Abstract 2820: Identification of a Silent Mutation that Perturbs LMNA Gene Splicing and Causes Dilated Cardiomyopathy
Objectives. Mutations in lamin A/C gene (LMNA) cause a variety of human diseases including muscular dystrophies, progeria, lipodystrophy and a severe form of dilated cardiomyopathy (DCM). This study examined the occurrence of LMNA mutations in a series of 57 patients who underwent heart transplant, therefore representing the population with the most severe DCM.
Methods. Genomic DNA and total RNA were extracted from the explanted heart tissue. LMNA gene mutation screening was performed by sequence analysis. LMNA cDNA was cloned and sequenced. Altered mRNA splicing was tested by minigene assay.
Results. We identified a silent mutation in the last codon (312) of exon 5 (CAG to CAA) in a patient with a history severe progressive DCM, atrial fibrillation, high serum creatine-kinase and non-specific EMG findings. Family investigations revealed skeletal muscle involvement, high creatine-kinase and conduction disease in his deceased father and overt DCM in his brother who carried the same mutation. The G936A mutation was not found in over 300 control chromosomes. Total RNA was extracted from the myocardial tissue and LMNA cDNA was cloned and sequenced: an alternative spliced mRNA was in 1:40 clones, whereas the mutant allele normally spliced was not found. These results indicate that the mutation inhibits normal splicing of the mutant allele, resulting in a haploinsufficient state. The rare alternative splicing product contains a predicted frameshift with disruption of the protein sequence from codon 311 and a premature stop codon. The altered splicing was confirmed by minigene assay.
Conclusion. We have identified a novel GC-AG alternative splicing isoform causing laminopathy and DCM. This is predicted to lead to nonsense-mediated mRNA decay and provides evidence that LMNA haploinsufficiency results in DCM.