In this issue of the Journal, Ficicioglu and colleagues (3) report that children (ages 1-6 years) who have Duarte galactosemia (DG),  a variant form of galactosemia, and are on a standard diet have typical concentrations of red blood cell (RBC) galactose 1-phosphate but increased concentrations of other galactose metabolites.
(3) demonstrated that older children with DG on a regular diet had typical concentrations of RBC galactose 1-phosphate, the galactose metabolite that is most often used to monitor the metabolic status of patients with galactosemia.
Erythrocyte galactose 1-phosphate quantified by isotope-dilution gas chromatography-mass spectrometry.
 Nonstandard abbreviations: DG, Duarte galactosemia; RBC, erythrocyte; Gal-1-P, galactose 1-phosphate. Table 1.
The hepatic and renal manifestations are caused by intracellular accumulation of galactose 1-phosphate, the substrate for GALT.
Galactokinase (GALK) converts galactose to galactose 1-phosphate. GALK deficiency leads to failure to generate the cytotoxic galactose 1-phosphate and therefore does not have the potentially fatal hepatic and renal manifestations.
Typically, the concentrations of red blood cell galactose 1-phosphate and urine galactitol are monitored for this purpose.
 Nonstandard abbreviations: NB, newborn; GALT, galactose-1-phosphate uridyltransferase; Gal, galactose; GALK, galactokinase; GALE, galactose-4-epimerase; D/G galactosemia, Duarte/classic galactosemia; Gal-1-P, galactose 1-phosphate
; PA DOH, Pennsylvania Department of Health.
The defect leads to the accumulation of galactose 1-phosphate
. Transferrin hypoglycosylation in these patients may be attributable to direct inhibition of galactosyltransferase activity by the accumulated galactose 1-phosphate
or to an effect on the formation of UDP-galactose, the donorsubstrate in the reaction (27).
(4) developed a MS/MS method for neonatal screening for galactosemia based on the presence of increased intracellular concentrations of galactose 1-phosphate
. Other studies reported accumulation of ribo-5P in human infant brain (9) and in tumor cells (10).
Galactosemia (OMIM 230400), a life-threatening disorder with severe symptoms in the neonatal period, is caused by deficiency of the enzyme galactose 1-phosphate uridyl transferase (GALT ; EC 220.127.116.11).
Accumulation of galactose 1-phosphate in the galactosemia fetus despite maternal milk avoidance.