Loss of GFAP cause retinal dysplasia and vision impairment

Alexander Disease is a rare leukodystrophy caused by gain-of-function variants in the gene encoding Glial Fibrillary Acidic Protein (GFAP), a major constituent of the intermediate filament of Astrocytes within the central nervous system. Currently, no phenotypic consequence of GFAP haploinsufficiency is known, and recent rodent experiments suggest that antisense oligonucleotide-mediated suppression of GFAP expression can reverse the disease progression in AxD. We investigated a six-generation family with ten individuals presenting with visual impairment, retinal dysplasia and pseudopapilledema. Whole genome sequencing of three affected individuals revealed a rare novel loss-of-function variant in GFAP, which segregated with disease in the family. The variant, c.928dup, results in frameshift and translation into a 422 aa protein (p.Met310Asnfs*113) wild type GFAP is 431-438 aa). Analysis of human embryonic tissues showed strong GFAP expression in retinal neural progenitors in the developing eye at 35-51 days post conception. Experiments using zebrafish models verified that the c.928dup variant does not result in extensive GFAP protein aggregation. Analysis of zebrafish loss-of-function gfap mutants, showed that depletion of GFAP causes vision impairment and retinal dysplasia, characterized by a significant loss of Müller glia cells and photoreceptor cells. Our findings provide novel insight into the function of GFAP and the consequence of GFAP deficiency. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement The study was supported by grants from the Velux Foundation and the Novo Nordisk Foundation. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: National Committee on Health Research Ethics, Denmark gave ethical approval for the clinical and genetic study of patients (journal number 1301394). Danish Regional Committee on Health Research Ethics gave ethical approval for analysis of human embryos and fetuses (KF V.100.1735/90) and (KF 11 2006 4838). All zebrafish experiments and animal handling procedures were approved and conducted under licenses from the Danish Animal Experiments Inspectorate (Protocol code: P18-120/P20-387). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes Individual genome sequencing data cannot be shared due to concerns over patient privacy. Other data generated or analyzed during this study are included in the main paper or its additional files.