This is the first study, to our knowledge, to demonstrate that Down syndrome is a novel independent risk factor for severe respiratory syncytial virus lower respiratory tract infections. These findings should prompt studies to investigate possible mechanisms that underlie severe respiratory syncytial virus lower respiratory tract infections in children with Down syndrome. The effect of respiratory syncytial virus prophylaxis in this specific population needs to be established.

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Children with Down syndrome (DS) have low numbers of naive T cells and abnormal thymus development and function. Because next to thymic production, peripheral proliferation greatly contributes to naive T cell generation in healthy children, we examined the cause of reduced naive T cell numbers in children with DS. Compared with aged matched controls, the total number of signal joint TCR excision circles (sjTREC) per ml blood was reduced in DS. Reduced frequencies and absolute numbers of protein tyrosine kinase 7-positive recent thymic emigrants, but similar levels of naive T cell apoptosis and Ag-driven activation in DS, suggested that reduced thymic output and not increased peripheral loss of naive T cells caused the reduced sjTREC numbers. We found no support for defective peripheral generation of naive T cells in DS. In DS the naive T cells responded to IL-7 and, based on Ki-67 expression, had similar proliferation rates as in healthy controls. sjTREC content per naive CD8+ T cells was not increased, but even decreased, pointing to increased survival or peripheral generation of naive T cells in DS. In conclusion, we show in this study that reduced thymic output, but not reduced peripheral generation nor increased loss of naive T cells, results in the low naive T cell numbers found in DS.

ABSTRACT. Objective. To evaluate efficacy of the recently introduced implantable loop recorder (ILR) in establishing symptom-rhythm correlation in young patients with syncope, near syncope, palpitations, and acute life-threatening events (ALTEs).Methods. A retrospective study was conducted with patients with ILR from 3 pediatric centers. Inclusion criteria were age <25 years and a minimum follow-up of 1 month. All ILR-stored events were analyzed regularly for the presence or absence of an arrhythmia at the time of the symptomatic event.Results. Twenty-one patients (12 male, 9 female) with an average age of 12.3 ؎ 5.3 years (range: 0.8 -22 years) were included in the study. Five (24%) patients had structural heart disease, 2 (10%) had a family history of sudden cardiac death, 3 (14%) had QT prolongation on electrocardiogram, and 11 had no cardiovascular disease. Indications for ILR were recurrent syncope and near syncope (n ‫؍‬ 15), palpitations (n ‫؍‬ 2), and ALTE (n ‫؍‬ 2). Fourteen (67%) patients continued to have symptoms, and 7 (33%) had no symptoms after ILR over a follow-up period of 8.4 ؎ 4.7 months (range: 1.9 -16 months). Symptom-rhythm correlation was possible in all 14 patients who continued to have symptoms (supraventricular tachycardia in 4, ventricular tachycardia in 2, torsades de points in 1, asystole in 1, junctional bradycardia in 1, and sinus rhythm in 5).Conclusions. ILR is useful in determining the presence or absence of an arrhythmia during symptoms of syncope, near syncope, and palpitations as well as ALTEs in patients with and without structural heart disease when conventional diagnostic testing, such as electrocardiogram, Holter monitoring, and/or external loop recording, is inconclusive. Pediatrics 2003;112:e228 -e233. URL: http://www.pediatrics.org/cgi/content/full/112/3/e228; implantable loop recorder, arrhythmias, syncope, palpitations.