While the high molecular weight splice form including the exon 5-encoded segment is the major slow TnT expressed in normal muscles, the low molecular weight slow TnT became predominant in overused prior polio muscle and significantly up-regulated in type 1 (demyelination), but not type 2, Charcot-Marie-Tooth disease (Larsson et al., 2008). This evidence concerns the gene TNNT1 and Charcot-Marie-Tooth disease.