none none none none no selenium no selenium none no selenium none no selenium
'Vitamin packets sold separately.
'Also available in prepacked capsules and fruit-flavored bars. 'Designed tor use in pregnancy
Mead J = Mead Johnson Nutritionals, Evansvilie, IN; Ross = Ross Products. Columbus, OH; SHS = SHS North America, Gaithersburg. MD: AN = Applied Nutrition Corp, Randolph. NJ: Milupa - Distributed in the United States by Mead Johnson.
Adequate energy intake from nonprotein sources is essential to provide for growth and minimize tissue cata-bolism that can lead to poorer metabolic control. Table foods such as fruits, vegetables, and limited grain products are supplemented with concentrated sweets and fats to provide adequate calories. Use of special low protein foods (pasta, breads, baked products) helps provide additional energy and variety in the diet without significantly increasing protein intake. Inadequate caloric intake may result from diet restrictions that severely limit food choices, unpleasant taste of medical foods containing L-amino acids, and poor appetite.
Recommended vitamin and mineral intakes follow the RDA guidelines. In low protein diets where chemically defined formulas provide the majority of protein intake, the v ariety of natural foods is very limited. Intake of vitamins and minerals needs to be monitored. Low plasma levels of ferritin, /inc. and retinol have been reported.Pharmacologic doses of vitamins, which function as cofactors to enzymes, are useful in some metabolic disorders.
Phenylketonuria (PKU) is the most common amino acid disorder. In PKl' there is a defect in the enzyme phenylalanine hydroxylase, which converts phenylalanine to tyrosine. The recommended diet is restricted in phenylalanine (substrate) and supplemented with tyrosine (product). Early treatment of PKU prevents severe mental retardation. This diet should be continued for life as learning difficulties and behavioral problems have been reported in children who have discontinued the diet or have poor dietary control.'4 Age-appropriate tasks that help children develop the knowledge and skills necessary to manage their diet successfully as an adult are outlined in Table 31-3.
Pregnant women with PKU who do not follow pheny-lalanine-restricted diets experience an increased incidence of low birth w eight, microcephaly, cardiac anomalies, and
Table 31-3. Developmental Steps Toward Dietary Independence in Phenylketonuria
Toddlers (2-3 years)
Drinks tormula out of a cup Helps prepare formula (pours, stirs) Names foods Knows yes and no foods Asks before eating foods he/she is uncertain of Is aware of difference in diet from family and friends Preschool (4-6 years)
Prepares formula (with assistance) Knows phenylalanine intake is limited Explains PKU diet in simple terms Knows basic reasons for his/her clinic visits Begins to deal with diet restrictions in social situations School age (7-10 years)
Prepares formula (with supervision) Reports foods eaten Takes blood sample with assistance Explains PKU and PKU diet
Knows what blood phenylalanine levels are safe and how to maintain them Makes appropriate diet choices in social situations Adolescence (11+ years)
Prepares formula independently Keeps diet diary independently Calculates daily phenylalanine intake Prepares low-protein recipes Takes blood samples independently Knows the genetics of PKU
Copes with social pressures pertaining to PKU and the PKU diet Understands the issue of maternal PKU
mental retardation in their offspring. These problems are believed to result from the effects of high maternal blood phenylalanine level on the developing fetus and are prevented by a strict phenylalanine-restricted diet implemented prior to conception.
Organic acidemias are inherited enzyme deficiencies affecting the catabolic pathways of amino acids The disorders propionic acidemia and methylmalonic acidemia are caused by defects in the enzymes propionyl-CoA carboxylase and methy Imaloin 1-CoA muíase, respectively. Clinical symptoms of the neonatal form of organic acidemias include vomiting anil dehydration, poor feeding. failure to thrive, hypotonia, metabolic ketoacidosis, and hyperammonemia. Immediate treatment is necessary to correct metabolic unbalances. Information on long-term outcomes is limited. Children show varying degrees of grow th retardation and neurologic impairment.
Long-term nutritional management of organic acidemias involves restricting the offending essential amino acids to the minimum requirement. In propionic acidemia and methylmalonic acidemia, the amino acids isoleucine. methionine, threonine, and valine are restricted, usually through the use of a chemically defined formula supplemented with small amounts of natural protein from standard formulas and table foods. Adequate nonprotein energy is essential to prevent tissue catabolism. Carnitine supplementation is recommended. T he intermittent use of antibiotics helps reduce gut bacteria loads, a major source of endogenous propionate production. Some patients with methylmalonic acidemia respond to pharmacologic doses of vitamin Bi:. Dietary management may be complicated by poor appetite, necessitating nasogastric or gastrostomy lube feedings. Frequent monitoring of growth, laboratory values, and nutrient intake is important.
During illness, acute metabolic decompensation can occur from catabolism of amino acids stored as protein, resulting in metabolic acidosis, hyperammonemia, and ketonuria. Nutritional therapy consists of discontinuing protein, providing adequate calories in the form of glucose to suppress gluconeogenesis. and increasing Huid lo prevent dehydration and assist in removal of abnormal metabolites 111 the urine. Intravenous dextrose or protein-
free formula are used for 24 to 48 hours to lower ammonia levels. Protein is gradually reintroduced. Inadequate energy intake or use of a protein-free diet for more than two days can lead to protein catabolism and rebound ketoacidosis and hyperammonemia. Parenteral nutrition can be used when enteral feedings are not tolerated, with protein supplied through specially formulated amino acid mixtures or with a standard solution providing 0.5 g protein/kg body weight.
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