Fingerprint body myopathy is a rare muscle disease characterized by weakness and reduced muscle mass and by subsarcolemmal, non-membrane-bound inclusions that are frequently adjacent to mitochondria. The author addresses major concerns with this rare condition and highlights specific case studies.
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• Fingerprint body is a rare congenital myopathy.
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• Only 6 cases of fingerprint myopathy have been described to date.
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• Fingerprint myopathy is defined by subsarcolemmal inclusions on muscle biopsy; the inclusions have a characteristic lamellar pattern on electron microscopy.
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• The cause of fingerprint myopathy is unknown, although one case was felt to be caused by mutations in a gene causative of nemaline myopathy (LMOD3).
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• An increasing number of protein aggregate myopathies are now recognized. The multitude of diverse proteins aggregating within muscle fibers suggests a common pathway of impaired extralysosomal degradation of proteins or defects in sarcomeric development and maturation.
Historical note and terminology
The first case of this ultrastructural myopathy described was in a 5-year-old girl with weakness (02). Five additional cases have since been reported, including 2 half-brothers (03), twin boys (01), and a boy first biopsied at 11 years of age. A similar abnormality was discovered in muscle obtained from a 54-year-old woman with static muscle weakness from early childhood (05) and in 2 adult siblings with proximal weakness from early childhood (14).
Light microscopy reveals either type 1 predominance or normal pattern. Inclusion bodies are generally not apparent histologically. When they are seen on light microscopy, fingerprint bodies may appear as pale or eosinophilic inclusions on the Gomori trichrome stain (14). Of the 6 children with congenital weakness (02; 03; 01; 08), 4 had type 1 fiber predominance, 1 had normal fiber typing, and muscle histology was not described in the sixth. Using their prior identification of ultrastructural fiber typing (11), Payne and Curless demonstrated type 1 specificity for the fingerprint inclusions (10).
Fingerprint bodies are occasionally seen in other neurologic conditions. Identical ultrastructural findings in patients without muscular signs or symptoms were noted in 3 adult patients with myotonic dystrophy (15) and in a patient with Marfan syndrome (06). Sengel and Stoebner found fingerprint bodies in the muscle of 5 adults; 2 had emphysema and the others had a progressive myopathy, cardiomyopathy, myotonic dystrophy, or progressive ataxia. These authors also reported fingerprint bodies in a child with a central nervous system degenerative disorder (13). Fingerprint bodies were also described in an adult with oculopharyngeal muscular dystrophy. There was no limb extremity weakness, and the biopsy was obtained from a deltoid muscle (07).