—The comment by Segal and Bouchard that we do not have laboratory or fingerprint ridge-count evidence of monozygosity is appropriate. Unfortunately, at this time it is impossible for us to obtain measurements, as one of the members of the twin pair is not available to us. However, it should be noted on examination that the patients appeared identical with regard to hair color, eye color, and general physical characteristics. The patients thought that they were monozygotic and this is noted to be a strong indicator of monozygosity.1 In the event that these twins are not monozygotic but dizygotic the point of our article is still valid. In monozygotic twins with one member having mitral valve prolapse, the probable concordance rate would approach 100%. In dizygotic twin pairs, the autosomal dominant mitral valve prolapse trait would appear in approximately 50% of the other twin-pair members. Therefore, in the
Fisher M. Zygosity Diagnosis of Twins in Medical Research-Reply. Arch Intern Med. 1984;144(7):1509. doi:10.1001/archinte.1984.00350190215040
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