Galactosemia is any disorder of galactose metabolism. It produces symptoms ranging from cataracts and liver damage to mental retardation and occurs in two forms: classic galactosemia and galactokinase-deficiency galactosemia. Although a galactose-free diet relieves most symptoms, galactosemia-induced mental impairment is irreversible; some residual vision impairment may also persist.
Both forms of galactosemia are inherited as autosomal recessive defects and occur in about 1 in 60,000 births in the United States. Up to 1.25% of the population is heterozygous for the classic galactosemia gene. Classic galactosemia results from a defect in the enzyme galactose-1-phosphate uridyl transferase. (See Metabolic pathway in galactosemia.) Galactokinase-deficiency galactosemia, the rarer form of this disorder, stems from a deficiency of the enzyme galactokinase. In both forms of galactosemia, the inability to normally metabolize the sugar galactose (which is mainly formed by digestion of the disaccharide lactose that’s present in milk) causes galactose accumulation.
In children who are homozygous for the classic galactosemia gene, signs are evident at birth or begin within a few days after milk ingestion, and include failure to thrive, vomiting, and diarrhea. Other clinical effects include liver damage (which causes jaundice, hepatomegaly, cirrhosis, and ascites), splenomegaly, galactosuria, proteinuria, and aminoaciduria. Cataracts may also be present at birth or develop later. Pseudotumor cerebri may occur.
Continued ingestion of galactose- or lactose-containing foods may cause mental retardation, malnourishment, progressive hepatic failure, and death — from the still-unknown process of galactose metabolites accumulating in body tissues. Although treatment may prevent mental impairment, galactosemia can produce a short attention span, difficulty with spatial and mathematical relationships, and apathetic, withdrawn behavior. Cataracts may be the only sign of galactokinase deficiency, resulting from the accumulation of galactitol, a metabolic by-product of galactose, in the lens.
Related laboratory results include increased galactose levels in blood (normal value in children is less than 20 mg/dl) and urine (must use galactose oxidase to avoid confusion with other reducing sugars). Galactose measurements in blood and urine must be interpreted carefully be-cause some children who consume large amounts of milk have elevated plasma galactose concentrations and galactosuria but aren’t galactosemic. Also, neonates excrete galactose in their urine for about a week after birth; premature infants, even longer.
Other test results include:
❑ liver biopsy: typical acinar formation
❑ liver enzymes (aspartate aminotransferase, alanine aminotransferase levels): elevated
❑ urinalysis: albumin in urine
❑ ophthalmoscopy: punctate lesions in the fetal lens nucleus (with treatment, cataracts regress)
❑ amniocentesis: prenatal diagnosis of galactosemia (recommended for heterozygous and homozygous parents).
Elimination of galactose and lactose from the diet causes most effects to subside. The infant is fed soy formula, meat-base formula, protein hydrolysate formula, or another lactose-free formula. The infant gains weight; liver anomalies, nausea, vomiting, galactosemia, proteinuria, and aminoaciduria disappear; and cataracts regress. As the child grows, a balanced, galactose-free diet must be maintained. A pregnant woman who’s heterozygous or homozygous for galactosemia should also follow a galactose-restricted diet. Such a diet supports normal growth and development and may delay symptoms in the neonate.
❑ To eliminate galactose and lactose from an infant’s diet, replace cow’s milk formula or breast milk with a meat-base or soybean formula.
❑ Teach the parents about dietary restrictions and stress the importance of compliance. (See Diet for galactosemia, page 892.) Warn them to read medication labels carefully and avoid giving any medication that contains lactose fillers.
❑ If the child has a learning disability, help parents secure educational assistance. Refer parents who want to have other children for genetic counseling. In some states, screening of all neonates for galactosemia is required by law.
❑ Instruct the parents to contact support groups, such as Parents of Galactosemic Children, for further information and support if appropriate.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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Title: Professional Guide to Diseases (Eighth Edition)
Authors: Springhouse
Publisher: Lippincott Williams & Wilkins
Copyright: 2005
ISBN: 1-58255-370-X
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