Polymorphisms are variations in a particular coding region of a gene sequence, with single nucleotide polymorphisms being known as SNPs (‘SNIPS’). Because genes code for proteins, polymorphisms produce variety in the phenotypes of those genes. Such variation is clearly visible on the outside of organisms, and it is self evident that animals of the same species, including humans, generally look different to one another. However, just as differences exist on the outside, internal variation creates differences between the enzymes and proteins that regulate metabolism. Such biochemical individuality can influence on the internal cellular milieu, which in turn can directly influence the long-term health and fitness of the individual. It is only recently that more attention has been paid by scientists to this internal biochemical variation and how it can alter the aetiology of the disease process. This is surprising because such biochemical individuality is embedded within Chinese and Ayurvedic medicine, both of which date back thousands of years.
Polymorphisms in the genes involved in metabolising plant compounds may influence disease because they can cause variation in the plasma levels of these compounds and their metabolites. Some such polymorphisms have been studied and their biochemical influences reported. For example in a recent study published in the American Journal of Clinical Nutrition1, researchers assessed the impact of polymorphisms in the β-carotene 15, 15’-monooxygenase 1 enzyme on blood levels of common dietary carotenoids. The results showed that SNPs were significantly associated with plasma concentrations of β-carotene, α-carotene, β-cryptoxanthin and lutein or zeaxanthin, variations of which between subjects were 48, 15, 15 and 36%, respectively. Because plasma levels of carotenoids are thought to be protective of cancer, polymorphisms have the potential to influence the disease aetiology. However, at present it is not fully understood to what degree these variations in plasma concentrations affect the risk of cancer in humans.
The β-carotene 15, 15’-monooxygenase 1 enzyme is responsible for a step in the pathway that converts carotenoids with provitamin A activity, to retinal. Polymorphisms within the β-carotene 15, 15’-monooxygenase 1 enzyme that decrease the effectiveness of the enzyme slow the conversion of these carotenoids to retinal and thus raise plasma levels of the relevant carotenoid. For example two SNPs within the coding region for for β-carotene 15, 15’-monooxygenase 1 have been identified that reduce the conversion of β-carotene to retinyl palmitate in female subjects, and thereby increase plasma concentrations of β-carotene. Such polymorphisms within plant metabolising enzyme may help explain inconsistencies within the literature with regard the effects of dietary phytonutrient intake on disease risk. In the study above, polymorphisms caused alterations in plasma levels of up to 50%, which may have significant implications for health, suggesting that biochemical individuality may play a pivotal role in the disease process.
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