Research in pharmacogenetics has provided evidence that individual variation in rate of metabolism of various drugs is genetically controlled. To evaluate the possibility of a genetic determinant of lithium ion distribution, a monozygotic (MZ)-dizygotic (DZ) twin study method was used. Red blood cell (RBC) lithium ion concentrations were assessed for ten MZ and seven DZ twin pairs following a 24-hour incubation in vitro.
The distributions of intrapair difference scores of MZ twin pairs and DZ twin pairs were relatively nonoverlapping, with MZ intrapair difference scores being smaller on the average. A heritability index of 0.85, calculated as a function of intrapair difference scores, indicated that a substantial genetic factor is operative in RBC uptake of lithium ion.