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Newborn screening efforts focusing on the quantification of T cell receptor excision circles (TRECs), as a biomarker for abnormal thymic production of T cells, have allowed for the identification and definitive treatment of severe combined immunodeficiency (SCID) in asymptomatic neonates. With the adoption of TREC quantification in Guthrie cards across the USA and abroad, typical, and atypical SCID constitutes only ~ 10% of cases identified with abnormal TRECs associated with T cell lymphopenia. Several other non-SCID-related conditions may be identified by newborn screening in a term infant. Thus, it is important for physicians to recognize that other factors, such as prematurity, are often associated with low TRECs initially, but often improve with age. This paper focuses on a challenge that immunologists face: the diagnostic evaluation and management of cases in which abnormal TRECs are associated with variants of T cell lymphopenia in the absence of a genetically defined form of typical or atypical SCID. Various syndromes associated with T cell impairment, secondary forms of T cell lymphopenia, and idiopathic T cell lymphopenia are identified using this screening approach. Yet there is no consensus or guidelines to assist in the evaluation and management of these newborns, despite representing 90% of the patients identified, resulting in significant work for the clinical teams until a diagnosis is made. Using a case-based approach, we review pearls relevant to the evaluation of these newborns, as well as the management dilemmas for the families and team related to the resolution of genetic ambiguities.

BackgroundEosinophilic esophagitis (EoE) is a chronic and increasingly prevalent antigen-driven disease. There is a paucity of information on long-term course in children.ObjectiveWe sought to understand the longitudinal trajectory of pediatric EoE during routine clinical care.MethodsWe prospectively enrolled children into an EoE database and reviewed their medical and pathologic records over 13 years.ResultsFrom 2011 to 2015, 146 children with EoE seen for their first visit at our center had 2 or more years of follow-up and 3 or more endoscopies over an average follow-up period of 5.13 years (range, 2-13 years). Longitudinal eosinophilic inflammation during treatment demonstrated 3 patterns over time. Children with less than 15 eosinophils/high-power field (hpf) for greater than 75% of their follow-up period were termed continuous responders (CRs). Children with waxing and waning inflammation of less than 15 eosinophils/hpf for less than 75% but 25% or more of the follow-up period were termed intermittent responders (IRs). Nonresponders (NRs) were defined as having less than 15 eosinophils/hpf for less than 25% of their follow-up. Fifty-nine (40%) of 146 patients were CRs, 65 (45%) of 146 were IRs, and 22 (15%) of 146 were NRs. CRs differed from IRs and NRs on the parameter of male/female ratio (1:1 in CRs, 4:1 in IRs, and 6:1 in NRs; P