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The MOGE(S) Classification for a Phenotype–Genotype Nomenclature of Cardiomyopathy: Endorsed by the World Heart Federation

The authors of the paper, endorsed by the World Heart Federation, propose a new classification for Cardiomyopathies based on the current knowledge on phenotype-genotype correlation. A 5 letter scheme called MOGE(S), similar to the TNM classification in oncology, is described in an attempt for standardization. Current classifications (AHA and ESC) have their limitations to appropriately address a constantly changing scenario with increasing sophistication.

The term “idiopathic cardiomyopathy” as a cardiomyopathy of unknown etiology is no-longer appropriate, as the cause of the disease, often genetic, and the mechanisms are partly identified in an increasing proportion of cardiomyopathies.

The field is gaining complexity. There is a significant genetic heterogeneity which is expected to increase with the recently implemented massive sequencing techniques. It is conceivable that although the diagnosis based on phenotype is still clinically useful, it is not sufficient to stratify prognosis in cardiomyopathies caused by mutations in different genes and that grouping cardiomyopathies per disease gene provides the basis for implementation of disease-specific research.

There is enough information in the literature to conclude that mutations in some genes causing Dilated Cardiomyopathy are associated to a particularly poor prognosis and in which indication of ICDs should be considered in early phases of the disease when systolic impairment is only mild or moderate. Based on the underlying gene mutations, numerous new terms such as: cardiodystrophinopathies, desminopathies, laminopathies, RASopathies, etc. have been proposed. Interestingly, mutations in the same genes, like MYBPC3 are associated with different phenotypes such as Hypertrophic, Dilated and Restrictive Cardiomyopathy.

The new classification aims to include all forms of cardiomyopathies including asymptomatic carriers, early forms and overlapping phenotypes. An extension of the MOGE(S) nomenclature to incorporate channelopathies is considered as possible in the future.

Cardiomyopathies, in this experts document, are described as disorders characterized by morphologically and functionally abnormal myocardium in the absence of any other disease that is sufficient, by itself, to cause the observed phenotype.

Under the “M” the morphofunctional phenotype is recorded: MD= dilated, MH= hypertrophic, MA= arrhythmogenic right ventricular, MR= restrictive and MLVNC= left ventricular non-compaction Cardiomyopathy. Mixed phenotypes are possible (MH+D), remarkable clinical features like AV-block, WPW, raised CK or the presence of epsilon waves (MD[WPW],  MH[WPW] MD[sCK] or MA[epsilon]), asymptomatic non-affected carriers (M0) and early forms (ME[H]) are also included in the notation.

Under the “O” the organ involvement is recorded. OH when the Heart is involved, OM for skeletal muscle involvement, with OK for Kidney, OL for liver, OMR for mental retardation, OO for ocular system, etc. All combinations are possible. 

Under the “G” the genetic pattern of inheritance is recorded. GAD for autosomal dominant, GXL for X-linked, GS for sporadic cases, GU unknown and G0 when family has not been  investigated.

Under the “E” etiological cause is recorded. EG-MYH7[p.Arg403Glu] in the case of cardiomyopathy genetic cause by a mutation in MYH7 gene in position Arg403Glu. Obligate carriers and non-carriers have also an specific notation in this system (EG-OC and EG-neg). Myocarditis is also a recognized cause (EM) with the option of including the suspected causative virus (EV-EBV if Ebstein-Barr virus), other options EM-sarcoidosis for cardiac sarcoidosis or EA-K for kappa AL amyloidosis.

Under the last letter “S” heart failure state (A to D) and or NYHA class is optionally included, which may come in handy for the description of early cardiomyopathy.

The MOGE(S) classification similarly as the TNM is dynamic and patients are coded differently as they develop the disease or after additional information arises from the examinations. A web application for MOGE(S) nomenclature is available at http://moges.biomeris.com



The authors of this paper highlight the importance of evaluation of associated cardiac and extracardiac features to make a correct diagnosis and their implications in prognosis and treatment (summarized in a very valuable table 1 and 3).

This is a very interesting exercise of trying to organize a field of the cardiology which is getting more and more complex, by categorizing patients with cardiomyopathies following an scheme that has been successful in other fields of medicine. As Prof. Elliott states in the editorial, there are some issues that makes cardiomyopathies different to cancer and some limitations in the proposed MOGE(S) classification system before this reach the clinical scenario.

TMN is a system which was implemented in order to stratify risk and hence to guide treatment, which is not the case of MOGE(S). MOGE(S) is a classification which aims to give a diagnosis to all individuals from early phases to mixed phenotypes, from unknown cause to deep genetic diagnosis. Probably the main achievement of the MOGE(S) classification is to standardize the diagnosis and to easy comparisons from centers to centers by unifying the “language”.

This new cardiomyopathy “barcode” would eventually be simple and useful for classification of most patients with hypertrophic and dilated cardiomyopathies, or for classification of families, but it is likely to fail in the attempt to extract the essence from patients with complex diagnosis, in particular in Arrhythmogenic Cardiomyopathy. Implementation of the MOGE(S) system is expected to depend on very specialized cardiac inherited units. This opens the discussion on whether cardiogenetics is getting complex enough to be a distinct cardiac specialty.

Conclusion:

This paper it is a good starting point for an interesting debate. The proposed classification needs to pass the feasibility test of the real-life clinical scenario. As the authors state in the text, there will be a monitoring phase and other options will be considered and new diseases could be incorporated.

References


1. Editorial by Elliott PM. Classification of cardiomyopathies: evolution or revolution?. J Am Coll Cardiol. 2013 Dec 3;62(22):2073-4.
2. Rapezzi C, Arbustini E, Caforio ALP, et al. Diagnostic work-up in cardiomyopathies: bridging the gap between clinical phenotypes and final diagnosis. A position statement from the ESC Working Group on Myocardial and Pericardial Diseases. Eur Heart J 2013;34:1448–58.
3. Elliott PM, Andersson B, Arbustini E, et al. Classification of the cardiomyopathies: a position statement from the European Society of Cardiology Working Group on Myocardial and Pericardial Diseases. Eur Heart J 2008;29:270–6.
4. Maron BJ, Towbin JA, Thiene G, et al. American Heart Association, Council on Clinical Cardiology, Heart Failure and Transplantation Committee, Quality of Care and Outcomes Research and Functional Genomics and Translational Biology Interdisciplinary Working Groups, Council on Epidemiology and Prevention. Contemporary definitions and classification of the cardiomyopathies: an American Heart Association Scientific Statement from the Council on Clinical Cardiology, Heart Failure and Transplantation Committee; Quality of Care and Outcomes Research and Functional Genomics and Translational Biology Interdisciplinary Working Groups; and Council on Epidemiology and Prevention. Circulation 2006;113:1807–16.
5. Richardson P, McKenna W, Bristow M, et al. Report of the 1995 World Health Organization/International Society and Federation of Cardiology Task Force on the Definition and Classification of Cardiomyopathies. Circulation 1996;93:841–2.

 

Notes to editor


The MOGE(S) Classification for a Phenotype–Genotype Nomenclature of Cardiomyopathy: Endorsed by the World Heart Federation.
J Am Coll Cardiol. 2013 Dec 3; 62(22):2046-72.

http://www.sciencedirect.com/science/article/pii/S0735109713057252
The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.