Abstract 20075: Mutations in NEXN, a Novel Z-disc Gene, are Associated with Hypertrophic Cardiomyopathy
Introduction: Hypertrophic cardiomyopathy (HCM) is characterized by increased ventricular wall thickness that cannot be explained by any underlying condition, cadiomyocyte hypertrophy and disarray, and increased myocardial brosis. In as many as 50% of HCM cases, the genetic cause remains unknown, suggesting that other genes may be involved. Nexilin, encoded by NEXN, is a novel cardiac Z-disc protein recently identified as a crucial protein that functions to protect cardiac Z-discs from forces generated within the sarcomere.
Hypothesis: We hypothesized that mutations in NEXN gene might be involved in the pathogenesis of HCM.
Methods: We studied 121 unrelated HCM patients from the Han Chinese population who had no mutations previously being found in eight common myofilament disease-causing genes. Genomic DNA was used to amplify the coding exons of NEXN by polymerase chain reaction (PCR), and the PCR products were purified and analyzed by direct sequencing. Bioinformatics approaches and an ethnically-matched control study were employed to classify the functional consequence of the variants identified. The human NEXN expression vectors were generated and the mutations were introduced by site-directed mutagenesis. Cellular transfection and immunofluorescence staining were performed to detect the distributions of wild type and mutant nexilin proteins.
Results: Two missense mutations, c.391C>G (p.Q131E) and c.835C>T (p.R279C), were identified in exon 5 and 8 of NEXN gene in two probands respectively. These mutations segregated with the HCM phenotype in the families and were not present in 384 control chromosomes. In silico analysis revealed that both of the mutations affect highly conserved amino acid residues located in the important functional domains of nexilin and are predicted to be deleterious. Cellular transfection studies showed that the two mutations resulted in local accumulations of nexilin and that the expressed fragment of actin-binding domain containing p.Q131E completely lost the ability to bind F-actin in C2C12 cells.
Conclusions: In conclusion, for the first time, we describe two missense mutations associated with HCM in the NEXN gene. Our findings further expand the knowledge of Z-disc genes in the pathogenesis of HCM.
- © 2010 by American Heart Association, Inc.