Familial incidence of twinning

Abstract

The frequency of twinning among women who have already borne twins, the 'repeat frequency', is significantly higher than in the general population. Individual propensity is not necessarily genetic in origin, but pedigree studies (for reviews see refs 1, 2) confirm that twinning is a family trait. Studies based on archives restrict this conclusion to dizygotic (DZ) twinning and the maternal side, while studies based on interviews of relatives of twins find monozygotic (MZ) twinning and the paternal side also to be involved. However, interview studies can overestimate, while archive studies can underestimate, the real frequency of twinning. We have now analysed the incidence of twinning in the families of 950 zygosity-determined, unselected twin pairs under complete ascertainment. Our results indicate that a propensity to MZ twinning, as well as one to DZ twinning, can be inherited through the maternal line, and that the two mechanisms of twinning might be related. We have also found a paternal role in DZ, but not in MZ twinning.

Protease inhibitor (Pi) locus, fertility and twinning

“…The presence of AAT in ovarian tissue has indeed been established (Bagdasarian et al 1981); indeed, proteolytic enzymes may play a role in the rupture of mature follicles. The increased frequency of S in mothers of MZ twins suggests that another mechanism is also at work, although it is also possible that MZ and DZ twinning are not independent phenomena (Parisi et al 1983;Philippe 1985). The Dutch data are more in line with earlier data of Cook (1975) and Lieberman et al (1979) who have found increased frequencies of S in both MZ and DZ twins.…”

No paternal effect on monozygotic twinning in the Swedish Twin Registry

“…The i ndi cati ons of a geneti c transmi ssi on of monozygoti c tw i nni ng i n w omen i n previ ous studi es, [2][3][4] together w i th the l ack of evi dence of paternal effect i n monozygoti c tw i nni ng suggest that the gene(s) i ncreasi ng the l i ability for division of the embryo are expressed i n the mother and not i n the feri ti l i sed egg. The data are congruent w i th the hypothesi s that one cause of monozygoti c tw i nni ng i s due to an i nheri ted abnormal i ty of the zona pel l uci da i n the mothers.…”

“…1 Further, w e have earl i er show n that monozygoti c mothers have an i ncreased probability of giving birth to monozygotic offspring in a popul ati on-based regi stry study, 2 i ndi cati ng that, i n addi ti on, geneti c effects are of i mportance for thi s trai t. Support for geneti c effects i n monozygoti c tw i nni ng al so comes from i ntervi ew studi es w here mothers of monozygoti c tw i ns report an excess of monozygoti c tw i ns among thei r rel ati ves. 3,4 There are al so reports of i ncreased monozygoti c tw i nni ng rates i n sel ected pedi grees. [5][6][7][8] Recent studi es suggesti ng that frequency of tw i nni ng i s mai ntai ned by natural sel ecti on agai n i ndi cate the i mportance of geneti c effects.…”

Two Italian Twin Registers for Research in Human Biology and Sport Science

“…The records were used for research purposes, and occasionally systematic twin series were directly studied or surveyed for specific purposes. Because twins were recruited on a voluntary basis, the register was not population-based; although in the 1970s, it could still have been considered to be fairly representative of the general population of Rome (Parisi et al, 1983). In later years, however, partly on account of changes in the Institute's policy and the generalized free medical care provided by the national health system, fewer pairs were recruited annually, and many old pairs were lost.…”