Gene therapy in humans was first practiced by Blease and Andresco to cure

In some children,$ADA$ deficiency can be cured by

The $C$-peptide is .......

Differentiate between diagnostics and therapeutics. Give one example for each category.

Consider the following statements about insulin.
$I.$ Human insulin is made up of $51$ amino acids arranged in two polypeptide chains.
$II.$ The two polypeptide chains are interconnected by two disulphide bridges.
$III.$ In mammals,including humans,insulin is synthesised as a pro-hormone,which contains an extra stretch called the $C$-peptide.
$IV.$ $C$-peptide is not present in the mature insulin.
Which of the statements given above are correct?

Gene therapy involves: