Monozygotic (or identical) twins among mongoloid imbeciles are rarely encountered. Of 16 reported cases of mongolism in both twins of the same sex (table 1), 3 of the pairs have been described as dizygotic and the remaining 13 as monozygotic. In the accounts of these cases, however, an adequate analysis of the type of twinning was given only by Lund and by Gordon and Fraser; so the true proportion of types is still a matter of doubt. The case to be reported here has been previously discussed by one of us (Miss Frumkin) from the psychologic angle, but no biologic analysis of the twins was made. Dr. Elizabeth Nesbitt brought us together.
The biologic study of twins usually gives an accurate determination of the type of twinning (whether identical or fraternal), and in the case of twins with mongolism this analysis is most desirable before final conclusions are reached regarding
FORD N, FRUMKIN S. MONOZYGOSITY IN MONGOLOID TWINS. Am J Dis Child. 1942;63(5):847-858. doi:10.1001/archpedi.1942.02010050011002