Later genetic testing revealed a genetic abnormality in two additional patients with non-informative biopsy results (one myotonic dystrophy type 1 in a patient with a CK level of 7300 IU/L and one MYH2 mutation in a patient with a CK level of 1200 IU/L), while genetic testing was negative in four other patients. This evidence concerns the gene MYH2 and myotonic dystrophy type 1.