Clinical and pathological features of Danon disease associated with a novel lysosome-associated membrane protein-2B mutation

Abstract

Objectives To report the clinical and myopathological features in a case with Danon disease caused by a novel mutation in the lysosome-associated membrane protein-2 ( LAMP2 ) B gene.Methods A 16-year-old boy presenting progressive muscle weakness and atrophy, accompanied with spinal ankylosis was clinically evaluated including electrocardiogram, echocardiogram and electromyogram.Muscle biopsy was carried out in the patient.The histological staining, ultrastructural examination, and immunohistochemical staining with antibodies against dystrophin, merosin and C5b9 were performed in frozen sections.LAMP2B sequence was analyzed in the patient and his parents.Results Electrocardiogram in the patient showed Ⅰ atrioventricular block; echocardiogram revealed focal hypertrophy in mitral valve with mild cardiac diastolic dysfunction; electromyogram indicated myogenic and neurogenic patterns.Muscle pathology study revealed numerous vacuoles located at the fibers.Dystrophin, merosin and C5b9 was immuno-positive around the vacuoles.Electron microscopy revealed vacuoles surrounded by sarcolemma and abnormal lysosome aggregating at the fibers.A novel nonsense mutation ( K402X ) in the LAMP2B gene has been identified in the patient but not in his mother and 50 normal controls.Conclusions Danon disease caused by K402X mutation in C-terminus of LAMP2B presented benign course of the disease characterized by prominent vacuolar skeletal myopathy, mild cardiac abnormalities and peripheral neuropathy. Key words: Glycogen storage disease type Ⅱ b; Lysosomal-associated membrane protein 2; Lysosomes; Muscle fibers