 The researchers want to find out if Venetoclax ABT-199 in addition to dexamethasone will reduce or eliminate AL amyloidosis plasma cells. In this study, varying doses of Venetoclax will be given to determine the maximum tolerated and safe dose for further study. The researchers may also gain a better understanding of whether Venetoclax and dexamethasone can counter the plasma cell disease that causes AL amyloidosis. 