Clinical and Molecular Data Define a Diagnosis of Arrhythmogenic Cardiomyopathy in a Carrier of a Brugada-Syndrome-Associated PKP2 Mutation

Abstract

Plakophilin-2 (PKP2) is the most frequently mutated desmosomal gene in arrhythmogenic cardiomyopathy (ACM), a disease characterized by structural and electrical alterations predominantly affecting the right ventricular myocardium. Notably, ACM cases without overt structural alterations are frequently reported, mainly in the early phases of the disease. Recently, the PKP2 p.S183N mutation was found in a patient affected by Brugada syndrome (BS), an inherited arrhythmic channelopathy most commonly caused by sodium channel gene mutations. We here describe a case of a patient carrier of the same BS-related PKP2 p.S183N mutation but with a clear diagnosis of ACM. Specifically, we report how clinical and molecular investigations can be integrated for diagnostic purposes, distinguishing between ACM and BS, which are increasingly recognized as syndromes with clinical and genetic overlaps. This observation is fundamentally relevant in redefining the role of genetics in the approach to the arrhythmic patient, progressing beyond the concept of "one mutation, one disease", and raising concerns about the most appropriate approach to patients affected by structural/electrical cardiomyopathy. The merging of genetics, electroanatomical mapping, and tissue and cell characterization summarized in our patient seems to be the most complete diagnostic algorithm, favoring a reliable diagnosis.

Keywords: Brugada syndrome; PKP2; arrhythmogenic cardiomyopathy; cardiac mesenchymal stromal cells; diagnosis; endomyocardial biopsy; functional studies; mutation.

Figure 1

Clinical data are not compatible with BS phenotypes. (A) Cardiac magnetic resonance showing biventricular dilation and areas suspicious for adipose infiltration at the apex of the right ventricle (RV). (B) Bipolar (left) and unipolar (right) electroanatomical mapping of the RV of the patient. Unipolar voltage mapping showed low-voltage areas in the RV outflow tract. (C) Endomyocardial biopsy showing fibro-fatty substitution, compatible with arrhythmogenic cardiomyopathy diagnosis. (D) 1 mg/kg of ajmaline was administered to the patient over 10 min followed by 5 min of wash-out observation: no type-1 BS electrocardiographic pattern was induced. BS, Brugada syndrome.

Figure 2

C-MSC data are distinctive of ACM. (A) Western blot shows higher PKP2 expression in ACM than in BS C-MSCs cultured in basal condition. GAPDH is shown as a loading control and used to normalize the quantification. (B) qRT-PCR data showing higher PLIN1 and PPARγ expression in ACM than in BS C-MSCs in adipogenic medium. (C) Higher ORO staining is detected in ACM vs. BS C-MSCs cultured in adipogenic medium for three days, as in the representative image and quantification. Scale bar is 20 μm. (D) Representative immunofluorescence images of C-MSCs cultured in adipogenic medium for three days and stained with PG or PPARγ antibodies. More positive nuclei/nuclei numbers were observed in ACM than in BS cells for both markers. Scale bar is 50 μm. The graphs show the mean and standard error of three technical replicates. *p < 0.05; **p < 0.01 ***p < 0.001 (two-tailed Student’s t-test). ACM, arrhythmogenic cardiomyopathy; C-MSC, cardiac mesenchymal stromal cells; GAPDH, glyceraldehyde 3-phosphate dehydrogenase; ORO, Oil Red O; PG, plakoglobin; PKP2, plakophilin 2; PLIN1, perilipin-1; PPARγ, peroxisome proliferator-activated receptor gamma.