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How is Genetic High Cholesterol (Familial Hypercholesterolaemia) Inherited?
Your body is made up of trillions of cells, each one of which has a nucleus that contains DNA. DNA is a unique code, providing the blue print for how our body is built and works.
The DNA inside the nucleus is broken up into small chunks called genes and these are arranged on chromosomes. Each gene is a piece of code which is needed to make a particular protein in the body.
Apart from the genes that we inherit on the X and Y chromosomes, we normally have two copies of the each gene, one which we inherit from our father and one from our mother.
Familial Hypercholesterolemia (FH) is caused by inheriting a gene that has a mistake in it. This is called a faulty or altered gene. We talk more about the specific genes involved in Familial Hypercholesterolemia elsewhere. There are three main genes, that we know of, which cause FH. These genes play a big role in making proteins that help remove cholesterol from the blood.
Most people who have FH have inherited just one faulty or altered gene, either from their mother or their father. This type of Familial Hypercholesterolemia occurs in at least 1 in 500 people (120,000) but may be more as in other European countries. Recent research has suggested it might be as many as 1 in 200 to 1 in 300 in other countries such as Holland but there is currently insufficient data in the UK to confirm this. If you have this kind of FH your doctor may refer to it as Heterozygous FH or HeFH for short.
Homozygous or Compound Heterozygous FH
It is possible to inherit two faulty or altered genes, one from each of your parents. This happens very rarely, and only when two people who have FH meet and have a baby together.
When a person inherits two faulty or altered genes this is usually a much more severe kind of FH.
If the two faulty genes are identical – this is referred to as Homozygous FH or HoFH
If the two faulty genes are different - this is called Compound Heterozygous FH, but it may be referred to as HoFH too.
What are chances of inheriting Homozygous FH or Compound Heterozygous FH
Only a few people in the UK are affected. At least one baby in a million will inherit this form of FH, so this means a minimum of 60-70 children and adults in the UK are affected.
If two people who have FH plan to have a family together, their chances of passing a faulty FH gene onto their child is high.
For example if two people with heterozygous FH (HeFH )have a family of 4 children, on average:
- 2 children will inherit the normal form of FH (HeFH) by inheriting one faulty gene and one healthy gene
- 1 child will inherit the more severe form of FH (HoFH) by receiving a faulty gene from each parent
- 1 child will not inherit FH at all because they receive a healthy gene from each parent
But this is an average situation. It is possible that all the children in the family could have FH or none of the children will have it.