Galactosemia

Definition

Galactosemia is an inherited disease in which the body is unable to metabolize the simple sugar galactose, which is found primarily in dairy products but is also produced by the body. If left unaddressed, galactose can increase to toxic levels in the body and may lead to damage of the liver, central nervous system, and various other body systems.

Description

Galactosemia is a rare but potentially life-threatening disease resulting from the body's inability to metabolize galactose. Galactose makes up half of lactose, the sugar that is found in milk. Persons with galactosemia either have very low levels of or are entirely lack the enzyme that assists the body in breaking down galactose. This enzyme is called galactose-1-phosphate uridyl transferase (GALT). The GALT enzyme enables the body to break down galactose into glucose for energy. The severity of the disease may vary from person to person, because some individuals with galactosemia have higher levels of this enzyme than do others.

The two main types of galactosemia are called classic and Duarte variant. Individuals with the classic type of galactosemia lack the enzyme activity necessary to metabolize galactose. Individuals with the Duarte variant have approximately 5–20 percent of the enzyme activity necessary to metabolize this sugar and often do not have signs or symptoms of galactosemia.

Transmission

Galactosemia is an hereditary disease. In order to understand this disorder, it is necessary to have a very basic knowledge of genetics. Genes, the basic components of hereditary material, contain the "blueprint" that directs the development and functioning of every cell and tissue in the human body. Genes are situated on larger structures called chromosomes that contain several thousand genes each. Genes and chromosomes exist in pairs. Every cell in the body has 23 pairs of chromosomes containing two copies of every gene. Human beings receive one copy of every gene from their mother, and another copy from their father. Most of the time, genes function normally. However, in some cases, a change or mutation in a gene can cause it to not function. These mutations can cause inherited or genetic disorders.

In galactosemia, the gene mutation which occurs is inherited in what is known as an autosomal recessive pattern. This means that a non-working copy of the gene must be inherited from both parents for a child to be affected with the disease. The parents of children are called "carriers" of the disorder, because though they themselves do not have galactosemia, they may have children who do.

Unfortunately, as of 2004, parents had no way of knowing if they carry the mutated gene that causes galactosemia until they have a child diagnosed with the disease. The chance that two parents each of whom has the defective gene will produce a child with a recessive disorder is one in four or 25 percent with each pregnancy. The chances that their child will be a carrier, like themselves, is one in two, or 50 percent, with each pregnancy.

Demographics

Galactosemia is an inherited disorder that occurs in approximately one out of 30,000 live births. The incidence for the Duarte variant type of galactosemia is estimated to be one in 16,000 live births. Although galactosemia occurs in all ethnic groups worldwide, some mutations cause a less severe type of disease and are more commonly seen in specific ethnic groups, such as African-Americans. In Japan, classic galactosemia is not diagnosed as frequently as it is in Caucasian populations in the United States.

Causes and symptoms

Galactosemia is an inherited disorder. People with the disease are unable to fully break down galactose. If an infant with galactosemia is given milk, byproducts of galactose will build up in the baby's body, causing damage to the liver, kidneys, brain, and eyes. Characteristically, a newborn with galactosemia who is fed milk products will have jaundice , vomiting , lethargy, irritability, and convulsions. Continued feeding of milk products to the infant will lead to cirrhosis, cataracts, kidney failure, and mental retardation .

When to call the doctor

Parents should notify their doctor if their child displays any of the symptoms of galactosemia. Couples should consult their physician if there is a family history of galactosemia, and they are considering having a child.

Diagnosis

As of late 2004, all 50 states had mandatory screening of newborns for galactosemia. If parents receive a call from a healthcare provider saying the screening test indicates possible galactosemia, they should promptly stop milk products and have a blood test done for galactosemia through their doctor. The physician may also perform enzyme studies on or look for the presence of "reducing substances" in the child's urine, look for ketones in the urine, and measure enzyme activity in the red blood cells.

Treatment

Galactosemia is treated by removing foods that contain galactose from the diet. Foods containing lactose and, therefore, galactose should be avoided. Because milk and milk products are the most common food source of galactose, persons with galactosemia should avoid ingesting these foods. It is recommended that persons with galactosemia avoid eating foods with galactose throughout their entire lives.

Nutritional concerns

The goal of dietary treatment is to minimize galactose intake. It is impossible to have a galactose-free diet. However, all persons with galactosemia should limit galactose intake as much as possible. The galactose-1-phosphate levels of the individual will establish the level of dietary restriction necessary. Infants can be fed soy, meat-based, or other lactose-free formulas. Abstinence from milk and milk products must continue throughout life. Parents need to find some of the many listings available that identify the galactose content in foods. Since the primary source of calcium is usually milk or milk-based foods, calcium must be supplemented. Parents of a child with galactosemia should note that lactose is often used as filler in medicines. This very frequently is not listed on the package. Parents should always check with the pharmacist before administering any new medications.

Prognosis

Approximately 75 percent of the babies with galactosemia who are not diagnosed and treated die within the first two weeks of life. By contrast, if an early diagnosis is made and if milk products are strictly avoided, most children lead a relatively normal life. With appropriate treatment, liver and kidney problems do not develop, and early mental development progresses in a normal manner. However, even with proper treatment, children with galactosemia often have a lower intelligence quotient (IQ) than their siblings, and they frequently have speech problems. Girls often have ovaries that do not function, and only a few are able to conceive naturally. Boys, however, have normal testicular function.

Prevention

Since galactosemia is a recessive genetic disease, it is usually first detected on a newborn screening test, as most people are not aware that they are carriers of a gene mutation causing the disease. If there is a family history of galactosemia, genetic counseling is recommended for prospective parents as they make decisions regarding pregnancy and prenatal testing. Once one child in a family is diagnosed with galactosemia, it is recommended that other members of the family receive genetic counseling as well.

Parental concerns

One of the most important things parents of a child with galactosemia can do is educate themselves thoroughly on an appropriate diet. All other caregivers or teachers involved with the child need to be notified of the child's dietary restrictions, and the potential consequences if they are not maintained.

Resources

PERIODICALS

Bosch, Annet M., et al. "Living with Classical Galactosemia: Health-Related Quality of Life Consequences." Pediatrics 113 (May 2004): 5.

Weese, S. Jean. "Galactose Content of Baby Food Meats: Considerations for Infants with Galactosemia." Journal of the American Dietetic Association (March 2003).

ORGANIZATIONS

National Newborn Screening and Genetics Resource Center. 1912 W. Anderson Lane, Suite 210, Austin, TX 78757. Web site: http://genes-r-us.uthscsa.edu .

"Parents of Galactosemic Children Inc." 885 Del Sol St., Sparks, NV 89436. Web site: http://www.galactosemia.org.

WEB SITES

"Galactosemia." MedlinePlus , January 2004. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000366.htm (accessed January 6, 2005).

"Galactosemia: An Overview." Adult Metabolic Transition Project. Available online at http://depts.washington.edu/transmet/gal.html (accessed January 6, 2005).

Deanna M. Swartout-Corbeil, RN