Classic Galactosemia and Clinical Variant Galactosemia

In: GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993–2020.
[updated ].


Clinical characteristics: The term "galactosemia" refers to disorders of galactose metabolism that include classic galactosemia, clinical variant galactosemia, and biochemical variant galactosemia. This GeneReview focuses on:

Diagnosis/testing: The diagnosis of classic galactosemia and clinical variant galactosemia is established by detection of elevated erythrocyte galactose-1-phosphate concentration, reduced erythrocyte galactose-1-phosphate uridylyltranserase (GALT) enzyme activity, and/or biallelic pathogenic variants in GALT. In classic galactosemia, erythrocyte galactose-1-phosphate is usually higher than 10 mg/dL and erythrocyte GALT enzyme activity is absent or barely detectable. In clinical variant galactosemia, erythrocyte GALT enzyme activity (which may be absent or barely detectable, as in African Americans) is much higher in brain and intestinal tissue (e.g., 10% of control values). Other individuals with clinical variant galactosemia may have erythrocyte GALT enzyme activity close to or above 1% of control values but probably never above 10%-15%. Virtually 100% of infants with classic galactosemia or clinical variant galactosemia can be detected in newborn screening programs that include testing for galactosemia in their panel. However, infants with clinical variant galactosemia may be missed if the program only measures blood total galactose level and not erythrocyte GALT enzyme activity.

Management: Prevention of primary manifestations: Standard of care in any newborn who is "screen-positive" for galactosemia is immediate dietary intervention while diagnostic testing is under way. If erythrocyte galactose-1-phosphate concentration is >10 mg/dL and erythrocyte GALT enzyme activity is ≤10% of control activity (i.e., the child has classic galactosemia or clinical variant galactosemia), restriction of galactose intake is continued and all milk products are replaced with lactose-free formulas (e.g., Isomil® or Prosobee®) containing non-galactose carbohydrates; management of the diet becomes less important after infancy and early childhood. Treatment of manifestations: In rare instances, cataract surgery may be needed in the first year of life. Childhood apraxia of speech and dysarthria require expert speech therapy. Developmental assessment at age one year by a psychologist and/or developmental pediatrician is recommended in order to formulate a treatment plan with the speech therapist and treating physician. For school-age children, an individual education plan and/or professional help with learning skills and special classrooms as needed. Hormone replacement therapy as needed for delayed pubertal development and/or primary or secondary amenorrhea. Prevention of secondary complications: Recommended calcium, vitamin D, and vitamin K intake to help prevent decreased bone mineralization. Surveillance: Routine monitoring for: the accumulation of toxic analytes (e.g., erythrocyte galactose-1-phosphate and urinary galactitol); cataracts; speech and development; POI; and osteoporosis. Agents/circumstances to avoid: Breast milk, proprietary infant formulas containing lactose, cow's milk, dairy products, and casein or whey-containing foods; medications with lactose and galactose. Pregnancy management: Women with classic galactosemia should maintain a lactose-restricted diet during pregnancy. Evaluation of relatives at risk: To allow for earliest possible diagnosis and treatment of at-risk sibs:

Genetic counseling: Classic galactosemia and clinical variant galactosemia are inherited in an autosomal recessive manner. Couples who have had one affected child have a 25% chance of having an affected child in each subsequent pregnancy. Molecular genetic carrier testing for at-risk sibs and prenatal diagnosis for pregnancies at increased risk are an option if the GALT pathogenic variants in the family are known. If the GALT pathogenic variants in a family are not known, prenatal testing can rely on assay of GALT enzyme activity in cultured amniotic fluid cells.

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