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Original research
A homozygous variant in CHMP3 is associated with complex hereditary spastic paraplegia
  1. Eran Cohen-Barak1,2,
  2. Nada Danial-Farran3,
  3. Elana Chervinsky3,
  4. Ola Alimi-Kasem3,
  5. Fadia Zagairy1,
  6. Ido Livneh2,
  7. Bannan Mawassi1,
  8. Maysa Hreish1,
  9. Morad Khayat3,
  10. Alexander Lossos4,
  11. Vardiella Meiner4,
  12. Nina Ehilevitch5,
  13. Karin Weiss2,5,
  14. Stavit Shalev2,6
  1. 1Department of Dermatology, Emek Medical Center, Afula, Israel
  2. 2Technion Israel Institute of Technology, The Ruth and Bruce Rappaport Faculty of Medicine, Haifa, Israel
  3. 3Genetic Institute, Emek Medical Center, Afula, Israel
  4. 4Hadassah-Hebrew University Medical Center, Jerusalem, Israel
  5. 5Rambam Health Care Campus, Haifa, Israel
  6. 6Emek Medical Center, Pediatric Department A and Genetic Institute, Afula, Israel
  1. Correspondence to Dr Eran Cohen-Barak, Emek Medical Center, Afula 1834111, Israel; erancb79{at}gmail.com

Abstract

Background Monogenic neurodegenerative diseases represent a heterogeneous group of disorders caused by mutations in genes involved in various cellular functions including autophagy, which mediates degradation of cytoplasmic contents by their transport into lysosomes. Abnormal autophagy is associated with hereditary ataxia and spastic paraplegia, amyotrophic lateral sclerosis and frontal dementia, characterised by intracellular accumulation of non-degraded proteins. We investigated the genetic basis of complex HSP in a consanguineous family of Arab-Muslim origin, consistent with autosomal recessive inheritance.

Methods Exome sequencing was followed by variant filtering and Sanger sequencing for validation and familial segregation. Studies for mRNA and protein expression used real-time PCR and immunoblots. Patients’ primary fibroblasts were analysed using electron microscopy, immunofluorescence, western blot analysis and ectopic plasmid expression for its impact on autophagy.

Results We identified a homozygous missense variant in CHMP3 (Chr2:86507484 GRCh38 (NM_016079.4): c.518C>T, p.Thr173Ile), which encodes CHMP3 protein. Segregation analysis validated the presence of the homozygous variant in five affected individuals, while healthy family members were found either heterozygous or wild type for this variant. Primary patient’s fibroblasts showed significantly reduced levels of CHMP3. Electron microscopy disclosed accumulation of endosomes, autophagosomes and autolysosomes in patient’s fibroblasts, which correlated with higher levels of autophagy markers, p62 and LC3-II. Ectopic expression of wild-type CHMP3 in primary patient fibroblasts led to reduction of the p62 particles accumulation and number of endosomes and autophagosomes compared with control.

Conclusions Reduced level of CHMP3 is associated with complex spastic paraplegia phenotype, through aberrant autophagy mechanisms.

  • neurology

Data availability statement

Data are available on reasonable request. Data are available from the corresponding author on reasonable request.

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Data availability statement

Data are available on reasonable request. Data are available from the corresponding author on reasonable request.

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Footnotes

  • Contributors Guarantor: SA-S; Conceptualisation: EC-B; data curation: EC-B, ND-F, OA-K, MK, AL, VM, NE, KW; formal analysis: EC-B, ND-F, FZ, IL, BM, MH, VM; funding acquisition: EC-B; investigation: EC-B, ND-F, FZ, IL, BM; methodology: EC-B, AL, VM; project administration: EC-B, SA-S; resources: EC-B, SA-S; software: ND-F, VM; supervision: EC-B, SA-S; validation: SA-S; visualisation: FZ, BM, MH; writing—original draft: EC-B; writing—review and editing: ND-F, VM, KW, SA-S.

  • Funding This study was funded by a Rappaport Short-Term Grant.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.