Two distinct truncated apolipoprotein B species in a kindred with hypobetalipoproteinemia.

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Abstract
Two novel, distinct truncated forms of apolipoprotein B (apo B) designated as apo B-90 and apo B-40 were found in five members of a kindred with hypobetalipoproteinemia. Sodium dodecyl sulfate gels and immunoblots of plasma or low density lipoprotein (LDL) (d = 1.019 to 1.063 g/ml) of the affected members demonstrated the presence of one or both of the truncated apo B bands. Employing four monoclonal anti-LDL antibodies with defined regional specificities, we demonstrated that amino terminal epitopes of the truncated apo Bs were intact, but that 10% and 60%, respectively, of the carboxyl terminal regions were absent. Thrombin digestion of apo B-90 generated an abnormally small T2 fragment, confirming that approximately 550 amino acids had been deleted from the carboxyl terminus of apo B-100. Restriction fragment length polymorphism analysis and variable number of tandem repeat typing of the 3' flanking hypervariable region of the apo B gene made it possible to distinguish all four parental alleles and the...