Transthyretin amyloid cardiomyopathy (ATTR-CM) is a progressive and ultimately fatal cardiomyopathy characterized by the deposition of misfolded transthyretin in the form of amyloid fibrils within the myocardial extracellular space, which disrupt cardiac structure and function. The sporadic, noninherited, wild-type ATTR-CM (wtATTR-CM) is a condition of older, predominantly male individuals, while the hereditary form of ATTR-CM (hATTR-CM) can present earlier in life with a varying clinical phenotype, often composed of both restrictive cardiomyopathy and polyneuropathy. The gene discussed is TTR; the disease is cutaneous mastocytosis.