Pathogenic variants of the bone morphogenetic protein receptor type 1 A (BMPR1A) gene underlie juvenile polyposis syndrome (JPS), a rare autosomal dominant condition characterized by multiple gastrointestinal hamartomatous polyps. Recent findings indicate that constitutional BMPR1A variants can also be associated with various non-JPS phenotypes without hamartomatous polyps. The basis of varying genotype - phenotype relationships is poorly understood. We investigated four families with non-truncating variants of BMPR1A affecting different functional domains. Clinical presentation resembled familial colorectal cancer type X-like syndrome with dominantly inherited microsatellite-stable gastrointestinal adenomas and carcinomas. To gain insights into genotype-phenotype associations, exome sequencing was conducted on normal and tumor tissue DNAs. Constitutional BMPR1A variants underwent a thorough evaluation for clinical significance, by, e.g., co-segregation analyses and in silico modeling, supplemented by haplotyping and genealogical studies. All available tumors were examined for histology and molecularly for BMPR1A "second hits" and mutational signatures. Targeted sequencing of blood DNA revealed a three-nucleotide deletion (BMPR1A c.264_266 del) in one family, a three-nucleotide insertion (BMPR1A c.506_507insTCC) in two families, and a missense change (BMPR1A c.766G > A) in a fourth family. The two families with BMPR1A c.506_507insTCC had a shared ancestral origin. Co-segregation of the variants with colorectal cancer and/or polyps, in-silico modeling, and two hit inactivation by loss of heterozygosity or somatic point mutations in tumors, together with the absence of other possible predisposing variants by exome sequencing, supported the idea of tumor predisposition being attributable to the BMPR1A variants. Polyps examined from variant carriers had adenomatous histology, except for three polyps with hamartomatous features, originating from two BMPR1A carriers from two families. While no hamartoma samples were available for molecular investigation, somatic mutational profiles of colorectal adenomas and carcinomas resembled those of mismatch repair-proficient colorectal tumors in general. Our findings support the notion that the clinical phenotype of BMPR1A variants may extend beyond classical JPS. Genotype-phenotype correlations are complex, since molecular comparison of constitutional and tumor features of our families to those published from JPS families in the literature show a significant overlap. The variety of clinical phenotypes warrants recognition in the clinical management of BMPR1A carriers and their family members.

Hereditary colorectal cancer (CRC) syndromes account for up to 5% of CRC. Patients have an increased risk of CRC and extracolonic cancers, both of which develop at an early age. The main polyposis syndromes include familial adenomatous polyposis, MYH-associated polyposis, Peutz-Jeghers syndrome, juvenile polyposis syndrome, and PTEN hamartoma syndrome. The non-polyposis syndromes include Lynch syndrome and familial colorectal cancer type X. Each of the syndromes have distinct but sometimes overlapping phenotypes. Clinical evaluation and ultimately the underlying germline genetic pathogenic variants define the syndromes. Each syndrome has polyp, CRC, and extracolonic risks and management is based on early and timely surveillance with therapeutic and often extended prophylactic surgery. Surgical intervention strategies are individualized, considering not only the earlier onset of malignancies and heightened risks for metachronous cancers but also the patient's needs and quality of life. This article reviews the different diagnostic approaches to hereditary CRC and highlights subsequent disease-specific management and surgical decision-making strategies.

