Elevated urinary beta 2 microglobulin in the first identified Japanese family afflicted by X-linked myopathy with excessive autophagy

Here we report what is to our knowledge the first identified Japanese family afflicted by X-linked myopathy with excessive autophagy. The index case is a 52-year-old man with almost 40 years of progressive proximal muscle weakness. High urinary beta 2 microglobulin, normal serum beta 2 microglobulin, autophagic vacuoles with sarcolemmal features, and a hemizygous c.164a7T>G mutation in the VMA21 gene were found. His two maternal uncles had similar clinicopathological findings. High urinary beta 2 microglobulin without obvious renal dysfunction might result from decreased urine acidification in the distal convoluted tubules caused by the VMA21 gene mutation. These findings might prove to be useful as a preliminary marker suggestive of X-linked myopathy with excessive autophagy.