Galactosemia is a rare, inherited metabolic disorder that affects the body’s ability to process the simple sugar galactose, which is found primarily in milk products as part of lactose. If an individual with this condition consumes milk, the body cannot properly break down the sugar, leading to the accumulation of toxic byproducts in the blood and tissues. This untreated buildup can quickly lead to severe, life-threatening complications affecting multiple organ systems, including the liver and brain. The rapid development of cataracts in the eyes of affected infants is one of the earliest and most common visible signs of this metabolic failure. Prompt diagnosis and immediate dietary intervention are necessary to prevent devastating short- and long-term consequences.
The Genetic Basis of Galactosemia
The disorder is passed down through families in an autosomal recessive inheritance pattern, meaning a child must inherit a non-working gene from both parents to be affected. The most severe and common form, known as Classic Galactosemia (Type 1), is caused by a defect in the GALT gene. This gene provides instructions for making the enzyme Galactose-1-phosphate uridylyltransferase (GALT), which is responsible for converting galactose into glucose, the body’s main energy source.
When the GALT enzyme is deficient or non-functional, the metabolic pathway for galactose is blocked. This metabolic failure causes galactose-1-phosphate, a toxic intermediate, to build up to harmful levels in the body’s tissues. This elevated metabolite drives the severe systemic damage seen in untreated infants. Two other, generally milder types exist, caused by deficiencies in the enzymes galactokinase (Type 2) or galactose epimerase (Type 3).
Acute Symptoms and Early Diagnosis
Infants with Classic Galactosemia typically appear healthy at birth but begin showing severe symptoms within days or weeks of starting milk feeding, as lactose is broken down into galactose. Initial signs include lethargy, vomiting, feeding difficulties, and failure to gain weight (failure to thrive). The accumulating toxic substances quickly injure the liver, causing jaundice and an enlarged liver (hepatomegaly).
Untreated infants face immediate life-threatening risks, including liver failure and a high susceptibility to severe bacterial infection, most notably E. coli sepsis. To prevent this irreversible damage, newborn screening for galactosemia is mandated in nearly all states in the United States and many countries. This screening, usually performed via a heel prick shortly after birth, measures the GALT enzyme activity or the amount of galactose metabolites in the blood. Immediate identification is necessary, as permanent damage can occur if treatment is delayed beyond the first week or two of life.
How Galactosemia Causes Cataracts
Cataract formation in galactosemia is a distinct biochemical process driven by the body’s inability to process galactose correctly. When the GALT enzyme is absent, the excess galactose in the bloodstream is shunted into an alternative metabolic pathway. The enzyme aldose reductase converts the abundant galactose into a sugar alcohol called galactitol, which is also sometimes referred to as dulcitol.
The lens of the eye is particularly susceptible to this process because its structure is relatively impermeable to galactitol once it forms. As galactitol accumulates inside the lens fibers, it creates a high concentration gradient, leading to an osmotic effect. This osmotic imbalance draws excess water into the lens tissue. The resulting swelling and over-hydration of the lens fibers causes the lens to become opaque. These opacities can present rapidly, sometimes within days of birth, often starting with a characteristic “oil drop” appearance.
Treatment and Long-Term Dietary Management
The primary treatment for galactosemia is the strict, lifelong exclusion of all sources of galactose from the diet. For infants, this means immediately stopping breast milk or standard formula, which contain lactose, and switching to a specialized formula, typically soy-based or elemental. This dietary restriction prevents acute symptoms, including liver damage and sepsis, and can lead to the partial or complete reversal of early cataracts.
Long-term management requires constant vigilance due to hidden sources of galactose in processed foods, certain medications, and even some non-dairy food items. Ongoing monitoring, including regular blood tests to measure galactose metabolites, is necessary to ensure strict dietary adherence. While the diet prevents acute complications, it does not fully prevent all long-term issues, such as developmental delays, speech problems, and premature ovarian insufficiency in females.
If a cataract significantly impairs an infant’s vision, surgical removal may be required, even with early dietary compliance. Dietary restriction remains the core of preventative care, mitigating the systemic and ocular damage caused by the disorder. Patients require consistent oversight from a metabolic dietitian and a specialized medical team throughout their lives.