Coital frequency and twinning. A comment

Heteropaternal twinning: Unique case of opposite-sex twins with different fathers

A presumably rare, but naturally occurring twinning event is heteropaternal (HP) twinning. HP twinning results from superfecundation, a reproductive process in which offspring share their mothers, but not their fathers. The resulting twins share an average of 25% of their segregating genes, the same proportion as half-siblings. A recently identified case of HP opposite-sex twins was confirmed by DNA analyses available for the twins and for multiple family members. Thus, an exceptional feature of the current report is the inclusion of data for the twins' brothers, sisters, half-siblings, nieces, nephews and cousins, as well as several parent-child pairs. HP twins often go unnoticed so are typically classified as dizygotic (DZ) twins whose genetic overlap is 50%, on average, but varies across traits. As a unique category of non-identical twins, HP twinning is important to acknowledge as it may affect twins' physical resemblance, behavioral similarity, personal identity, family relations and health concerns. While including HP pairs in twin research has been shown to have minimal impact on heritability estimates, it could conceivably affect the outcomes of small-scale studies. Given a lack of consistent and known prevalence, case studies provide valuable knowledge regarding the occurrence of HP twinning. Its implications for forensic science and for twin research are considerable.

The Rare Sides of Twin Research: Important to Remember/Twin Research Reviews: Representation of Self-Image; Twins With Kleine–Levin Syndrome; Heteropaternal Lemur Twins; Risk of Dental Caries/In the Media: High-Society Models; ‘Winkelevii’ Super Bowl Twins; Multiple Birth × Three; Twin Sister Surrogate; A Presidential Twin?

This article explores some rare sides of twin research. The focus of this article is the sad plight of the Dionne quintuplets, born in Canada in 1934. However, several other studies belong in this category, such as Dr Josef Mengele’s horrifying twin research conducted at the Auschwitz concentration camp, Dr John Money’s misguided attempt to turn an accidentally castrated male twin into a female, Russian scientists’ cruel medical study of conjoined female twins and Dr Peter Neubauer’s secret project that tracked the development of separated twins. Reviews of current twin research span twins’ representation of self-image, twins with Kleine–Levin Syndrome, heteropaternal twinning in lemurs and factors affecting risk of dental caries. Media coverage includes a pair of high-society models, a book about the ‘Winkelevii’ twins, Super Bowl twin teammates, a family with three sets of fraternal twins, a twin sister surrogate and a near presidential twin.

Zygosity Diagnosis: When Physicians and DNA Disagree

Physicians and other medical professionals do not always provide new parents with an accurate diagnosis of their twins' zygosity. An overview of this problem is presented, supplemented by an interview with a mother who recently learned that her 2-year-old 'dizygotic (DZ)' twin girls are actually 'monozygotic (MZ)'. Reviews of two case studies, one of twins with sex-discordance and chimerism and the other of twins with congenital amegakaryotic thrombocytopenia, follow. Two additional studies, one a twin analysis of attractiveness to mosquitoes and the other a study of twins coping with crisis, are also described. Several articles and letters from the popular media, concerning less favored twins, paternity issues surrounding superfecundation, twins with late-onset Tay-Sachs disease, and triplets admitted to MIT are informative and insightful.

Identical twin parents; research reviews: twin pregnancy risk factors, a new twin type and a school legislation update; twin parents and twin researchers in the news

Some legal and social complications that arise when identical twins have children are examined. The specific case presented concerns assignment of paternity. This section is followed by a review of recent studies of multiple birth pregnancy risk factors, namely mother to infant HIV transmission and congenital hypothyroidism. Honors given to recently recognized twin researchers are noted, as is the birth of twins to an older mother in the United States.