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A monoclonal antibody (MB-19) was used to investigate the polymorphism of apolipoprotein B in a large family and in unrelated subjects. Apolipoprotein B was shown to exhibit high-, intermediate- or low-affinity binding to this antibody. Thus, MB-19 bound strongly to the Ag(c) epitope, An Ag antigenic domain previously characterized by human antisera, while it bound only weakly to the allelic epitope Ag(g). It proved therefore useful for the detection of the two corresponding allelic apoB species designated apoBc (high-affinity binding) and apoBg (low-affinity binding), and for confirming their co-dominant transmission. Intermediate binding resulted from the presence of a mixture of both apoB populations in heterozygous subjects.

Hypercalcaemia is a recognised complication of hypothyroidism. We describe three patients who developed hypercalcaemia after thyroidectomy when thyroid supplements were discontinued. They were treated with thyroxine, dihydrotachysterol, and calcium after operation, and in all three cases serum calcium concentrations remained constant during combined treatment. Thyroxine treatment was discontinued several weeks before a radioiodine scan was performed; dihydrotachysterol and calcium were continued throughout. Serum calcium concentrations rose to hypercalcaemic levels in all cases. Elimination of dihydrotachysterol from plasma may be delayed in hypothyroidism, resulting in hypervitaminosis D. It is advisable to reduce the dose of dihydrotachysterol and to check serum calcium concentrations regularly in patients whose thyroid treatment is interrupted.

A 43-year-old female patient is currently being treated by us for a recurrence of adrenal cortical carcinoma associated with Cushing's syndrome and virilization. Despite many relapses of metastatic spread she has not only survived for 25 yr after the removal of the primary tumor but also until now preserved her ability to work in a textile factory.

The immunoreactivities of LDL (low density lipoprotein) samples obtained from a variety of subjects were analyzed by comparing their capacities to compete with 125I-labeled LDL for binding to various monoclonal anti-LDL antibodies in competitive binding assays. A marked variation in epitope expression was observed. In comparison to an LDL standard, different preparations exhibited immunoreactivities (expressed as apparent apoB content) ranging from 30 to 400% of the LDL standard. Some epitopes were much more uniformly expressed than others. The number of epitopes expressed in different LDL preparations appeared to be related to the percentage composition of various lipid constituents in LDL. The results support the hypothesis that the epitope expression of apoB is modulated by the composition of the lipids associated with it.

A G- to A-DNA sequence change in exon 26 of the human apolipoprotein B (apo B) gene leads to a glutamine substitution for arginine at codon 3611 of the mature apolipo-protein B100 and causes a loss of an MspI site. In 106 Finnish individuals, a complete correspondence exists between this MspI polymorphic site and the Ag (h/i) immunochemical polymorphism. Linkage disequilibrium was found between this MspI polymorphic site and the apo B XbaI and EcoRI variable sites and the Ag (al/d) and (c/g) epitope pairs; there is apparent linkage equilibrium with the apo B PvuII variable site. Based on three population studies (samples from London. Finland and Italy), no significant association was found between this RFLP and serum cholesterol and apo B levels. These data suggest that the arginine 3611----glutamine 3611 substitution has no significant effect on apo B function.