Lymphoid malignancy as a presenting sign of ataxia-telangiectasia

Ataxia-telangiectasia (AT) is an uncommon genetic disorder characterized by cerebellar ataxia, oculocutaneous telangiectasias, progressive immunodefic iency, and a predisposition to lymphoid malignancy. The genetic defect in A T predisposes not only to malignancy but also to severe toxicity from anti- neoplastic therapies. It is important to consider the diagnosis of AT in an y child with a lymphoid malignancy at a younger than expected age, or who h as a pre-existing ataxia, to anticipate unusually severe toxicities from th e antineoplastic therapy, to avoid confusing the development of ataxia with toxicity from therapy, and to provide appropriate genetic counseling.. We describe two children at a young age with a lymphoid malignancy diagnosed b efore the diagnosis of AT. One patient had severe toxicity from his chemoth erapy, requiring truncation of the planned course of treatment. The other c hild was able to tolerate his entire planned course of therapy, but ataxia that was initially interpreted as toxicity from chemotherapy rather than as a sign of his AT developed. Lymphoid malignancy may be the presenting sign of AT. Making this diagnosis may influence therapy of the malignancy. The neurologic manifestations of the disease can be misinterpreted as toxicitie s of the chemotherapy, and diagnosis of AT allows appropriate genetic couns eling for the family.