Galactosemia is a genetic condition that renders the body incapable of digesting galactose, a sugar that makes up half of lactose, a sugar in dairy products. When the body cannot digest galactose, the sugar and its byproducts build up in the blood and tissues. Without prompt diagnosis and treatment, galactosemia can have serious complications including organ damage.
Classic galactosemia is the most common and severe type of this recessive genetic disorder. Individuals who have classic galactosemia have a deficiency in the galactose-1-phosphate uridyl transferase (GALT) enzyme necessary for breaking down galactolose. Both parents must pass on a defective copy of the gene for their child to develop galactosemia. Two parents who carry the defective gene have a 25% chance of having a child with galactosemia.
Duarte galactosemia is a less severe form of classic galactosemia. It also results from a mutation in the GALT gene. However, while the body is unable to break down any galactose in classic galactosemia, in the Duarte variety, the enzyme's activity is decreased by approximately 75%. People with variant Duarte galactosemia typically do not have serious symptoms and may or may not require treatment.
Galactokinase deficiency galactosemia is due to a mutation in the GALK1 gene, which results in a loss of activity of the galactokinase enzyme. People with galactokinase deficiency are not able to fully break down galactose. Not all newborn galactosemia screening tests screen for this version of the deficiency. Therefore, an infant who receives a normal result on a newborn galactosemia test could still have a galactokinase deficiency.
Galactosemia type III results from inheriting mutated GALE genes, which causes a partial loss of activity in the GALE enzyme. Three types of epimerase deficiency exist - generalized, intermediate, and peripheral. Generalized epimerase deficiency is similar to classic galactosemia in terms of severity. As with galactokinase deficiency, many newborn galactosemia screening tests do not screen for epimerase deficiency.
If an affected infant drinks formula or breast milk containing lactose, he may show signs of galactosemia within his first few days of life. Lethargy, excessive vomiting, diarrhea, irritability, convulsions, weight loss, and a refusal to eat are some signs of galactosemia. Bacterial infection and jaundice are other early signs of the condition. Liver enlargement and build-up of fluid in the abdomen leading to swelling may also occur. If a baby is not treated promptly, weakness, tissue wasting, and excessive weight loss may result. Cataracts and cirrhosis of the liver may also develop.
Unfortunately, even if infants are treated promptly, learning and developmental delays and speech problems are common later in life. Types of learning disabilities commonly seen in children with galactosemia include delays in speech acquisition, difficulties with math and reading, speech disorders, and fine and gross motor skill difficulties. Neurological problems may also occur with galactosemia. These include problems with balance, walking, and tremors, involuntary muscle contractions, coordination problems, and an inability to estimate distance during muscular activity accurately, or dysmetria. Nearly all women with classic galactosemia have a condition in which the ovaries stop releasing eggs earlier than normal -- premature ovarian insufficiency. Most women with galactosemia are unable to have children as a result.
In the U.S., many states use newborn screening tests to look for galactosemia. Blood tests may identify bacterial E. coli sepsis and can also measure enzyme activity within the infant's red blood cells. A urinalysis can look for ketones in the infant's urine.
Individuals with galactosemia must avoid all milk and food products containing lactose and galactose. Infants can be fed lactose-free formula, soy formula, or meat-based formula instead of breast milk or formula containing lactose. People with this condition must read product labels carefully to ensure they do not consume products containing lactose or galactose, and doctors may recommend calcium supplements. Some children may require various therapies as they grow, including speech therapy for developed disorders.
Depending on the diagnostic criteria of a newborn screening test, galactosemia occurrence ranges from 1 in 16,000 to 1 in 48,000 births worldwide. It is seen in all ethnicities, though people of Irish ancestry have increased incidence. Variant Duarte galactosemia occurs most frequently in African-Americans and native Africans living in South Africa.
People who have their galactosemia treated early and follow doctor-recommended dietary restrictions can generally live a normal life. However, even infants treated early may have learning and developmental delays and speech disorders later in life. Additionally, nearly all women with classic galactosemia will experience ovarian failure, resulting in an inability to bear children.
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