CHEK2 and neoplasm: Moreover the CHEK2 gene, which encodes a checkpoint kinase important for the cell's response to DNA damage, has been recognized as a multi-organ cancer susceptibility gene and is located on chromosome 22 about 1 Mb centromeric to NF2. Thus a second hit in these alternative tumour suppressor genes in r(22) carriers that already have lost the ring in a number of cells can result in other tumour types than those typically seen in NF2.