Concentrations of Serum α₂-Macroglobulin in Twins

Abstract

IF monozygotic twins (MZ) are more similar with respect to a given characteristic than dizygotic (DZ) twins, the characteristic is usually considered to be regulated genetically. With this in mind we have studied the concentrations of serum α₂-macroglobulin in a series of twins previously described in detail by Rowe et al.¹; the likelihood of correct diagnosis of dizygosity was 100 per cent and that of monozygosity more than 90 per cent. Sera from eighty-two like-sex twin pairs were available for study after storage for 3–4 years at −20° C. We have shown that prolonged storage does not influence the α₂-macroglobulin levels of sera kept at this temperature. Details of age, sex and zygosity of the twins are given in Table 1. Serum α₂-macroglobulin was assayed by radial immunodiffusion in agar gel² with rabbit antibody raised against human α₂-macroglobulin by the method of Goudie et al.³. Each agar plate contained twenty-four assays consisting of duplicate tests on twelve specimens, namely, the serum of five twin pairs, a repeat test on one of these sera to assess the measurement error within one plate, and a standard serum; the twenty-four assays were placed randomly within the plates and pairs of sera from both monozygotic and dizygotic twins were allocated randomly among the plates. The diameters of the rings of precipitate formed after 48 h at 20° C were read to 0.1 mm by an observer who did not know the arrangement of sera on the plates, and the arithmetic mean of the duplicate tests on each specimen was used in the calculations. Four entire assay plates were repeated to assess the measurement error between plates, and two further plates were used to prepare calibration curves with varying concentrations of standard serum and a serum of known α₂-macroglobulin content (Behringwerke Ag).