LETTER TO THE EDITOR Reduced serum vitamin D levels in neuromyelitis optica Erdem Tu ¨zu ¨n 1 • O ¨ zlem Ku ¨c ¸u ¨khu ¨ seyin 2 • Murat Ku ¨rtu ¨ncu ¨ 3 • Recai Tu ¨ rkog ˘lu 4 • I ˙ lhan Yaylım 2 Received: 8 October 2014 / Accepted: 20 April 2015 Ó Springer-Verlag Italia 2015 Dear Sir, Vitamin D deficiency has been associated with several autoimmune disorders and increased autoimmune re- sponses in healthy individuals. One of many potential factors underlying this association is the well-established anti-inflammatory action of vitamin D administration re- sulting in reduced proinflammatory cytokine production and enhanced regulatory T cell activity [1]. Although vi- tamin D deficiency is well known in multiple sclerosis (MS) [2], its significance in neuromyelitis optica (NMO), another autoimmune disease of the central nervous system (CNS), is less well understood. NMO, NMO spectrum disorder and recurrent transverse myelitis patients have been recently shown to display reduced vitamin D levels [3, 4]. Although, these studies have shed some light on the impact of vitamin D on NMO pathogenesis, associations between vitamin D levels and clinical–demographic fea- tures of NMO patients are yet to be characterized. In this study, 25-hydroxy vitamin D (25OH-VitD) levels were measured in sera of 24 NMO patients (20 women, 4 men; mean age ± standard deviation, 41.3 ± 11.6 years) satisfying NMO diagnostic criteria [5] and age–gender matched controls (19 relapsing remitting MS patients and 22 healthy individuals) by an ELISA kit (DLD Diagnostika, Hamburg, Germany), as per manufacturer’s instructions. Measurements were made in the archived sera obtained during relapses prior to steroid treatment. Patients and controls who had received vitamin D supplementation at any time were not included. None of the NMO patients had a monophasic disease course or a concomitant autoimmune disease. All NMO patients had received pulse methylpred- nisolone treatment during attacks and azathioprine to pre- vent relapses. Serum aquaporin-4 antibody (Aqp-4 Ab) was investigated by a cell-based assay (Euroimmun, Luebeck, Germany). 25OH-VitD level differences were adjusted for age, gender, season during blood sampling (winter, spring, summer or fall) and EDSS scores by linear regression analysis. Since all patients belonged to the same ethnicity and were living in cities located on the same latitude, no statistical adjustment was done for these parameters. Both NMO and MS patients had significantly lower serum 25OH-VitD levels than healthy controls (p = 0.025 by ANOVA) (Fig. 1a). After adjusting for age, gender, season and EDSS, 25OH-VitD levels were still significantly lower in patients (p = 0.032, 95 % confidence interval 5.7–13.8). While gender and Aqp-4 Ab status did not affect 25OH-VitD levels, NMO patients with shorter disease du- ration ( \ 10 years) and with cerebrospinal fluid oligoclonal bands (OCB) showed significantly lower 25OH-VitD levels (p = 0.017 and p = 0.046 by Student’s t test, respectively) (Table 1). Pearson’s test revealed a modest correlation be- tween serum 25OH-VitD levels and disease duration in NMO (Fig. 1b). No significant correlation could be found between 25OH-VitD levels and age (p = 0.162, R = 0.211), number of relapses (p = 0.071, R = 0.309) and EDSS values (p = 0.262, R = 0.137) of NMO patients. & Erdem Tu ¨zu ¨n drerdem@yahoo.com 1 Department of Neuroscience, Institute for Experimental Medical Research (DETAE), Istanbul University, Vakif Gureba Street, Capa, 34390 Istanbul, Turkey 2 Department of Molecular Medicine, Institute for Experimental Medical Research (DETAE), Istanbul University, Istanbul, Turkey 3 Department of Neurology, Istanbul Faculty of Medicine, Istanbul University, Istanbul, Turkey 4 Department of Neurology, Haydarpasa Numune Education and Research Hospital, Istanbul, Turkey 123 Neurol Sci DOI 10.1007/s10072-015-2229-7