Mice homozygous for the dystrophia-muscularis spontaneous mutations (Lama2dy and Lama2dy-2J) are characterized by progressive weakness and paralysis beginning at about 3 1/2 weeks of age. The hindlimbs are affected first, later the axial and forelimb musculature. Death usually occurs before 6 months of age, and mutant mice are usually sterile. Skeletal muscle shows degenerative changes with proliferation of sarcolemmal nuclei, increase in amount of interstitial tissue, and size variation among individual muscle fibers. In the dorsal and ventral roots of the peripheral nerves, both spinal and cranial, Schwann cells fail to separate and ensheathe axons so that groups of closely apposed naked axons, normally seen only in early stages, persist into adulthood. In the rest of the PNS, the basement membrane of Schwann cells is interrupted by gaps, the internodal gap in the nodes of Ranvier is lengthened, and there is delayed onset of myelination with fewer myelinated axons and shorter internode length. Homozygotes are usually sterile.
In an attempt to offer alleles on well-characterized or multiple genetic backgrounds, alleles are frequently moved to a genetic background different from that on which an allele was first characterized. This is the case for the strain above. It should be noted that the phenotype could vary from that originally described. We will modify the strain description if necessary as published results become available.
