Alternative splicing expands the clinical spectrum of NDUFS6-related mitochondrial disorders

Camila Armirola-Ricaurte; Noortje Zonnekein; Georgios Koutsis; Silvia Amor-Barris; Ana Lara Pelayo-Negro; Derek Atkinson; Stephanie Efthymiou; Valentina Turchetti; Argyris Dinopoulos; Antonio Garcia; Mert Karakaya; German Moris; Ayşe Ipek Polat; Uluç Yiş; Carmen Espinos; Liedewei Van de Vondel; Els De Vriendt; Georgia Karadima; Brunhilde Wirth; Michael Hanna; Henry Houlden; Jose Berciano; Albena Jordanova

doi:10.1016/j.gim.2024.101117

Alternative splicing expands the clinical spectrum of NDUFS6-related mitochondrial disorders

Genet Med. 2024 Mar 6;26(6):101117. doi: 10.1016/j.gim.2024.101117. Online ahead of print.

Authors

Camila Armirola-Ricaurte¹, Noortje Zonnekein¹, Georgios Koutsis², Silvia Amor-Barris¹, Ana Lara Pelayo-Negro³, Derek Atkinson¹, Stephanie Efthymiou⁴, Valentina Turchetti⁴, Argyris Dinopoulos⁵, Antonio Garcia⁶, Mert Karakaya⁷, German Moris⁸, Ayşe Ipek Polat⁹, Uluç Yiş⁹, Carmen Espinos¹⁰, Liedewei Van de Vondel¹¹, Els De Vriendt¹, Georgia Karadima², Brunhilde Wirth⁷, Michael Hanna⁴, Henry Houlden⁴, Jose Berciano³, Albena Jordanova¹²

Affiliations

¹ Molecular Neurogenomics group, VIB Center for Molecular Neurology, VIB, Antwerp, Belgium; Molecular Neurogenomics group, Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium.
² Neurogenetics Unit, 1st Department of Neurology, Eginitio Hospital, Medical School, National and Kapodistrian University of Athens, Athens, Greece.
³ University Hospital Marqués de Valdecilla (IFIMAV), University of Cantabria, Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas (CIBERNED), Santander, Spain.
⁴ Department of Neuromuscular Disorders, UCL Institute of Neurology, Queen Square, London, United Kingdom.
⁵ 3rd Department of Pediatrics, Attiko Hospital, Medical School, National and Kapodistrian University of Athens, Athens, Greece.
⁶ Service of Clinical Neurophysiology, University Hospital Marqués de Valdecilla, Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas (CIBERNED), Santander, Spain.
⁷ Institute of Human Genetics, Center for Molecular Medicine Cologne, Center for Rare Diseases, University Hospital of Cologne, University of Cologne, Cologne, Germany.
⁸ Service of Neurology, University Hospital Central de Asturias, University of Oviedo, Oviedo, Spain.
⁹ Department of Pediatric Neurology, Dokuz Eylül University, Izmir, Turkey.
¹⁰ Rare Neurodegenerative Disease Laboratory, Centro de Investigación Príncipe Felipe (CIPF), CIBER on Rare Diseases (CIBERER), Valencia, Spain.
¹¹ Translational Neurosciences, Faculty of Medicine and Health Sciences, University of Antwerp, Antwerp, Belgium; Laboratory of Neuromuscular Pathology, Institute Born-Bunge, University of Antwerp, Antwerp, Belgium.
¹² Molecular Neurogenomics group, VIB Center for Molecular Neurology, VIB, Antwerp, Belgium; Molecular Neurogenomics group, Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium; Department of Medical Chemistry and Biochemistry, Medical University-Sofia, Sofia, Bulgaria. Electronic address: albena.jordanova@uantwerpen.be.

PMID: 38459834
DOI: 10.1016/j.gim.2024.101117

Abstract

Purpose: We describe 3 families with Charcot-Marie-Tooth neuropathy (CMT), harboring a homozygous NDUFS6 NM_004553.6:c.309+5G>A variant previously linked to fatal Leigh syndrome. We aimed to characterize clinically and molecularly the newly identified patients and understand the mechanism underlying their milder phenotype.

Methods: The patients underwent extensive clinical examinations. Exome sequencing was done in 4 affected individuals. The functional effect of the c.309+5G>A variant was investigated in patient-derived EBV-transformed lymphoblasts at the complementary DNA, protein, and mitochondrial level. Alternative splicing was evaluated using complementary DNA long-read sequencing.

Results: All patients presented with early-onset, slowly progressive axonal CMT, and nystagmus; some exhibited additional central nervous system symptoms. The c.309+5G>A substitution caused the expression of aberrantly spliced transcripts and negligible levels of the canonical transcript. Immunoblotting showed reduced levels of mutant isoforms. No detectable defects in mitochondrial complex stability or bioenergetics were found.

Conclusion: We expand the clinical spectrum of NDUFS6-related mitochondrial disorders to include axonal CMT, emphasizing the clinical and pathophysiologic overlap between these 2 clinical entities. This work demonstrates the critical role that alternative splicing may play in modulating the severity of a genetic disorder, emphasizing the need for careful consideration when interpreting splice variants and their implications on disease prognosis.

Keywords: Charcot-Marie-Tooth; Mitochondrial disorders; NDUFS6; Peripheral neuropathy; Splicing.