The diagnosis of chromosome breakage disorders such as Fragile-X, Fanconi anemia, Ataxia Telangiectasia, Sister Chromatid exchnage and Blooms syndrome involves addition of chromosome breakage inducing agents specific for each disorder, to the blood culture. The test is run simultaneously with blood of a matched control. Multiple cultures of the patient and control samples are set up. A positive sample will show a higher frequency of breaks, fragile sites, radial figures or sister chromatid exchanges, compared to the control.