FISH assay results. DNA samples from normal controls (n = 180 cell lines, n = 15 DBS, and n = 88 buccal specimens) were negative for the deletion. Limiting dilution experiments demonstrated that accurate results could be obtained from as little as 1 ng of DNA. This method represents a reliable and low-cost alternative for detection of the common 22q11.2 microdeletions and can be adapted to high-throughput population screening.