Ge et al. (1) consider the extension of Fisher’s classic model for heritability to the case where there are repeated measurements on subjects. One approach to analyzing repeated measurements is to average observations. The authors show empirically and via simulations that estimates of heritability derived from averaging repeated measurements lead to underestimates of heritability. Some may find...

The Fullerton Virtual Twin Study has been assessing the behaviors of an unusual sibship since 1982. Virtual twins (VTs) are same-age, unrelated siblings reared together since infancy. They replicate the rearing situation of twins but without the genetic link, enabling direct assessment of shared environmental effects on behavior. An updated analysis of IQ data, based on an increased sample of 1...

This article discusses studies of separated twins, with special emphasis on the Minnesota Study of Twins Reared Apart (MISTRA), to determine whether they support the existence of an important genetic component in behavioral and personality differences. The methods and conclusions of the MISTRA team are discussed in the context of earlier studies of separated identical twins. I argue that volunt...

12 cases of conjoined twins from West Africa were reported between 1936 and 1978. Eight sets were liveborn and were surgically separated either in local hospitals or abroad. Four were stillborn. Two new cases of stillborn conjoined twins were recently delivered at this hospital. The most common type and the ones most likely to be born alive were the omphalopagi. Surgical separation was successf...

Highlights from the 15th International Congress of Twin Studies are presented. The congress was held November 16-19, 2014 in Budapest, Hungary. This report is followed by summaries of research addressing the differentiation of MZ co-twins by single nucleotide polymorphisms (SNPs), an unusual error in infant twin-singleton hospital registration, twins with childhood-onset narcolepsy with cataple...

Given the associated intricacies associated with surgery and anesthetic management, the care of conjoined twins requires a multidisciplinary approach. Due to the complexity of these patients, anesthetic care may be required for radiologic imaging, placement of tissue expanders, insertion of permanent or temporary vascular access devices, and definitive separation surgery. We present a case of p...

Siamese or conjoined twins have intrigued both the physician and layperson for centuries. The craniopagus type (joined at the head) is exceedingly rare, with an incidence of one in 2.5 million births. Most clinicians never see a case of craniopagus, and those who do rarely see more than one. The authors present a case of the craniopagus type of conjoined twins born and recently separated in Bri...

The aetiology of conjoined twins is unknown with no established risk factors. The pathogenesis is also uncertain but if cell differentiation takes place after the 14th day of embryonic development, incomplete cleavage will result in the formation of conjoined twins. A system of classification established by St Hiliaire in 1832 is still used today and is based on which structures are fused. The ...

Dicephaly is a peculiar type of conjoined twins, which is observed in cattle and other vertebrates. The analysis demonstrates the course and division of arteries of the cranium of a one-day-old two-headed conjoined calf. In comparison with the normal pattern of the bovine cranial vasculature, the arteries of the head of the conjoined animal were considerably modified. The absence of the arterie...