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Ranta-Aho J, Felice KJ, Jonson PH, Sarparanta J, Yvorel C, Harzallah I, Touraine R, Pais L, Austin-Tse CA, Ganesh VS, O'Leary MC, Rehm HL, Hehir MK, Subramony S, Wu Q, Udd B, Savarese M. Protein-extending ACTN2 frameshift variants cause variable myopathy phenotypes by protein aggregation. Ann Clin Transl Neurol 2024. [PMID: 39095936 DOI: 10.1002/acn3.52154] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2024] [Revised: 06/19/2024] [Accepted: 07/08/2024] [Indexed: 08/04/2024] Open
Abstract
OBJECTIVE The objective of the study is to characterize the pathomechanisms underlying actininopathies. Distal myopathies are a group of rare, inherited muscular disorders characterized by progressive loss of muscle fibers that begin in the distal parts of arms and legs. Recently, variants in a new disease gene, ACTN2, have been shown to cause distal myopathy. ACTN2, a gene previously only associated with cardiomyopathies, encodes alpha-actinin-2, a protein expressed in both cardiac and skeletal sarcomeres. The primary function of alpha-actinin-2 is to link actin and titin to the sarcomere Z-disk. New ACTN2 variants are continuously discovered; however, the clinical significance of many variants remains unknown. Thus, lack of clear genotype-phenotype correlations in ACTN2-related diseases, actininopathies, persists. METHODS Functional characterization in C2C12 cell model of several ACTN2 variants is conducted, including frameshift and missense variants associated with dominant and recessive actininopathies. We assess the genotype-phenotype correlations of actininopathies using clinical data from several patients carrying these variants. RESULTS The results show that the missense variants associated with a recessive form of actininopathy do not cause detectable alpha-actinin-2 aggregates in the cell model. Conversely, dominant frameshift variants causing a protein extension do form alpha-actinin-2 aggregates. INTERPRETATION The results suggest that alpha-actinin-2 aggregation is the disease mechanism underlying some dominant actininopathies, and thus, we recommend that protein-extending frameshift variants in ACTN2 should be classified as pathogenic. However, this mechanism is likely elicited by only a limited number of variants. Alternative functional characterization methods should be explored to further investigate other molecular mechanisms underlying actininopathies.
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Affiliation(s)
- Johanna Ranta-Aho
- Folkhälsan Research Center, Haartmaninkatu 8, 00290, Helsinki, Finland
- Department of Medical Genetics, Medicum, University of Helsinki, Haartmaninkatu 8, Helsinki, 00290, Finland
| | - Kevin J Felice
- Department of Neuromuscular Medicine, Hospital for Special Care, 2150 Corbin Avenue, New Britain, Connecticut, 06053, USA
| | - Per Harald Jonson
- Folkhälsan Research Center, Haartmaninkatu 8, 00290, Helsinki, Finland
- Department of Medical Genetics, Medicum, University of Helsinki, Haartmaninkatu 8, Helsinki, 00290, Finland
| | - Jaakko Sarparanta
- Folkhälsan Research Center, Haartmaninkatu 8, 00290, Helsinki, Finland
- Department of Medical Genetics, Medicum, University of Helsinki, Haartmaninkatu 8, Helsinki, 00290, Finland
| | - Cédric Yvorel
- Cardiology Department, Hôpital Nord, Hôpital Nord, CHU de Saint Etienne, Avenue Albert Raimond, Saint Priest-en-Jarez, 42270, France
| | - Ines Harzallah
- Genetic Department, Hôpital Nord, CHU de Saint Etienne, Avenue Albert Raimond, Saint Priest-en-Jarez, 42270, France
| | - Renaud Touraine
- Genetic Department, Hôpital Nord, CHU de Saint Etienne, Avenue Albert Raimond, Saint Priest-en-Jarez, 42270, France
| | - Lynn Pais
- Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, 105 Broadway, Cambridge, Massachusetts, 02142, USA
- Division of Genetics and Genomics, Boston Children's Hospital, Harvard Medical School, 2 Brookline Place, Boston, Massachusetts, 02445, USA
| | - Christina A Austin-Tse
- Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, 105 Broadway, Cambridge, Massachusetts, 02142, USA
