An excess of the Pi Sallele in dizygotic twins and their mothers

Abstract

A significant excess of the alpha 1-antitrypsin (protease inhibitor) PiS allele has been found in 147 pairs of dizygotic (DZ) twins, but frequencies in 170 pairs of monozygotic (MZ) twins do not differ from those in a sample of 1007 blood donors. In 51 mothers of DZ twins the frequency of the PiS allele was double that in the same sample of donors, but there was no corresponding increase in the fathers of DZ twins nor in the parents of MZ twins. In an independent sample of 66 mothers of twins of unknown zygosity, there was also a significant excess of PiMPiS and PiMPiZ phenotypes, and this was particularly marked in the subsample of mothers of opposite-sex twin pairs. We speculate that lowered protease inhibitor levels in women carrying the PiS allele may enhance sperm migration, increase the probability of multiple ovulation, or both.

Protease inhibitor (Pi) locus, fertility and twinning

“…We have replicated the results of Clark and Martin (1982) in showing a large excess of the S allele in mothers of DZ twins compared with controls, and an intermediate frequency in DZ twins themselves. Unlike Clark and Mar-…”

“…We show an increased frequency of the Z allele in mothers of DZ twins, but not in any other group. The pattern of gene frequencies from their study led Clark and Martin (1982) to postulate that the sole effect of S (and perhaps Z) on fertility was mediated through an increased ovulation rate in women who carried these alleles, the most obvious manifestation of this being that these women show a higher frequency of bearing DZ twins. In the present study, the most striking increase in the frequency of the S allele is also seen in mothers of DZ twins.…”

“…There was also an increased frequency of the S allele in fathers of dizygotic twins; however, this may be a secondary effect of assortative mating for family size (indicating by the number of siblings of the parents), for which a correlation of 0.2 was observed. Parents of dizygotic twins came from larger families than parents of monozygotic twins, but no effect of Pi type on family size was seen.Clark and Martin (1982) found that the frequenc of the S allele in mothers of dizygotic (DZ) twins (0.088) was double that in controls (0.044). The frequency of S in monozygotic (MZ) twin parents and in fathers of DZ twins was no higher than in controls.…”

“…Clark and Martin (1982) found that the frequenc of the S allele in mothers of dizygotic (DZ) twins (0.088) was double that in controls (0.044). The frequency of S in monozygotic (MZ) twin parents and in fathers of DZ twins was no higher than in controls.…”

Variation in bone morphogenetic protein 15 is not associated with spontaneous human dizygotic twinning

“…Taken together, our results suggest GDF9 plays a more important role than BMP15 in the regulation of twinning in humans (Montgomery et al, 2004;Palmer et al, 2006). Associations between DZ twinning and variants in other genes including FMR (Vianna-Morgante, 1999; Marozzi et al, 2000) and SERPINA1 (Clark and Martin, 1982;Boomsma et al, 1992) have been reported, but none have been replicated in large samples.…”