Dementia, a brain disease, changed the line up for AC/DC.
AC/DC . The band 's line-up remained the same until 2014 with Malcolm Young 's retirement due to early-onset dementia and Rudd 's legal troubles . Malcolm Mitchell Young ( born 6 January 1953 ) is an Australian retired musician and songwriter , best known as a co-founder , rhythm guitarist , backing vocalist and songwriter for the hard rock band AC/DC .