Studies on the metabolic defect in Broad-beta disease (hyperlipoproteinaemia type III).

The apoprotein composition of the main lipoprotein fractions (VLDL, LDL-1, LDL-2 and HDL) was studied initially in 15 patients with Broad-beta disease. Analytical isoelectric focusing of urea-soluble apo-VLDL and apo LSL-1 demonstrated a variant pattern of the polymorphic Apoprotein E with a deficient Apo E-III band in all patients. The Apo E-III deficiency pattern was seen in only six out of 304 hyperlipidaemic controls. These six Apo E-III deficient controls had characteristic signs of Broad-beta disease, and thus represented patients not previously recognized as having the disorder. The Apo E focusing patterns were constant on repeated examinations and were stable under different metabolic conditions. The data show that Apo E-III deficiency in VLDL is a specific qualitative marker for Broad-beta disease, allowing an unequivocal diagnosis that had not been possible previously. Indirect evidence suggests that Apo E-III deficiency is the basic lipoprotein abnormality underlying the familial dyslipoproteinaemia.