A T-to-A transversion at nucleotide position 1536, in exon 2, results in substitution of arginine for tryptophan at amino acid position 480 (W408R) in a highly conserved region of the active signaling domain of the growth differentiation factor 5 protein. The mutant protein is secreted and dimerizes normally, but it inhibits the function of the wild-type protein in a dominant negative fashion.