Which human medicine was the first to be produced using recombinant $DNA$ technology?

Which of the following is/are correct about Adenosine Deaminase $(ADA)$ deficiency?
$I$. In the absence of adenosine deaminase enzyme,purine metabolism is disturbed and $T$-lymphocytes fail to function.
$II$. $ADA$ deficiency is caused by the deletion of the gene for $ADA$.
$III$. In some cases,it can be cured by bone marrow transplantation and enzyme replacement therapy. But in both approaches,the patients are not completely cured.
$IV$. For permanent cure,genes isolated from the bone marrow cells producing $ADA$ at early embryonic stages can be a possible cure.
Which of the above statements are correct?

Gene therapy was first used for the treatment of ..........

Identify the incorrect statement.

The two polypeptide chains of human insulin are linked together by which of the following?

Which one of the following techniques does not serve the purpose of early diagnosis of a disease for its early treatment?