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Immunoglobulin Rearrangement Enzyme 1

Immunoglobulin rearrangement enzyme
immunology

Question

Vignette: A 4-year-old boy is brought to the pediatrician by his parents due to recurrent bacterial infections. His medical history shows that he has had several bouts of pneumonia, sinusitis, and otitis media since birth. Laboratory tests show normal T-cell count but a significantly low B-cell count. He also has low levels of all immunoglobulin classes. A genetic testing is performed and reveals a defect in an enzyme involved in the rearrangement of immunoglobulin heavy-chain and T-cell receptor genes.

Question: Which enzyme is most likely defective in this patient?

Choices

A) ADA enzyme

B) Bruton Tyrosine Kinase

C) RAG-1/ RAG-2 enzyme

D) CD40 ligand

E) MHC II molecules

Answer

C) RAG-1/ RAG-2 enzyme

Explanation

The patient's history of recurrent bacterial infections, low B-cell count, and low levels of all immunoglobulin classes point towards a combined B- and T-cell immunodeficiency. Given the defect in the rearrangement of immunoglobulin heavy-chain and T-cell receptor genes, the most likely diagnosis is severe combined immunodeficiency (SCID), which is frequently caused by a defect in the RAG-1 or RAG-2 enzyme. These enzymes play a crucial role in the V(D)J recombination, a process that allows the immune system to recognize a broad range of antigens. Without them, B and T cells cannot mature properly, leading to the immunodeficiency seen in this patient.

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