GuitaristMalcolm Young, a founding member of the more than 40-year-old rock band AC/DC, has left the group due to a severe mental-health issue, his family revealed yesterday. In a statement, they told People magazine: "Malcolm is suffering from dementia and the family thanks you for respecting their privacy." In April, Young, 61, had taken "a break from the band" because of unspecified "ill health," AC/DC said at the time. Last Wednesday, the band said that "due to the nature of Malcolm's condition, he will not be rejoining."