This mutation, discovered because of its obvious homozygous phenotype among progeny of ENU-mutagenized mice, comprises a T-to-C transition at nucleotide position 2343 in exon 9 of the gene (GenBank Accession NM_008520) that results in the Cys452Arg amino acid substitution. Cys452 resides in the predicted 4th domain of the protein, which contains twelve EGF-like repeats and two 8-Cys motifs/TGF-bp repeats; the first of the latter (which is the third 8-Cys motif of the protein) is involved in disulfide bonding with inactive transforming growth factor, beta 1. (J:133615)