Raised cholesterol levels in the blood - hypercholesterolaemia - are generally caused by a poor diet and lifestyle in combination with the way an individual produces cholesterol in their liver.

However, in some individuals (1 in 500 of the population), the high cholesterol level in the blood is caused by a specific genetic defect. People with inherited or familial hypercholesterolaemia (FH) are lacking in the low-density lipoprotein (LDL) receptors that remove cholesterol from the bloodstream.

The raised cholesterol level in the blood is present from birth and it leads to an early development of atherosclerosis and vascular diseases. The disease is transmitted from generation to generation in such a way that siblings and children of a person with FH have a 50 per cent risk of getting FH. The disease does not skip generations which means that children and grandchildren of family members who do not have a defective gene are therefore not at risk from FH.

The ailment is mostly treated with medicines and special diets. Treatment with genetic manipulation is still at the experimental stage.

People with FH cannot feel that they have a raised cholesterol level, but they might have symptoms of cardiovascular disease, which develops as a result of the narrowing of the arteries. The symptoms can include:

• pressing, crushing pain behind the breastbone, possibly radiating to the arm or to the neck, associated with physical exertion or cold (angina pectoris).
• if the symptoms become more severe and sustained it may be a sign of an acute coronary thrombosis (heart attack).

The development of atherosclerosis begins in childhood and can be compared to calcium deposits in a water pipe. Gradually, the opening gets smaller and smaller, the inner surface becomes more irregular, the blood can no longer flow freely, leading to symptoms.

When the blood supply to the tissue stops, the tissue dies. This means that if a blood clot is situated in one of the vessels of the heart (the coronary arteries), the area of the heart muscle supplied by that vessel is injured irreversibly. Scar tissue forms and the heart is left weakened.