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Galactosemia: a Rare Genetic Disorder
Galactosemia is a rare genetic disorder that affects the metabolism of a simple sugar: galactose. This genetic disease interferes with the individual's ability to properly utilize galactose. An unaffected person is able to metabolize lactose (contained in milk and milk products), by breaking it down into glucose and galactose. However, in patients with the rare genetic metabolic disorder galactosemia the enzymes needed for galactose metabolism are either missing or are not there in sufficient quantities.
The body is unable to break down galactose into glucose and so it accumulates and can reach toxic levels within cells. According to the NIH Genetics Home Reference galactosemia (classic) occurs in 1 in 30,000 to 60,000 newborns.
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Genetics of Galactosemia
To understand the genetics of galactosemia we need to look at the enzymes that convert galactose to glucose; there are three:
- galactose-1-phosphate uridyl transferase (GALT)
- UDP galactose epimerase
A normal person, that is, the person unaffected by galactosemia and with normal levels of the galactose-1-phosphate uridyl transferase (GALT enzyme) inherits two normal (N) copies of the GALT enzyme gene. Thus, this person would be an N/N genotype.
If one copy of the altered GALT enzyme gene is inherited from one parent then the person would have a genotype (N/G) and he/she would have less than normal GALT enzyme activity but enough to carry on with a normal life.
The problem arises when a child inherits both copies of the GALT altered gene, one from each parent. This patient would be a G/G genotype and the GALT enzyme activity would be zero. People with the G/G genotype are galactosemic. Mutations in the GALT gene are responsible for classic galactosemia (type I). However, mutations in other genes (GALE, GALK1, and GALT) may also cause galactosemia. Galactosemia therefore follows an autosomal recessive pattern of inheritance, where parents each carry a copy of the mutated gene, but do not usually show signs of having the disorder - they are carriers.
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Health Problems Associated with Galactosemia
People who have problems with galactose metabolism face a variety of difficulties during life if not treated accordingly. The first issue is the danger posed by consuming milk and milk products. Children and people with galactosemia need to be on a restricted diet and a diet free of milk and milk products.
Children with galactosemia may experience some life-threatening complications within a few days after birth if the disease is not detected. Infants typically experience lack of energy (lethargy), failure to thrive (failure to gain weight and grow as expected), jaundice, damage to the liver, and bleeding. Children with galactosemia and on a restricted milk diet are expected to grow with some health issues like speech difficulties, learning disabilities, tremors, neurological impairment and ovarian failure in women.