The accurate identification and interpretation of germline mutations in mismatch repair genes in colorectal cancer cases is critical for clinical management.
Current data suggest that mismatch repair mutations are highly heterogeneous and that many mutations are not detected when conventional DNA sequencing alone is used.
Dr Casey and colleagues undertook a study to evaluate the potential of conversion analysis compared with DNA sequencing alone to detect heterogeneous germline mutations in MLH1, MSH2, and MSH6 in colorectal cancer patients.
The researchers conducted a multicenter study with patients who participate in the Colon Cancer Family Registry.
The investigators performed a mutation analyses in participant samples determined to have a high probability of carrying mismatch repair germline mutations.
The research team analyzed samples from a total of 64 hereditary nonpolyposis colorectal cancer cases, 8 hereditary nonpolyposis colorectal cancer–like cases, and 17 cases diagnosed prior to age 50 years from June 2002 to June 2003.
The researchers compared the genomic DNA sequencing with the classification of family members as carriers or noncarriers of germline mutations in MLH1, MSH2, or MSH6.
The researchers also compared mutation data from conversion analysis compared with genomic DNA sequencing.
| Conversion analysis identified all mutations detected by genomic DNA sequencing|
Using genomic DNA sequencing the investigators identified 28 likely deleterious exon mutations, 4 in-frame deletion mutations, 16 missense changes, and 22 putative splice site mutations.
Conversion analysis identified all mutations detected by genomic DNA sequencing.
In addition the team found an exon mutation, 12 large genomic deletions, and 1 exon duplication mutation.
This yielded an increase of 33% in diagnostic yield of deleterious mutations.
After the conversion analysis the researchers were able to show that 4 of 16 missense changes resulted in exon skipping in transcripts and that 17 of 22 putative splice site mutations affected splicing or mRNA transcript stability.
Analysis provided an increase of 56% in the diagnostic yield of genetic testing compared with genomic DNA sequencing alone.
Dr Casey commented, "The data confirm the heterogeneity of mismatch repair mutations and reveal that many mutations in colorectal cancer cases would be missed using conventional genomic DNA sequencing alone."
"Conversion analysis substantially increases the diagnostic yield of genetic testing for mismatch repair mutations in patients diagnosed as having colorectal cancer."