RYR1 and cardiomyopathy: A primary cardiomyopathy has not yet been reported in patients with confirmed mutations in the SEPN or RYR1 genes; however, cores on muscle biopsy are non-specific and may be found as an additional feature in patients with primary cardiomyopathies due to mutations in the DES, TTN, LMNA and ACTA1 genes (see paragraph on differential diagnosis).