Younger animals show intermittent hind limb spasms and curled front or hind limb toes, however, the phenotype becomes more severe with age; mutants are then barely able to use their hind limbs which frequently remain closely clasped to their body. While moving or sitting, hind limbs may also turn flaccid, and occasionally cross over or become intertwined. When picked up by their tail, mutants of any age keep hind limbs closely clasped to their body; the hind limb flexor reflex is quite brisk. The phenotype becomes observable at 4.6+/-2.2 weeks of age (average; n=36); it might be possible to maintain a colony through regular breeding, however some mutants were found to be unproductive, and age or severity of phenotype expression may have contributed to that.
Standard pathology work-up on two mutants (10 or 31 days of age) revealed thin cerebellar folia in the older mouse; no other abnormalities were noted in either animal. Whole muscle mounts of the hind limb of an additional mutant (59 days of age) stained with fluorescent-labeled bungarotoxin, SV2, or SMI 31 also revealed no abnormalities.
