Very occasionally a child will inherit a more severe form of FH.
This happens when they inherit two copies of an altered gene that causes FH, one from each parent. This is referred to as either compound heterozygous or homozygous FH (HoFH). Experts agree that HoFH may affect as many as 1 in 160,000 to 1, in 300,000 people.
Because two FH causing genes are inherited this type of FH is more severe than heterozygous FH. Cholesterol levels are usually higher than 12mmol/l and, if it is not treated, it can cause heart disease at a very young age. It is particularly important that children with HoFH are diagnosed and treated early.
- Compound heterozygous FH is rare and only occurs if you inherit two different types of gene alterations, one from each parent. These alterations may be different alterations in the same gene, or alterations in two of the three different genes associated with FH. This type of FH can only happen in a family where both parents have FH.
- Homozygous FH is very rare and only happens if you inherit two copies of exactly the same gene alteration, one from each parent. In most cases the parents will have both inherited the original altered gene from a common ancestor. This type of FH appears to be more common in specific populations, such as French Canadians, Afrikaners in South Africa, or Christian Lebanese.
- If both parents have FH the probability of inheriting FH changes. There is a one in two chance of inheriting HeFH (one altered gene); a one in four chance of inheriting HoFH (two altered genes) and a one in four chance of inheriting two normal (non FH causing) genes.
Because cholesterol levels are usually much higher and because statins may not always be effective in people with HoFH; other treatments to bring their cholesterol levels down sufficiently may be required.
Until recently, there were few treatment options for people who have HoFH. However, significant research in this area has led to some exciting new developments.
FH Europe is supported by an educational grant from Amgen Limited, Sanofi, Regeneron, Akcea Therapeutics Inc. and Amryt