The rate of germline mutations and large deletions of SMAD4 and BMPR1A in juvenile polyposis.

Juvenile polyposis (JPS) is an autosomal dominant syndrome that predisposes individuals to develop gastrointestinal polyps and cancer. Germline point mutations in SMAD4 and BMPR1A have been identified as causing JPS in approximately 40-60% of patients, but few studies have looked at the rate of large deletions. In this study, we determined the overall prevalence of genetic changes of SMAD4 and BMPR1A by sequencing and by screening for larger deletions. DNA was extracted from 102 JPS probands, and each exon and intron-exon boundary of SMAD4 and BMPR1A were sequenced. Coding and non-coding exons of SMAD4 and BMPR1A were screened for deletions with multiplex ligation-dependent probe amplification (MLPA). By sequencing, 20 probands had point mutations of SMAD4 and 22 of BMPR1A. By MLPA, one proband had deletion of most of SMAD4, one of both BMPR1A and PTEN, one of the 5' end of BMPR1A, and another of the 5' end of SMAD4. The overall prevalence of SMAD4 and BMPR1A point mutations and deletions in JPS was 45% in the largest series of patients to date. Large deletions are less frequent in JPS patients, but represent other heritable causes of JPS, which should be screened for in pre-symptomatic genetic testing.

The prevalence of MADH4 and BMPR1A mutations in juvenile polyposis and absence of BMPR2, BMPR1B, and ACVR1 mutations.

BACKGROUND: Juvenile polyposis (JP) is an autosomal dominant syndrome predisposing to colorectal and gastric cancer. We have identified mutations in two genes causing JP, MADH4 and bone morphogenetic protein receptor 1A (BMPR1A): both are involved in bone morphogenetic protein (BMP) mediated signalling and are members of the TGF-beta superfamily. This study determined the prevalence of mutations in MADH4 and BMPR1A, as well as three other BMP/activin pathway candidate genes in a large number of JP patients. METHODS: DNA was extracted from the blood of JP patients and used for PCR amplification of each exon of these five genes, using primers flanking each intron-exon boundary. Mutations were determined by comparison to wild type sequences using sequence analysis software. A total of 77 JP cases were sequenced for mutations in the MADH4, BMPR1A, BMPR1B, BMPR2, and/or ACVR1 (activin A receptor) genes. The latter three genes were analysed when MADH4 and BMPR1A sequencing found no mutations. RESULTS: Germline MADH4 mutations were found in 14 cases (18.2%) and BMPR1A mutations in 16 cases (20.8%). No mutations were found in BMPR1B, BMPR2, or ACVR1 in 32 MADH4 and BMPR1A mutation negative cases. DISCUSSION: In the largest series of JP patients reported to date, the prevalence of germline MADH4 and BMPR1A mutations is approximately 20% for each gene. Since mutations were not found in more than half the JP patients, either additional genes predisposing to JP remain to be discovered, or alternate means of inactivation of the two known genes are responsible for these JP cases.