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Chapter 22: Lipids and Lipoprotein Abnormalities

Andrea Schlune; Muhidien Soufi; Juergen R. Schaefer; Ertan Mayatepek

LIPID METABOLISM

Triglycerides and fatty acids are necessary for both energy supply and energy storage, whereas cholesterol is a vital compound required for cell proliferation, cell integrity, synthesis of steroid hormones, and bile acids.

Highly specialized lipoproteins are responsible for the transport of water-insoluble lipids to different body tissues.1 These contain esterified and unesterified cholesterol, triglycerides (TG), phospholipids, and proteins.2 Lipoprotein-associated proteins, the so-called apolipoproteins (apo), play a central role in lipid metabolism (Tables 22-2 and 22-3). They provide structure for the integrity of the particle (ie, apo B100, apo A-I) and serve as cofactors for enzymes (ie, apo C-II, apo A-I, apo A-IV) or ligands for specific receptors (ie, apo B100, apo E).3,4,5 Descriptions of several mutations and defects of apolipoproteins with major implications for lipid metabolism6,7 have demonstrated the crucial role of these components for lipid and lipoprotein metabolism in humans. The lipid transport system consists of three distinct but interacting pathways: the exogenous, the endogenous, and the reverse lipoprotein pathway.

TABLE 22-1Recommended Screening Strategies by the AHA and AAP
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TABLE 22-1 Recommended Screening Strategies by the AHA and AAP
AHA 200780 AAP 200881
Screening Indication
Positive family history of dyslipidemia or Positive family history of dyslipidemia or
Positive family history of dyslipidemia or Positive family history of dyslipidemia or
Unknown family history and other CHD risk factors or Unknown family history or
Overweight/obesity Other CHD risk factors (overweight/obesity, hypertension, cigarette smoking, diabetes)
Screening Age
At age 2 years or older Between 2 and 10 years of age
Screening Approach
By fasting lipid profile By fasting lipid profile

AHA, American Heart Association; AAP, American Academy of Pediatrics; CHD, coronary heart disease.

TABLE 22-2Apolipoproteins
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TABLE 22-2 Apolipoproteins
Apo Chromosome Mol. Weight (kDa) Concentration (mg/dL) Fraction Site of Production Function
A-I 11q23-q24 28.5 120–140 HDL, chylomicron Liver, gut Activation of LCAT, binding to SRBI and HDL-receptor
A-II 1q21-q23 17 35–50 HDL Liver Activation of HL
A-IV 11q23 46 <5 HDL, chylomicron Gut Activation of LCAT, binding to LDLR
A-V 11q23 38 <2 VLDL, HDL Liver Activation of hepatic triglyceride lipase
B-100 2p24-p23 550 70–90 Chylomicron, VLDL, IDL, LDL Liver Structural protein of VLDL, IDL, and LDL, ligand for the LDLR
B-48 2p24-p23 265 <5 Chylomicron, VLDL Gut Structural protein of chylomicrons, binding to LRP
C-I 19q13.2 6.5 5–8 HDL, chylomicron, VLDL Liver Activation of LCAT
C-II 19q13.2 8.8 3–7 HDL, chylomicron, VLDL Liver Activation of LPL
C-III 11q23.1-q23.2 8.9 10–12 HDL, chylomicron, VLDL Liver Inhibitor of LPL
D 3q26.2 29 8–10 HDL Liver Activation of LCAT
E 19q13.2 34 3–5 VLDL, IDL, HDL, chylomicron Liver Ligand of the LDL/VLDL-receptor and LRP
H 17q23-qter 50 5–30 VLDL, HDL, chylomicron Liver Participation in different physiologic pathways (lipoprotein metabolism, coagulation, and production ...

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