60  old man presented with 5 year history of progressive proximal lower limb weakness as manifested by difficulty raising from a chair and climbing stairs. Since about 2 years before, he developed abnormal gait, arm weakness, exertional shortness of breath, and...

Note the marked prolongation of distal latency of the right median nerve motor response (normal < 4.1 ms) and also prolongation of right ulnar nerve motor distal latency at the wrist (normal <3.8 ms). There is also slowing of the conduction velocity ...

The positive FH for malignant hyperthermia lead us to test  for skeletal muscle ryanodine receptor (RYR1) gene mutation. A previously described, disease associated,  heterozygous mutation in Exon 47 of the RYR1 gene was discovered. Diagnosis: myopathy...