Multiple marriages in this pedigree strengthen the evidence of a genetic basis for the inheritance of torsion. The apparent progenitor (I-1) was married twice, transmitting the abnormality to offspring of both marriages. Two later marriages of the mate of II-1 substantiate this conclusion, since none of the progeny of these two unions show the trait.
Examination of Chart I reveals that only those individuals possessing the trait transmit it to their offspring; that the trait manifests itself in every generation; that approximately one-half of the total number of individuals in the family are affected; and that the abnormality affects males and females alike.
A Mendelian autosomal dominant type of inheritance is demonstrated for bilateral medial tibial torsion in this pedigree.