AP4 deficiency: A novel form of neurodegeneration with brain iron accumulation?

OBJECTIVE: To describe the clinico-radiological phenotype of 3 patients harboring a homozygous novel AP4M1 pathogenic mutation. METHODS: The 3 patients from an inbred family who exhibited early-onset developmental delay, tetraparesis, juvenile motor function deterioration, and intellectual deficiency were investigated by magnetic brain imaging using T1-weighted, T2-weighted, T2*-weighted, fluid-attenuated inversion recovery, susceptibility weighted imaging (SWI) sequences. Whole-exome sequencing was performed on the 3 patients. RESULTS: In the 3 patients, brain imaging identified the same pattern of bilateral SWI hyposignal of the globus pallidus, concordant with iron accumulation. A novel homozygous nonsense mutation was identified in AP4M1, segregating with the disease and leading to truncation of half of the adap domain of the protein. CONCLUSIONS: Our results suggest that AP4M1 represents a new candidate gene that should be considered in the neurodegeneration with brain iron accumulation (NBIA) spectrum of disorders and highlight the intersections between hereditary spastic paraplegia and NBIA clinical presentations

Generation of a human iPSC line, INMi002-A, carrying the most prevalent USH2A variant associated with Usher syndrome type 2

International audienceWe generated an induced pluripotent stem cell (iPSC) line using dermal fibroblasts from a patient with Usher syndrome type 2 (USH2). This individual was homozygous for the most prevalent variant reported in the USH2A gene, c.2299delG localized in exon 13. Reprogramming was performed using the non-integrative Sendai virus reprogramming method and the human OSKM transcription factor cocktail under feeder-free culture conditions. This iPSC line will be an invaluable tool for studying the pathophysiology of USH2 and for testing the efficacy of novel treatments

A ROD-CONE DYSTROPHY IS SYSTEMATICALLY ASSOCIATED TO THE RTN4IP1 RECESSIVE OPTIC ATROPHY

International audiencePurpose: RTN4IP1 biallelic mutations cause a recessive optic atrophy, sometimes associated to more severe neurological syndromes, but so far, no retinal phenotype has been reported in RTN4IP1 patients, justifying their reappraisal. Methods: Seven patients from four families carrying biallelic RTN4IP1 variants were retrospectively reviewed, with emphasis on their age of onset, visual acuity, multimodal imaging including color and autofluorescence frames, spectral-domain optical coherence tomography with RNFL and macular analyses. Results: Seven patients from four RTN4IP1 families developed in their first decade of life a bilateral recessive optic atrophy with severe central visual loss, and primary nystagmus developed in 5 of 7 patients. Six patients were legally blind. In a second stage, the seven individuals developed a rod-cone dystrophy, sparing the macular zone and the far periphery. This retinal damage was identified by 55°field fundus autofluorescence frames and also by spectral-domain optical coherence tomography scans of the temporal part of the macular zone in five of the seven patients. Full-field electroretinography measurements disclosed reduced b-wave amplitude of the rod responses in all patients but two. Family 4 with the p.R103H and c.601A. T (p.K201*) truncating mutation had further combined neurological signs with cerebellar ataxia, seizures, and intellectual disability. Conclusion: RTN4IP1 recessive optic atrophy is systematically associated to a rodcone dystrophy, which suggests that both the retinal ganglion cells and the rods are affected as a result of a deficit in the mitochondrial respiratory chain. Thus, systematic widefield autofluorescence frames and temporal macular scans are recommended for the evaluation of patients with optic neuropathies

A rod-cone dystrophy is systematically associated to the RTN4IP1 recessive optic atrophy

