Rare autosomal recessive metabolic disorders causing a deficiency of enzyme necessary to metabolize galactose, usually discovered when infant is introduced to milk. The most severe type is classic galactosemia I (GALT mutation), characterized by neonatal onset of vomiting, diarrhea, jaundice, failure to thrive, hepatosplenomegaly, fatigue, hypotonia, and cataracts. Patients are predisposed to Escherichia coli sepsis, hemorrhagic diathesis, progressive liver dysfunction, and developmental delay. A small number of non-neonate patients present with tremor, ataxia, apraxia, dysarthria, and primary ovarian insufficiency. A milder variation is galactosemia II (GALK1 mutation). Galactosemia III (GALE mutation) resembles classic galactosemia I.

If untreated, can become life-threatening. Recommended management is discontinuing lactose feeding, treating sepsis infection, addressing hearing, optical, and blood clotting abnormalities, and initiating speech therapy.