Chromosome instability syndromes

The chromosome instability syndromes, ataxia telangiectasia (A-T), Fanconi anaemia (FA) and Bloom syndrome (BS) have been known for many years. More r ecently Nijmegen breakage syndrome (NBS) and ataxia telangiectasia-like dis order (ATLD) have been identified. A-T, ATLD and NBS form a group of disord ers all of which show very similar cellular features that result from the c onsequences of increased sensitivity to ionizing radiation (IR). They also share some clinical features, particularly A-T and ATLD, and all show an im munodeficiency. A-T and NBS both show a predisposition to lymphoid tumours. Fanconi anaemia can be caused by mutations in eight different genes, altho ugh the majority of mutations are accounted for by FANCA and FANCC. The ver y rare Bloom syndrome is caused by mutation in a single gene, BLM. An impor tant feature which all of these disorders have in common is that the genes identified are involved in aspects of recombination repair of DNA damage.