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About Galactosaemia

What is Galactosaemia?

Background

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.

What Causes Galactosaemia?

The enzyme is deficient or absent because of a mistake or mutation in the genetic code, the DNA. Our chromosomes are made of DNA and carry a coded message rather like a computer programme and make us what we are, for example giving us a particular hair colour.

We have two copies of all our chromosomes (except the sex chromosomes) and we inherit one copy from our mother and one from our father. In galactosaemia the child inherits a mistake in the area that codes for the missing enzyme from both parents. The parents are perfectly healthy because they have one normal gene which allows them to make enough of the enzyme to keep them healthy. There is no way of knowing that a parent may carry this disorder until they have an affected child. In each and every pregnancy there is a 1:4 chance of having another affected baby.

We can look for the genetic mistake (or mutation) in the DNA and when we do this we find that in quite a high proportion of children there is the same mutation. We are trying to look to see whether the mutation is related in any way to the sorts of problems that children with galactosaemia have, but at the moment there only seems to be a loose association between the mutation and outcome of affected children.

How Common is Galactosaemia?

Galactosaemia is rare. In the UK, about 1 child in 45,000 is born with this condition so between 12 and 18 children are born each year with it.