The goal of this study to investigate if exercise predisposes to transthyretin instability. The investigators will evaluate the effect of exercise on transthyretin biochemistry.

This is an investigator initiated observational study, designed to study the effect of exercise on transthyretin stability in three main populations: Group 1: healthy master athletes who are 60 years or older. Group 2: Genotype positive (G+) cardiac phenotype negative (P-) patients with variant ATTR (i.e. carriers without evidence of disease). Group 3: Patients with ATTR CA who have not been on a stabilizer (tafamidis) within the last 14 days prior to enrollment.

Inclusion Criteria:

General inclusion criteria: patients should be able to exercise on a treadmill or a bike, willing to consent to the study procedures and willing to return to site during the follow up period of 72 hours for repeated blood and urine collection

Specific inclusion criteria:

• Group 1: Subjects must be at least 60 years of age and meet the master athlete definition of: athletes engaged in cycling ≥8 hours per week or running ≥6 hours per week or triathlon training (combination of swimming, cycling, running) ≥8 hours per week, or equivalent sports activities, for at least 6 months prior to enrollment.
• Group 2: Genotype positive (G+) cardiac phenotype negative (P-) patients with variant ATTR (i.e. carriers without evidence of disease)
• Group 3: Patients with ATTR CA who have not been on a stabilizer (tafamidis) within the last 14 days prior to enrollment.

Exclusion Criteria:

Taking diflunisal or daily non-steroidal anti-inflammatory drugs (NSAIDs) use within 2 weeks.

Master athletes without evidence of transthyretin amyloidosis. Genotype positive phenotype negative transthyretin amyloidosis, and phenotype positive transthyretin amyloidosis.