The major gene defect prominent in South Africa is known as familial hypercholesterolaemia (FH). It is inherited in a dominant fashion which means that the presence of only a single FH gene from one affected parent can produce the condition in the child who inherits it - that is, in an average of 50% of the offspring.

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In a person with the gene for FH, cholesterol levels, mainly LDL cholesterol, are raised from birth making early diagnosis possible. However, clinical disease usually shows itself in adulthood.

As many as 85% of affected men have clinical CAD by the age of 60 years while women follow on a decade later. Significant numbers show severe symptoms in their thirties or forties while a few affected individuals are healthy until their seventies or eighties.

The condition is surprisingly common amongst the Afrikaans population, with an incidence of around one in 75. This is because the disease arrived in South Africa with one Huguenot couple and spread from them. This phenomenon is known as the “founder effect” in genetics. The disease also occurs in all the other South African population groups with the lowest incidence in the black community.

Diagnosis can often be made clinically and from routine laboratory measurements, but molecular techniques now permit definite identification of affected individuals and, even more importantly, prenatal testing.

The genetic defect prevents LDL cholesterol from being effectively removed from the bloodstream by the LDL receptor. This also stimulates increased cholesterol synthesis in the body.

Much more rarely an individual inherits an FH gene from two affected parents. This is called the homozygous condition and is much more severe, with CAD generally present by the age of 20. Unlike the more common single gene, or heterozygous form, it cannot be effectively treated by means of drugs alone and requires the facilities of a specialised lipid clinic.

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