On the Diagnosis and Pathogenesis of Type III Hyperlipoproteinemia

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Type III hyperlipoproteinemia (HLP) is clinically manifested by palmar xanthomatosis and a high incidence of premature atherosclerosis. However, regarding the defmition and diagnosis of type III HLP there are many conflicting reports. Proving "β-VLDL" by ultracentrifugation and lipoprotein electrophoresis has been a specific diagnostic test for type III HLP. However, electrophoretic determination of the presence of β-VLDL requires subjective interpretation and yields only qualitative information. In fact, β-VLDL has recently been proved not to be specific for type III HLP. Thus, various chemical criteria have been proposed to be more specific and sensitive for type III HLP by many authors, but none of these criteria are satisfactory at present. In an effort to find a more specific and sensitive chemical criteria, we made serial determinations of serum lipoproteins in three patients with type III HLP. The VLDL-chol/VLDL-TG ratios were between 0.27 and 1.93, and were found to be useful in differentiating type III from normal, type IIa and IIb HLPs. However, it was impossible to differentiate type III from type IV by the ratio. The VLDL-chol/TG ratios in type III HLP were greater than 0.20, but a few patients with normal lipids, type IIa and IIb HLPs showed a ratio greater than 020. Ratio above 0.30, which is the criterion for type III HLP introduced by Fredrickson et al.,was proved to be definite for type III HLP. However, in 13 out of 28 samples of type III the ratios were less than 0.30. From the present study, it seemed to be logical to conclude that the VLDL-chol/VLDL-TG ratio above 0.33 should be considered as diagnostic of type III HLP, when the VLDL-chol is above 55mg/dl. Several clinical studies were made to elucidate some aspects of pathophysiology of type III HLP. In a case of type III HLP associated with Sheehan's syndrome, postheparin lipase activity (PHLA), particularly hepatic PHLA was low. During replacement therapy with hydrocortisone and desiccated thyroid, the serum cholesterol and triglyceride levels decreased to the normal levels, however, broad-β band on agarose gel electrophoresis and β-VLDL remained. In 5 cases of hypothyroid with type III HLP, hepatic PHLA were low. and after thyroid hormone replacement PHLA restored to the normal level. Administration of heparin to type III HLP resulted in rapid clearance of rapid-moving VLDL and accumulation of β-VLDL. These results suggested that hepatic PHLA may some roles in the pathogenesis of type III HLP. High carbohydrate diet converted type IIa HLP associated with hypothyroidism to type III HLP, and after high fat diet type III HLP returned to type IIa HLP. Thus, carbohydrate inducibility in type III HLP was proved to be pronouned in hypothyroidism.
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On the Diagnosis and Pathogenesis of Type III Hyperlipoproteinemia

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