Infantile autophagic vacuolar myopathy is distinct from Danon disease Article abstract—Lysosomal glycogen storage disease with normal acid maltase (Danon) is caused by primary lysosome-associated membrane protein-2 (LAMP-2) deficiency. Typically, the disease begins after the first decade; however, two infantile patients had similar histologic features. The infantile disorder is distinct from Danon disease, because, in both infants, LAMP-2 protein is present in skeletal muscle. Deposition of C5b-9 and multi- layered basal lamina in one patient suggest that the infantile disease is pathogenically similar to X-linked myopathy with excessive autophagy. NEUROLOGY 2001;57:903–905 A. Yamamoto, MD; Y. Morisawa, MD; A. Verloes, MD; N. Murakami, MD, PhD; M. Hirano, MD; I. Nonaka, MD, PhD; and I. Nishino, MD, PhD Two forms of autophagic vacuolar myopathy have been identified: lysosomal glycogen storage disease with normal acid maltase 1 and X-linked myopathy with excessive autophagy (XMEA). 2 XMEA usually begins in childhood, progresses slowly, and affects skeletal muscle exclusively. The pathologic hall- mark of this disease is multilayered basal lamina and complement deposition over the surface of muscle fibers in addition to the presence of autoph- agic vacuoles. 3 Lysosomal glycogen storage disease with normal acid maltase is characterized clinically by hypertro- phic cardiomyopathy, myopathy, and variable men- tal retardation. Both patients described in the seminal report by Danon et al. had vacuolar myop- athy with increased glycogen and clinical manifesta- tions similar to glycogen storage disease type II; however, acid maltase activity was normal. 1 Accord- ingly, the disease was called “lysosomal glycogen storage disease with normal acid maltase.” Patients show X-linked inheritance, develop cardiac symp- toms in the second decade, and die of cardiac failure or arrhythmia around age 30 years. We identified primary deficiency of lysosome-associated membrane protein-2 (LAMP-2), a major lysosomal membrane protein, as the cause of the disease. 4 Therefore, we have redefined “Danon disease” as X-linked vacuolar cardiomyopathy and myopathy due to LAMP-2 deficiency. Two well-documented infants with autophagic vacuolar myopathy were described as having lysoso- mal glycogen storage disease with normal acid maltase. 5,6 Both patients presented with muscle weakness and hypotonia at birth and died early in their lives. Muscle biopsies showed extensive vacuo- lar changes with increased glycogen, but acid maltase activity was normal in both patients. Never- theless, atypical clinical manifestations raised the question: is infantile autophagic vacuolar myopathy genetically distinct from Danon disease? To assess this question and to further characterize the infantile disease, we performed immunohisto- chemical and electron microscopic analysis on the skeletal muscle from the patients and compared the morphologic features of the infantile cases with those of Danon disease and XMEA patients. Patients and methods. Patient 1. This patient was re- ported previously. 6 Briefly, this boy was a floppy infant from birth and had marked developmental delay. He had mild cardiomegaly. Muscle biopsy was performed at age of 2 months. After recurrent respiratory infections, he died of pneumonia at age 2 years 3 months. Acid maltase activity in the skeletal muscle was normal. Patient 2. The first patient with a fatal neonatal form of lysosomal glycogen storage disease without acid maltase deficiency. 5 This male neonate was hypotonic, developed progressive hypertrophic cardiac myopathy, and died 41 days after birth. Postmortem study showed increased gly- cogen content and normal acid maltase activity in heart, skeletal muscle, and liver. Immunohistochemical analysis. We immunostained skeletal muscle from the patients with monoclonal anti- bodies against LAMP-2 (H4B4, Developmental Studies Hybridoma Bank [DSHB], University of Iowa, IA), limp-I (H5C6, DSHB), and C5b-9 (Dako, Glostrup, Den- mark). Frozen muscle samples were available from Patient 1 and a patient with Danon disease. A formalin- fixed and paraffin-embedded sample was available from Patient 2. Transverse serial 8-m-thick frozen or 6 m-thick formalin-fixed paraffin sections were used. One section was stained with hematoxylin-eosin (H-E) while others were immunostained. The sections for immunostaining were blocked with 5% goat serum in phosphate-buffered saline (PBS). The concentration of first antibodies was as follows: LAMP-2, 1:100; limp-I, 1:100; and C5b-9, 1:50 for frozen tissue and undiluted for formalin-fixed muscle. The From the Department of Ultrastructural Research (Drs. Yamamoto, Mu- rakami, Nonaka, and Nishino), National Institute of Neuroscience, National Center of Neurology and Psychiatry (NCNP), Kodaira, Tokyo, Japan; De- partment of Pediatrics (Dr. Morisawa), Kochi Medical School, Nankoku, Japan; Walloon University Centre For Human Genetics (Dr. Verloes), Liège University, Liège, Belgium; Department of Neurology (Dr. Hirano), Colum- bia University, New York, NY; and Department of Pediatrics (Dr. Mu- rakami), Dokkyo Medical School, Saitama, Japan. Supported by the Research Grant (11B-1) for Nervous and Mental Disor- ders from the Ministry of Health and Welfare. Received January 30, 2001. Accepted in final form April 27, 2001. Address correspondence and reprint requests to Dr. Ichizo Nishino, De- partment of Ultrastructural Research, National Institute of Neuroscience, National Center of Neurology and Psychiatry (NCNP), 4-1-1 Ogawahigashi- cho, Kodaira, Tokyo, 187-8502 Japan; e-mail: nishino@ncnp.go.jp Copyright © 2001 by AAN Enterprises, Inc. 903