Galactosemia
Galactosemia is a rare genetic disorder characterized by the body's inability to properly metabolize galactose, a sugar commonly found in milk and dairy products. This condition stems from a deficiency in the enzyme galactose-1-phosphate uridyl transferase (GALT), which leads to the accumulation of galactose in the blood and various tissues, causing potentially toxic effects. The disorder is inherited in an autosomal recessive manner, meaning that both parents must be carriers for a child to be affected, with an estimated incidence of one in forty thousand newborns. Symptoms typically emerge shortly after birth and can include jaundice, vomiting, an enlarged liver, cataracts, and failure to thrive, with severe cases leading to intellectual disability or death if left untreated.
Management of galactosemia focuses on dietary modification, specifically the complete avoidance of foods containing galactose, particularly dairy products. Although a completely galactose-free diet is not feasible, individuals with the condition should maintain a very low galactose intake, tailored to their specific enzyme activity levels. Regular monitoring and consultations with a dietician are essential for effective dietary management, ensuring that potential health complications are mitigated. Early diagnosis through newborn screening is crucial for preventing serious health issues associated with this metabolic disorder.
On this Page
Subject Terms
Galactosemia
Anatomy or system affected: Eyes, liver
Definition: An inherited disorder of carbohydrate metabolism in which an infant is unable to utilize galactose from food
Causes: Genetic enzyme deficiency
Symptoms: Varies; may include jaundice, vomiting, liver enlargement, cataracts, failure to thrive, and mental problems if foods containing galactose (milk sugar) are eaten
Duration: Chronic
Treatments: Avoidance of foods containing galactose
Causes and Symptoms
In classic I galactosemia, a congenital deficiency of the enzyme galactose-1-phosphate uridyl transferase (GALT) causes galactose to accumulate instead of being converted to glucose for energy production. As galactose accumulates in the child’s tissues and organs, it will have a toxic effect and cause various signs and symptoms. Galactosemia means “galactose in the blood.” Galactose is a sugar that may be found alone in foods but is usually associated with lactose, a milk sugar.
A gene mutation on the short arm of chromosome 9 has been identified in babies with galactosemia. About one in forty thousand newborns is affected with this autosomal recessive disorder. Both parents serve as carriers; they are not themselves affected, but each conception carries a one in four chance that the child will be born with galactosemia. Prenatal diagnosis is possible in cultured fibroblasts from amniotic fluid. Mandatory screening programs in many states test all newborns for galactosemia during the first week of life.
Galactosemia is an example of a multiple-allele system. In addition to the normal allele (G) and the recessive allele (g), a third allele, known as GD, has been found. The D allele is named after Duarte, California, where it was discovered. The existence of three alleles produces six possible genotypic combinations in the deoxyribonucleic acid (DNA). These enzymatic activities may range from 0 to 100 percent. Consequently, it is very important to monitor each patient with biochemical studies.
Homozygous recessive infants (gg) are unaffected at birth but develop symptoms a few days later, including jaundice, vomiting, an enlarged liver from extensive fatty deposits, cataracts, and failure to thrive. Mental retardation and death may also occur if dietary treatment has not been started.
Treatment and Therapy
Galactosemia is treated by removing foods that contain galactose from the diet. Since milk and milk products are the most common source of galactose, infants with galactosemia should not be given these foods. Serious problems can be prevented through this early exclusion of galactose.
While it is not possible for a child with galactosemia to have an entirely galactose-free diet, all persons with galactosemia should limit galactose intake from foods to a very low level. The galactose-1-phosphate levels determine the degree of dietary restriction for each individual. Advice from a dietician is needed.
Bibliography
Badash, Michelle. "Galactosemia." Health Library, November 26, 2012.
Berry, Gerard T. "Galactosemia: When is it a Newborn Screening Emergency?" Molecular Genetics & Metabolism 106, no. 1: 7–11.
Cummings, Michael R. Human Heredity: Principles and Issues. 8th ed. Pacific Grove, Calif.: Brooks/Cole, 2009.
"Galactosemia." MedlinePlus, May 1, 2011.
Icon Health. Galactosemia: A Medical Dictionary, Bibliography, and Annotated Research Guide to Internet References. San Diego, Calif.: Author, 2004.
Kasper, Dennis L., et al., eds. Harrison’s Principles of Internal Medicine. 16th ed. New York: McGraw-Hill, 2005.
Rudolph, Colin D., et al., eds. Rudolph’s Pediatrics. 21st ed. New York: McGraw-Hill, 2003.
Succoio, M., et.al. "Galactosemia: Biochemistry, Molecular Genetics, Newborn Screening, and Treatment." Biomolecules, vol. 12, no. 7, p. 968, 11 July 2022, doi.org/10.3390%2Fbiom12070968. Accessed 1 Aug. 2023.