PURPOSE: RTN4IP1 biallelic mutations cause a recessive optic atrophy, sometimes associated to more severe neurological syndromes, but so far, no retinal phenotype has been reported in RTN4IP1 patients, justifying their reappraisal. METHODS: Seven patients from four families carrying biallelic RTN4IP1 variants were retrospectively reviewed, with emphasis on their age of onset, visual acuity, multimodal imaging including color and autofluorescence frames, spectral-domain optical coherence tomography with RNFL and macular analyses. RESULTS: Seven patients from four RTN4IP1 families developed in their first decade of life a bilateral recessive optic atrophy with severe central visual loss, and primary nystagmus developed in 5 of 7 patients. Six patients were legally blind. In a second stage, the seven individuals developed a rod–cone dystrophy, sparing the macular zone and the far periphery. This retinal damage was identified by 55° field fundus autofluorescence frames and also by spectral-domain optical coherence tomography scans of the temporal part of the macular zone in five of the seven patients. Full-field electroretinography measurements disclosed reduced b-wave amplitude of the rod responses in all patients but two. Family 4 with the p.R103H and c.601A > T (p.K201*) truncating mutation had further combined neurological signs with cerebellar ataxia, seizures, and intellectual disability. CONCLUSION: RTN4IP1 recessive optic atrophy is systematically associated to a rod–cone dystrophy, which suggests that both the retinal ganglion cells and the rods are affected as a result of a deficit in the mitochondrial respiratory chain. Thus, systematic widefield autofluorescence frames and temporal macular scans are recommended for the evaluation of patients with optic neuropathies

SF3B2, a novel candidate gene for autosomal dominant retinitis pigmentosa, encodes a component of the U2 small nuclear ribonucleoprotein

Purpose: Identification and functional characterisation of a novel candidate gene for autosomal dominant retinitis pigmentosa (adRP). Methods: Five affected and five unaffected individuals of a Belgian adRP family in which known adRP loci were excluded, were enrolled. They underwent genome-wide (GW) linkage analysis (BeadChip, Illumina). Whole exome sequencing was carried out in two affected individuals (HiSeq, Illumina; CLC bio). Segregation analysis of variants was done using Sanger sequencing and testing of 300 controls by HRM (LightScanner). Targeted resequencing of SF3B2 was performed (Miseq, Illumina) in 472 unrelated adRP patients. SF3B2 expression was tested using a commercial cDNA panel. Localization studies were carried out in 661W mouse cells using commercial anti-SF3B2 antibodies. Sf3b2 knockdown in Xenopus was done using targeted injection of a splicing blocking morpholino (MO) (GeneTools). Results: GW linkage analysis revealed two novel candidate loci with a maximum LOD score of 1.7. In the 11q13 region, a missense variant c.2417A>G p.(Tyr806Cys) was found in the SF3B2 gene encoding the splicing factor 3b, subunit 2. The Tyr residue is highly conserved, the Grantham distance between Tyr and Cys is 194, predictions suggest an effect on protein function. The change is predicted to disrupt a phosphorylation site. The variant co-segregates with adRP and is absent in 300 controls. No additional SF3B2 mutations were found in a large adRP cohort. Ubiquitous expression of SF3B2 was demonstrated in human tissues, including retina and RPE, and localization in perinuclear and nuclear areas was shown in 661W mouse cells. Targeted MO knockdown in Xenopus showed gross developmental anomalies affecting the retina. Rescue experiments are ongoing. Conclusions: SF3B2 was identified as a novel candidate gene for adRP. SF3B2 is required for binding of the U2 small nuclear ribonucleoprotein (snRNP) to the branchpoint and is involved in early spliceosome assembly. Interestingly, protein-protein interactions have been identified between SF3B2, SNRNP200 and PRPF8, the latter being two proteins implicated in adRP. So far, of the seven known adRP genes involved in splicing, six encode components of the U4/U6-U5 triple small nuclear ribonucleoprotein (tri-snRNP) complex. Our study potentially involves other components of the spliceosome apart from the tri-snRNP complex in adRP

Novel missense mutations in PRPF6 cause autosomal dominant retinitis pigmentosa with incomplete penetrance and impairment of PRPF6 protein localization within the nucleus

