[Ataxia telangiectasia syndrome: clinical picture and immunological abnormalities].

Ataxia-telangiectasia (AT) is the primary immunodeficiency with chromosomal instability. AT is a multisystem, autosomal recessive disorder characterised by progressive cerebellar ataxia, oculocutaneous telangiectasia, and increased susceptibility to recurrent respiratory tract infections and cancer predisposition. The cells from AT patients are radiosensitive to ionizing radiation and DNA repair damage. The gene responsible for AT is localised at chromosome 11q23.1, and encodes protein ATM that is important in the cell cycle control. In AT, both the humoral and cellular immune systems are affected including deficiency of serum IgA (70% of patients), IgG2 and IgG4, and deficiency of serum IgG (30% of patients). Functional tests of lymphocytes T revealed poor proliferative responses to phytohemagglutinin.