Galactosemia is a rare genetic disorder where galactose (a by-product of lactose digestion) fails to convert to glucose.
Lactose is one of the main carbohydrate components present in milk. In the infant intestine, this lactose is broken down into glucose and galactose, which are then used as a source of energy.
In healthy babies, galactose is further metabolized and converted to glucose via a series of enzymatic reactions, one of which involves the enzyme galactose-1-phosphate uridyl transferase (GALT).
In galactosemia, this enzyme is either defective or missing. When this happens, an infant is unable to convert the galactose into glucose, which causes galactose to accumulate in the blood. This can lead to serious problems such as liver enlargement, kidney failure, brain damage and cataracts. Left untreated, this condition kills up to 75% of sufferers.
As milk is the staple diet for babies, the condition needs to be diagnosed as soon as possible to improve the child’s chances of survival.
Causes of galactosemia
Galactosemia is caused by a mutation in the gene that codes for the GALT enzyme. The condition is inherited in an autosomal recessive manner, which means a child only develops the condition if they inherit two abnormal copies of the GALT gene, one from each of their parents.
Each child born to carrier parents has a 50% chance of inheriting one defective gene and also being a carrier; a 25% chance of inheriting both defective copies and developing the condition themselves, and a 25% chance of not inheriting a defective gene, meaning they neither develop the condition or become a carrier.
Prenatal tests can be performed to check for galactosemia as early on as the 15th to 16th week of pregnancy. However, the condition is usually first detected through a heel prick test that is performed 72 hours after birth as part of newborn screening.
The condition is managed by feeding infants on a diet that is free of lactose and galactose. This helps to prevent complications such as liver and kidney damage, although some individuals still go on to develop long-term complications.
Reviewed by Sally Robertson, BSc