Independence of brachymesophalangia-5 from brachymesophalangia-5 with cone mid-5.

Analysis of hand radiographs of juvenile siblings of juvenile propositi indicates that brachymesophalangia-5 alone (without cones) is separately inherited without apparent sex bias while brachymesophalangia-5 with the cone-epiphysis of mid-5 and the cone-epiphysis of mid-5 alone are both apparently inherited as a complex and with a marked excess of females over males. Brachymesophalangia-5 is a not-uncommon variant of the hand skeleton with population frequencies ranging from below 1 % to over 10% in different human groups (Garn, '71; Garn et al., '67; Hertzog, '67; Abbie, '70; Greulich, '70). Prior to complete epiphyseal union, brachymesophalangia-5 may also be associated with a peg-shaped or cone-shaped epiphysis (Hertzog et al., '68) and some authors have assumed a cone-epiphysis is subject to premature union and therefore leads to length restriction of the affected phalanx (cf. Giedion, '65; Caffey and Silverman, '67; de Iturriza and Tanner, '69). The extent of association between brachymesophalangia-5 and a cone-epiphysis can best be ascertained in subjects large enough to evidence a well-developed epiphysis, yet prior to epiphyseal union. This we have done using radiographs of 8854 juvenile participants in the Ten State Nutrition Survey of 1968-1970 and limiting subjects to those between 3.5 and 12.0 years. Of the total number of children considered, 186 exhibited brachymesophalangia-5 and 51% of those affected were also characterized by a coneepiphysis, including the full cone-andcrater complex. Separately, 163 boys and girls evidenced a cone-epiphysis of mid-5 and 58% of those with cones also exhibited brachymesophalangia-5 (cf. table 1). Clearly, there is an association between the two variants with a larger AM. J. PHYS. ANTHROP., 36: 295-298. proportion of those with cones showing brachymesophalangia-5 than vice versa. A second approach to the association between brachymesophalangia-5 and the cone-epiphysis of mid-5 is through the siblings of affected propositi, noting whether the siblings of index cases tend to resemble the propositi. This we have also explored, first separating propositi with brachymesophalangia-5 alone, from those with the cone-epiphysis alone, and both groups of propositi from those with the combination brachymesophalangia-5 and cone-epiphysis mid-5 (see fig. 1). As explained above, both propositi and siblings were restricted to the age limits 3.5 to 12.0, no propositus was used more than once, and only sibships with one or more siblings in the designated age range were considered. This sibling analysis proved especially revealing, because brachymesophalangia-5 alone segregated out separately from cones-alone and the combination of brachymesophalangia and cones. To begin with, 109 siblings of 49 propositi with brachymesophalangia alone evidenced a far higher incidence of the short middle phalanx (1 1 % ) than in the population sample considered (2.1 % ), a difference significant at any reasonable level of confidence. Of even greater interest, the 12 affected siblings of propositi with brachymesophalangia alone were largely of the variant brachymesophalan-