This strain shows gait disturbance and growth retardation. These mice spontaneously appeared in the colony of inbred C57BL/6N Jcl mice. These mice show significant postnatal growth retardation and almost all babies die in infancy. Even if babies survive after weaning, they become gait disturbance. The result of breeding test showed that phenotypes of this strain were autosomal dominant inheritance and heterozygous mice also showed such symptoms. As a result of soft X-ray analysis, these mice observed tibial dysgenesis, compensatory hypertrophy of fibula and mirror-image polydactyly in all four limbs. This strain is similar to phenotypes of hemimelic extratoes (Hx) reported in mice, but these mice don't observe any mutation such as base substitution in close to Hx mutation sites. As a result of microsatellite analysis after mating with DBA/2, it found that this strain had mutation in the chromosome 5. At present, this strain is maintained as hybrid strain between C57BL/6N Jcl and DBA/2Cr Slc.