Two children, A and B aged 4 and 5 years respectively visited a hospital with a similar genetic disorder. The girl A was provided enzyme-replacement therapy and was advised to revisit periodically for further treatment. The girl, B was, however, given a therapy that did not require revisit for further treatment.
(a) Name the ailments the two girls were suffering from.
(b) Why did the treatment provided to girl A required repeated visits?
(c) How was the girl B cured permanently?

a) Both the girls are suffering from adenosine deaminase deficient (ADA). Due to the absence of this enzyme, the immune system is weakened as the T and B lymphocyte does not function properly.

b) In case of girl A, ADA is given intravenously or the lymphocytes of the patient may be cultured and cDNA encoding ADA are introduced in the culture. Since healthy lymphocytes will die after a certain time, so this treatment is not permanent.

c) The girl B must have undergone gene therapy. In this therapy, genes are extracted from the bone marrow. ADA is added at the early embryonic stages. This is a permanent cure.