Nexilin-related cardiomyopathy (NEXN-CMP) - an island's perspective

Abstract Introduction The phenotypic features of Nexilin related cardiomyopathies (NEXN-CMP) are poorly understood and under-reported. A better understanding of the genotype-phenotype association is paramount. Objectives The main objective of this study was to investigate the causative role and phenotypic expression of the NEXN gene in the Maltese Islands. Methodology Probands and relatives referred for a cardiac gene panel were evaluated. Subjects harbouring NEXN variants were identified. Those finally classified as having NEXN-CMP were evaluated for the purpose of this study. Results Out of 444 probands (confirmed or suspected cardiomyopathy), 12 probands were labelled with NEXN-CMP. This equates to a prevalence of 2.7% in the local cardiomyopathy pool, substantially higher to what has been previously reported. Genetic testing identified 19 individuals (probands [n=15] and relatives [n=4]) all harbouring the same novel frameshift variant: NEXN c.1589_1590del p.(Arg530LysfsTer3), classified as likely pathogenic according to ACMG criteria. Three (15.8%) harboured a second pathogenic variant (n=2 MYH7, n=1 TTN). Another 3 were not clinically affected (n=1 FH of SCD, n=2 first degree relatives of NEXN-CMP probands). These individuals were excluded from further analysis. The NEXN-CMP cohort (n=13) consisted of a dominant male (68.8%) population (54±22 years at presentation, 7.7% athletes, 12 families). Most were probands (n=12/13). DCM was the dominant phenotype (n=8, 61.5%) followed by HNDLVC (n=3, 23.1%) and HCM (n=2, 15.4%). One infantile DCM was homozygous for the NEXN variant. Symptoms were the most frequent method of presentation (n=6, 46.2%), followed by a FH of SCD and/or cardiomyopathy (n=3, 23.1%), abnormal echocardiogram (n=2 15.4%), OHCA (n=1, 7.7%) and inutero diagnosis (n=1, 7.7%). A FH of SCD was present in a third (n=4/12, 33.3%). The ECG was abnormal in the majority (n=10/11, 90.9%). Most patients had a LBBB (6/11, 54.5%) followed by inferolateral TWI (n=3, 27.3%), ventricular arrhythmias/high-grade AVB (n=1, 9.1% each). NEXN-CMP appears to be a left dominant cardiomyopathy. LV dilation and reduced LVEF were present in 84.6%. Non-ischaemic scar was present in 3/8 cases (37.5%), 2 had a ring-like pattern. RV morphology and function was normal in all cases. Tachyarrhythmias were frequently observed (n=4/6, 66.7%) during holter monitoring or exercise testing (n=2 NSVTs, n=1 VEs, n=1 SVEs). A fourth (n=3/11, 27.3%) were implanted with an electrop