Studies support the theory that there are several causes, instead of a single environmental cause or genetic problem.

VOA: special.2009.01.06

Scientists have believed that S.I.V.did not cause a similar immune system problem for primates.

VOA: special.2009.09.08

Anything you see as a problem can cause stress.

VOA: special.2009.03.24

Stuttering's cause has long been a mystery, but it has frequently been diagnosed as a psychological problem.

VOA: standard.2010.02.11

Engineers discovered the problem during fueling, and worried that any excess hydrogen on the launch pad could cause an explosion during engine ignition.

VOA: standard.2009.03.15