Control of plasma LDL production and uptakeby liver LDL receptors. (a) In normal human subjects, VLDL issecreted by the liver and converted to IDL in the capillaries ofthe peripheral tissues. About half of the plasma IDL particlesbind to the LDL receptor and are taken up by the liver.Theremainder are converted to LDL at the peripheral tissues.
(c) In normal individuals who have a long-termhigh-cholesterol diet, the liver is filled with cholesterol, whichrepresses the rate of LDL receptor production. Receptordeficiency, whether of genetic or dietary cause, raises the plasmaLDL level by increasing the rate of LDL production anddecreasing the rate of LDL uptake.
(b) Inindividuals with familial hypercholesterolemia (FH), liver LDLreceptors are diminished or eliminated because of a genetic
Fredrickson’s 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.