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In kindred A, 15 individuals from four generations, and in kindred B, four individuals from three generations had clinical features of RMD. The most consistent clinical findings were percussion-induced rapid muscle contractions (PIRCs) and m uscle mounding, which were present in all 19 affected individuals. Only 12 individuals exhibited muscle rippling, indicating that rippling is not always present in RMD. Twelve of 19 individuals had muscle-related complaints, primarily exertional cramps and stiffness. The mean age at the onset of complaints was 22 years (range, 5 to 54 years). Seven of 19 individuals showed only mechanical-induced muscle irritability but did not have muscular symptoms. Genetic analysis excluded linkage to the RMD locu s on chromosome 1q4 in both kindreds. The phenotype of RMD is variable but generalized PIRCs are the most obvious and reliable clinical feature of RMD. Diagnostic criteria of RMD should include generalized PIRCs in addition to muscle mounding, rippling, and creatine kinase elevation. |
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