MLIP-related myopathy: two unreported pathogenic variants. Case report.

Introduction The muscle disorder known as myopathy with myalgia, increased serum levels of Creatine kinase, and with or without episodic rhabdomyolysis-1 (MMCKR1) (MIM: 620138), is a MLIP-related myopathy characterized by muscle cramps and stiffness on exertion of variable age onset, cardiac involvement, episodic spikes of high levels of CK, and rhabdomyolysis. The electromyography shows myopathic changes and on muscle biopsy: nonspecific myopathic and degenerative features. To date, around 15 cases have been reported worldwide. Case presentation Here we describe 2 cases with MLIP-related myopathy, case 1 was a compound heterozygous for c.645+2T>C and c.1905_1912del in the MLIP gene; case 2 was homozygous for c.1905_1912del. We described their findings and compared them with previously reported cases. Discussion Here we report the first two Mexican cases with MLIP-related myopathy; they showed two previously unreported variants. In both cases, the predominant clinical manifestations were muscle stiffness triggered by walking or running. No case presented myalgia, cramps, or rhabdomyolysis. We highlight the joint, neurologic and behavioral findings in case 1, none of which have been previously described in patients with MLIP-related myopathy.