Clinical meaning
Galactosemia is an autosomal recessive inborn error of metabolism in which the body cannot properly metabolize galactose, a simple sugar that is a component of lactose (the primary carbohydrate in breast milk and cow's milk formula). Lactose is a disaccharide composed of glucose and galactose; it is broken down by the enzyme lactase in the small intestine into its two component monosaccharides. In normal metabolism, free galactose undergoes a three-step enzymatic conversion known as the Leloir pathway to ultimately be converted to glucose-1-phosphate, which can enter glycolysis for energy production. The three enzymes in this pathway are galactokinase (GALK), galactose-1-phosphate uridylyltransferase (GALT), and UDP-galactose-4-epimerase (GALE). Classic galactosemia, the most severe form, results from a deficiency of the GALT enzyme due to mutations in the GALT gene on chromosome 9p13. When GALT is deficient or absent, galactose-1-phosphate and galactitol (an alternative metabolite produced by aldose reductase) accumulate in tissues throughout the body, producing toxic effects on multiple organ systems. In the liver, galactose-1-phosphate accumulation causes hepatocellular damage leading to hepatomegaly, jaundice, and potentially cirrhosis and liver failure. The accumulation inhibits glucose metabolism by depleting hepatic phosphate and uridine diphosphate, further compromising cellular energy production. In the eyes, galactitol accumulates in the lens through the action of aldose reductase, creating an osmotic gradient that draws water into the lens fibers, causing swelling and opacification -- resulting in bilateral cataracts that can develop within the first few weeks of life. In the brain, galactose-1-phosphate and galactitol interfere with normal myelination and neurotransmitter production, leading to developmental delays and intellectual disability if treatment is delayed. In the kidneys, galactose-1-phosphate disrupts proximal tubular function, producing a Fanconi-like syndrome with aminoaciduria, proteinuria, and galactosuria. Classic galactosemia occurs in approximately 1 in 30,000 to 60,000 live births. Newborn screening programs in all Canadian provinces and US states test for galactosemia using the Beutler fluorescent spot test (which measures GALT enzyme activity in dried blood spots) and/or measurement of total galactose levels. A positive screening result requires immediate intervention: cessation of all lactose-containing feeds and initiation of soy-based or elemental formula. Even with early treatment and lifelong dietary restriction, many individuals with classic galactosemia experience long-term complications including speech and language delays, learning disabilities, motor coordination difficulties, ovarian insufficiency in females (premature ovarian failure occurs in approximately 80-90% of affected females), and decreased bone mineral density. The practical nurse must understand the urgency of dietary intervention, the importance of newborn screening follow-up, and the long-term monitoring needs of affected children.