An unusual family with brachydactyly

To the Editor:

The isolated brachydactylies were classified by Bell [1951] into five types (BDA-E) and three subtypes (BDA1-3). In the A-1 subtype, the middle phalanges of the fingers and toes are severely shortened or fused to the distal phalanges together with shortening of the proximal phalanges of the thumbs and halluces. Shortening is confined to the middle phalanges of the 2nd fingers/toes and of the 5th fingers, respectively, in BDA2 and BDA3. In type B, the middle and distal phalanges of fingers/toes are short/rudimentary or absent. BDC is characterized by shortening of the middle and/or proximal phalanges of the 2nd , 3rd, and 5th fingers associated with hypersegmentation of the proximal phalanges (2nd and 3rd fingers). The terminal phalanges of the thumbs and halluces are short and broad in BDD. Type E is characterized by shortening of metacarpals and/or metatarsals.

Additional BDA subtypes have been proposed: A4, absent middle phalanges of the fingers/toes and duplicated distal phalanges of the thumbs [Bass, 1968]; A5, shortening of the middle phalanges of the 2nd and 5th fingers together with absence of the middle phalanges of the lateral four toes [Temtamy and McKusick, 1978]; A6, hypoplastic or absent middle phalanges of hands and feet associated with carpal and tarsal bones coalescence [Osebold et al., 1985]; and A7, a combination of features of BDA2 and BDD with dislocated thumbs [Meiselman et al., 1989]. Fitch [1979] subdivided BDE into five types, involving shortening of only the 2nd metacarpal, only the 4th metacarpal, only the 4th metatarsal, or shortening of both 4th metacarpal and metatarsal; the fifth type was reserved for those cases with short metacarpals and distal phalanges. Short stature—as the result of the shortening of the long bones [Fitch, 1979]—may be a feature, specially in patients with BDE or BDA1.

The above types of brachydactyly are inherited as autosomal dominant phenotypes with variable expressivity. Reduced penetrance has been reported in association with some types [Bell, 1951; Temtamy and McKusick, 1978; Gray and Hurt, 1984].

This report concerns a family from the Northeast of Brazil with isolated brachydactyly primarily of the feet and with notable phenotypic variability. The pedigree (Fig. 1) illustrates the autosomal dominant pattern of inheritance with reduced penetrance. Living affected individuals ranged in age from 14 to 53 years. Clinical examination was performed on all individuals in this pedigree, and radiological studies of hands and feet were performed on all living affected persons. The main radiological findings are described in Table I and illustrated in Figure 2. Other features include bilateral hallux valgus in most patients, wide gap between the 1st and 2nd toes (II.7 and III.6), clinodactyly of the 4th (III.8) and 5th (III.6) toes, synostosis of the proximal and middle phalanges of the 3rd toes (III.6), and short nails in the affected digits. All patients have normal stature and intelligence. Deceased I.1 had short 4th toes and normal hands. Radiographs of his feet are not available. Individual II.10 is apparently a nonpenetrant carrier of the brachydactyly mutation, since he is clinically and radiologically normal and has two affected children. As presented in Table I, the phenotypic variability within this kindred is remarkable, ranging from only mild anomalies in the left foot of patient III.8 to severe defects in both feet of III.6 (Fig. 2). As all except one (III.8) of the patients have short metatarsal 4 (two of them also with short metatarsal 3), the diagnosis of BDE could be considered. On the other hand, all affected individuals have normal stature and metacarpals. Moreover, a variety of other digital defects found in this family are not clinical components of the BDE phenotype. Considering that Bell's classification is based mainly on the shortening of tubular bones of the hands and that two of our patients (II.7 and III.5) have short/broad distal phalanx of the thumb (the only defect in the osseous hand components in this kindred), BDD is also a possible type of brachydactyly in the family according to Bell's classification, despite the marked intrafamilial variability, the shortening involves mainly the tubular bones of the feet, and the phenotypic overlap with other BD types. Thus, a distinct type of brachydactyly cannot be excluded.