- Center for Genomic Medicine, Massachusetts General Hospital, Harvard Medical School, 55 Fruit Street, Boston, Massachusetts, 02114, USA
| | - Vijay S Ganesh
- Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, 105 Broadway, Cambridge, Massachusetts, 02142, USA
- Department of Neurology, Brigham and Women's Hospital, 60 Fenwood Road, Boston, Massachusetts, 02115, USA
| | - Melanie C O'Leary
- Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, 105 Broadway, Cambridge, Massachusetts, 02142, USA
| | - Heidi L Rehm
- Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, 105 Broadway, Cambridge, Massachusetts, 02142, USA
- Center for Genomic Medicine, Massachusetts General Hospital, Harvard Medical School, 55 Fruit Street, Boston, Massachusetts, 02114, USA
| | - Michael K Hehir
- Department of Neurology, Larner College of Medicine at the University of Vermont, 149 Beaumont Avenue, Burlington, Vermont, 05405, USA
| | - Sub Subramony
- Department of Neurology, University of Florida College of Medicine, 1505 SW Archer Road, Gainesville, Florida, 32610, USA
| | - Qian Wu
- Department of Pathology, University of Connecticut School of Medicine, 263 Farmington Avenue, Farmington, Connecticut, 06030, USA
| | - Bjarne Udd
- Folkhälsan Research Center, Haartmaninkatu 8, 00290, Helsinki, Finland
- Tampere Neuromuscular Center, Tampere University and Tampere University Hospital, Biokatu 8, Tampere, 33520, Finland
| | - Marco Savarese
- Folkhälsan Research Center, Haartmaninkatu 8, 00290, Helsinki, Finland
- Department of Medical Genetics, Medicum, University of Helsinki, Haartmaninkatu 8, Helsinki, 00290, Finland
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Ranta-Aho J, Felice KJ, Jonson PH, Sarparanta J, Palmio J, Tasca G, Sabatelli M, Yvorel C, Harzallah I, Touraine R, Pais L, Austin-Tse CA, Ganesh V, O'Leary MC, Rehm HL, Hehir MK, Subramony S, Wu Q, Udd B, Savarese M. Rare ACTN2 Frameshift Variants Resulting in Protein Extension Cause Distal Myopathy and Hypertrophic Cardiomyopathy through Protein Aggregation. MEDRXIV : THE PREPRINT SERVER FOR HEALTH SCIENCES 2024:2024.01.17.23298671. [PMID: 38293186 PMCID: PMC10827258 DOI: 10.1101/2024.01.17.23298671] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2024]
Abstract
Distal myopathies are a group of rare, inherited muscular disorders characterized by progressive loss of muscle fibers that begins in the distal parts of arms and legs. Recently, variants in a new disease gene, ACTN2 , have been shown to cause distal myopathy. ACTN2 , a gene previously only associated with cardiomyopathies, encodes alpha-actinin-2, a protein expressed in both cardiac and skeletal sarcomeres. The primary function of alpha-actinin-2 is to link actin and titin to the sarcomere Z-disk. New ACTN2 variants are continuously discovered, however, the clinical significance of many variants remains unknown. Thus, lack of clear genotype-phenotype correlations in ACTN2 -related diseases, actininopathies, persists. Objective The objective of the study is to characterize the pathomechanisms underlying actininopathies. Methods Functional characterization in C2C12 cell models of several ACTN2 variants is conducted, including frameshift and missense variants associated with dominant actininopathies. We assess the genotype-phenotype correlations of actininopathies using clinical data from several patients carrying these variants. Results The results show that the missense variants associated with a recessive form of actininopathy do not cause detectable alpha-actinin-2 aggregates in the cell model. Conversely, dominant frameshift variants causing a protein extension do produce alpha-actinin-2 aggregates. Interpretation The results suggest that alpha-actinin-2 aggregation is the disease mechanism underlying some dominant actininopathies, and thus we recommend that protein-extending frameshift variants in ACTN2 should be classified as pathogenic. However, this mechanism is likely elicited by only a limited number of variants. Alternative functional characterization methods should be explored to further investigate other molecular mechanisms underlying actininopathies.
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