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Galactosemia is an autosomal recessive disorder that results from a deficiency of any 1 of the 3 enzymes catalyzing the conversion of galactose to glucose: galactose-1-phosphate uridyltransferase (GALT), galactokinase (GALK), and uridine diphosphate galactose-4-epimerase (GALE). GALT deficiency is the most common cause of galactosemia and is often referred to as classic galactosemia. The complete or near-complete deficiency of GALT enzyme is life-threatening if left untreated. Complications in the neonatal period include failure to thrive, liver failure, sepsis, and death; even with survival, long-term intellectual disability can result.
Galactosemia is treated by a galactose-restricted diet, which allows for rapid recovery from the acute symptoms and a generally good prognosis. Despite adequate treatment from an early age, individuals with galactosemia remain at increased risk for developmental delays, speech problems, and abnormalities of motor function. Females with galactosemia are at increased risk for premature ovarian failure. Based upon reports by newborn screening programs, the frequency of classic galactosemia in the United States is approximately 1 in 30,000, although literature reports range from 1 in 10,000 to 1 in 60,000 live births.
A comparison of plasma and urine galactose and blood galactose-1-phosphate (Gal-1-P) levels may be useful in distinguishing among the 3 forms of galactosemia; however, these are only general patterns and further confirmatory testing would be required to make a diagnosis.
For more information regarding diagnostic strategy, refer to Galactosemia: Current Testing Strategy and Aids for Test Selection, Mayo Medical Laboratories Communique 2005 May;30(5).
See Galactosemia Testing Algorithm in Special Instructions for additional information.
Screening test for galactosemia
Additional testing is required to investigate the cause of abnormal results.
In patients with galactosemia, elevated galactose in plasma or urine may suggest ineffective dietary restriction or compliance; however, the concentration of galactose-1-phosphate in erythrocytes (GAL1P / Galactose-1-Phosphate [Gal-1-P], Erythrocytes) is the most sensitive index of dietary control. Increased concentrations of galactose may also be suggestive of severe hepatitis, biliary atresia of the newborn, and, in rare cases, galactose intolerance.
If galactosemia is suspected, additional testing to identify the specific enzymatic defect is required. See Galactosemia Testing Algorithm in Special Instructions for follow-up of abnormal newborn screening results, comprehensive diagnostic testing, and carrier testing. See GALT / Galactose-1-Phosphate Uridyltransferase (GALT), Blood for GALT testing and GALK / Galactokinase, Blood for GALK testing, and GALE / UDP-Galactose 4' Epimerase (GALE), Blood for GALE testing. Results should be correlated with clinical presentation and confirmed by specific enzyme or molecular analysis.
This test is not recommended for follow-up of positive newborn screening results. For this purpose GAL1P / Galactose-1-Phosphate (Gal-1-P), Erythrocytes and GCT / Galactosemia Reflex Test, Blood are the most appropriate tests.
The preferred test for monitoring dietary therapy is GAL1P / Galactose-1-Phosphate (Gal-1-P), Erythrocytes.
1. Berry GT: Classic Galactosemia and Clinical Variant Galactosemia. In GeneReviews. Edited by RA Pagon, MP Adam, HH Ardinger, et al. Available at: http://www.ncbi.nlm.nih.gov/books/NBK1518/. Retrieved 03/11/2015
2. Walter JH, Fridovich-Keil JL: Galactosemia. In The Metabolic and Molecular Bases of Inherited Disease. Edited by Valle D, Beaudet AL, Vogelstein B, et al. New York, McGraw-Hill, 2014. Accessed January 26, 2016. Available at: http://ommbid.mhmedical.com/content.aspx?bookid=971&Sectionid=62672411