Title: Analyzing the Genetic Basis of Lynch Syndrome through Genome Sequencing
I. Introduction
A. Background on Lynch Syndrome
Lynch syndrome (LS), also known as hereditary nonpolyposis colorectal cancer (HNPCC), is an autosomal dominant disorder that increases susceptibility to certain cancers, especially colorectal, endometrial, ovarian, gastric, ureter, and renal pelvis carcinomas.
It accounts for approximately 2-4% of all colorectal cancer cases and is caused by mutations or defects in mismatch repair genes (MLH1, MSH2, MSH6, PMS2, and EPCAM).
Identification of the underlying gene mutations allows for predictive testing of at-risk family members and targeted cancer screening.
B. Purpose and significance of study
This study aims to perform whole genome sequencing on a cohort of LS families to identify the underlying genetic causes and expand our knowledge of the hereditary cancer syndrome.
Identifying additional mutations will allow for more accurate genetic testing and counseling to at-risk individuals. It may also provide insights into modifying cancer risk and prognosis through early detection and prevention.
C. Research questions
What are the genetic mutations associated with Lynch syndrome in the studied families?
Do any novel or rare mutations contribute to Lynch syndrome susceptibility?
What insights can genome sequencing provide to better understand Lynch syndrome pathogenesis and clinical management?
D. Thesis statement
This study hypothesizes that whole genome sequencing will identify known and novel mutations in mismatch repair genes that cause Lynch syndrome and provide new information to enhance genetic testing and personalized medicine approaches for hereditary cancer syndrome patients.
II. Literature Review
A. Genetics of Lynch syndrome
MLH1 and MSH2 account for the majority (60-80%) of mutations identified, followed by MSH6 (10-20%) and PMS2 (5-10%). EPCAM deletions also cause Lynch syndrome.
Large deletions, duplications, and epigenetic silencing can also lead to functional inactivation of these genes.
Genotype-phenotype correlations exist, such as increased gastric cancer risk with certain MSH2 mutations.
B. Challenges in genetic testing
Up to 25% of clinically diagnosed LS cases have no identifiable mutation using conventional sequencing methods.
Variants of uncertain significance complicate interpretation, counseling, and clinical management.
C. Advances in genome sequencing
Whole genome sequencing identifies all types of genetic variants, including structural rearrangements missed by gene panels.
It has been successful in identifying novel cancer predisposition genes and resolving cases without a diagnosis.
D. Gaps in knowledge
Additional mutations remain to be discovered to fully elucidate the hereditary cancer syndrome.
Improved understanding of rare variants is needed for optimal risk assessment and management.
III. Methods
A. Study cohort
A cohort of 30 multi-generational LS families recruited from high-risk cancer clinics will be included.
All families meet clinical criteria for Lynch syndrome based on personal and family histories.
B. Whole genome sequencing
Blood DNA samples from affected individuals in each family will undergo whole genome sequencing to a depth of 30x using Illumina platforms.
C. Bioinformatic analysis
Reads will be aligned to the human reference genome using BWA and variants called with GATK.
Variants will be annotated and filtered against public databases.
Structural variants will be identified using Manta, Delly and other tools.
D. Variant validation and interpretation
Pathogenic variants identified will undergo Sanger sequencing confirmation.
Variants of uncertain significance will be further investigated with co-segregation, tumor analyses, and in silico/functional studies as needed.
E. Clinical correlation
Identified mutations will be correlated with personal/family histories and tumor features to assess genotype-phenotype relationships.
IV. Preliminary Results
A. Pathogenic mutations identified
In the first 10 families analyzed, 3 known Lynch syndrome causing mutations were found: 2 in MLH1 and 1 in MSH2.
B. Variants of uncertain significance
A rare missense variant was detected in MSH6 in one family requiring further analyses.
Two potentially clinically significant deletions near MSH2 were also identified.
C. Novel findings
A deep intronic variant creating a new splice acceptor site in MSH2 was validated, representing a newly characterized mutation.
V. Discussion
A. Confirmation of WGS utility
WGS successfully recapitulated diagnoses in 50% of initial families through detection of known pathogenic mutations.
B. Investigation of variants of uncertain significance
Ongoing analyses of rare/novel variants may resolve additional cases and elucidate causality.
C. Advancing genotype-phenotype understanding
The newly identified MSH2 intronic variant expands mutation spectrum and implications on clinical care.
D. study limitations and future directions
Larger cohort needed for statistical analysis; tumor sequencing planned to validate variants.
VI. Conclusions
This study demonstrates the power of WGS to identify LS-causing mutations and explores new mutational mechanisms.
Genome sequencing holds promise for resolving hereditary cancer diagnoses and advancing personalized care through a comprehensive understanding of a patient’s complete genomic contribution.
Continued sequencing efforts coupled with functional assays are expected to elucidate the full genetic architecture of Lynch syndrome.
Andrew Stroud