International audiencePurpose : To characterize clinically and genetically two families with autosomal dominant retinitis pigmentosa (adRP) with new causative mutations in PRPF6, a gene described to be associated with this condition in a single study.Methods : A large adRP and sporadic RP cohort was screened for mutations using targeted next-generation sequencing. Clinical investigations included visual acuity and visual field testing, fundus examination, high-resolution spectral-domain optical coherence tomography (OCT), fundus autofluorescence imaging, full-fields and multifocal electroretinogram (ERG) recording. Cellular localization of GFP-tagged wild-type or mutated PRPF6 in HEK293 transfected cells was observed by confocal microscopy.Results : Two heterozygous mutations c.680C>T (p.Thr227Met) and c.514C>T (p.Arg172Trp) in PRPF6 were identified in an adRP family and in a sporadic RP patient, respectively. Both variants segregated with the disease phenotype and were predicted to be pathogenic. An asymptomatic heterozygous carrier of the p.Arg172Trp mutation was also identified. In HEK293 transfected cells, an abnormal accumulation of the two mutated GFP-PRPF6, but not wild-type, within Cajal bodies was observed.Conclusions : We identified two novel causative mutations in PRPF6, responsible for autosomal dominant retinitis pigmentosa with variation of penetrance. Presence of asymptomatic carriers is common among patients with adRP, especially when the cause of the disease is due to a mutation in splicing factors’ genes. The two mutations identified lead to a mislocalization of the PRPF6 protein within the nucleus, which could indicate a possible alteration in the assembly or recycling of the tri-snRNP complex of the spliceosome

Novel missense mutations in PRPF6 cause autosomal dominant retinitis pigmentosa with incomplete penetrance and impairment of PRPF6 protein localization within the nucleus

International audiencePurpose : To characterize clinically and genetically two families with autosomal dominant retinitis pigmentosa (adRP) with new causative mutations in PRPF6, a gene described to be associated with this condition in a single study.Methods : A large adRP and sporadic RP cohort was screened for mutations using targeted next-generation sequencing. Clinical investigations included visual acuity and visual field testing, fundus examination, high-resolution spectral-domain optical coherence tomography (OCT), fundus autofluorescence imaging, full-fields and multifocal electroretinogram (ERG) recording. Cellular localization of GFP-tagged wild-type or mutated PRPF6 in HEK293 transfected cells was observed by confocal microscopy.Results : Two heterozygous mutations c.680C>T (p.Thr227Met) and c.514C>T (p.Arg172Trp) in PRPF6 were identified in an adRP family and in a sporadic RP patient, respectively. Both variants segregated with the disease phenotype and were predicted to be pathogenic. An asymptomatic heterozygous carrier of the p.Arg172Trp mutation was also identified. In HEK293 transfected cells, an abnormal accumulation of the two mutated GFP-PRPF6, but not wild-type, within Cajal bodies was observed.Conclusions : We identified two novel causative mutations in PRPF6, responsible for autosomal dominant retinitis pigmentosa with variation of penetrance. Presence of asymptomatic carriers is common among patients with adRP, especially when the cause of the disease is due to a mutation in splicing factors’ genes. The two mutations identified lead to a mislocalization of the PRPF6 protein within the nucleus, which could indicate a possible alteration in the assembly or recycling of the tri-snRNP complex of the spliceosome

Hereditary spastic paraplegia and prominent sensorial involvement: think MAG mutations!

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Optic neuropathy linked to ACAD9 pathogenic variants: a potentially riboflavin-responsive disorder?

International audienceMitochondrial complex I (CI) deficiencies (OMIM 252010) are the commonest inherited mitochondrial disorders in children. Acyl-CoA dehydrogenase 9 (ACAD9) is a flavoenzyme involved chiefly in CI assembly and possibly in fatty acid oxidation. Biallelic pathogenic variants result in CI dysfunction, with a phenotype ranging from early onset and sometimes fatal mitochondrial encephalopathy with lactic acidosis to late-onset exercise intolerance. Cardiomyopathy is often associated. We report a patient with childhood-onset optic and peripheral neuropathy without cardiac involvement, related to CI deficiency. Genetic analysis revealed compound heterozygous pathogenic variants in ACAD9, expanding the clinical spectrum associated to ACAD9 mutations. Importantly, riboflavin treatment (15 mg/kg/day) improved long-distance visual acuity and demonstrated significant rescue of CI activity in vitro

Dominant mutations in mtDNA maintenance gene SSBP1 cause optic atrophy and foveopathy

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