A neonate develops severe bacterial infections and requires granulocyte transfusions for survival. Laboratory evaluation shows absence of all lymphocyte subsets and markedly reduced serum immunoglobulins. Adenosine deaminase (ADA) activity is 5% of normal. What is the most likely mode of inheritance of this condition?

• A Autosomal recessive ✓
• B X-linked recessive
• C Autosomal dominant
• D X-linked dominant

Explanation

ADA-SCID is caused by autosomal recessive mutations in the ADA gene on chromosome 20q13, leading to accumulation of deoxyadenosine and dATP that are selectively toxic to lymphocytes, causing combined T and B cell lymphopenia. It accounts for approximately 15% of all SCID cases and is the commonest autosomal recessive form. The X-linked form of SCID is caused by mutations in the IL-2 receptor gamma chain (common gamma chain) and presents similarly but is X-linked.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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