The variability of magnesium and zinc concentrations in plasma and erythrocytes was investigated by twin and family studies. Twins were sampled in two distinct ways and in two different West-European regions. In one of the samples, a distinction was made between twins living together and twins living apart. Two series of families were studied, one in a homogeneous environment, the other in a more diverse environment. Samples were compared by variance analysis. The results show 1) that genetic variability is significant for red blood cell (RBC) magnesium and zinc, minor for plasma magnesium and absent for plasma zinc; 2) that the family environment affects the extent of resemblance between twins and between siblings more for plasma levels than for RBC levels of magnesium and zinc. Furthermore, the intercorrelation analysis suggests that the genetic regulation systems of RBC magnesium and zinc are different, whereas some of the environmental regulation systems of plasma magnesium and zinc are the same. Biological interpretations are brought forward and discussed.

The best time for twin delivery is at 38 or 39 weeks gestation. Systematic Caesarean section or induction is decided upon during these weeks. Thanks to this policy, the good results formerly obtained have been maintained and an important decrease in emergency Caesarean sections has been noted thus reducing the risks inherent in this method. However, a randomized trial is necessary to confirm these results.

This article is a review of the technique of matching as it applies to epidemiological investgations of the etiology of disease. It is written for researchers who wish to use twins as the matched pairs in studies of this type.

Anti-A and anti-B titers were measured in 60 twin pairs and their families. Family data shows high correlations of antibody titer values for first degree relatives but no significant spousal correlations.

In a recent paper in this journal [5], Wilson offers a revision of his previously published method [4] for diagnosing the zygosity of twins from bloodtype findings. Wilson notes that his revised method will yield the same results (given the same estimates of gene frequencies) as will the methods described by Smith and Penrose [2], Sutton et al [3], and Lykken [1], and he advocates his new method, over the others, as being “simplest and most direct.” He also reinterprets various quantities employed by Lykken and proposes a different index of the efficiency of a genetic marker for zygosity diagnosis. In this note, I attempt to clarify the relationship between Wilson's revised method and my own, so that the reader can more accurately assess their relative advantages.