Mouse Genome Informatics
phenotype observed in females
phenotype observed in males
N normal phenotype
• mice die after a few weeks to a few months of age

• when lifted by its tail, a mutant mouse keeps its hind limbs close to its body
• homozygous mutant mice exhibit intense body tremor both during movement and when at rest
• the hind limbs of homozygous mice often move together
• mutants' hind limbs appear weak, remaining low during locomotion

• at P20, mice exhibit increased type 1 slow msucle fibers in the gastrocnemius compared with wild-type mice
• Background Sensitivity: more severe on a C57BL/6J or DBA background than on other backgrounds
• homozygous mutants experience brief spasms of the front and/or hind limbs
• cross sections of axial muscle from 3 mutant mice ages 27 - 34 days revealed neurogenic myopathy; atrophied, denervated muscle fibers and small, regenerating fibers exist among normal-appearing muscle fibers

nervous system
• mice exhibit normal axon numbers and size
• mice exhibit abnormal neuromuscular junctions (NMJs) morphology with smaller, simpler postsynaptic sites than in wild-type mice
• diaphragm NMJs are abnormal at birth, severly affected at P4, and virtually completely degraded by P14 compared to in wild-type mice
• NMJ defects arise by P13 in the triangularis sterni with pre- and postsynaptic degradation at P18
• tibialis anterior NMJs are disaggregated by P14 compared to in wild-type mice
• NMJ postnatal degradation varies in different muscles
• however, mice do not exhibit die-back neuropathy


• homozygotes' toes, particularly those of the hind paws, may not extend fully
• hindlimb atrophy

Mouse Models of Human Disease
Myasthenia, Limb-Girdle, Familial 254300 J:176117