Hereditary spastic paraplegias (HSP) are rare, inherited neurodegenerative or neurodevelopmental disorders that mainly present with lower limb spasticity and muscle weakness due to motor neuron dysfunction. Whole genome sequencing identified bi-allelic truncating variants in AMFR, encoding a RING-H2 finger E3 ubiquitin ligase anchored at the membrane of the endoplasmic reticulum (ER), in two previously genetically unexplained HSP-affected siblings. Subsequently, international collaboration recognized additional HSP-affected individuals with similar bi-allelic truncating AMFR variants, resulting in a cohort of 20 individuals from 8 unrelated, consanguineous families. Variants segregated with a phenotype of mainly pure but also complex HSP consisting of global developmental delay, mild intellectual disability, motor dysfunction, and progressive spasticity. Patient-derived fibroblasts, neural stem cells (NSCs), and in vivo zebrafish modeling were used to investigate pathomechanisms, including initial preclinical therapy assessment. The absence of AMFR disturbs lipid homeostasis, causing lipid droplet accumulation in NSCs and patient-derived fibroblasts which is rescued upon AMFR re-expression. Electron microscopy indicates ER morphology alterations in the absence of AMFR. Similar findings are seen in amfra-/- zebrafish larvae, in addition to altered touch-evoked escape response and defects in motor neuron branching, phenocopying the HSP observed in patients. Interestingly, administration of FDA-approved statins improves touch-evoked escape response and motor neuron branching defects in amfra-/- zebrafish larvae, suggesting potential therapeutic implications. Our genetic and functional studies identify bi-allelic truncating variants in AMFR as a cause of a novel autosomal recessive HSP by altering lipid metabolism, which may potentially be therapeutically modulated using precision medicine with statins.
|Early online date||29 Apr 2023|
|Publication status||E-pub ahead of print - 29 Apr 2023|
Bibliographical noteFunding Information:
We thank all patients and families for participation in this study, and all members of the Barakat lab for helpful discussions. RD and YS are supported by a China Scholarship Council (CSC) PhD Fellowship (201906300026 to RD, 202008500138 to YS) for their PhD studies at the Erasmus Medical Center, Rotterdam, The Netherlands. SLZ is supported in her PhD studies by Stichting 12q. Some results reported here were generated using funding received from the Solve-RD project within the European Rare Disease Models & Mechanisms Network (RDMM-Europe). The Solve-RD project has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No 779257. Part of this research was made possible through access to the data and findings generated by the 100,000 Genomes Project. The 100,000 Genomes Project is managed by Genomics England Limited (a wholly owned company of the Department of Health and Social Care). The 100,000 Genomes Project is funded by the National Institute for Health Research and NHS England. The Wellcome Trust, Cancer Research UK, and the Medical Research Council have also funded research infrastructure. The 100,000 Genomes Project uses data provided by patients and collected by the National Health Service as part of their care and support. SB was supported by the NIHR Manchester Biomedical Research Centre (NIHR203308) and acknowledges the grant funding support of the Spastic Paraplegia Foundation (USA). NKa was supported by the King Salman Center for Disability Research through Award No. RAC: #2180-004. RR and STA were supported by funding from King Abdullah University of Science and Technology (KAUST), Office of Sponsored Research (OSR), FCC/1/1976-25 and REI/1/4446-01. For computational protein modelling, the resources of the Supercomputing Laboratory at KAUST were used. The Barakat lab was supported by the Netherlands Organisation for Scientific Research (ZonMw Veni, grant 91617021; ZonMw Vidi, grant 09150172110002), an Erasmus MC Fellowship 2017, and Erasmus MC Human Disease Model Award 2018. Funding bodies did not have any influence on study design, results, and data interpretation or final manuscript.
© 2023, The Author(s).