A Novel Exonic Rearrangement Affecting MLH1 and the Contiguous LRRFIP2 is a Founder Mutation in Portuguese Lynch Syndrome Families

Purpose: Although Lynch syndrome is characterized by marked genetic heterogeneity, some specific mutations are observed at high frequency in well-defined populations or ethnic groups due to founder effects.

Methods: Genomic breakpoint identification, haplotype analysis, and mutation age determination were performed in 14 unrelated patients and 95 family members presenting the same MLH1 exonic rearrangement, among a series of 84 Lynch syndrome families with germline mutations in MLH1, MSH2, or MSH6.

Results: All 14 probands harbored an identical deletion, comprising exons 17-19 of the MLH1 gene and exons 26-29 of the LRRFIP2 gene, corresponding to the MLH1 mutation c.1896 + 280_oLRRFIP2:c.1750-678del. This mutation represents 17% of all deleterious mismatch repair mutations in our series. Haplotype analysis showed a conserved region of approximately 1 Mb, and the mutation age was estimated to be 283 ± 78 years. All 14 families are originated from the Porto district countryside.

Conclusion: We have identified a novel MLH1 exonic rearrangement that is a common founder mutation in Lynch syndrome families, indicating that screening for this rearrangement as a first step may be cost-effective during genetic testing of Lynch syndrome suspects of Portuguese ancestry, especially those originating from the Porto district.