LAUSR

Dear Editor, X-linked myopathy with excessive autophagy (XMEA) was firstly reported by Kalimo et al. in 1988 [1]. Five male patients from a Finnish family experienced proximal weakness in both lower extremities from 5–6 years of age [1]. Pathological results showed a small number of autophagic vesicles secreted under the membrane under the muscle fibers [1]. The typical clinical features of XMEA begin onset under the age of 10 and the first symptoms are often abnormal gaits. The lower limbs, shoulder joints, pelvis, and ankle joints could be slowly involved. The walking ability of the patients can generally be maintained until the age of 50 [1, 2]. In 2013, Canadian scholars identified the VMA21 gene as the gene affected in this type of myopathy. The VMA21 protein is an assembly chaperone of the vacuolar adenosine triphosphatase (V-ATPase). V-ATPase is a proton pump that widely exists to maintain the acidic environment in the lysosome [3]. Mutation in the VMA21 can cause a decrease of VMA21 expression, affect the function of V-ATPase, and increase the lysosomal pH [3]. This affects the function of lysosomes and may stimulate the motor alternative pathway, resulting in excessive phagocytosis of lysosomes and in the gathering of incompletely digested lysosomes under the muscle fiber membrane and the surrounding cells. This report is the first Chinese XMEA patient. Ultrapathological observation of this case has been reported in 2020 [4].