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| familial amyloid cardiomyopathy ： ウィキペディア英語版 |
familial amyloid cardiomyopathy
Transthyretin Amyloid Cardiomyopathy (ATTR-CM), or Familial Amyloid Cardiomyopathy (FAC), results from the aggregation of mutant and/or wild-type transthyretin protein in the heart.〔Jacobson, D. R., Pastore, R. D., Yaghoubian, R., Kane, I., Gallo, G., Buck, F. S. & Buxbaum, J. N. (1997). Variant-sequence transthyretin (isoleucine 122) in late-onset cardiac amyloidosis that occurs in black Americans. The New England Journal of Medicine 336, 466-73.〕 Both mutant and wild-type transthyretin comprise the aggregates because the TTR blood protein is a tetramer composed of mutant and wild-type TTR subunits in heterozygotes. The TTR tetramer has to dissociate in a rate-limiting step before the monomer can misfold and become aggregation competent.〔Colon, W. & Kelly, J. W. (1992). Partial denaturation of transthyretin is sufficient for amyloid fibril formation ''in vitro''. Biochemistry 31, 8654-60.〕 Senile systemic amyloidosis,〔Westermark, P., Sletten, K., Johansson, B. & Cornwell, G. G., 3rd. (1990). Fibril in Senile Systemic Amyloidosis is derived from normal transthyretin. Proceedings of the National Academy of Sciences of the United States of America 87, 2843-5.〕 a highly related cardiomyopathy, results from the aggregation of wild-type transthyretin exclusively.〔Ng, B., Connors, L. H., Davidoff, R., Skinner, M. & Falk, R. H. (2005). Senile systemic amyloidosis presenting with heart failure: a comparison with light chain-associated amyloidosis. Arch Intern Med 165, 1425-9.〕〔Westermark, P., Bergstrom, J., Solomon, A., Murphy, C. & Sletten, K. (2003). Transthyretin-derived senile systemic amyloidosis: clinicopathologic and structural considerations. Amyloid 10 Suppl 1, 48-54.〕 In these maladies, TTR amyloid fibrils infiltrate the myocardium, leading to diastolic dysfunction. Eventually, progression to restrictive cardiomyopathy and heart failure is seen.〔(【引用サイトリンク】url=http://www.amyloidosis.org/treatmentinformation/familial.html )〕 Several mutations in TTR are primarily associated with FAC, including V122I, V20I, P24S, A45T, Gly47Val, Glu51Gly, I68L, Gln92Lys, and L111M. One common mutation (V122I), which is a substitution of isoleucine for valine at position 122, occurs with high frequency in African-Americans, with a prevalence of approximately 3.5%.
==Clinical presentation==
The onset of FAC caused by aggregation of the V122I mutation and wild-type TTR, and senile systemic amyloidosis caused by the exclusive aggregation of wild-type TTR, typically occur after age 60. Greater than 40% of these patients present with carpal tunnel syndrome before developing ATTR-CM. Cardiac involvement is often identified with the presence of conduction system disease (sinus node or atrioventricular node dysfunction) and/or congestive heart failure, including shortness of breath, peripheral edema, syncope, exertional dyspnea, generalized fatigue, or heart block.〔Falk, R. H. & Elkayam, U. (2010). Cardiomyopathy: the importance of recognizing the uncommon diagnosis. Prog Cardiovasc Dis 52, 262-3.〕〔Snyder, M. E., Haidar, G. R., Spencer, B. & Maurer, M. S. (2011). Transthyretin cardiac amyloidosis diagnosed by analyzing a prostatic tissue sample: a case report. J Am Geriatr Soc 59, 1745-7.〕 Unfortunately, echocardiographic findings are indistinguishable from those seen in AL amyloidosis, and include thickened ventricular walls (concentric hypertrophy, both right and left) with a normal-to-small left ventricular cavity, increased myocardial echogenicity, normal or mildly reduced ejection fraction (often with evidence of diastolic dysfunction and severe impairment of contraction along the longitudinal axis), and bi-atrial dilation with impaired atrial contraction. Unlike the situation in AL amyloidosis, the ECG voltage is often normal, although low voltage may be seen (despite increased wall thickness on echocardiography). Marked axis deviation, bundle branch block, and AV block are common, as is atrial fibrillation.
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