Twinning, nonrighthandedness, and fusion malformations: Evidence for heritable causal elements held in common

Abstract

Certain relatively common congenital malformations that are reported to be excessive in frequency among twins are also found in excess among first-degree relatives of twins. They are familially associated with each other. Like twinning, they are familially associated with nonrighthandedness (NRH). They also share the fact that they affect structures that are built by the fusion of bilateral embryonic halves and then remodeled under the influence of neural crest mesenchyme. This conjunction of associations suggests that twinning, NRH, and the fusion malformations share causal elements, some of which may be heritable. Determination of spatial relationships in embryogenesis ("embryonic body symmetry determination") and the functions of neural crest mesenchyme may be mechanisms unifying these effects.

Human Embryogenesis

“…The parents of twins are more often nonrighthanded than their same-sex siblings -the maternal aunts and paternal uncles of the twins (calculated separately because of the consistent sex difference in frequency of nonrighthandedness in the general population). Each nonrighthanded parent increases probability of nonrighthandedness in the children -regardless of multiplicity -by a factor of about 1.5 (Boklage 1976(Boklage , 1977a(Boklage ,b, 1981(Boklage , 1987a.…”

“…Neither differs as a function of zygosity or chorionicity (Boklage, 1981(Boklage, , 1985(Boklage, , 1987aCarlier et al, 1996;Derom et al 1996) Something about establishing an unusual version of motor brain function asymmetry during embryogenesis and something about becoming twins at about that same time in embryogenesis is the same or closely related.…”

“…Following fusion of the asymmetric half-structures, the resulting midline structures are remodeled with and by mesenchyme cells descended from neural crest cells. Like nonrighthandedness, the malformations that are more frequent among twins than among singletons are also more frequent among the sibs and offspring of twins, without zygosity www.intechopen.com differences except in a few situations where the correlation is in fact stronger among the dizygotics and their families (Boklage 1985(Boklage , 1987a(Boklage ,b, 2010.…”

The value of twins in dental research

“…Twinning has been associated with a high peri-natal mortality rate 28 and there is also a higher frequency of congenital abnormalities in MZ twins, many of which seem to be related to failure of bilateral structures to fuse during development. 29 Martin et al 6 acknowledge that certain disorders are more common in twins, particularly in MZ twins, but claim that the potentially harmful effects of twin gestation have been over-emphasized. However, of considerable interest are the results of ultrasound scanning that indicate a large proportion of twins, possibly as high as 80 per cent, fail to develop past 16 weeks post-conception.…”

“…35 This has prompted the suggestion that there may be some common mechanism within certain families that accounts for both left-handedness and the twinning event. 29 However, further research is needed to confirm whether this is so.…”