Protease inhibitor (Pi) locus, fertility and twinning

D.I. Boomsma, R.R. Frants, R.A. Bank, N.G. Martin

Research output: Contribution to JournalArticleAcademicpeer-review

197 Downloads (Pure)


In a sample of 160 Dutch twin pairs and their parents, we found that mothers of dizygotic twins had frequencies of the S and Z alleles at the protease inhibitor (Pi) locus that were 3 times higher than a control sample. Mothers of identical twins also had a higher frequency of S than controls. The S allele may thus both increase ovulation rate and enhance the success of multiple pregnancies. 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. © 1992 Springer-Verlag.
Original languageEnglish
Pages (from-to)329-332
JournalHuman Genetics
Issue number3
Publication statusPublished - 1992

Cohort Studies

  • Netherlands Twin Register (NTR)


Dive into the research topics of 'Protease inhibitor (Pi) locus, fertility and twinning'. Together they form a unique fingerprint.

Cite this