Most homozygous mice die before 30 days, although a few live longer. Homozygotes appear smaller, have difficulty feeding, and exhibit an accelerated myopathy characterized by increased fiber size variation and vacuolar structures within muscle fibers. Mice heterozygous for the mutation exhibit continuous myotonia of skeletal muscles, progressive age-related myopathy, reduced contractile force, delayed relaxation and potassium sensitive skeletal muscle weakness. A switch from a mixture of glycolytic and oxidative muscle fibers to an increased number of oxidative fibers is observed in multiple muscle types. The donating investigator reports that the Scn4atm1.1Ljh allele (neo out) has the same phenotype as the Scn4atm1Ljh allele (neo in) reported in Hayward et al, 2009. This mutant strain may be useful in studies of myotonia, vacuolar myopathy and hyperkalemic periodic paralysis (HyperKPP).
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. 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.

This targeted mutation of the sodium channel, voltage-gated, type IV, alpha (Scn4a) gene displays myotonia, muscle fiber type switching and potassium-sensitive weakness and may be useful in studies of myotonia, vacuolar myopathy and hyperkalemic periodic paralysis (HyperKPP).

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