Recently, evidence has been presented that adult patients with classical galactosemia
have higher than expected galactose tolerance. This may be caused by a decrease of
endogenous galactose production with ageing. Alternatively, suppression of endogenous
galactose production by exogenous galactose might be implicated. The aim of this study
was to determine if the rate of appearance of galactose is suppressed by exogenous
galactose.
Two adult patients with classical galactosemia and three healthy control subjects
were given a primed continuous infusion of D-[1-13C]galactose to determine the rate
of appearance of galactose (GAR, expressed as micromol/kg/h) before and during additional
galactose supplementation. After initial assessment of GAR (GAR1), GAR was determined
during doubled (GAR2) or quadrupled (GAR4) galactose infusion.
GAR1 was 2.48 and 2.44 in patients 1 and 2, and 0.46, 0.34, and 0.39 in control subjects
1, 2, and 3, respectively. GAR(2) was 2.43 and 2.13 in patients 1 and 2, and 0.57,
0.38, and 0.47 in control subjects 1, 2, and 3, respectively. In patient 1 the experiment
was repeated during quadrupled galactose infusion. Here GAR1 was 3.01 and GAR4 was
3.26.
No significant differences between GAR before and during additional galactose infusion
were found in patients and in control subjects. GAR1 was significantly higher in patients
than in control subjects. We conclude that the rate of appearance of galactose is
not influenced by exogenous galactose, at least under short-term conditions, in patients
with classical galactosemia and in control subjects.