Heritable oligodactyly occurring only in male rats

Heritable oligodactylism in male rats was discovered in Wistar-derived rats. In this study, external and skeletal features of the limb anomalies were examined to clarify the type of oligodactyly. External observation revealed absence and hypoplasia (with respective percentage incidence) in digits II (100, 0), III (87, 13), and IV (23, 1) of the forefeet and in digits II (26, 34), III (34, 11), and V (0, 3) of the hindfeet. Fusion was also observed in digits IV and V in the forefeet (4%) and in digits I and II in the hindfeet (15%). Skeletal examination disclosed absence of all three (proximal, middle, and distal) phalanges in digits II (97%), III (93%), and IV (67%) and of the middle phalanx in digit V (12%) of the forefeet. In the hindfeet, the missing pattern of phalanges in digits II and III was similar to, but less severe than that in the forefeet; the incidence of absence of the three phalanges in digits II and III was 43% and 45%, respectively. Digit V was more affected than that in the forefeet; absence of the middle phalanx was found at 30%. Although no absence was found in the bones proximal to the phalanges, hypoplasia and/or fusion were detected with various degree and incidences among carpi/metacarpi and tarsi/metatarsi. Based on these observations, the types of limb anomalies in this mutant rat were classified as oligodactyly of digits II-V in the forefeet and II, III, and V in the hindfeet with hypoplasia and/or fusion of the carpi/metacarpi and tarsi/metatarsi.