What's Really Happening
People with Galactosemia have a missing or inactive enzyme that is needed to correctly process galactose. Galactose is then converted into a toxic substance called galactitol.
Normally, an enzyme called GALK turns galactose into another substance, galactose-1-phosphate (Gal-1p).
Everbody makes Gal-1p. However, people with Galactosemia will experience an excess build-up of Gal-1p. This is because they are missing a key enzyme called GALT, which is needed to process Gal-1p. Gal-1p is important in the monitoring of Galactosemia.
Children and adults with Galactosemia have high levels of Gal-1p in their blood. After an infant has been diagnosed with Galactosemia, their doctor may do a blood test to see how much Gal-1p is in their blood. Once a child with Galactosemia has been on a Galactosemia-friendly diet, their doctor may check their blood again periodically to see how the Gal-1p levels have changed.
Although Gal-1p is monitored, there is no evidence that it directly causes health issues that people with Galactosemia may experience.
Because people with Galactosemia cannot complete the process of metabolizing Gal-1p, excess galactose backs up and is abnormally converted by an enzyme called Aldose Reductase through another pathway that is not usually involved. Then, this enzyme turns galactose into toxic galactitol.
Galactitol is harmful to the body. It has been shown that galactitol can build up in the blood, tissues, and organs, including the brain. Using magnetic resonance spectroscopy (MRS) technology, researchers can see build-up of galactitol in the brain.
There is evidence that toxic galactitol is responsible for a range of health issues that people with Galactosemia may experience, including:
Cognitive and developmental delays
This is important to understand because galactitol is harmful to people living with Galactosemia.
Galactosemia is a genetic condition, meaning that it is passed down through a child's parents.
When a baby is conceived, it receives genes from each parent, creating thousands of pairs of genes that determine things like the color of their eyes and hair. There is also a gene pair that enables the production of an enzyme that helps our bodies process galactose—this is the GALT gene.
Galactosemia occurs when each of the infant's parents carry one form of the gene that makes a working GALT enzyme and one nonworking gene that does not make the GALT enzyme. When a child inherits a nonworking form of the GALT gene from both parents to form a nonworking GALT gene pair, their GALT enzyme will not work as it should and causes Galactosemia. This kind of genetic inheritance is known as "autosomal recessive" inheritance.
GALT mutation analysis
Done to determine the genetic code changes in the GALT gene. Figuring out the type of mutation helps confirm whether the GALT enzyme is missing or to what degree it is functioning.
GALT enzyme activity
Confirms the amount of GALT enzyme activity present in red blood cells—the less GALT enzyme you have, the less you are able to process galactose into energy for the body.