==== Front Int J Appl Basic Med ResInt J Appl Basic Med ResIJABMRInternational Journal of Applied and Basic Medical Research2229-516X2248-9606Medknow Publications & Media Pvt Ltd India IJABMR-8-20210.4103/ijabmr.IJABMR_71_18Letter to EditorThe Role of Cilia in the Setting of Isomerism and why Isomerism is not a Subset of Heterotaxy Loomba Rohit S Anderson Robert H 1Department of Cardiology, Cincinnati Children's Hospital, Cincinnati, OH, USA1 Department of Cardiology, Newcastle University, Newcastle Upon Tyne, United KingdomAddress for correspondence: Prof. Rohit S Loomba, Cincinnati Children's Hospital, Cincinnati, OH, USA. E-mail: loomba.rohit@gmail.comJul-Sep 2018 8 3 202 202 Copyright: © 2018 International Journal of Applied and Basic Medical Research2018This is an open access journal, and articles are distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as appropriate credit is given and the new creations are licensed under the identical terms. ==== Body We read with great interest the case report by Narahari et al. regarding “primary ciliary dyskinesia” in a patient with left isomerism.[1] The authors do not share in this case report how the diagnosis of ciliary dyskinesia was made. They correctly share in the discussion that video microscopy to characterize ciliary beat is one such method. This is of particular importance in those with isomerism as ciliary ultrastructure can often be normal in these patients despite having ciliary dysfunction as noted by abnormal ciliary beat. Thus, electron microscopy may be normal while a ciliary function may still be impaired. This also implies that this may not be “primary ciliary dyskinesia” in its purest sense. Ciliary dysfunction has been noted in a large proportion of patients with isomerism, with most having normal ciliary ultrastructure. Low exhaled nitric oxide levels have also been noted in those with isomerism and ciliary dysfunction.[2] While the current studies have focused on investigating motile cilia in the setting of isomerism, it is likely that sensory cilia are also dysfunctional in the setting of isomerism. Future investigations regarding this are necessary. As stated by Narahari et al., this abnormal ciliary function may not only be a result of isomerism but is felt to likely be implicated, at least in part, to the development of isomerism. In addition, it should be noted that isomerism is the term that best describes this clinical situation and that isomerism is not a subset of heterotaxy. While both terms have been proposed to describe such clinical situations, the two are separate nomenclature systems. Isomerism is subdivided into right- and left-sided varieties based on the morphology of the atrial appendages while heterotaxy is subdivided by splenic anatomy. Emerging molecular data regarding this clinical situation indicates the concept of isomerism is of greater utility as the same mutation in animal models results in consistent atrial appendage findings but not consistent splenic findings.[3] We also offer that the term “situs ambiguus” be avoided. Indeed, nothing is ambiguous as the authors describe by clearly defining the location of organs which is more helpful.[4] The nuances of isomerism are subtle but vital as we improve our understanding and management of this complex, multisystem clinical entity. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest. ==== Refs References 1 Narahari KN Kapoor A Sanamandra SK Varma Gunturi SR Primary ciliary dyskinesia and situs ambiguus: A rare association Int J Appl Basic Med Res 2018 8 48 50 29552537 2 Nakhleh N Francis R Giese RA Tian X Li Y Zariwala MA High prevalence of respiratory ciliary dysfunction in congenital heart disease patients with heterotaxy Circulation 2012 125 2232 42 22499950 3 Loomba RS Hlavacek AM Spicer DE Anderson RH Isomerism or heterotaxy: Which term leads to better understanding? Cardiol Young 2015 25 1037 43 26088959 4 Tremblay C Loomba RS Frommelt PC Perrin D Spicer DE Backer C Segregating bodily isomerism or heterotaxy: Potential echocardiographic correlations of morphological findings Cardiol Young 2017 27 1470 80 28367761