Control of plasma LDL production and uptake
by liver LDL receptors. (a) In normal human subjects, VLDL is
secreted by the liver and converted to IDL in the capillaries of
the peripheral tissues. About half of the plasma IDL particles
bind to the LDL receptor and are taken up by the liver.The
remainder are converted to LDL at the peripheral tissues.
(c) In normal individuals who have a long-term
high-cholesterol diet, the liver is filled with cholesterol, which
represses the rate of LDL receptor production. Receptor
deficiency, whether of genetic or dietary cause, raises the plasma
LDL level by increasing the rate of LDL production and
decreasing the rate of LDL uptake.
(b) In
individuals with familial hypercholesterolemia (FH), liver LDL
receptors are diminished or eliminated because of a genetic
Fredricksonโs classification to hyperlipoproteinmias is very important because:
1) They focus on different groups of metabolic abnormalities related to hyperlipoproteinmias.
2) Associated different lipoprotein types with certain clinical features.
3) Provide basis for diet & drug therapy.
Lipoprotein disorders may be classified also as:
1- Primary disorder : a) genetic (familial) b- non-genetic (sporadic).
2- Secondary disorder : arise from another cause eg. Diet , alcohol, drugs, or disease of metabolic cause a) hormonal (hypothyroidism , diabetes ) or b) malignant or infectious.
