Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.108 (lactase)
 2,133 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Observational epidemiologic studies of nutrition and cancer have faced formidable methodologic obstacles, including dietary measurement error and confounding. We consider whether Mendelian randomization can help surmount these obstacles. The Mendelian randomization strategy, building on both the accuracy of genotyping and the random assortment of alleles at meiosis, involves searching for an association between a nutritional exposure-mimicking gene variant (a type of "instrumental variable") and cancer outcome. Necessary assumptions are that the gene is independent of cancer, given the exposure, and also independent of potential confounders. An allelic variant can serve as a proxy for diet and other nutritional factors through its effects on either metabolic processes or consumption behavior. Such a genetic proxy is measured with little error and usually is not confounded by nongenetic characteristics. Examples of potentially informative genes include LCT (lactase), ALDH2 (aldehyde dehydrogenase), and HFE (hemochromatosis), proxies, respectively, for dairy product intake, alcoholic beverage drinking, and serum iron levels. We show that use of these and other genes in Mendelian randomization studies of nutrition and cancer may be more complicated than previously recognized and discuss factors that can invalidate the instrumental variable assumptions or cloud the interpretation of these studies. Sample size requirements for Mendelian randomization studies of nutrition and cancer are shown to be potentially daunting; strong genetic proxies for exposure are necessary to make such studies feasible. We conclude that Mendelian randomization is not universally applicable, but, under the right conditions, can complement evidence for causal associations from conventional epidemiologic studies.
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PMID:Mendelian randomization: how it can--and cannot--help confirm causal relations between nutrition and cancer. 1917 78

Hereditary hemochromatosis is caused by a potentially lethal recessive gene (HFE, C282Y allele) that increases iron absorption and reaches polymorphic levels in northern European populations. Because persons carrying the allele absorb iron more readily than do noncarriers, it has often been suggested that HFE is an adaptation to anemia. We hypothesize positive selection for HFE began during or after the European Neolithic with the adoption of an iron-deficient high-grain and dairying diet and consequent anemia, a finding confirmed in Neolithic and later European skeletons. HFE frequency compared with rate of lactase persistence in Eurasia yields a positive linear correlation coefficient of 0.86. We suggest this is just one of many mutations that became common after the adoption of agriculture.
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PMID:Hemochromatosis: Niche Construction and the Genetic Domino Effect in the European Neolithic. 2641 21