Adenosine Deaminase (ADA) Deficiency and Its Cause
Biology · Biotechnology and Its Applications · NEET
Adenosine deaminase (ADA) deficiency is a hereditary disease caused by the deletion of the gene for the enzyme adenosine deaminase. This enzyme is crucial for the immune system to work, so when it is missing the immune system fails (a form of SCID). Memory hook: "No ADA gene = No immune defence." It was the first disease treated by gene therapy, in 1990, in a 4-year-old girl.
The cause of ADA deficiency: the gene for adenosine deaminase is deleted, so the enzyme is not made, so the immune system fails. It was the first disease treated by gene therapy in 1990.
Your doubts, answered
What is the exact cause of ADA deficiency?
It is caused by the deletion of the gene for adenosine deaminase. Because the gene is missing, the body cannot make the enzyme. NCERT states this clearly: the disorder is caused due to the deletion of the gene for adenosine deaminase. So the cause is genetic (a missing gene), not an infection or a diet problem.
Why does losing one enzyme damage the whole immune system?
Adenosine deaminase (ADA) is crucial for the immune system to function. Without it, toxic products build up and immune cells (lymphocytes) cannot develop properly. This leaves the child unable to fight infections, so a single enzyme defect causes a serious immune failure.
Is ADA deficiency the same as SCID?
ADA deficiency is one cause of Severe Combined Immunodeficiency (SCID). For NEET, remember the NCERT chain: gene for ADA is deleted -> enzyme not made -> immune system does not work. NCERT does not require the term SCID, but knowing ADA deficiency leads to immune dysfunction is enough.
Is this disease inherited or caught during life?
It is hereditary. NCERT places it under gene therapy, which corrects a gene defect diagnosed in a child or embryo. A person is born with the defect because the ADA gene is missing, so it is inborn and not acquired later.
How can ADA deficiency be treated apart from gene therapy?
NCERT lists two other options. In some children it can be cured by bone marrow transplantation. In others it can be treated by enzyme replacement therapy, where functional ADA is given to the patient. Gene therapy is the third, more permanent attempt.
⚠️ The NEET trap ✗ ADA deficiency is caused by a lack of adenosine (a base) in the diet or a digestive problem. ✓ It is caused by deletion of the GENE for the enzyme adenosine deaminase, which then cripples the immune system. 🧠 The trap word is 'adenosine'. NEET mixes it with the nucleoside adenosine from Class 11. Here it means the ENZYME adenosine deaminase, and the fault is a missing gene, not a missing base or a stomach issue.
Real NEET questions
NEET 2021
The Adenosine deaminase deficiency results into:
A · Digestive disorder
B · Addison's disease
C · Dysfunction of Immune system ✓
D · Parkinson's disease
Solution: The enzyme adenosine deaminase is crucial for the immune system to function. Its deficiency, caused by deletion of the ADA gene, impairs immune function. So the result is dysfunction of the immune system. NCERT Ch 10: 'This enzyme is crucial for the immune system to function.'
NEET 2016 (Phase 2)
Which kind of therapy was given in 1990 to a four-year-old girl with adenosine deaminase (ADA) deficiency?
A · Gene therapy ✓
B · Chemotherapy
C · Immunotherapy
D · Radiation therapy
Solution: The first clinical gene therapy was given in 1990 to a 4-year-old girl with ADA deficiency. A functional ADA cDNA is delivered into the patient's lymphocytes using a retroviral vector. NCERT Ch 10: 'The first clinical gene therapy was given in 1990 to a 4-year old girl.'
NEET 2020
Match the columns: (a) Bt cotton (b) Adenosine deaminase deficiency (c) RNAi (d) PCR with (i) Gene therapy (ii) Cellular defence (iii) Detection of HIV infection (iv) Bacillus thuringiensis.
A · (a)-(ii),(b)-(iii),(c)-(iv),(d)-(i)
B · (a)-(i),(b)-(ii),(c)-(iii),(d)-(iv)
C · (a)-(iv),(b)-(i),(c)-(ii),(d)-(iii) ✓
D · (a)-(iii),(b)-(ii),(c)-(i),(d)-(iv)
Solution: ADA deficiency is treated by the first clinical gene therapy, so (b) pairs with (i) Gene therapy. Bt cotton uses Bacillus thuringiensis (a-iv), RNAi is a method of cellular defence (c-ii), and PCR detects HIV infection (d-iii). This gives option C.
Solved Biotechnology and Its Applications NEET PYQs
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