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.
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