Brief communication A secondary analysis of racial differences in periodic leg movements in sleep and ferritin in hemodialysis patients Jung Hie Lee a , Kathy P. Parker b , Fari P. Ansari c , Donald L. Bliwise d, * a Department of Psychiatry, Kangwon National University College of Medicine, Chunchon, Kangwon-do, South Korea b Emory University School of Nursing, Atlanta, GA, USA c Department of Neurology, Emory University School of Medicine, Atlanta, GA, USA d Department of Neurology, Emory University School of Medicine, Wesley Woods Center, 1841 Clifton Road, Atlanta, GA 30329, USA Received 27 May 2005; received in revised form 12 January 2006; accepted 13 January 2006 Available online 5 June 2006 Abstract Background and objective: Hemodialysis (HD) is associated with restless legs syndrome (RLS) and periodic leg movements in sleep (PLMS), but the mechanisms underlying these relationships remain unclear. African–American HD patients have been reported pre- viously to have a reduced likelihood of RLS. Alterations in iron metabolism, known to be a risk factor for idiopathic forms of RLS, could represent the basis for these racial differences. Patients and methods: In secondary data analyses from a previously published study, we examined raw and log-transformed values for plasma ferritin and polysomnographically recorded PLMS in Caucasian and African–American HD patients. Results: African–American (n = 36) HD patients had higher ferritin and lower PLMS than Caucasians (n = 10). However, within the African–American population, ferritin levels were unrelated to PLMS. Conclusions: These results are compatible with previously reported racial differences in RLS to the extent that PLMS were less com- mon in the African–American population. However, they suggest that if a differential genetic vulnerability underlies those racial differences, it may not manifest as a deficiency in iron metabolism, at least within the constraints of the marker of iron stores used here (e.g. serum ferritin) and in the specific population studied (hemodialysis). Future studies with larger, more representative sam- ples of African–Americans and Caucasians will be required to replicate such differences. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Restless legs syndrome; Periodic leg movements in sleep; Hemodialysis; Racial differences; Ferritin 1. Introduction Periodic limb movements in sleep (PLMS) are often considered supportive features for restless legs syndrome (RLS) [1], and both RLS and PLMS are thought to be critically dependent upon iron stores, often as reflected by low levels of ferritin in serum [2], high transferrin receptor in cerebrospinal fluid (CSF) [3] and reduced levels of iron in the substantia nigra in magnetic reso- nance imaging (MRI) [4]. Hemodialysis (HD) patients are a population particularly susceptible to PLMS/ RLS [5,6]. Although the mechanisms underlying the higher prevalence of PLMS/RLS in the HD population remains unclear and whether deficient iron metabolism plays a role is equivocal [6], RLS symptoms may be of considerable prognostic significance in HD, as they have been related to earlier mortality [7,8]. Recently, racial differences in RLS symptoms in HD patients have been reported [9]. In this report, we present secondary data analyses of polysomnographically recorded PLMS in Caucasian and African–American HD patients and examined relationships with serum ferritin. We hypoth- esized that because of higher iron stores in the African– American population [10,11] we would detect reduced levels of PLMS in these patients. 1389-9457/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.sleep.2006.01.007 * Corresponding author. Tel.: + 1 404 728 4751; fax: + 1 404 728 4756. E-mail address: dbliwis@emory.edu (D.L. Bliwise). www.elsevier.com/locate/sleep Sleep Medicine 7 (2006) 646–648