The spontaneous mutation Dmd^mdx arose just prior to 1977 at the Agricultural Research Council's Poultry Research Centre, U.K., in C57BL/10ScSn mice obtained from M. Festing (MRC Laboratory Animals Centre, Carshalton, Surrey, U.K.). Mice carrying the mdx allele were imported to The Jackson Laboratory as Stock No. 001801 in 1984 by Dr. Thomas Roderick, who received them from Dr. Karen Moore (Department of Genetics, University of California, Berkley). Upon arrival, some mice were bred to DBA/2J inbred mice (Stock No. 000671) using a marker-assisted, speed congenic approach to generate a DBA/2J-congenic strain.

For the Utrn^tm1Ked targeted mutation, a targeting vector containing a PGK-Neo cassette was used to disrupt exon 7. The construct was electroporated into (129X1/SvJ x 129S1/Sv)F1-Kitl⁺ derived R1 embryonic stem (ES) cells. Correctly targeted ES cells were injected into C57BL/6 blastocysts. The resulting male chimeric animals were crossed to (DBA/2 X C57BL/6) F1 female mice. Heterozygotes were interbred to generate homozygotes. Upon arrival at The Jackson Laboratory as Stock No. 013158, the mice were crossed to B6D2F1/J mice (Stock No. 100006) at least once to establish the colony. Some mice were bred to DBA/2J inbred mice using a marker-assisted, speed congenic approach to generate a DBA/2J-congenic strain.

This double mutant strain (Stock No. 022506) was generated by crossing DBA/2J backcrossed Dmd^mdx/J mice and Utrn^tm1Ked/J mice.