Biochemical expression of the galactosemic defect in lymphocytes and the effects on glycoprotein synthesis

Incorporation of radioactive galactose, fucose, mannose, glucosamine, and N-acetylmannosamine into acid-precipitable glycoproteins of purified peripheral blood lymphocytes froom three patients with congenital galactosemia, their healthy parents, and control subjects have been measured. In the galactosemic lymphocytes, the incorporation of galactose into acid-precipitable glycoproteins was less than 7% of values obtained with controls and the presumed heterozygotes. The incorporation of other sugars into the glycoprotein fraction did not differ significantly from normal. Attempts to demonstrate a deficiency in cell-surface galactose groups proved negative. Galactosemic lymphocytes responded well to galactose-binding mitogens and were fully sensitive to a galactose-binding toxic lectin. We conclude that a defect in the galactose-1-phosphate uridyl transferase pathway to uridine diphosphate-galactose does not affect appreciably normal carbohydrate chain assembly in galactosemic lymphocytes. However, we cannot rule out minor changes which might account for the decreased responsiveness to serotonin in an experimental animal model of galactosemia. The approaches used in this paper may be useful in detecting other inborn errors of carbohydrate metabolism.