Homozygotes are approximately 25% smaller than normal littermates by 1 to 3 weeks of age and by 8 to 12 weeks of age begin to display hind-limb clasping in toward the body, instead of splaying the hind-legs, when lifted by the tail. This phenotype has variable expressivity and males have failed to breed but females will generally breed. Thinner growth plates of the tibia and femur with disorganized columns of chondrocytes were found in the one male assessed histologically.
The abnormal hind leg mutation arose spontaneously in the NOD.CB17-Prkdcscid/J strain at The Jackson Laboratory. A mutant female was bred to NOD.B10Sn-H2b/J and the offspring were intercrossed to produce a mutant female that was then outcrossed to C57BL/6J. The line was found to be free of the Prkdcscid mutation and sperm was cryopreserved from heterozgyous male offspring at generation N1F1+B6N1. The line was outcrossed twice more to C57BL/6J and maintenance continued by sibling intercrossing. It is now maintained primarily by breeding homozygous females with heterozygous males.