Bad omens

Abstract

Omenn syndrome is a rare phenotypic presentation of severe combined immunodeficiency (SCID). Diagnosis of Omenn syndrome requires fulfillment of four criteria as outlined by the PIDTC in a 2022 consensus document.1 As the diagnosis of inborn errors of immunity (IEI) moves increasingly into the realm of molecular testing, Omenn syndrome (OS) remains a diagnosis that requires significant immunopathological testing. Here we describe a case of ‘typical’ Omenn syndrome in an infant with SCID due to RAG2 deficiency highlighting the laboratory tests involved in diagnosis. We then describe a unique ‘atypical’ case of Omenn-like syndrome occurring in a patient with SCID due to ADA deficiency while on treatment with pegylated-ADA and hypothesize about the pathological mechanism at play. Both cases highlight this rare phenotype and the importance of the immunology laboratory in making the diagnosis. Reference 1. Dvorak CC, Haddad E, Heimall J, et al. The diagnosis of severe combined immunodeficiency (SCID): the Primary Immune Deficiency Treatment Consortium (PIDTC) 2022 Definitions. J Allergy Clin Immunol 2023; 151: 539–46.