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Food, and the nutrients it contains, has long been known to influence the health and well-being of humans. Included in the list of nutrition-related diseases that afflict humankind are the specific nutrient deficiency diseases and several of the chronic diseases, including some of the most common ones. Each of these conditions has both a nutrition component and a genetic component. With respect to the nutrient deficiency diseases, there is considerable variation in nutrient requirements since the genetics of the consumer dictates how much of each essential nutrient is needed. If the individual's requirement is met, the deficiency disease is prevented. Table 1 lists the essential nutrients and the symptoms of the deficient state caused by inadequate intake of the nutrients. Some symptoms (i.e., anemia) characterize several different nutrient deficiency states.

In addition to the diseases that are clearly nutritionally related, many of the chronic diseases have a nutritional component. They are also influenced by genetics, and often these two factors interact so that when certain dietary behaviors are found with a susceptible genotype, the disease results. A third kind of nutrient gene interaction relevant to health occurs when dietary constituents either promote or protect against changes in DNA that result in aging or disease. Nutrients that affect the redox balance within the cell are important in this case.

Some disease states result from alterations in a single gene. Function of the gene product is compromised and the specific pathology develops. Acroder-matitis enteropathica is an example of this, in which the affected individual has impaired zinc absorption due to a mutation in the gene encoding a zinc transporter. Menkes' disease is another example; copper absorption is impaired due to an X-linked mutation in the protein needed to release absorbed copper from the enterocyte into the circulation. People with this disorder develop symptoms of copper deficiency. Single gene mutations have been identified that affect the use of a single nutrient. However, in many genetically determined instances of nutrient malabsorption or abnormal use, the situation is more complex and the disease state may develop as a result of small changes in several genes. These situations may be more common than individual

Table 1 Nutrient deficiency disorders3

Nutrient

Disease: signs of inadequate intake

Ascorbic acid

Thiamin

Riboflavin

Niacin

Vitamin B6

Folic acid

Vitamin B12 Vitamin A

Vitamin D

Vitamin K

Vitamin E

Phosphorus

Magnesium

Iron

Zinc

Copper

Selenium

Iodine

Scurvy: hyperkeratosis, congestion of the hair follicles, skin hemorrhages, conjunctival lesions, gum swelling and bleeding, peripheral neuropathy with hemorrhages into the nerve sheaths, painful joints, deformed chests in children Beriberi: muscle tenderness and peripheral neuropathy, edema, fast pulse, high blood pressure, decreased urine volume, disorientation, memory loss, ataxia, jerky movements of the eyes Ill-defined symptoms that are not necessarily related to inadequate intake: poor growth, poor appetite, cracks in the corners of the mouth, dermatitis of the scrotum Pellagra: black, roughened skin especially in areas exposed to sunlight; insomnia; loss of appetite; sores in mouth and tongue; indigestion; diarrhea; mental confusion; nervousness; headache; apprehension; forgetfulness Ill-defined symptoms: poor growth, muscular weakness, fatty liver, convulsions, anemia, reproductive impairment, edema, neural degeneration, enlarged adrenal glands Anemia; macrocytic anemia. Neural tube defects in infants are associated with inadequate folic acid intakes of the mother during the first trimester of pregnancy Pernicious anemia; macrocytic anemia. Also loss of peripheral nerve function

Night blindness, poor growth and reproduction, roughened skin (keratomalacia); xerophthalmia, leading to blindness, anemia, reduced immune function Rickets; inadequate calcification of bones resulting in bone deformities Poor blood clotting

Red cell fragility, increase in blood peroxides

Anorexia, muscle weakness, rickets, impaired growth, bone pain

Muscle spasms, twitching, tremor, anorexia, nausea

Anemia; microcytic anemia due to low hemoglobin, fatigue, inability to concentrate

Growth failure, hypogonadism, impaired immune function, enlarged liver and spleen, mental lethargy

Anemia, poor wound healing

Keshan disease: fragile red blood cells, enlarged heart, cardiomyopathy, growth retardation, skeletal muscle degeneration, cataract formation Goiter: enlarged thyroid gland, poor growth, reduced metabolic rate, mental retardation if deficiency occurs in the perinatal period aSome nutrients have no defined deficiency syndromes.

gene mutations. They are also much more complex and more difficult to identify.

Before discussing the different kinds of nutrient-gene interactions in detail, an outline of the kind of variability found within the human genome is presented.

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