Type A3 brachydactyly is shortening of the middle phalanx of the fifth finger. Slanting of the distal articular surface of the middle phalanx leads to radial deflection of the distal phalanx. Because of rhomboid or triangular shape of ... Type A3 brachydactyly is shortening of the middle phalanx of the fifth finger. Slanting of the distal articular surface of the middle phalanx leads to radial deflection of the distal phalanx. Because of rhomboid or triangular shape of the rudimentary middle phalanx, radial curvature (clinodactyly) of the fifth finger results (Temtamy and McKusick, 1978). Bauer (1907) described this anomaly in 4 generations. Dutta (1965) described 'simple radial deviation of the distal phalanx' without bony deformity of the middle or distal phalanx and with normal length of the digit. Whether this is a separate trait is not certain. Type A3 brachydactyly is variable and may encompass the cases described by Dutta (1965) (Temtamy and McKusick, 1978). Hertzog (1967) defined shortened fifth medial phalanges as those less than half the length of the fourth medial phalanx. Hertzog (1967) studied 296 children in Philadelphia, 200 Black and 96 Chinese, and found the trait in 12 of the Chinese children and in none of the Black children. The trait occurred more frequently in females. Two of the affected Chinese children had clinodactyly. X-rays showed well-proportioned diaphyses and cone-shaped epiphyses with early union. In a study of BDA3 among youth in the Jiral population in Nepal, Williams et al. (2007) found that the incidence of cone-shaped epiphyses with BDA3 was nearly double for females compared to males. They suggested that BDA3 with cone-shaped epiphyses is transmitted differently, and separately, from BDA3 and that the former has a strong sex-bias (female:male, 5:2).
Buschang and Malina (1980) noted that 2 indices had been used in previous studies of brachymesophalangy V in various populations: Index 1, based on the ratio of the width to the length of the fifth mid-phalanx, and Index ... Buschang and Malina (1980) noted that 2 indices had been used in previous studies of brachymesophalangy V in various populations: Index 1, based on the ratio of the width to the length of the fifth mid-phalanx, and Index 2, based on the ratio of the length of the fifth to the length of the fourth mid-phalanges. They used both indices to identify the trait among 2,012 individuals from 5 samples of children of different ethnic backgrounds. Index 1 consistently produced higher frequencies than index 2. However, both indices indicated highest relative frequencies among Mexican children, moderate frequencies among children of European ancestry (Pennsylvania White, Canadian, West German), and lower frequencies in Pennsylvania Black children. Buschang and Malina (1980) suggested that Index 2 provides a more accurate indicator within a population as well as a measure that is more comparable between different populations. Their Table 1 listed the results of previous population studies of brachymesophalangy V along with the index used in each study. Williams et al. (2007) noted that as part of a genetic epidemiologic study of the growth and development of children in rural Nepal (Jiri Growth Study), hand-wrist radiographs were taken annually of children of the Jirel ethnic group. From a study of the latest radiographs of 1,357 Jirel youths (676 boys, 681 girls), aged 3 to 20 years, for the presence or absence of BDA3 (based on length, width, and shape of the bone), they found an overall prevalence of BDA3 of 10.5% (12.9% of males and 8.9% of females). Their Table 2 listed the results of previous population studies of 'a short, broad middle phalanx of the fifth digit.'