Explain enzyme-replacement therapy to treat adenosine deaminase deficiency. Mention two disadvantages of this procedure. [3]

Adenosine deaminase (ADA) deficiency in patients can be treated by gene replacement therapy or enzyme replacement therapy. In the enzyme-replacement therapy, patients are regularly injected with the functional ADA enzyme. [1]

Disadvantages of this procedure : [1 mark for each point]

(i) It does not completely eradicate the disease.

(ii) Requirement of repeated doses of the enzyme makes it expensive.