Galactosemia: Description, Causes and Risk Factors:
An inborn error of galactose metabolism due to congenital deficiency of the enzyme galactosyl-1-phosphate uridylyltransferase, resulting in tissue accumulation of galactose 1-phosphate; manifested by nutritional failure, hepatosplenomegaly with cirrhosis, cataracts, mental retardation, galactosuria, aminoaciduria, and albuminuria that regress or disappear if galactose is removed from the diet; autosomal recessive inheritance; caused by mutation in the galactose-1-phosphate uridyltransferase gene (GALT) on 9p.
Galactosaemia literally means `galactose in the blood'. Galactose is a sugar which mainly comes from lactose, the sugar found in milks. Lactose is normally broken down into the two simple sugars, galactose and glucose. The galactose is then broken down further and used in many parts of the body including the brain. In galactosaemia it cannot be broken down completely and used because of deficiency or absence of an enzyme, galactose-1-phosphate uridyl transferase or Gal-1-PUT. Galactose, galactose-1-phosphate and other harmful chemicals build up and lead to the serious illness that occurs in the first few weeks of life once the baby is fed on milk containing lactose. It is a lifelong condition.
The gene that codes for galactosemia is located on chromosome 9. Many different mutations within this gene have been identified, and the most common mutation is called "Q188R". Most people with galactosemia have this mutation. A milder form of galactosemia known as the "Duarte variant" is also caused by a mutation within the GALT gene. Different changes within the GALT (galactosyl-1-phosphate uridylyltransferase) gene are what lead to variations in enzyme levels between individuals with galactosemia.
The gene mutation that causes galactosemia is inherited in what is called 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 disorder. The parents' health is not affected because the other copy of the gene is working correctly, and compensates for the non-working copy. Parents of children who have an autosomal recessive disorder are called "carriers" of the disorder. This is because they themselves do not have the disorder, but can have sons and daughters who are affected. It is important to remember that every person carries several non-working recessive genes. Only when both parents carry the same non-working gene is there a chance of having a child with a recessive disorder.
The incidence of true galactosaemia is 1:50,000 or about 2 babies a year in New South Wales. Babies are screened for galactosaemia so that they can be treated early.
Unrecognised and untreated, galactosaemia can be a rapidly fatal disorder. There is a risk of neonatal death from E. coli sepsis but the life expectancy in those who reach adult life has not been investigated. Fatty infiltration and inflammatory changes can progress to cirrhosis. With long-term control, even cataracts may reverse. There is much that remains unknown about how this metabolic abnormality affects those who suffer from it and why dietary restriction is only partially effective and outcome does not appear to be related to stage of diagnosis and compliance with diet. It is possible that endogenous production of galactose is a problem.
There is often feeding difficulty, with vomiting and failure to gain weight, with poor growth in the first few weeks of life.
- Lethargy and hypotonia occur.
- Jaundice and hepatomegaly develop.
- There are often associated coagulation defects.
- Sepsis (often with E. coli) can be fatal.
- Cataracts may be apparent even in the early days of life.
- Ascites may even be apparent in early life.
- The fontanelle is full.
- Developmental delay may affect speech, language and general learning.
- Adults may have short stature, ataxia and/or tremor.
- Hypergonadotrophic hypogonadism is common and in women, premature ovarian failure. Those who conceive often have variant disease.
Long term complication of galactosemia includes:
- Diminished bone density.
- Premature ovarian failure.
Infants are routinely screened for galactosemia in the US, and the diagnosis is made while the person is still an infant. Infants affected by galactosemia typically present with symptoms of lethargy, vomiting, diarrhea, failure to thrive, and jaundice. None of these symptoms are specific to galactosemia, often leading to diagnostic delays. Luckily, most infants are diagnosed on newborn screening. If the family of the baby has a history of galactosemia, doctors can test prior to birth by taking a sample of fluid from around the fetus (amniocentesis) or from the placenta (chorionic villus sampling or CVS).
A galactosemia test is a blood test (from the heel of the infant) or urine test that checks for three enzymes that are needed to change galactose sugar that is found in milk and milk products- nto glucose, a sugar that your body uses for energy. A person with galactosemia does not have one of these enzymes. This causes high levels of galactose in the blood or urine.
Galactosemia is normally first detected through newborn screening, or NBS. Affected children can have serious, irreversible effects or even die within days from birth. It is important that newborns be screened for metabolic disorders without delay. Galactosemia can even be detected through NBS before any ingestion of galactose-containing formula or breast milk.
Detection of the disorder through newborn screening (NBS) does not depend on protein or lactose ingestion, and, therefore, it should be identified on the first specimen unless the infant has been transfused. A specimen should be taken prior to transfusion. The enzyme is prone to damage if analysis of the sample is delayed or exposed to high temperatures. The routine NBS is accurate for detection of galactosemia. Two screening tests are used to screen infants affected with galactosemia - the Beutler's test and the Hill test. In fact a third test, called the "Florida test", is also normally performed on all galactosemia positives. The Beutler's test screens for galactosemia by detecting the level of enzyme of the infant. Therefore, the ingestion of formula or breast milk does not affect the outcome of this part of the NBS, and the NBS is accurate for detecting galactosemia prior to any ingestion of galactose.
The treatment for galactosemia involves eliminating as much of the galactose as possible from the diet. At this time there are no medications available that lower galactose levels.
For young babies, treatment means changing from breast milk or a milk-based infant formula to a formula that contains little or no galactose. This is usually a formula that is made with the protein extracted from soybeans. Soybeans do not contain lactose and contain only minimal amounts of galactose.
Treatment for children and adults is the same - eliminate as much galactose from the diet as possible. Eliminating galactose is much more complex for children and adults than for babies since you or your child eat a wide variety of foods. Any foods that contain milk or milk products must be avoided in the diet for galactosemia. Milk or various milk-based ingredients are added to many foods, so labels must be carefully checked for ingredients that contain galactose. In addition, galactose can be found in many plant products; legumes especially contain quite a bit of galactose. Legumes are dried peas and beans like split peas, black beans and garbanzo beans. In addition, some fruits and vegetables contain galactose. It can be confusing to decide what is and what is not okay in this diet.
NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.