Introduction: Inborn errors of immunity (IBD) (formerly called primary immunodeficiencies), are rare diseases that usually begin in childhood and, if not diagnosed and treated promptly, usually have a fatal development for the patient.

Methods: Analytical, retrospective, descriptive study in patients with molecular diagnosis of inborn error of immunity, using the clinical record and whole exome sequencing.

Results: Twenty-eight patients with clinical and molecular diagnosis of IBD were included. The State of Mexico was the most frequent place of residence (56%), followed by CDMX (20%), Oaxaca (8%), Hidalgo (4%), Michoacán (4%), Morelos (4%), and San Luis Potosi (4%). Seventy-six percent were men and 24% were women. The onset of symptoms was, on average, at 25 months of age, and the mean age at diagnosis was 52.7 months of age. Sixty-eight percent had severe or recurrent infections as the initial manifestation; 20% had clinical manifestations of allergy, and 4% had lymphoproliferation and autoimmunity. Twelve percent had a history of severe reaction associated with vaccination, and 16% had a significant hereditary – familial history. 52% had alterations in lymphocyte subpopulations, 80% in immunoglobulin levels, 72% in blood biometry, and 12% in NBT. The two most frequently altered genes were ELANE (20%) and CYBB (12%).
In the IUIS classification, 32% belong to group V; 20% to group I; 16% to group II; 12% to group III; 12% to group IV; 4% to group VI, and 4% to group VII.

Conclusion: In Mexico we do not have a screening, so patients are diagnosed after the onset of symptoms. Diagnosis is complex. In our institution we do not have diagnostic algorithms; however, altered basic immunological studies can lead to clinical suspicion in these patients.