Mechanism of cancer susceptibility associated with PCS (premature chromatid separation) genetic trait

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1. The PCS (premature chromatid separation) syndrome was established as a clinical entity (OMIM#176430) on the basis of our experiences in 7 Japanese families, being recognized to be a cancer-prone genetic trait due to the impairment of mitotic spindle checkpoint, or to the decreased expression of BUB1B-endoding protein (BubR1).2. The frequency of cells in PCS is the most important hallmark for diagnosis of PCS syndrome. Hypotonic treatment of cells at 37℃ for 20 min was found to be most suitable among the conditions tested for the detection of PCS in individuals with the homozygous or heterozygous for the PCS trait.3. Chromosomal and DNA polymorphic marker studies revealed that the tumors developing in PCS patients had uniparental (paternal) disomy (UPD) specifically for chromosome 11, suggesting that the increased dosage of imprinted genes such as paternally expressed IGF2 was primarily involved in tumor development.4. Molecular analysis of BUB1B (encoding BubR1 protein) was performed in 7 Japanese families with PCS syndrome. In all the families studied, monoallelic BUB1B mutations were found : a single-base deletion in 4 families, and a splice site mutation, a nonsence mutation, and a missene mutation in one family each. Further analysis of haplotypes in the secomd alleles, where no mutations were detected, is now in progress.5. Lymphoblastoid cell lines (LCLs) and fibroblasts derived from the two PCS patients and a number of LCLs from heterozygous carriers were established and stored.