MLIP-Related Myopathy: Two Unreported Pathogenic Variants - A Case Report

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 with a variable age at onset, cardiac involvement, episodic spikes of high levels of CK, and rhabdomyolysis. Electromyography shows myopathic changes, and muscle biopsy shows nonspecific myopathic and degenerative features. To date, around 15 cases have been reported worldwide.

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 and case 2 was homozygous for c.1905_1912del. We described their findings and compared them with previously reported cases.

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, neurological, and behavioral findings in case 1, none of which have been previously described in patients with MLIP-related myopathy.