Impaired Iron-Sulfur Cluster Assembly Due to Biallelic Variants in CIAO1 Leads to a Novel Neuromuscular Disease

Topic:

Translational Research

Poster Number: T371

Author(s):

Rotem Orbach, MD, NINDS/NIH, Nunziata Maio, National Institute of Child Health and Human Development, NIH, Irina Zaharieva, Great Ormond Street Institute of Child Health, UCL, Ana Töpf, Translational and Clinical Research Institute, Newcastle University, Sandra Donkervoort, MS, CGC, NINDS/DIR/CNP/NGB/NNDCS, Pinki Munot, MD, Great Ormond Street Institute of Child Health, UCL, Juliane Mueller, Great Ormond Street Institute of Child Health, UCL, Tracey Willis, MD, Robert Jones and Agnes Hunt Orthopaedic NHS Trust Hospital, UK, Sumit Verma, MD, Department of Neurology, Emory University School of Medicine, Stojan Peric, MD, PhD, University of Belgrade, Deepa Krishnakumar, Paediatric Neurology, Cambridge University Hospitals NHS Foundation Trust, Sniya Sudhakar, Great Ormond Street Institute of Child Health, UCL, Reghan Foley, MD, National Institutes of Health, Sarah Silverstein, Neuromuscular and Neurogenetic Disorders of Childhood Section, NINDS, NIH, Ganka Douglas, GeneDx, Gaithersburg, MD 20877, USA, Lynn Pais, MS, Broad Institute of MIT and Harvard, Christopher Grunseich, MD, Neuromuscular and Neurogenetic Disorders of Childhood Section, NINDS, NIH, Ying Hu, MS, National Institutes of Health, Caroline Sewry, Great Ormond Street Institute of Child Health, UCL; Robert Jones and Agnes Hunt Orthopaedic Hospital, Anna Sarkozy, Great Ormond Street Institute of Child Health, UCL, Volker Straub, PhD, Newcastle University and Newcastle Hospitals NHS Foundation Trust, Francesco Muntoni, FRCPCH, FMedSci, University College London, National Institute for Health Research Great Ormond Street Hospital, Tracey Rouault, National Institute of Child Health and Human Development, NIH, Carsten Bonnemann, MD, PhD, National Institutes of Health

Iron-sulfur clusters are essential cofactors in various biological processes, including oxidative phosphorylation, numerous enzymatic reactions and in DNA replication and repair. We report the clinical manifestations and the biochemical characterization associated with a novel neuromuscular disease gene, CIAO1, a key component of the cytoplasmic iron-sulfur assembly (CIA) machinery. We identified four unrelated individuals with biallelic variants in CIAO1 (P1: p.H302P/p.F250_L339del; P2 and P3: p.H302P/p.R65W; P4: p.D171G/p.H251L) who presented with a consistent phenotype of early to adolescent onset of progressive proximal and axial muscle weakness, facial and bulbar weakness, and respiratory insufficiency (FVC 51 – 63% predicted). In addition, patients presented with CNS symptoms including learning difficulties (n=4) and neurobehavioral comorbidities (n=2), neuroimaging findings of iron deposition in deep brain nuclei (n=2), macrocytic anemia (n=2) and gastrointestinal symptoms (n=2). Creatine kinase was elevated in all patients, and muscle MRI revealed mild diffuse atrophy and fatty infiltration with greater involvement of proximal posterior thigh, sartorius and medial gastrocnemius muscles. Muscle histopathology revealed myopathic and mildly dystrophic features and prominent mitochondria with oxidative stains. Muscle ultrastructural features included large and morphologically abnormal mitochondria. Muscle biochemical analyses, activity assays, and native immunoblots indicated dysfunction of the mitochondrial respiratory chain. CIAO1 disease-associated variants exhibited impaired interaction with CIA components and failed to recruit recipient proteins for iron-sulfur cluster delivery. Variant analysis and functional assays revealed reduced stability of the variants compared to wild-type CIAO1. Loss of CIAO1 resulted in impaired DNA helicases, polymerases and repair enzymes that are known to acquire their Fe-S cofactors from the CIA complex, and lentiviral restoration reversed all patient-derived cellular abnormalities. Our study identifies CIAO1 as a novel neuromuscular disease gene and provides insights into the broader implications of the iron-sulfur assembly pathway in human health and disease.