Oral Presentation 43rd Lorne Genome Conference 2022

Bi-allelic loss-of-function OBSCN variants predispose individuals to severe, recurrent rhabdomyolysis (#7)

Macarena Cabrera-Serrano 1 , Marco Savarese 2 , Anna Vihola 2 , Bjarne Udd 2 , Jerry Vockley 3 , Ros Quinlivan 4 , Stefen Brady 5 , Halil Aydin 6 , Rhonda Taylor 7 , Chiara Folland 7 , Hayley Goullee 7 , Alistair Forrest 7 , Drago Bratkovic 8 , Nick Manton 9 , Thomas Robertson 10 , Pamela McCombe 11 , Nigel Laing 7 , Liza Phillips 9 , Pascale De Lonlay 12 , Gina Ravenscroft 7
  1. Unidad de Enfermedades Neuromusculares. Servicio de Neurologia y Neurofisiologia. Hospital Virgen del Rocio , Sevilla, Spain
  2. Folkhälsan Research Center, Helsinki, Finland
  3. University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
  4. MRC Centre for Neuromuscular Diseases, University College Hospitals, London, United Kingdom
  5. Southmead Hospital, Bristol, United Kingdom
  6. Baskent University, Ankara, Turkey
  7. University of Western Australia, Nedlands, WA, Australia
  8. Women and Children’s Hospital, North Adelaide, SA, Australia
  9. SA Pathology, North Adelaide, SA, Australia
  10. QLD Pathology, Brisbane, QLD, Australia
  11. Royal Brisbane and Women's Hospital, Brisbane, QLD, Australia
  12. Necker-Enfants-Malades Hospital, Paris University, Paris, France

Rhabdomyolysis is the acute breakdown of skeletal myofibres in response to an initiating factor, most commonly toxins and over exertion. A variety of genetic disorders predispose to rhabdomyolysis through different pathogenic mechanisms, particularly in patients with recurrent episodes. However, most cases remain without a genetic diagnosis. Here we present six patients who presented with severe and recurrent rhabdomyolysis, usually with onset in the teenage years; other features included a history of myalgia and muscle cramps. We identified ten bi-allelic loss-of-function variants in the gene encoding obscurin (OBSCN) predisposing individuals to recurrent rhabdomyolysis. We show reduced expression of OBSCN and loss of obscurin protein in patient muscle. Obscurin is proposed to be involved in SR function and Ca2+ handling. Patient cultured myoblasts appear more susceptible to starvation as evidenced by a greater decreased in SR Ca2+ content compared to control myoblasts. This likely reflects a lower efficiency when pumping Ca2+ back into the SR and/or a decrease in Ca2+ SR storage ability when metabolism is diminished. OSBCN variants have previously been associated with cardiomyopathies. None of the patients presented with a cardiomyopathy and cardiac examinations were normal in all cases in which cardiac function was assessed. There was also no history of cardiomyopathy in first degree relatives, in particular in any of the carrier parents. This cohort is relatively young, thus follow-up studies and the identification of additional cases with bi-allelic null OBSCN variants will further delineate OBSCN-related disease and the clinical course of disease.