Copyright © 2008 The American Society of Human Genetics. All rights reserved.
The American Journal of Human Genetics, Volume 82, Issue 3, 593-599, 3 March 2008
doi:10.1016/j.ajhg.2007.12.020
Article
A. Cecile J.W. Janssens1,
,
, Marta Gwinn2, Linda A. Bradley2, Ben A. Oostra3, Cornelia M. van Duijn4 and Muin J. Khoury2
1 Department of Public Health, Erasmus MC University Medical Center, PO Box 2040, 3000 CA Rotterdam, The Netherlands
2 National Office of Public Health Genomics, Centers for Disease Control and Prevention, Atlanta, GA 30341, USA
3 Department of Clinical Genetics, Erasmus MC University Medical Center, PO Box 2040, 3000 CA Rotterdam, The Netherlands
4 Department of Epidemiology & Biostatistics, Erasmus MC, University Medical Center, PO Box 2040, 3000 CA Rotterdam, The Netherlands
Corresponding authorAbstract
Predictive genomic profiling used to produce personalized nutrition and other lifestyle health recommendations is currently offered directly to consumers. By examining previous meta-analyses and HuGE reviews, we assessed the scientific evidence supporting the purported gene-disease associations for genes included in genomic profiles offered online. We identified seven companies that offer predictive genomic profiling. We searched PubMed for meta-analyses and HuGE reviews of studies of gene-disease associations published from 2000 through June 2007 in which the genotypes of people with a disease were compared with those of a healthy or general-population control group. The seven companies tested at least 69 different polymorphisms in 56 genes. Of the 56 genes tested, 24 (43%) were not reviewed in meta-analyses. For the remaining 32 genes, we found 260 meta-analyses that examined 160 unique polymorphism-disease associations, of which only 60 (38%) were found to be statistically significant. Even the 60 significant associations, which involved 29 different polymorphisms and 28 different diseases, were generally modest, with synthetic odds ratios ranging from 0.54 to 0.88 for protective variants and from 1.04 to 3.2 for risk variants. Furthermore, genes in cardiogenomic profiles were more frequently associated with noncardiovascular diseases than with cardiovascular diseases, and though two of the five genes of the osteogenomic profiles did show significant associations with disease, the associations were not with bone diseases. There is insufficient scientific evidence to conclude that genomic profiles are useful in measuring genetic risk for common diseases or in developing personalized diet and lifestyle recommendations for disease prevention.
| The Methylenetetrahydrofolate Reductase 677C→T Polymorphism as a Modulator of a B Vitamin Network with Major Effects on Homocysteine Metabolism The American Journal of Human Genetics, Volume 80, Issue 5, 1 May 2007, Pages 846-855 Steinar Hustad, Øivind Midttun, Jørn Schneede, Stein Emil Vollset, Tom Grotmol and Per Magne Ueland Abstract Folates are carriers of one-carbon units and are metabolized by 5,10-methylenetetrahydrofolate reductase (MTHFR) and other enzymes that use riboflavin, cobalamin, or vitamin B6 as cofactors. These B vitamins are essential for the remethylation and transsulfuration of homocysteine, which is an important intermediate in one-carbon metabolism. We studied the MTHFR 677C→T polymorphism and B vitamins as modulators of one-carbon metabolism in 10,601 adults from the Norwegian Colorectal Cancer Prevention (NORCCAP) cohort, using plasma total homocysteine (tHcy) as the main outcome measure. Mean concentrations of plasma tHcy were 10.4 μmol/liter, 10.9 μmol/liter, and 13.3 μmol/liter in subjects with the CC (51%), CT (41%), and TT (8%) genotypes, respectively. The MTHFR 677C→T polymorphism, folate, riboflavin, cobalamin, and vitamin B6 were independent predictors of tHcy in multivariate models (P<.001), and genotype effects were strongest when B vitamins were low (P≤.006). Conversely, the MTHFR polymorphism influenced B vitamin effects, which were strongest in the TT group, in which the estimated tHcy difference between subjects with vitamin concentrations in the lowest compared with the highest quartile was 5.4 μmol/liter for folate, 4.1 μmol/liter for riboflavin, 3.2 μmol/liter for cobalamin, and 2.1 μmol/liter for vitamin B6. Furthermore, interactions between B vitamins were observed, and B vitamins were more strongly related to plasma tHcy when concentrations of other B vitamins were low. The study provides comprehensive data on the MTHFR–B vitamin network, which has major effects on the transfer of one-carbon units. Individuals with the TT genotype were particularly sensitive to the status of several B vitamins and might be candidates for personalized nutritional recommendations. Abstract | | |
| The “Thermolabile” Variant of Methylenetetrahydrofolate Reductase and Neural Tube Defects: An Evaluation of Genetic Risk and the Relative Importance of the Genotypes of the Embryo and the Mother The American Journal of Human Genetics, Volume 64, Issue 4, 1 April 1999, Pages 1045-1055 Denis C. Shields, Peadar N. Kirke, James L. Mills, Dorothy Ramsbottom, Anne M. Molloy, Helen Burke, Donald G. Weir, John M. Scott and Alexander S. Whitehead Abstract Summary:
Recent reports have implicated the “thermolabile” (T) variant of methylenetetrahydrofolate reductase (MTHFR) in the causation of folate-dependent neural tube defects (NTDs). We report herein the largest genetic study of NTD cases (n=271) and families (n=218) to date, establishing that, in Ireland, the “TT” genotype is found in 18.8% of cases versus 8.3% of controls (odds ratio 2.57; confidence interval [CI] 1.48–4.45; P=.0005). The maternal and paternal TT genotypes have intermediate frequencies of 13.8% and 11.9%, respectively, indicating that the predominant MTHFR-related genetic effect acts via the TT genotype of the developing embryo. Analysis of the 218 family triads of mother, father, and affected child with log-linear models supports this interpretation, providing significant evidence that the case TT genotype is associated with NTDs (P=.02) but no evidence of a maternal TT genotypic effect (P=.83). The log-linear model predicted that the risk of NTDs conferred by the case TT genotype is 1.61 (CI 1.06–2.46), consistent with the paramount importance of the case TT genotype in determining risk. There is no compelling evidence for more than a modest additional risk conferred by a maternal TT genotype. These results favor a biological model of MTHFR-related NTD pathogenesis in which suboptimal maternal folate status imposes biochemical stress on the developing embryo, a stress it is ill-equipped to tolerate if it has a TT genotype. Abstract | | |