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CASE FILES: BIOCHEMISTRY
A N SW E R S TO C A SE 35: H Y PE R T R IG L Y C E R ID E M IA
(L IPO PR O T E IN L IPA SE D E F IC IE N C Y )
Summary:
A 9-year-old boy with acute abdominal pain consistent with pan-
creatitis, hepatosplenomegaly, eruptive xanthomas, and a family history of
hypertriglyceridemia and heart disease.
Etiology of abdominal pain: Acute pancreatitis
Underlying biochemical disorder: Disorder of lipoprotein metabolism
Role of lipoprotein lipase: Hydrolysis of triglycerides from VLDL and
chylomicrons
C L IN IC A L C O R R E L A T IO N
Lipoprotein lipase (LPL) is an enzyme found on the capillary endothelial sur-
face of adipose tissue, heart, and skeletal muscle and is required, along with
apoC-II, for the hydrolysis of triglycerides. ApoC-II, found on the surface of
chylomicrons and VLDL, serves as an activator of LPL. A deficiency in LPL
results in elevated levels of triglycerides (VLDL and chylomicrons). The cho-
lesterol level may be normal or slightly elevated. LPL deficiency is inherited in
an autosomal recessive pattern. Patients with LPL deficiency often present with
recurrent episodes of pancreatitis in their childhood and may have other clini-
cal signs of hypertriglyceridemia such as: xanthomas, hepatosplenomegaly, and
lipemia retinalis. Reduced serum LPL activity, after an injection of intravenous
heparin, confirms the diagnosis of either LPL or apoC-II deficiency. The initial
therapeutic intervention consists primarily of dietary modification (reduction of
fat intake).
A PPR O A C H TO L IP ID T R A N SPO R T
O bjectives
1.
Describe the metabolism and transport of lipoproteins.
2.
Understand the rationale for serum blood test results with the different
hypertriglyceridemias.
D efinitions
Apolipoprotein C-II (apoC-II): The apolipoprotein on the surface of chy-
lomicrons and very-low-density lipoproteins (VLDLs) that binds to and
activates lipoprotein lipase.
Apolipoprotein E (apoE): The apolipoprotein on the surface of several
lipoproteins including chylomicrons, chylomicron remnants, VLDL,
VLDL remnants, and IDL. It mediates the binding of apoE-containing
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