Ataxia-telangiectasia (A-T) is a rare disease characterized by neurodegenerative alterations, telangiectasia, primary immunodeficiency, extreme sensitivity to radiation, and susceptibility to neoplasms. A-T patients have inactivation of ataxia-telangiectasia-mutated (ATM) protein, which controls DNA double-strand break repair and is involved in oxidative stress response, among other functions; dysfunctional control of reactive oxygen species may be responsible for many of the clinical manifestations of this disease. To the best of our knowledge, hepatic lesions of steatohepatitis have not previously been reported in A-T patients. The present study reports the case of a 22-year-old man diagnosed with A-T at the age of 6 years who was referred to our Digestive Disease Unit with a three-year history of hyperlipidemia and liver test alterations. Core liver biopsy showed similar lesions to those observed in nonalcoholic steatohepatitis. Immunohistochemical staining disclosed the absence of ATM protein in hepatocyte nuclei. We suggest that the liver injury may be mainly attributable to the oxidative stress associated with ATM protein deficiency, although other factors may have made a contribution. We propose the inclusion of A-T among the causes of nonalcoholic steatohepatitis, which may respond to antioxidant therapy. 1. Introduction Ataxia-telangiectasia (A-T) is a rare autosomal recessive hereditary neurodegenerative and progressive disease caused by mutations in the ataxia-telangiectasia-mutated (ATM) gene that produce the absence or inactivation of ATM protein kinase. Clinical manifestations of A-T include early-onset neurological alterations (cerebellar ataxia caused by Purkinje and granule cell degeneration), late-onset oculocutaneous telangiectasias, early aging, sterility, hypersensitivity to ionizing radiation, immunodeficiency, and susceptibility to neoplasms [1, 2], especially leukemia, lymphomas, and breast cancer [3, 4]. Patients with A-T can also have impaired cellular and humoral immunity (IgA, IgE, or IgG2 immunodeficiency) and elevated serum alpha-fetoprotein (AFP), which can be useful for the diagnosis [4, 5]. ATM protein participates in double-strand-break repair mechanisms and can be activated by exogenous and endogen oxidative stress; ATM activation increases antioxidant levels and induces DNA oxidative damage repair [6]. Along with p53, ATM plays an important role in maintaining genomic integrity [5]. Many of the clinical alterations observed in A-T patients may be related to the dysfunctional control of reactive oxygen species (ROS)
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