Genetic susceptibility to familial colorectal cancer (CRC), including for individuals classified as Familial Colorectal Cancer Type X (FCCTX), remains poorly understood. We describe a multi-generation CRC-affected family segregating pathogenic variants in both BRCA1, a gene associated with breast and ovarian cancer and RNF43, a gene associated with Serrated Polyposis Syndrome (SPS). A single family out of 105 families meeting the criteria for FCCTX (Amsterdam I family history criteria with mismatch repair (MMR)-proficient CRCs) recruited to the Australasian Colorectal Cancer Family Registry (ACCFR; 1998-2008) that underwent whole exome sequencing (WES), was selected for further testing. CRC and polyp tissue from four carriers were molecularly characterized including a single CRC that underwent WES to determine tumor mutational signatures and loss of heterozygosity (LOH) events. Ten carriers of a germline pathogenic variant BRCA1:c.2681_2682delAA p.Lys894ThrfsTer8 and eight carriers of a germline pathogenic variant RNF43:c.988 C > T p.Arg330Ter were identified in this family. Seven members carried both variants, four of which developed CRC. A single carrier of the RNF43 variant met the 2019 World Health Organization (WHO2019) criteria for SPS, developing a BRAF p.V600 wildtype CRC. Loss of the wildtype allele for both BRCA1 and RNF43 variants was observed in three CRC tumors while a LOH event across chromosome 17q encompassing both genes was observed in a CRC. Tumor mutational signature analysis identified the homologous recombination deficiency (HRD)-associated COSMIC signatures SBS3 and ID6 in a CRC for a carrier of both variants. Our findings show digenic inheritance of pathogenic variants in BRCA1 and RNF43 segregating with CRC in a FCCTX family. LOH and evidence of BRCA1-associated HRD supports the importance of both these tumor suppressor genes in CRC tumorigenesis.

Hereditary genetic mutations causing predisposition to colorectal cancer are accountable for approximately 30% of all colorectal cancer cases. However, only a small fraction of these are high penetrant mutations occurring in DNA mismatch repair genes, causing one of several types of familial colorectal cancer (CRC) syndromes. Most of the mutations are low-penetrant variants, contributing to an increased risk of familial colorectal cancer, and they are often found in additional genes and pathways not previously associated with CRC. The aim of this study was to identify such variants, both high-penetrant and low-penetrant ones. We performed whole exome sequencing on constitutional DNA extracted from blood of 48 patients suspected of familial colorectal cancer and used multiple in silico prediction tools and available literature-based evidence to detect and investigate genetic variants. We identified several causative and some potentially causative germline variants in genes known for their association with colorectal cancer. In addition, we identified several variants in genes not typically included in relevant gene panels for colorectal cancer, including CFTR, PABPC1 and TYRO3, which may be associated with an increased risk for cancer. Identification of variants in additional genes that potentially can be associated with familial colorectal cancer indicates a larger genetic spectrum of this disease, not limited only to mismatch repair genes. Usage of multiple in silico tools based on different methods and combined through a consensus approach increases the sensitivity of predictions and narrows down a large list of variants to the ones that are most likely to be significant.

Colorectal cancer (CRC) is a highly prevalent disease in developed countries. Inherited Mendelian causes account for approximately 5% of CRC cases, with Lynch syndrome and familial adenomatous polyposis being the most prevalent forms. Scientific efforts are focused on the discovery of new candidate genes associated with CRC and new associations of phenotypes with well-established cancer-related genes. BRCA1-associated ring domain (BARD1) gene deleterious germline variants are associated with a moderate increase in the relative risk of breast cancer, but their association with other neoplasms, such as CRC, remains unclear. We present the case of a 49-year-old male diagnosed with rectal adenocarcinoma whose maternal family fulfilled Amsterdam clinical criteria for Lynch syndrome. Genetic test confirmed the presence in heterozygosis of a germline pathogenic deletion of exons 8-11 in BARD1 gene. The predictive genetic study of the family revealed the presence of this pathogenic variant in his deceased cancer affected relatives, confirming co-segregation of the deletion with the disease. To the best of our knowledge, this is the first published work in which this BARD1 deletion is detected in a family with familial colorectal cancer type X (FCCTX) syndrome, in which the clinical criteria for Lynch syndrome without alteration of the DNA mismatch repair (MMR) system are fulfilled. Whether this incidental germline finding is the cause of familial colorectal aggregation remains to be elucidated in scientific forums. Patients should be carefully assessed in specific cancer genetic counseling units to account for hypothetical casual findings in other genes, in principle unrelated to the initial clinical suspicion, but with potential impact on their health.