DIFFERENCES in growth and development of monozygotic twins may be due to various causes. Inequalities in fetal blood supply account for early differences, and various environmental causes are under consideration for differences arising in postnatal life. If monozygotic twins are discordant in many respects, it is often not possible to find a common factor responsible for the dissimilarity.
In the cases reported below, hypothyroidism of one of the twins accounted for great differences in many physical and mental traits. The differences were marked at times but decreased later under intensive thyroid medication.
The twins are the only children of young, intelligent, and cooperative parents. The father's family history is noncontributory. Twinning had occurred in the mother's family. The mother's father was an identical twin who had twin grand-uncles. A maternal aunt became obese, tired, and chronically constipated when 17 years of age and improved on thyroid medication. The twin's mother
WARKANY J, SELKIRK TK. DISCORDANT MONOZYGOTIC TWINS: Hypothyroidism. AMA Am J Dis Child. 1955;89(2):144–148. doi:https://doi.org/10.1001/archpedi.1955.02050110186002
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