In this metabolic pathway, galactose is taken up by galactose permease (Gal2p) and converted into glucose-6-phosphate by the actions of galactokinase (Gal1p), galactose-1-phosphate
uridylyltransferase (Gal7p), UDP-galactose-4-epimerase (Gal10p) and phosphoglucomutase.
Classic galactosemia is an autosomal recessive disorder of carbohydrate metabolism caused by a severe deficiency of the enzyme galactose-1-phosphate
When the enzyme is absent, an infant cannot metabolize galactose-1-phosphate
and it cumulates in liver, kidney, brain, tongue, lens, and skin.
D-gal is first converted to galactose-1-phosphate
(gal-1-P) by galactokinase (GALK).
Unfortunately, despite dietary restriction of galactose intake, some patients with GALT deficiency eventually show persistent increases in erythrocyte concentration of galactose-1-phosphate
and in the excretion of urinary galactitol (10).
The metabolism of galactose involves 3 enzymes of the Leloir pathway, galactokinase (GALK, EC 220.127.116.11), galactose-1-phosphate
uridylyltransferase (GALT, EC18.104.22.168), (4) and uridine diphosphate galactose-4'epimerase (GALE, EC 22.214.171.124).
The most common form of this disease is caused by galactose-1-phosphate
uridyltransferase (GALT) enzyme activity deficiency and is often referred to as classic galactosaemia.
The urine showed 4+ galactose and the red cells showed reduced galactose-1-phosphate
uridyl transferase (GALT) activity.
They undergo monitoring of galactose-1-phosphate
levels, have regular eye exams to look for cataracts, and are referred to endocrinologists.
These 13 children included nine with positive screening test results for congenital hypothyroidism, two with classic galactosemia (galactose-1-phosphate
uridyl transferase deficiency), one with maple syrup urine disease (MSUD), and one with tyrosinuria.
The most serious of the three types of galactosemia occurs with the absence or near absence of galactose-1-phosphate
uridyl transferase (GALT), the enzyme responsible for the second phase of galactose metabolism (see Figure 1).
The red blood cell levels of galactose or its metabolites (Galactose-1-phosphate
) may be used as a monitor to gauge the adherence to the d iet and restriction of galactose.