What Is Galactosemia?
Galactosemia is a rare genetic disorder affecting approximately 1/60,000 live births. Galactosemia literally means “too much galactose in the blood.” Galactose, a sugar, enters the body through food consumption and the body produces it on its own. The galactose is not broken down correctly because a body with galactosemia is missing an important enzyme. The galactose can become toxic and cause various issues including cataracts, liver issues, mental retardation, tremors, speech issues and more.
Galactosemia is GENETIC, meaning it is a disease caused by a defect in an individual’s DNA. Galactosemia is passed from BOTH father AND mother through genes (see below for more detailed information). Galactosemia is a METABOLIC disorder meaning it involves the process of converting food into energy.
To understand what GALACTOSEMIA is, you first have to understand what GALACTOSE is and how it works in the human body. Galactose is a sugar that enters the body through food consumed and is produced by the body on its own (called endogenous galactose). The human body uses sugar, both consumed and endogenous, to make energy. All the sugar in our bodies is broken down by different sets of enzymes and then converted into glucose, the main sugar in our blood.
In a body that does NOT have galactosemia, the process for converting galactose into glucose (so the body can use it for energy) involves 3 enzymes: galactokinase, galactose-1-phosphouridyl transferease (GALT) and UDP-gal-4-epimerase. Galctokinase works first to break galactose down into galactose-1-phosphate (Gal-1-P). Next, the other 2 enzymes break the Gal-1-P into smaller parts. GALT breaks the Gal-1-P into glucose-1-phosphate and UDP-gal-4-epimerase breaks it down into UDP-galactose. Now the galactose can be used as energy in the form of glucose.
A body that has GALACTOSEMIA is missing the GALT enzyme, making the above process incomplete and hindering galactose from being converted into glucose. The first enzyme, galactokinase, breaks the galactose into galactose-1-phosphate (Gal-1-P), but the gal-1-p never gets converted into glucose (energy) because the GALT isn’t there to do its job. Therefore, in the body of one with galactosemia, gal-1-p builds up becoming toxic and causing a range of issues.
HOW IS GALACTOSEMIA DIAGNOSED AND WHAT ARE ITS SYMPTOMS?
All 50 states in the U.S. conduct a Newborn Screening looking for several different disorders. Thankfully, galactosemia is one of them. This test is often referred to as the “PKU test” (after one of the other disorders being screened) or the “heel prick” (because the baby’s heel is pricked as a way of collecting a small blood sample). If there is an indication the baby could have galactosemia, he/she is referred to a pediatric geneticist for further testing. The geneticist will generally perform a more precise blood test to confirm or deny the screening results. A positive diagnosis is given from the geneticist after the additional test. The newborn screen itself is NOT a solid diagnostic tool. It is possible to have a positive screen, but actualy NOT have galactosemia. For those parents who know they are carriers, prenatal diagnosis by amniocentesis is also available.
Symptoms of galactosemia are seen almost immediately when initiating breast or bottle feeding (if using a lactose-based formula). These typically include vomiting, rapid weight loss, enlarged liver, sepsis, lethargy and jaundice. Without the proper diet, 75% of babies die within the first 2 weeks of birth. This is why the newborn screening is so important. The sooner families know the baby may have galactosemia, the sooner the correct nourishment (a soy or elemental based formula) can be started and major complications can be avoided.
HOW IS GALACTOSEMIA TREATED?
Currently, the only treatment for galactosemia is a restricted diet. Cows milk products and breast milk should be avoided because they contain high levels of galactose and can cause complications for the patient with galactosemia. Please see the “Dietary Resources” page on this website for more detailed information. The dietary resources page includes a link to the latest dietary guide, Understanding Galactosemia: A Dietary Guide.
HOW IS GALACTOSEMIA INHERITED?
The human body is made up of thousands of sets of genes that carry information like skin and eye color. We get 1/2 of our genes from our mother and a matching 1/2 from our father. Genes are found on our chromosomes which are in every cell in our body.
We all have genes that are abnormal in some way; either mutated or missing. In the case of galactosemia, the gene that contains information about GALT is mutated or missing. Galactosemia is generally passed down from parents who have one working GALT gene and one mutated or missing GALT gene (making the parent a “carrier” of galactosemia). The parent is able to process galactose appropriately with their working “GALT gene” so they do NOT have galactosemia, but carry it and can pass it to their children. When the mutated or missing GALT gene is passed to the baby from BOTH the mother and father, the baby has galactosemia. If only ONE parent passes the mutated or missing GALT gene, the child is a “carrier” but does NOT have galactosemia. The child must inherited TWO mutated or missing GALT genes to have galactosemia. This is why galactosemia is rare!