With the help of T-NGS, genetic cause could be identified in 24 cases with 9 cases of JAK3 deficiency (*1 case was identified with whole exome sequencing), 6 MHC class II deficient cases, 3 RAG 1/2mutations, 2 IL2RG defects, 1 PRKDC defect, 2 cases of DCLER1C, an atypical case of ZAP70 deficiency. Here, IL2RG is linked to hyperinsulinemic hypoglycemia, familial, 4.