六亲不认-------- cut loose from old ties

例句：
A: I wonder why he is always so serious about the business.
我想知道为何他对公事老是如此一本正经。
B: As to the business, he often cuts loose from old ties.
关于公事,他经常六亲不认。

同义词：
turn one's back on one's own flesh and blood