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Hereditary mixed polyposis syndrome is caused by a 40-kb upstream duplication that leads to increased and ectopic expression of the BMP antagonist GREM1.

Jaeger E, Leedham S, Lewis A, Segditsas S, Becker M, Cuadrado PR, Davis H, Kaur K, Heinimann K, Howarth K, East J, Taylor J, Thomas H, Tomlinson I - Nat. Genet. (2012)

Bottom Line: This unusual mutation is associated with increased allele-specific GREM1 expression.The HMPS duplication contains predicted enhancer elements; some of these interact with the GREM1 promoter and can drive gene expression in vitro.Increased GREM1 expression is predicted to cause reduced bone morphogenetic protein (BMP) pathway activity, a mechanism that also underlies tumorigenesis in juvenile polyposis of the large bowel.

View Article: PubMed Central - PubMed

Affiliation: Molecular and Population Genetics Laboratory, Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK.

ABSTRACT
Hereditary mixed polyposis syndrome (HMPS) is characterized by apparent autosomal dominant inheritance of multiple types of colorectal polyp, with colorectal carcinoma occurring in a high proportion of affected individuals. Here, we use genetic mapping, copy-number analysis, exclusion of mutations by high-throughput sequencing, gene expression analysis and functional assays to show that HMPS is caused by a duplication spanning the 3' end of the SCG5 gene and a region upstream of the GREM1 locus. This unusual mutation is associated with increased allele-specific GREM1 expression. Whereas GREM1 is expressed in intestinal subepithelial myofibroblasts in controls, GREM1 is predominantly expressed in the epithelium of the large bowel in individuals with HMPS. The HMPS duplication contains predicted enhancer elements; some of these interact with the GREM1 promoter and can drive gene expression in vitro. Increased GREM1 expression is predicted to cause reduced bone morphogenetic protein (BMP) pathway activity, a mechanism that also underlies tumorigenesis in juvenile polyposis of the large bowel.

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The HMPS duplicationA, array-CGH analysis of the region around the HMPS duplication. The region of copy number gain, estimated to be 3:2 ratio relative to controls and hence resulting from a single-copy gain, is indicated. Results from the full region analysed are shown in Supplementary Figure 1.B, schematic of the 40kb duplication showing the involvement of the 3′ half of SCG5 extending to a region upstream of GREM1.The locations on chromosome 15 of coding sequences, introns, selected SNPs and CpG islands are shown. Arrows show direction of transcription.
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Figure 1: The HMPS duplicationA, array-CGH analysis of the region around the HMPS duplication. The region of copy number gain, estimated to be 3:2 ratio relative to controls and hence resulting from a single-copy gain, is indicated. Results from the full region analysed are shown in Supplementary Figure 1.B, schematic of the 40kb duplication showing the involvement of the 3′ half of SCG5 extending to a region upstream of GREM1.The locations on chromosome 15 of coding sequences, introns, selected SNPs and CpG islands are shown. Arrows show direction of transcription.

Mentions: We therefore wondered whether the underlying HMPS mutation might take the form of a copy number change. We designed a custom oligonucleotide array to search for copy number variation in the region. This analysis showed the presence of a heterozygous, single-copy duplication of about 40kb centred on chr15:30.77Mb in two HMPS patients and in none of three unaffected relatives (Figure 1, Supplementary Figure 1). PCR amplification across the duplication breakpoints subsequently mapped it to chr15:30,752,231-30,792,051. The change was found to be a simple, tandem tail-head duplication with the insertion of a 30bp sequence of unknown origin and no homology to known sequences between the duplicons. The duplication extended from intron 2 of SCG5 to a site just upstream of the GREM1 CpG island (Figure 1). In order to investigate the duplication further, we designed PCR primers that spanned the duplication boundary and produced a unique, specific amplification product of 190bp. As a control, we chose a region upstream of GREM1 present in all individuals that generated a product of 435bp. We tested 40 affected individuals (Supplementary Figure 2) and 50 unaffected individuals (either polyp-free, but at-risk and aged >40 years old, or spouses) from 6 putative HMPS families. There was perfect concordance between presence of the 190bp product and affected status (Supplementary Figure 1, Supplementary Table 1). We then tested 188 unselected Ashkenazi controls and none showed amplification of the 190bp product; this group included one duplication-negative individual who shared the HMPS haplotype, suggesting that the duplication had arisen on that haplotype background.


