$A$ patient is suffering from $ADA$ deficiency. Can he be cured? How?

(N/A) Yes,a patient suffering from $ADA$ deficiency can be treated. $ADA$ deficiency is caused by the deletion of the gene for adenosine deaminase,which is essential for the immune system.
$1$. Bone Marrow Transplantation: In some children,the disease can be cured by transplanting healthy bone marrow.
$2$. Enzyme Replacement Therapy: Functional $ADA$ enzyme is injected into the patient. However,this is not a permanent cure as it requires repeated administration.
$3$. Gene Therapy: This is the most promising approach. Lymphocytes from the patient's blood are grown in a culture outside the body. $A$ functional $ADA$ $cDNA$ is introduced into these lymphocytes using a retroviral vector. These genetically engineered cells are then returned to the patient. Since these cells are not immortal,periodic infusions are required. $A$ permanent cure is possible if the gene is introduced into cells at early embryonic stages.