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Is an Appreciation of Isomerism the Key to Unlocking the Mysteries of the Cardiac Findings in Heterotaxy?

1
Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne NE1 3BZ, UK
2
Division of Pediatric Cardiology, University of Florida, Gainesville, FL 32610, USA
3
Division of Pediatric Cardiology, Advocate Children’s Hospital, Oak Lawn, IL 60453, USA
*
Author to whom correspondence should be addressed.
J. Cardiovasc. Dev. Dis. 2018, 5(1), 11; https://doi.org/10.3390/jcdd5010011
Received: 2 January 2018 / Revised: 29 January 2018 / Accepted: 5 February 2018 / Published: 6 February 2018
(This article belongs to the Special Issue Left–Right Asymmetry and Cardiac Morphogenesis)
Pediatric cardiologists treating patients with severe congenital cardiac defects define “visceral heterotaxy” on the basis of isomerism of the atrial appendages. The isomeric features represent an obvious manifestation of disruption of left-right asymmetry during embryonic development. Thus, there are two subsets of individuals within the overall syndrome, with features of either right or left isomerism. Within the heart, it is only the atrial appendages that are truly isomeric. The remainder of the cardiac components shows variable morphology, as does the arrangement of the remaining body organs. Order is provided in this potentially chaotic arrangement simply by describing the specific features of each of the systems. These features as defined by clinicians, however, seem less well recognized by those investigating the developmental origins of the disruption of symmetry. Developmental biologists place much greater emphasis on ventricular looping. Although the direction of the loop can certainly be interpreted as representing an example of asymmetry, it is not comparable to the isomeric features that underscore the clinical syndromes. This is because, thus far, there is no evidence of ventricular isomerism, with the ventricles distinguished one from the other on the basis of their disparate anatomical features. In similar fashion, some consider transposition to represent abnormal lateralization, but again, clinical diagnosis depends on recognition of the lateralized features. In this review, therefore, we discuss the key questions that currently underscore the mismatch in the approaches to “lateralization” as taken by clinicians and developmental biologists. View Full-Text
Keywords: situs ambiguus; right isomerism; left isomerism; dextrocardia; ventricular looping; ventricular topology; sequential segmental analysis situs ambiguus; right isomerism; left isomerism; dextrocardia; ventricular looping; ventricular topology; sequential segmental analysis
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Anderson, R.H.; Spicer, D.E.; Loomba, R. Is an Appreciation of Isomerism the Key to Unlocking the Mysteries of the Cardiac Findings in Heterotaxy? J. Cardiovasc. Dev. Dis. 2018, 5, 11.

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