Skeletal muscle of patients with gyrate atrophy of the choroid and retina and hyperornithinaemia in ultralow‐field magnetic resonance imaging and computed tomography

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Abstract
Gyrate atrophy of the choroid and retina with hyperornithinaemia (GA), an autosomal recessive disease, affects skeletal muscle in addition to the eye. Muscle biopsy samples show prominent type 2 muscle fibre atrophy. Atrophic fibres also contain accumulations of tubular aggregates in electron microscopy. To evaluate skeletal muscle involvement in detail, the thigh muscles of 7 patients with GA were examined using semi-open conchotome muscle biopsies, computed tomography (CT) and ultralow-field magnetic resonance imaging (MRI) at 0.02 T. In MRI, the T1 and T2 proton relaxation times were measured. Type 2 muscle fibre atrophy was found in all biopsy samples (100%) and tubular aggregates in 6 of the 7 samples studied (87%). The CT density of the muscle tissue was increased in the only child of the study, decreased in 3 elderly subjects, and normal in the remaining 3 patients. Mean T1 relaxation times of the patients were decreased (135±5 ms) as compared to those of 6 healthy controls (157±12 ms) (p=0.002). The T2 relaxation time was slightly increased (40±3 ms) as compared to the controls (35±7 ms; not significant,p=0.3). Our findings suggest that the thigh muscles of the patients with GA universally show changes in CT and MRI studies, but relaxation time measurements gave little additional information on the muscle metabolism.