A six-year old child presents for evaluation of a medical condition associated with recurrent infections. After reviewing all of the medical history, gene therapy is offered to treat a deficiency in adenosine deaminase (ADA). ADA deficiency is the most common autosomal recessive mutation in which of the following diseases?
1.Digeorge synndome
2.Severe combined immunodeficiency
3.Hyper-IgM syndrome
4.Wiskott-Aldrish syndrome
5.Bruton’s Agammaglobulinemia
sol:
Severe Combined Immunodeficiency (SCID) can be caused by various genetic defects, however, the most common autosomal recessive cause is a deficiency in adenosine deaminase (ADA).
Most cases of SCID are due to defective cytokine receptors resulting from a X-linked mutation of the common gamma-chain of the receptors. Another deficiency responsible for SCID is a deficiency in ADA, which is inherited in an autosomal recessive pattern. Cells lacking this enzyme generate high levels of deoxyadenosine, which is toxic to developing lymphocytes. Bone marrow transplantation and gene therapy are possible treatments.
Illustration A depicts the process of gene therapy for patients suffering from SCID. Illustration B displays the major primary immunodeficiencies and what cells they affect.