Ataxia-telangiectasia (AT) is the most frequent progressive cerebellar ataxia in infancy and childhood. Immunodeficiency which includes both cellular and humoral arms has variable severity. Since the clinical presentation is extremely variable, a high clinical suspicion will allow an early diagnosis. Serum alpha-fetoprotein is elevated in 80–85% of patients and therefore could be used as a screening tool. Here, we present a case of a 5-year-old female infant who was admitted to our department at the age of 16 months because of gait disorders and febrile episodes that had begun at 5 months after the cessation of breastfeeding. Serum alfa-fetoprotein level was elevated. Other investigations showed leukocytopenia with lymphopenia, reduced IgG2 and IgA levels, and low titers of specific postimmunization antibodies against tetanus toxoid and Haemophilus B polysaccharide. Peripheral lymphocytes subsets showed reduction of T cells with a marked predominance of T cells with a memory phenotype and a corresponding reduction of na？ve T cells; NK cells were very increased (41%) with normal activity. The characterization of the ATM gene mutations revealed 2 specific mutations (c.5692C > T/c.7630-2A > C) compatible with AT diagnosis. It was concluded that AT syndrome should be considered in children with precocious signs of cerebellar ataxia and recurrent fever episodes. 1. Introduction Ataxia-telangectasia (AT) is a complex multisystem disorder characterized by progressive neurological impairment, variable immunodeficiency, and oculocutaneous telangiectasia [1]. AT is a member of chromosomal breakage syndromes caused by a mutation in the ataxia-telangiectasia mutated (ATM) gene [2, 3]. The immunodeficiency is of variable severity in relation to the specific ATM mutation and is associated with sinopulmonary infections, radiation hypersensitivity, and increased incidence of malignancy [3, 4]. Cells from patients show increased sensitivity to ionizing radiation, defective DNA repair, and frequent chromosomal abnormalities [5, 6]. Gait instability with or without recurrent infection is the earliest symptom and oculocutaneous teleangiectasias will appear later [7]. The complete phenotype occurs over a number of years, usually within the school age [8, 9]. An easy and reliable marker in case of suspected AT is the elevated serum level of alpha-fetoprotein which is present in 80–85% of the affected patients [1]. An early diagnosis is possible today by using the molecular approach which will identify the specific ATM mutations and by measuring the ATM protein levels and the
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