Mechanisms of twinning. II. Laterality and intercellular bonding in monozygotic twinning.
OBJECTIVE
To utilize observations on laterality and handedness to gain insight into the initiating mechanism of monozygotic human quadruplets.


METHODS
In a study of thumbprints and handedness in sets of monozygotic quadruplets, homolateral and heterolateral comparisons were used to distinguish mirror-image from symmetric divisions.


RESULTS
Data were consistent with a mechanism involving a mirror-image duplication in the first division and a subsequent symmetric separation of the daughters. In addition, these data failed to substantiate a genetic linkage between dermatoglyphics and handedness.


CONCLUSIONS
Reported and reviewed data tend to support the analogy of monozygotic polyembryony in armadillos and humans. The plausible roles of delayed implantation and intercellular bonding are explored, especially as they relate to ambient calcium concentration. Factors tending to enhance the likelihood of monozygotic twinning include calcium channel blockers, lactation, ovulation induction and prolonged in vitro fertilization incubation.
Steinman
G
G
Department of Obstetrics and Gynecology, Long Island Jewish Medical Center, New Hyde Park, New York, USA. dav4601@aol.com
D003878:Dermatoglyphics; D005260:Female; D007839:Functional Laterality / Q000235:genetics*; D008040:Genetic Linkage; D006801:Humans; D011247:Pregnancy; D011272:Pregnancy, Multiple; D014430:Twins, Monozygotic / Q000235:genetics*