Why Lactase Cannot Be Used in Classic Galactosemia
Lactase supplementation is absolutely contraindicated in classic galactosemia because lactase breaks down lactose into glucose and galactose, and patients with GALT enzyme deficiency cannot metabolize the resulting galactose, leading to toxic accumulation of galactose-1-phosphate that causes life-threatening liver failure, sepsis, and death. 1, 2
The Fundamental Problem with Lactase
Lactase enzyme cleaves lactose (milk sugar) into its two component monosaccharides: glucose and galactose. 3
In classic galactosemia, the GALT enzyme (galactose-1-phosphate uridyltransferase) is profoundly deficient or absent, preventing conversion of galactose-1-phosphate to UDP-galactose in the Leloir pathway. 1
Taking lactase would actually worsen the condition by liberating free galactose from lactose, making it immediately available for absorption and subsequent toxic accumulation. 1, 4
The Toxic Cascade
When galactose enters the body of a patient with classic galactosemia, it is phosphorylated to galactose-1-phosphate by galactokinase (the first enzyme in the pathway, which remains functional). 1
Without functional GALT enzyme, galactose-1-phosphate accumulates to toxic levels in tissues, particularly the liver, brain, and kidneys. 3, 4
This accumulation causes the acute life-threatening manifestations: failure to thrive, hepatocellular insufficiency progressing to liver failure with jaundice and coagulopathy, E. coli sepsis (particularly in the first week of life), and renal tubular dysfunction. 2, 4
Why Complete Galactose Elimination Is Required
The only effective treatment for classic galactosemia is immediate and lifelong dietary restriction of all galactose sources, with complete elimination of galactose as soon as the diagnosis is suspected. 2, 3
After the neonatal period, a lactose-free diet is maintained, though some countries allow galactose-containing fruits and vegetables in small amounts. 3
Lactase supplementation would directly contradict this therapeutic principle by generating the exact substrate (galactose) that must be eliminated. 1, 2
Clinical Context and Common Pitfall
A critical pitfall to avoid: lactase is sometimes recommended for lactose intolerance in the general population, but this recommendation is dangerous and potentially lethal in galactosemia patients. 4
Classic galactosemia is a medical emergency requiring immediate galactose restriction to prevent death from sepsis and liver failure. 4, 2
Even with strict dietary galactose restriction, long-term complications including mental retardation, verbal dyspraxia, motor abnormalities, and hypergonadotrophic hypogonadism frequently occur, possibly due to endogenous galactose synthesis or abnormal galactosylation. 3, 5
The severity of classic galactosemia (occurring in approximately 1:53,554 newborns in the United States) makes any galactose exposure potentially catastrophic. 1