GALT disease, formally known as classic galactosemia, is a rare genetic condition where the body cannot properly break down galactose, a sugar found in milk and many other foods. It affects roughly 1 in 35,000 newborns in the United States. Without early detection and dietary changes, GALT disease can be fatal in the first weeks of life.
The name comes from the GALT enzyme (galactose-1-phosphate uridylyltransferase), which is missing or barely functional in people with this condition. Newborn screening programs in all 50 states now test for it, meaning most cases are caught before serious damage occurs.
How the GALT Enzyme Works
Your body uses a series of chemical steps called the Leloir pathway to convert galactose into glucose, a sugar your cells can use for energy. The GALT enzyme handles the second step in this process: it transforms galactose-1-phosphate into glucose-1-phosphate. Think of it as a critical relay in a chain. When the GALT enzyme is missing or nearly inactive, galactose-1-phosphate builds up to toxic levels in the blood, liver, brain, and other organs.
In classic galactosemia, GALT enzyme activity is less than 1% of normal. A milder form called clinical variant galactosemia has enzyme activity between roughly 1% and 10%. There is also a much milder condition called Duarte galactosemia, where enzyme activity sits around 15% to 33% of normal. Duarte galactosemia is far more common (the underlying gene variant is present in about 5% of the U.S. population) and is generally considered benign, especially after infancy.
Symptoms in Newborns
Signs of classic galactosemia typically appear within the first few days of life, once a newborn starts feeding on breast milk or standard formula, both of which contain lactose (a sugar that breaks down into galactose and glucose during digestion). Early symptoms include:
- Poor feeding and vomiting
- Jaundice (yellowing of the skin and eyes)
- Lethargy (unusual sleepiness, low energy)
- Failure to thrive (slow weight gain or poor growth)
- Diarrhea
- E. coli sepsis (a serious bloodstream infection)
E. coli sepsis in particular is a hallmark of undiagnosed galactosemia in newborns and can be life-threatening. If lactose is not removed from the diet promptly, damage to the liver, kidneys, and brain can escalate rapidly.
Genetics and Inheritance
GALT disease is inherited in an autosomal recessive pattern, meaning a child must receive one faulty copy of the GALT gene from each parent. Parents who carry one faulty copy and one working copy are unaffected carriers.
Several specific gene mutations account for most cases. The most common is called Q188R, responsible for 54% to 70% of classic galactosemia gene copies worldwide. Among African Americans, a different mutation called S135L is the most frequent, accounting for about 50% of the faulty gene copies in that population. A third mutation, K285N, is more common in people of Eastern European descent, making up around 8% of European cases. These different mutations can influence disease severity, though all produce the classic form when two copies are present.
How It Is Diagnosed
Most cases are identified through newborn screening, which uses a blood sample taken from the baby’s heel within the first day or two of life. The screening measures GALT enzyme activity and may also measure levels of galactose or galactose-1-phosphate in the blood.
A confirmed diagnosis requires a combination of findings: elevated galactose-1-phosphate in red blood cells (normally below 1 mg/dL, but usually above 10 mg/dL in classic galactosemia), very low or undetectable GALT enzyme activity, and often genetic testing to identify the specific mutations involved. Infants whose enzyme activity falls at or below 10% of normal with elevated galactose-1-phosphate need immediate dietary intervention.
Dietary Management
The primary treatment for GALT disease is a strict lifelong restriction of galactose in the diet. This means eliminating all dairy milk, cheese, yogurt, butter, and cream. Infants are switched to soy-based formula immediately after diagnosis.
The restrictions go beyond obvious dairy products. Galactose hides in many processed foods. Margarine, for instance, is considered unacceptable when listed as an ingredient in packaged foods. Hydrolyzed protein, commonly found in canned meats like tuna, is also off-limits (though hydrolyzed vegetable protein is acceptable). Families managing this condition learn to read ingredient labels carefully, since galactose-containing compounds appear in unexpected places.
With consistent dietary control, the goal is to keep galactose-1-phosphate levels in the blood below 5 mg/dL, which is considered the therapeutic range.
Long-Term Complications
One of the most frustrating aspects of classic galactosemia is that even with strict dietary management from birth, many people develop long-term complications. The body actually produces some galactose on its own through internal metabolic processes, which means complete elimination is impossible regardless of diet.
Common long-term issues include speech and language difficulties, particularly a motor speech disorder called apraxia of speech, where the brain struggles to coordinate the movements needed to form words. Some individuals experience learning difficulties or mild cognitive challenges, though the severity varies widely. Motor coordination problems, including tremor and balance difficulties, can also develop over time.
Ovarian Insufficiency in Women
Perhaps the most significant long-term complication affects women with classic galactosemia. Approximately 90% develop primary ovarian insufficiency, meaning the ovaries stop functioning normally well before the typical age of menopause. In severe cases, ovarian tissue has been found to be almost entirely replaced by fibrous tissue, with few or no viable egg follicles remaining.
Researchers believe this happens because toxic galactose metabolites, particularly galactose-1-phosphate and galactitol, trigger cell death in the ovaries. Oxidative stress caused by these metabolites leads to progressive destruction of follicles. This process appears to begin early in life, and hormone replacement therapy is often needed to support bone health and development through puberty and beyond. Fertility is significantly reduced, though not always completely absent.
Treatments Under Investigation
Beyond dietary restriction, researchers are exploring new approaches. One promising candidate is govorestat, a drug that blocks an enzyme called aldose reductase, which converts excess galactose into galactitol, a sugar alcohol toxic to the brain and eyes. In a phase 1/2 clinical trial involving 14 people with classic galactosemia, govorestat reduced galactitol levels by roughly 50%, matching the effect seen in animal studies where treated rats showed improved neurological, behavioral, and eye-related outcomes. The drug showed a favorable safety profile, though it did not lower galactose-1-phosphate levels, meaning it targets only one of the toxic buildup pathways.
This is still early-stage research, but it represents the first real pharmacological option being tested for a condition that has relied entirely on diet for decades.