Question

You have diagnosed one of your patients with severe combined immunodeficiency syndrome (SCIDS). SCIDS is characterized by a lack of an immune response to infectious diseases. In one variant of SCIDS, patients have a deficiency of adenine deaminase, elevated dATP levels, and lower than normal levels of other deoxynucleotides.

a) Explain how an adenine deaminase deficiency affects the levels of the deoxynucleotides.  

b) Explain how this compromises the immune response

Answer 1

Note: Enzyme deficiency in the question is wrongly mentioned as adenine deaminase. Th actual enzyme is adenosine deaminase.

Metabolism of DNA:-

Deficiency of adenosine deaminase will result in brake in the reaction at deoxyadenosine level. The levels of dAMP, dADP, dATP will become high. The deoxyadenosine and dAMP, dADP and dATP ARE TOXIC TO RAPIDLY DIVIDING IMMATURE LYMPHOCYTES especially those of T cell lineage. Hence there is a greater reduction of T cells as compared to B cells.

SCID is an x linked recessive disorder which is mostly seen in males. Clinical features are recurrent infections since birth. There is absence of identifiable lymph node or tonsil or adenoids or thymus. Treatment is bone marrow transplant or gene therapy.