Mutations in BEST1 cause several phenotypes including autosomal dominant (AD) Best vitelliform macular dystrophy type 2 (BVMD), AD vitreo-retino-choroidopathy (ADVIRC), and retinitis pigmentosa-50 (RP50). A rare subtype of Bestrophinopathy exists with biallelic mutations in BEST1.

Purpose: We report the case of a neurologically asymptomatic young boy presenting with an unusual phenotype of CYP2U1 related macular dystrophy associating bilateral macular telangiectasia (MacTel) and fibrotic choroidal neovascularization (CNV), assessed with complete multimodal imaging including optical coherence tomography angiography (OCT-A). Case presentation: A twelve-year-old boy from a non-consanguineous family complained of bilateral progressive visual loss and photophobia. The best-corrected visual acuity was 2/10 on the right eye and 3/10 on the left eye. Fundus examination showed central pigmented fibrotic macular scar and yellowish punctuate deposits in both eyes. En face OCT-A detected typical macular telangiectasia (MacTel) in both eyes with dilated telangiectatic capillaries in the deep capillary plexus associated with vascular anomalies in the superficial and deep capillary plexus. Typical hypo-reflective cavities were observed within the inner foveal layers on structural OCT. En face OCT-A also confirmed the presence of bilateral inactive CNV within the fibrotic scars, showing high-flow vascular network at the level of the subretinal hyperreflective lesions. Whole exome sequencing identified a known homozygous pathogenic variant in CYP2U1 gene (c.1168C > T, p.Arg390*), which is a disease-causing mutation in autosomal recessive spastic paraplegia type 56 (SPG56). The neurological examination was normal, and electromyography and brain magnetic resonance imaging were unremarkable as well. Conclusion: Macular dystrophy can be the first manifestation in SPG56. A particular phenotype with MacTel was observed, and neovascular complications are possible. CYP2U1 should be included in the panels of genes tested for macular dystrophies, especially in the presence of MacTel and/or neurological manifestations.

Retinal dystrophies (RD) are a rare genetic disorder with high genetic heterogeneity. This study aimed at identifying disease-causing variants in fifteen consanguineous Tunisian families. Full ophthalmic examination was performed. Index patients were subjected to IROme analysis or whole exome sequencing followed by homozygosity mapping. All detected variations were confirmed by direct Sanger sequencing. Mutation analysis in our patients revealed two compound heterozygous mutations p.(R91W);(V172D) in RPE65, and five novel homozygous mutations: p.R765C in CNGB1, p.H337R in PDE6B, splice site variant c.1129-2A > G and c.678_681delGAAG in FAM161A and c.1133 + 3_1133 + 6delAAGT in CERKL. The latter mutation impacts pre-mRNA splicing of CERKL. The other changes detected were six previously reported mutations in CNGB3 (p.R203*), ABCA4 (p.W782*), NR2E3 (p.R311Q), RPE65 (p.H182Y), PROM1 (c.1354dupT) and EYS (c.5928-2A > G). Segregation analysis in each family showed that all affected individuals were homozygotes and unaffected individuals were either heterozygote carriers or homozygous wild type allele. These results confirm the involvement of a large number of genes in RD in the Tunisian population.

We report the molecular basis of the largest Tunisian cohort with inherited retinal dystrophies (IRD) reported to date, identify disease-causing pathogenic variants and describe genotype–phenotype correlations. A subset of 26 families from a cohort of 73 families with clinical diagnosis of autosomal recessive IRD (AR-IRD) excluding Usher syndrome was analyzed by whole exome sequencing and autozygosity mapping. Causative pathogenic variants were identified in 50 families (68.4%), 42% of which were novel. The most prevalent pathogenic variants were observed in ABCA4 (14%) and RPE65, CRB1 and CERKL (8% each). 26 variants (8 novel and 18 known) in 19 genes were identified in 26 families (14 missense substitutions, 5 deletions, 4 nonsense pathogenic variants and 3 splice site variants), with further allelic heterogeneity arising from different pathogenic variants in the same gene. The most common phenotype in our cohort is retinitis pigmentosa (23%) and cone rod dystrophy (23%) followed by Leber congenital amaurosis (19.2%). We report the association of new disease phenotypes. This research was carried out in Tunisian patients with IRD in order to delineate the genetic population architecture.