X-linked myotubular myopathy in Rottweilers is an inherited muscle disease that manifests with severe, progressive muscle atrophy in puppies.

Phenotype: Puppies appear normal at birth but muscle atrophy is often seen by 7 weeks of age. Affected puppies often appear noticeably smaller than littermates and may have problems with coordination and mobility. Within weeks, the puppies may have difficulty in holding their head up and may an exhibit an inability to stand or may collapse after exertion. The disease is severe and most affected dogs being euthanized before 6 months of age.

Female dogs with N/N genoytpe and male dogs with N genotype will not have X-linked myotubular myopathy, and cannot transmit this variant to their offspring.

Female dogs with MTMR/N genotype will not have X-linked myotubular myopathy, but are carriers. If a carrier female is bred to a normal (N) male, all female puppies will be normal but 50% of them will be carriers. Among male puppies from this type of cross, 50% will be normal and 50% will be affected by X-linked myotubular myopathy.

Female dogs with MTMR/MTMR genotype and male dogs with MTMR genotype will have X-linked myotubular myopathy, a severe, progressive muscle disease.