A twin pair, discordant for congenital spinal cervical anomalies, is described. Zygosity chances are calculated on the basis of initial dizygosity chance, sex likeness, red cell antigens, serum types, red cell enzymes, and dermatoglyphic data. The chance for monozygosity adds up to 0.9992. Literature data on cervical anomalies in twins are reviewed.
It is concluded that, although the inheritance of spinal anomalies, such as hemivertebra, is still an open question, this twin pair supports the present trend of ideas that most of these anomalies are caused by peripheral, nongenetic factors.