Most genetic disorders are severe diseases that cannot be treated. In the majority of them, enzyme and gene therapy can be significantly curtailed by technical difficulties and the nature of the physiological defects and affected tissues. A rational search for drug treatment for such diseases must be based on understanding the corresponding molecular defects. For example, in a disease stemming from a defective signaling pathway, a drug that can activate redundant pathways could be useful. Screening for such a drug would then depend on the availability of a laboratory assay that faithfully reflects the molecular defect in the corresponding disease, and a technology for applying the assay in a high throughput setup. Deficiencies in various components of the DNA damage response lead to genomic instability syndromes characterized by tissue degeneration, sensitivity to DNA damaging agents, and cancer predisposition. A typical example is ataxia-telangiectasia (A-T), caused by deficiency of the nuclear protein kinase ATM, which activates the cellular response to double strand breaks in the DNA. ATM phosphorylates a multitude of substrates, each of which in turn modulates a branch of the damage response network. A certain redundancy among ATM and related proteins gives hope that activation of ATM-redundant activities might form a basis for drug treatment of A-T. This article describes a high throughput strategy for drug screening for A-T that is based on the above principles. A similar strategy can potentially be applied to drug screening for other genetic disorders.