Introduction. Lynch syndrome, previously more commonly known as hereditary nonpolyposis colorectal cancer, is a hereditary cancer syndrome with an autosomal dominant inheritance pattern. Usually it is caused by mutations the MMR genes. In 20 - 25% of cases patients are not found to have mutations in any of these genes. Chromosomal aberrations as a cause of the Lynch syndrome were examined in this study. Aim of the study. To identify chromosomal aberrations which may lead to colorectal cancer.

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... terial and methods. Twelve patients, corresponding to either Amsterdam I/II criteria or Bethesda guidelines, which have been tested negative for mutations in Lynch genes have been karyotyped were karyotyped with SNP array chips, in order to determine if they had potentially heritable chromosomal aberrations which could be responsible for increased risk of malignancy. Results. One patient with a 14.7Mbp duplication framed by small deletions was chosen to be the most likely patient to suffer from an inherited carcinogenic chromosomal aberration. The preceding deletion was found to contain the coding region of BRE, encoding a component of the BRCA1-A complex; we believe that this deletion is the most carcinogenic component of the aberration and likely responsible for Lynch syndrome in this case. The larger duplication furthermore contained the coding regions for 83 genes, some of which have been shown to promote malignant disease when overexpressed. Conclusion. Because of the clinically grossly tolerable nature of the aberration it is possible that it was vertically transmitted and contributed to the onset of colorectal cancer in the patient and his mother and maternal aunt.