Hereditary mixed polyposis syndrome is caused by a 40-kb upstream duplication that leads to increased and ectopic expression of the BMP antagonist GREM1.

Jaeger E, Leedham S, Lewis A, Segditsas S, Becker M, Cuadrado PR, Davis H, Kaur K, Heinimann K, Howarth K, East J, Taylor J, Thomas H, Tomlinson I - Nat. Genet. (2012)

The HMPS duplicationA, array-CGH analysis of the region around the HMPS duplication. The region of copy number gain, estimated to be 3:2 ratio relative to controls and hence resulting from a single-copy gain, is indicated. Results from the full region analysed are shown in Supplementary Figure 1.B, schematic of the 40kb duplication showing the involvement of the 3′ half of SCG5 extending to a region upstream of GREM1.The locations on chromosome 15 of coding sequences, introns, selected SNPs and CpG islands are shown. Arrows show direction of transcription.
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Related In: Results  -  Collection

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Figure 1: The HMPS duplicationA, array-CGH analysis of the region around the HMPS duplication. The region of copy number gain, estimated to be 3:2 ratio relative to controls and hence resulting from a single-copy gain, is indicated. Results from the full region analysed are shown in Supplementary Figure 1.B, schematic of the 40kb duplication showing the involvement of the 3′ half of SCG5 extending to a region upstream of GREM1.The locations on chromosome 15 of coding sequences, introns, selected SNPs and CpG islands are shown. Arrows show direction of transcription.
Mentions: We therefore wondered whether the underlying HMPS mutation might take the form of a copy number change. We designed a custom oligonucleotide array to search for copy number variation in the region. This analysis showed the presence of a heterozygous, single-copy duplication of about 40kb centred on chr15:30.77Mb in two HMPS patients and in none of three unaffected relatives (Figure 1, Supplementary Figure 1). PCR amplification across the duplication breakpoints subsequently mapped it to chr15:30,752,231-30,792,051. The change was found to be a simple, tandem tail-head duplication with the insertion of a 30bp sequence of unknown origin and no homology to known sequences between the duplicons. The duplication extended from intron 2 of SCG5 to a site just upstream of the GREM1 CpG island (Figure 1). In order to investigate the duplication further, we designed PCR primers that spanned the duplication boundary and produced a unique, specific amplification product of 190bp. As a control, we chose a region upstream of GREM1 present in all individuals that generated a product of 435bp. We tested 40 affected individuals (Supplementary Figure 2) and 50 unaffected individuals (either polyp-free, but at-risk and aged >40 years old, or spouses) from 6 putative HMPS families. There was perfect concordance between presence of the 190bp product and affected status (Supplementary Figure 1, Supplementary Table 1). We then tested 188 unselected Ashkenazi controls and none showed amplification of the 190bp product; this group included one duplication-negative individual who shared the HMPS haplotype, suggesting that the duplication had arisen on that haplotype background.

Bottom Line: This unusual mutation is associated with increased allele-specific GREM1 expression.The HMPS duplication contains predicted enhancer elements; some of these interact with the GREM1 promoter and can drive gene expression in vitro.Increased GREM1 expression is predicted to cause reduced bone morphogenetic protein (BMP) pathway activity, a mechanism that also underlies tumorigenesis in juvenile polyposis of the large bowel.

View Article: PubMed Central - PubMed

Affiliation: Molecular and Population Genetics Laboratory, Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK.

ABSTRACT
Hereditary mixed polyposis syndrome (HMPS) is characterized by apparent autosomal dominant inheritance of multiple types of colorectal polyp, with colorectal carcinoma occurring in a high proportion of affected individuals. Here, we use genetic mapping, copy-number analysis, exclusion of mutations by high-throughput sequencing, gene expression analysis and functional assays to show that HMPS is caused by a duplication spanning the 3' end of the SCG5 gene and a region upstream of the GREM1 locus. This unusual mutation is associated with increased allele-specific GREM1 expression. Whereas GREM1 is expressed in intestinal subepithelial myofibroblasts in controls, GREM1 is predominantly expressed in the epithelium of the large bowel in individuals with HMPS. The HMPS duplication contains predicted enhancer elements; some of these interact with the GREM1 promoter and can drive gene expression in vitro. Increased GREM1 expression is predicted to cause reduced bone morphogenetic protein (BMP) pathway activity, a mechanism that also underlies tumorigenesis in juvenile polyposis of the large bowel.

Show MeSH
Related in: MedlinePlus