595235 Disclosed is an isolated anti-ActRIIB antibody or functional therapeutic protein that binds to ActRIIB, wherein said antibody or functional protein comprises heavy chain complementarity determining regions 1-3 and heavy chain complementarity determining regions 1-3 having at least 95% identity to the CDR1 GYTFTSSYIN; CDR2 XINXXXGXAXYAQKFQG; and CDR3 GGWFDY; the light chain variable region CDR1 TGTSSDVGSYNYVN; CDR2 LMIYGVSKRPS; and CDR3 QAWTSKMAG, SSYTRMGHP, ATYGKGVTPP or GTFAGGSYYG.