THE PRIMARY HYPERLIPIDAEMIAS: THE FREDERICKSON CLASSIFICATION

Type II hyperlipidaemia the most common primary hyperlipidaemia. The picture is similar to familial hypercholesterolaemia but milder. It is characterised by increased levels of LDL-cholesterol (> 4.0 mmol/L). Triglyceride levels are < 2.3 mmol/L. Type IIa hypercholesterolaemia causes heart disease as there is predominantly raised cholesterol and high LDL. There is also increased triglycerides cause eruptive skin xanthomas, lipaemia retinalis (white TG deposits in the retina) and pancreatitis. Cholesterol has an affinity for deposition around the tendons, tendon xanthoma is characteristic of hypercholesterolaemia.

Type II b hypercholesterolaemia  also causes elevated cholesterol and triglycerides.

Type III hyperlipidemia is when cholesterol and triglyceride are both increased, and is associated with atherogenesis. Homozygosity for the E2 genotype (E2/E2) is found in most patients with type III hyperlipidemia. The palmar striae (palmar

xanthomata) are considered pathognonomic for the disorder and occur in less than

50% of patients but tubero-eruptive xanthomata, typically on the elbows and knees, as

well as xanthelasma have been described. The underlying biochemical defect is one of a reduced clearance of chylomicron and VLDL remnants.

Type IV hyperlipidemia causes an isolated hypertrigIVceridaemia. There is normal or slightly raised plasma cholesterol. There are increased triglyceride levels due to increased VLDLs

Type I and V hyperlipidaemia have lipoprotein lipase defects, and lead to raised chylomicrons and triglyceride levels.