THE USE OF GLYCOMACROPEPTIDE IN NUTRITIONAL MANAGEMENT OFPHENYLKETONURIA PATIENTS

Abstract

Classical Phenylketonuria (PKU) is a rare metabolic disorder caused by a deficiency in the production of the hepatic enzyme phenylalanine hydroxylase (PAH) referred to as "hyperphenylalaninemia". Classical PKU is an inherited, autosomal recessive disorder. It is the most common genetic disease involving "amino acid metabolism." PKU is incurable, but early, effective treatment can prevent the development of serious mental incapacity. The PAH gene and its PKU mutations are found on chromosome 12 in the human genome. Untreated PKU patients develop a broad range of symptoms related to severely impaired cognitive function and mental retardation. Other symptoms can include extreme patterns of behavior, delayed speech development, seizures, a characteristic body odor, and light body pigmentation. The light pigmentation is due to a lack of melanin, which normally colors the hair, skin and eyes. Melanin is made from the amino acid tyrosine, which is lacking in untreated cases of PKU. Physiologically, PKU patients show high levels of phenylalanine and low levels of tyrosine in the blood. Babies do not show any visible symptoms of the disease for the first few months of life. However, typical PKU symptoms usually do show up by a baby's first birthday. The primary diagnostic test for PKU is the measurement of phenylalanine levels in a drop of blood taken from the heel of a newborn baby's foot. The severity of the PKU symptoms experienced by people with this disease is determined by both lifestyle as well as genetic factors. Phenylalanine-restricted diets could eliminate most of the typical PKU symptoms except for mental retardation. Dietary therapy (also called nutrition therapy) is the most common form of treatment for PKU patients. PKU patients who receive early and consistent dietary therapy can develop fairly normal mental capacity to within about five IQ points of their healthy peers, while untreated PKU patients have IQ scores below 50. Phenylalanine is actually an essential amino acid and has to be obtained from food as the body cannot produce it. Typical diets prescribed for PKU patients provide very small amounts of phenylalanine and higher quantities of other amino acids, including tyrosine. The amount of allowable phenylalanine can be increased slightly as a child becomes older. In addition, PKU diets include all the nutrients normally required for good health and normal growth, such as carbohydrates, fats, vitamins, and minerals. High protein foods like meat, fish, chicken, eggs, nuts, beans, milk, and other dairy products are banned from PKU diets. Small amounts of moderate protein foods (such as grains and potatoes) and low protein foods (some fruits and vegetables, low protein breads and pastas) are allowed. Sugar-free foods, which contain the artificial sweetener aspartame, are also prohibited foods for PKU patients. The amount of natural foods allowed in a diet could be adjusted to ensure that the level of phenylalanine in the blood is kept within a safe range two to 6