BMPR1A and juvenile polyposis syndrome: Furthermore, germline mutations in the genes encoding the TGF-β signalling proteins, SMAD4 (Howe, et al., 1998; MIM# 600993) and BMPR1A (Howe, et al., 2001; MIM# 601299) have been shown to cause juvenile polyposis, an autosomal dominant polyposis syndrome which confers a high risk of colorectal cancer (CRC).