Galactosemia is a rare genetic disorder that causes an inability to digest galactose, which is a breakdown product of lactose.
Lactose is one of the main carbohydrates in milk. In the infant intestine, this lactose is broken down into glucose and galactose, which are then used as a source of energy. The galactose is further converted to glucose via a series of enzymatic reactions.
One of the enzymes involved is galactose-1-phosphate uridyl transferase (GALT) and 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 as many as 75% of sufferers.
As milk is the staple diet for babies, the condition needs to be diagnosed as soon as possible to improve the chance of survival.
Galactosemia affects around 1 in every 60,000 infants of European origin. The condition is caused by a mutation in the gene that codes for the GALT enzyme.
Galactosemia is inherited in an autosomal recessive manner, which means a child only develops the condition if they inherit an abnormal copy of the GALT gene from each of their parents.
Therefore, each child born to carrier parents has a 50% chance of being born a carrier of the condition, a 25% chance of developing the condition and a 25% chance of neither developing or carrying the condition.
Most babies born with galactosemia do not present with symptoms initially but jaundice, diarrhea and vomiting soon develop. The baby fails to thrive and may lose weight.
If the condition is not detected and treated early, infants eventually develop serious conditions such as liver disease, brain damage and are even at risk of dying.
Diagnosis and treatment
Prenatal tests can be performed to check for galactosemia as early on as in the 15th to 16th week of pregnancy. The condition is usually first detected through a heel prick test performed 72 hours after birth as part of newborn screening.
The condition is managed by feeding infants on a diet that is lactose and galactose free. 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