Article: Galactosemia

Galactosemia is a rare genetic metabolic disorder which affects an individual's ability to properly digest the sugar galactose. Lactose in food (such as dairy products) is broken down by the body into glucose and galactose. Normally, galactose is then converted into glucose by the enzyme GALT (galactose-1-phosphate uridylyltransferase). In individuals with galactosemia, GALT activity is severely diminished, leading to toxic levels of galactose to build up in the blood, resulting in hepatomegaly (an enlarged liver), renal failure, cataracts, and brain damage. Without treatment, mortality in infants with galactosemia is about 75%.

Goppert first described the disease in 1917. Its incidence is about 1 per 47,000 births (classic type). It is much rarer in Japan.

Different Types

There are two variants of the gene responsible for galactosemia.

• One variant causes so-called classic galactosemia, in which there is an extreme deficiency in galactose-1 phosphate uridyltransferase. It is an autosomal recessive condition. The gene for GALT was mapped at 9p13. Most serious conditions are prominent.
• The variant gene, responsible for Duarte galactosemia, leads to about half the normal levels of GALT. Individuals with Duarte galactosemia may experience few or none of the serious symptoms of classic galactosemia.

The severity of the symptoms is dependent on a number of factors, most importantly the amount of lactose in the individual's diet. It is also possible to have one each of the classic and Duarte genes, in which case GALT activity is intermediate.

Diagnosis

Infants are now routinely screened for galactosemia in the United States, and these diagnoses are often made early.

Treatment

The only treatment for classic galactosemia is eliminating lactose and galactose from the diet. Even with an early diagnosis and a restricted diet, however, some individuals with galactosemia experience long-term complications such as learning disability, and in girls, ovarian failure. Such complications have not been associated with Duarte galactosemia, and many individuals with Duarte galactosemia do not need to restrict their diet at all.

Galactosemia is sometimes confused with lactose intolerance, but the galactosemia is a more serious condition. Lactose intolerant individuals have an acquired or inherited shortage of the enzyme lactase, and experience abdominal pains after ingesting dairy products, but no long-term effects. In contrast, a galactosemic individual who consumes galactose can cause permanent damage to their bodies.

Reference

• Goppert F. Galaktosurie nach Milchzuckergabe bei angeborenem, familiaerem chronischem Leberleiden. Klin Wschr 1917;54:473-477.