In conclusion, BAFF, not APRIL, joins a short list of other putative CSF biomarkers of disease activity in pediatric OMS that includes B cell frequency (total B cells and B-cell subsets), B-cell chemoattractants (CXCL10, CXCL13), and oligoclonal bands [2-5]. The gene discussed is TNFSF13; the disease is opsoclonus-myoclonus syndrome.