This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Pathology
Senile cardiac amyloid associated protein is 
Select and explain. 
A. Transthyretin, B. ANP, C. Beta 2 microglobulin, D. Gelsolin
A: Transthyretin
Answer: A: Transthyretin 
Explanation: Transthyretin (TTR) is a normal serum protein that binds and transpos thyroxine and retinol. Several distinct mutant forms of TTR (and its fragments) are deposited in a group of genetically determined disorders referred to as familial amyloid polyneuropathies. Normal TTR is also deposited in the hea of aged individuals (senile systemic amyloidosis)Reference: Robbins and Cotran Pathologic Basis of Disease; 9th edition; Chapter 6; Diseases of the Immune System