Abstract 12946: Identification of a LMNA Synonymous Variant Associated With Severe Dilated Cardiomyopathy

Abstract

Dilated cardiomyopathy (DCM) is one of the most common cardiac phenotypes caused by mutations of lamin A/C (LMNA) gene in humans. Almost 50% of LMNA variants reported in ClinVar as pathogenic or likely pathogenic are due to frameshift, nonsense, or splicing variants, predictive of haploinsufficiency for LMNA protein. In contrast, synonymous variants that do not immediately suggest a haploinsufficiency mechanism are much harder to interpret. We evaluated a cohort of 57 patients who underwent heart transplant for dilated cardiomyopathy for LMNA variants and identified a novel synonymous variant c.936G>A in the last nucleotide of exon 5 of LMNA in a DCM family. Clinically, LMNA c.936G>A carriers presented with severe DCM, conduction disease and high creatine-kinase levels. Sanger sequencing showed the presence of LMNA c.936G>A in the genomic DNA but not in the cDNA derived from one family member’s heart tissue. RT-PCR using RNA from the patient’s heart tissue was performed with primers that amplified LMNA exons 4-6. DNA fragments amplified by RT-PCR were then cloned into pcDNAII vector and 40 clones were picked and sequenced. An aberrantly spliced mRNA containing the variant and a premature stop codon was identified in 1 of the 40 clones. Real-time quantitative PCR showed significantly lower LMNA mRNA levels in the patient’s heart compared to the controls. Our findings suggest that the c.936G>A LMNA variant resulted in aberrant RNA splicing, which possibly triggers nonsense-mediated RNA decay, leading to reduced mRNA and likely protein expression. These results expand the understanding on the association between synonymous LMNA variants and the molecular pathogenesis of LMNA-DCM.