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Clinical, Histopathologic, and Genetic Features of Patients With Myofibrillary and Distal Myopathies: Experience From
Sara Bortolani1, Marco Savarese1, Gaetano Vattemi1
1From the UOC di Neurologia (S. Bortolani, G.P., C.S., M.L., M. Mirabella, S.S., M. Monforte, E.R., G.T.), Fondazione Policlinico Universitario "A. Gemelli" IRCCS, Rome; Department of Neurosciences Rita Levi Montalcini (S. Bortolani, T.E.M.), University of Torino, Italy; Folkhälsan Research Center (M.S.), Helsinki, Finland; Department of Neurosciences, Biomedicine and Movement Sciences (G.V., P.T.), University of Verona; Neuroimmunology and Neuromuscular Disorders Unit (S. Bonanno, M.C., A. Ruggieri, L.M.), Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan; Institute of Experimental Neurology (INSPE) (Y.M.F., S.C.P.), Division of Neuroscience, IRCCS San Raffaele Scientific Institute, Milan; ERN-NMD Center for Neuromuscular Disorders of Messina (A. Pugliese, C.R., A.T.), Department of Clinical and Experimental Medicine, University of Messina; Fondazione UILDM Lazio Onlus (G.P., C.S.), Rome; Department of Medicine, Surgery and Neurosciences (D.L., A.M.), University of Siena; Neuromuscular Diseases Unit (G.G., R.M.), Department of Systems Medicine, University of Rome Tor Vergata, Rome; Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics and Maternal Infantile Sciences (C.G., M. Grandis), University of Genoa; IRCCS Ospedale Policlinico San Martino (C.G., M. Grandis), Genova; IRCCS Mondino Foundation (S.R.), Pavia; Dipartimento di Neuroscienze e Scienze Riproduttive ed Odontostomatologiche (R.P.B., L.R.), Università degli Studi di Napoli "Federico II," Naples; Neuromuscular and Rare Diseases Unit (D.V.), Department of Neuroscience and Mental Health, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico; Neurology Unit (F.M., G.P.C.), Department of Neuroscience and Mental Health, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan; IRCCS Institute of Neurological Sciences of Bologna (M.L.V., R.L.), UOC Clinica Neurologica; Department of Biomedical and NeuroMotor Sciences (M.L.V., R.L.), University of Bologna; Università Cattolica del Sacro Cuore (E.T., M. Mirabella, S.S., E.R.); Center for Neuromuscular and Neurological Rare Diseases S. Camillo Forlanini Hospital (A. Petrucci), Rome; Department of Clinical and Experimental Medicine (G.R., G.S.), Neurological Clinic, University of Pisa; Neuromuscular and Rare Disease Center (M. Garibaldi, G. Antonini), Department of Neuroscience, Mental Health and Sensory Organs (NESMOS), SAPIENZA University, Sant'Andrea Hospital, Rome; Molecular Medicine for Neurodegenerative and Neuromuscular Diseases Unit (G. Astrea, A. Rubegni, F.M.S.), IRCCS Stella Maris Foundation, Pisa; Department of Neurosciences (C.I.A.), University of Padova; Department of Neurosciences (A.A.), University Hospitals of Modena; Department of Clinical and Experimental Sciences (M.F.), University of Brescia; NeMo-Brescia Clinical Center for Neuromuscular Diseases (M.F.), Brescia; Department of Pathophysiology and Transplantation (G.P.C.), Dino Ferrari Center, University of Milan, Italy; and John Walton Muscular Dystrophy Research Centre (J.D.-M., G.T.), Newcastle University and Newcastle Hospitals NHS Foundation Trusts, Newcastle Upon Tyne, United Kingdom.
Background And Objectives:
The diagnostic process for myofibrillar myopathies (MFM) and distal myopathies (DM) is particularly complex because of the large number of causative genes, the existence of still molecularly undefined disease entities, and the overlapping features between the 2 categories. This study aimed to characterize a large cohort of patients affected by MFM and DM and identify the most important diagnostic and prognostic aspects of these diseases.
Methods:
Patients with either a myopathological diagnosis of MFM or a clinical diagnosis of DM were included in this retrospective multicentric national study. Demographic, genetic, clinical, and histopathologic data of anonymized patients were collected from the neuromuscular centers of the Italian Association of Myology network.
Results:
Data regarding 132 patients with MFM (mean age 57.0 ± 15.8 years, 49% female) and 298 patients with DM (mean age 50.7 ± 15.9 years, 40% female) were gathered from 20 neuromuscular centers. 69 patients fulfilled the criteria for both groups (distal myopathies with myofibrillar pathology, DM-MP). Molecular confirmation was achieved in 63% of the patients. Fifty-two percent of the patients with MFM carried pathogenic variants in either DES (n = 30), MYOT (n = 20), or DNAJB6 (n = 18), which were also the most frequent disease-causing genes in DM-MP, while GNE (n = 44) and MYH7 (n = 23) were the genes most commonly carrying pathogenic variants in DM. The mean age at onset varied from <25 years in patients with causative variants in MYH7 and DYSF to 59 years in patients with myotilinopathies. Cardiac involvement was reported in 29% of patients with MFM and 16% of patients with DM, with DES and MYH7 variants significantly associated with the development of cardiomyopathy. Respiratory impairment was more prevalent in patients with TTN and DES variants and rare in other disorders such as GNE myopathy and dysferlinopathies, which were instead associated, together with DNAJB6-related and PLIN4-related myopathies, with the risk of losing ambulation during the disease course.
Discussion:
The Italian cohort of patients with MFM and DM recapitulates the phenotypic heterogeneity and the partial overlap between the 2 groups. However, in relative contrast to the encountered phenotypic variability, only 5 genes accounted for most of the molecular diagnoses. Specific genetic entities are associated with significantly increased risk of developing cardiorespiratory complications or loss of ambulation, which has relevant prognostic implications.
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