# DBT JRF 2022 — Question 28

Exam: DBT JRF 2022 · Section: B · Topic: Immunology › Immunodeficiency Disorders · Difficulty: Medium

## Question

Which one of the immunodeficiency is caused by a mutation in BTK gene:

## Options

- **A.** X-linked SCID
- **B.** X-linked agammaglobulinemia
- **C.** DiGeorge syndrome
- **D.** Chronic granulomatous disease

## Answer

Option B

## Explanation

BTK gene mutation and immunodeficiency: BTK (Bruton's Tyrosine Kinase) is a non-receptor tyrosine kinase essential for B cell development: • BTK is required for pro-B cell → pre-B cell transition in the bone marrow. • Mutations in BTK (X-linked gene) → B cell development arrests at the pro-B stage → virtually no mature B cells in periphery → absence of all immunoglobulins (agammaglobulinemia). Disease: X-linked agammaglobulinemia (XLA), also called Bruton's disease: • X-linked recessive (gene on X chromosome, males affected) • Presents in early childhood with recurrent bacterial infections • Treatment: regular intravenous immunoglobulin (IVIG) infusions Distractors: • X-linked SCID: caused by mutations in the IL-2 receptor gamma chain (IL2RG), affecting both T and NK cells. • DiGeorge syndrome: 22q11.2 deletion, thymus aplasia → T cell deficiency. • Chronic granulomatous disease: mutations in NADPH oxidase genes (phagocyte killing defect). Answer: X-linked agammaglobulinemia (Option 2).

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