Examples for changing the treatment modality based on molecular diagnosis was a SCID male infant with T-B-NK- phenotype, the molecular diagnosis of adenosine deaminase deficiency allowed the clinician to instantly start polyethylene-glycol-conjugated bovine adenosine deaminase (PEG-ADA), and in the absence of an HLA matched sibling donor, the patient was treated with autologous hematopoietic stem cell gene therapy (HSC-GT) for the correction of his immunodeficiency [23]. This evidence concerns the gene ADA and hyperinsulinemic hypoglycemia, familial, 4.