Lipid-storage myopathy with glycogen storage disease gene mutations mimicking polymyositis: a case report and review of the literature

Abstract

A 26-year-old Asian woman with persistent muscle weakness was diagnosed with polymyositis based on biopsy findings at another hospital 11 years ago. However, her symptoms fluctuated repeatedly under treatment with prednisone and immunosuppressive agents, and worsened 2 months prior to the current presentation. A second muscle biopsy suggested metabolic myopathy, and genetic testing revealed a novel c.1074C > T variant in the glycogen synthase 1 gene (GYS1), which is implicated in muscle glycogen storage disease type 0. However, no abnormalities in glycogen deposition were found by biopsy; rather, muscle fibers exhibited large intracellular lipid droplets. Furthermore, muscle strength was greatly restored and circulating levels of creatine kinase indicative of muscle degeneration greatly reduced by vitamin B2 treatment. Therefore, the final diagnosis was lipid storage myopathy.

Keywords: GYS1; Lipid storage myopathy; case report; glycogen storage disease type 0; polymyositis muscle; vitamin B2.

Figure 1.

Medication prescribed to the patient from 2017 to 2021.

Figure 2.

Changes in CK and LDH from 2017 to 2021. CK, creatine kinase; LDH, lactate dehydrogenase.

Figure 3.

Electropherogram of the patient’s variant showing a homozygous variation (antisense chain) of c.1074c > t.

Figure 4.

Electropherogram of the patient's mother’s variant showing a heterozygous variation (antisense chain) of c.1074c > t.