10-month-old male patient, two healthy sisters, history of BCG vaccine, 4 month evolution oral cadidiasis, chronic diarrhea with growth retardation, chronic malnutrition with the following somatometry on examination: W:6 kg L:67 cm CF:120 RF:32. Acute dehydration, irritability, generalized paleness, cervical adenomegaias, predominantly on the right, mobile, not attached to deep planes, BCG scar with green discharge, with disseminated dermatosis, symmetrical chest with subcrepitant rales in both lung fields, distended abdomen with hepatosplenomegaly. A central venous catheter is placed with blood cultures with isolation of Escherichia coli that produce beta lactamase, antibiotic coverage with carbapenem is started. Hemoglobin 8.4g/dL, total neutrophils 1300 cells/mcgL, total lymphocytes 80 cells/mcgL, lymphocyte subpopulations: CD3+ T lymphocytes 48 cells/mcgL, CD3+CD4+ T lymphocytes 4 cells /mcgL, CD3+CD8+ T Lymphocytes 0, CD16+CD56+ NK Lymphocytes 0, CD19+ Lymphocytes 32 cells/mcgL. IgG 667 mg/dL, IgM 87 mg/dL, IgA 26 mg/dL. HIV non-reactive, Quantiferon TB Gold positive. SCID-X1 is suspected, antibiotic coverage for grampositives is started with vancomycin and for Pneumocystis jirovecci with trimethoprim sulfamethoxazole, in addition to an antifungal scheme. IV immunoglobulin is administered at a dose of 1gkg and exome sequencing analysis is requested, finding a missense mutation in the second exon of the IL2RG gene, which gave rise to an alteration in the folding of the protein at the three-dimensional level due to the characteristics of hydrophobicity of the amino acids involved. Presented for bone marrow transplantation, however, he presented septic shock with a fatal outcome. Genetic sequencing has made possible to establish various mutations in the IL2RG gene, in this case we describe the mutation c.191T>A p.(Val64Glu) that causes amino acid change from valine to glutamic acid at position 64 and, according to the American College of Genetics and Genomics (ACMG) is considered a variant of uncertain significance, however, in our patient it manifested as SCID-X1.