Genetic screening of LCA in Belgium: predominance of CEP290 and identification of potential modifier alleles in AHI1 of CEP290-related phenotypes

Abstract

Leber Congenital Amaurosis (LCA), the most severe inherited retinal dystrophy, is genetically heterogeneous, with 14 genes accounting for 70% of patients. Here, 91 LCA probands underwent LCA chip analysis and subsequent sequencing of 6 genes (CEP290, CRB1, RPE65, GUCY2D, AIPL1and CRX), revealing mutations in 69% of the cohort, with major involvement of CEP290 (30%). In addition, 11 patients with early-onset retinal dystrophy (EORD) and 13 patients with Senior-Loken syndrome (SLS), LCA-Joubert syndrome (LCA-JS) or cerebello-oculo-renal syndrome (CORS) were included. Exhaustive re-inspection of the overall phenotypes in our LCA cohort revealed novel insights mainly regarding the CEP290-related phenotype. The AHI1 gene was screened as a candidate modifier gene in three patients with the same CEP290 genotype but different neurological involvement. Interestingly, a heterozygous novel AHI1 mutation, p.Asn811Lys, was found in the most severely affected patient. Moreover, AHI1 screening in five other patients with CEP290-related disease and neurological involvement revealed a second novel missense variant, p.His758Pro, in one LCA patient with mild mental retardation and autism. These two AHI1 mutations might thus represent neurological modifiers of CEP290-related disease.

Figure 1

Clinical characteristics of eight LCA patients with an established molecular diagnosis, illustrating characteristic phenotypic features associated with different genotypes. CEP290. A & B: Early and later stage phenotype in right eye (RE) in LCA-3 at age 3 and 18 years respectively; note marbleized aspect of midperiphery at age 3, evolving towards atrophy later; macula stays well-preserved throughout evolution. C & D: Fundus and autofluorescence (AF) image of RE of LCA-25 at age eight years; note concentric hyperautofluorescent ring around macula suggesting a watershed zone between better and more affected retina with probably central area the better; midperipheral retina shows diffuse mottled hyperautofluorescence suggesting widespread outer retinal disease. E & F: Fundus image of RE and infrared image of left eye (LE) of LCA-7 at age 33 and 49 years respectively; note pigment epithelium alterations in the mid- and far periphery of retina but no intraretinal pigmentation, and with fair preservation of macular area at age 33; at age 49 macula is still fairly well-preserved, but outer retinal atrophy and spicular intraretinal pigmentation is now prominent. CRB1.G: Fundus of RE of LCA-3 9a at age 16, showing typical yellowish discoloration of atrophic macula, surrounded by nummular type of intraretinal pigmentation; mild pseudopapilledema and prepapillary paravascular fibrosis also visible, as is peripheral greyish hue of outer retinal atrophy with fine white flecks and nummular pigmentation. GUCY2D. H & I: Fundus and AF image of RE of LCA-55 at age 9 years; fundus is essentially quite normal with only mild pigment epithelium alterations in the retinal periphery; however, AF image shows hyperautofluorescence in central macular area. RPE65. J: Fundus of LE of LCA-49 at age 10 who subsequently underwent gene therapy with AAV2-hRPE65v2 in RE (Maguire et al. 2009); apart from some discrete pigment epithelium alterations fundus is essentially normal; autofluorescence imaging could not be obtained due to lack of lipofuscin accumulation in retinal pigment epithelium (RPE) typical of this type of LCA. AIPL1. K & L: Fundus and AF image of RE of LCA-61 at age 19 years; central macular atrophy with yellowish hue is surrounded by area of better preserved peripheral macula; outer retinal atrophy with spicular intraretinal pigmentation visible in periphery; AF shows black area of atrophic central macula, but is typically not surrounded by hyperautofluorescent ring. RDH12. M & N: Fundus of EORD-7 at age 5 and 19 years respectively; note mild macular RPE changes which become more prominent with age; mild predominantly spicular intraretinal pigmentation also increases with age; however, preservation of patches of normal peripheral retina are most striking feature; these patches remain over time.

Figure 2

Magnetic resonance imaging (MRI) showing characteristic molar tooth sign (MTS) in five patients with Joubert syndrome/cerebello-oculo-renal syndrome due to mutations in CEP290 (all are axial sections through midbrain). Images organized from left to right; arrows indicate MTS of midbrain present in all due to midbrain malformation with hypoplastic cerebellar vermis and midline cleft (all images are T1 weighted except for panel D which is T2 weighted). A) CORS-1 at age 5 years; B) LCA-JS-1 at age 7 years; C) LCA-JS-2 II-1 at age 14 years; D) LCA-JS-2 II-2 at age 17 years and E) LCA-JS-3 at age 2 years.