The New Sesquizygotic Twins and More: Exotic Twin Types/Twin Research Reviews: Parental Affection and Co-Twins’ Personality; Prenatal Demise in Twin Pregnancies; Heteropaternal Superfecundation; Selective Feticide in Dichorionic Twins/In the News: Identical Twin Oscar Winner; ‘Superfecundated’ Twins with Gay Fathers; Partly Living Apart; Which Twin Committed the Crime?

The mystery of monozygotic twinning II: What can monozygotic twinning tell us about Amyoplasia from a review of the various mechanisms and types of monozygotic twinning?

Monozygotic (MZ) twins ("identical twins") are essentially unique to human beings. Why and how they arise is not known. This article reviews the possible different types of MZ twinning recognized in the previous article on twins and arthrogryposis. There appear to be at least three subgroups of MZ twinning: spontaneous, familial, and those related to artificial reproductive technologies. Each is likely to have different etiologies and different secondary findings. Spontaneous MZ twinning may relate to "overripe ova." Amyoplasia, a specific nongenetic form of arthrogryposis, appears to occur in spontaneous MZ twinning and may be related to twin-twin transfusion.