Breeds Affected: Labrador Retriever
Samples Accepted: Blood, Buccal Swabs
Disease Information: Myotubular Myopathy 1 (MTM1), also known as X-linked Myotubular Myopathy (XLMTM) affects male dogs. Clinical symptoms are noted as early as 10 weeks of age, and include progressive muscle atrophy and weakness, difficulty rising or walking, difficulty swallowing, and a hoarse bark. Disease progress is swift, and most pups are euthanized within 4 weeks of diagnosis.
Inheritance Information: MTM1 is X-linked recessive, because the MTM1 gene is located on the X-chromosome. Male animals with the mutation (which have only one X chromosome) are affected. Females may have one normal and one mutated version and be asymptomatic carriers.
The possible genotypes are:
XX This dog is a normal female.
XXMTM1 This dog is a carrier female. She is clinically normal, but will pass the mutation (XMTM1) to 50% of her offspring. When bred to a normal male, she can have pups of all four genotypes: normal female (XX), carrier female (XXMTM1), normal male (XY), and affected male (XMTM1Y).
XY This dog is a normal male.
XMTM1Y This dog is an affected male.
– Female offspring of a carrier female should be genetically tested to determine if they are normal or carriers (XX or XXMTM1).
– Carrier females (XXMTM1) should not be bred, because affected males can be produced.
Test Information: This mutation test identifies a single base change in exon 7 of the MTM1 gene.
Beggs, A.H., Böhm, J., Snead, E., Kozlowski, M., Maurer, M., Minor, K., Childers, M.K., Taylor, S.M., Hitte, C., Mickelson, J.R., Guo, L.T., Mizisin, A.P., Buj-Bello, A., Tiret, L., Laporte, J., Shelton, G.D.: MTM1 mutation associated with X-linked myotubular myopathy in Labrador Retrievers. Proc Natl Acad Sci USA 107:14697-702, 2010. Pubmed reference: 20682747. Doi: 10.1073/pnas.1003677107.
Further information is available at the Online Mendelian Inheritance in Animals website.