Ataxia telangiectasia (AT) is a rare combined immunodeficiency syndrome with multisystem involvement, characterized by progressive cerebellar ataxia, dysarthria, recurrent infections, movement disorders, oculocutaneous telangiectasias, and a risk of cancer. With a prevalence of 1 in 40,000 to 300,000 individuals, it accounts for 5.2% of the causes of primary immunodeficiencies worldwide. It is caused by variable mutations in the ATM gene (11q22-23) with autosomal recessive inheritance, leading to abnormal expression of the ATM protein, which is responsible for DNA repair, and also involving genes encoding for the T cell receptor. Immunologically, it has been described with cellular immunodeficiency in 67% of cases (predominantly T lymphopenia) and humoral immunodeficiency in 10%, with decreased IgG, IgA, or IgM. Genetic counseling is essential in management, as the parents are obligatory heterozygous carriers.

Presentation:
We present a series of two related female patients (sisters). Patient A was diagnosed at the age of 5 years with the onset of language abnormalities and progressive cerebellar ataxia with cerebellar degeneration. She also presented with hypogammaglobulinemia G and meningitis, peritoneal, and renal tuberculosis. She has a positive ATM mutation and is managed with intravenous immunoglobulin. Patient B was intentionally diagnosed at the age of 3 years due to a family history. She manifested telangiectasias at 3 years, language abnormalities at 6 years, and ataxia at 7 years with cerebellar atrophy. She is also managed with intravenous immunoglobulin.

Conclusions:
AT is a rare disease with an inheritance pattern that carries a 25% risk of presentation in children of carrier parents, with a typical onset and presentation in these cases. It is of utmost importance to establish genetic diagnoses that allow providing counseling to parents and, in the case of affected offspring, to make a timely diagnosis and provide appropriate treatment