Panel-Based Genetic Testing for Inherited Retinal Disease screening 176 Genes

Background: This case series reports the performance of a next-generation sequencing (NGS) panel of 176 retinal genes (NGS 176) in patients with inherited retinal disease (IRD). Methods: Subjects are patients who underwent genetic testing between 1 August 2016 and 1 January 2018 at Moorfields Eye Hospital, London, UK. Panel-based genetic testing was performed unless a specific gene (e.g., RS1) or small group of genes (e.g., ABCA4, PRPH2) were suspected. If a novel variant was identified, a further comment on their predicted pathogenicity and evolutionary conservation was offered and segregation studies performed. The main outcome measure is the likelihood of obtaining a genetic diagnosis using NGS 176. Results: 488 patients were included. A molecular diagnosis was obtained for 59.4% of patients. Younger patients were more likely to receive a molecular diagnosis; with 92% of children under the age of 6 years receiving a conclusive result. There was a change in their initially assigned inheritance pattern in 8.4% of patients following genetic testing. Selected IRD diagnoses (e.g., achromatopsia, congenital stationary night blindness) were associated with high diagnostic yields. Conclusion: This study confirms that NGS 176 is a useful first-tier genetic test for most IRD patients. Age and initial clinical diagnosis were strongly associated with diagnostic yield

Classical and Quantum Critical Phenomena in the Dipolar Antiferromagnet LiErF4

The collective behavior of systems consisting of interacting dipoles is a subject of considerable studies. The anisotropic nature of such interactions opens an arena to explore fundamental questions in correlated electron physics, ranging from quantum entanglement, phase transitions, spin glass states to disorder and fluctuations. LiHoF4 is a textbook example of a ferromagnetic Ising-dipolar model, offering a simple and well-understood Hamiltonian. The system undergoes a quantum phase transition (QPT) in a field transverse to the easy axis, which induces quantum fluctuations between the ground state doublet. Dilution of Ho sites with non-magnetic Yttrium ions lowers only the transition temperature (Tc), and eventually lead to spin-glass state. While Tc decreases in a linear fashion, as expected from simple mean-field (MF) calculation, critical field decreases much faster. The behavior upon dilution has been pointed out to be related to randomness and off-diagonal dipolar interactions. In chapter 5 of this thesis I quantify the deviation of experimental results from neutron scattering studies from MF prediction, with the aim that this analysis can be used in future theoretical efforts towards a quantitative description. The aim of this thesis, however, deals with LiErF4 which is an unexplored planar dipolar antiferromagnetic member of LiReF4 family, with TN ≃ 370 mK. The system undergoes a QPT in an applied field H∥c = 4.0±0.1 kOe, confirmed by a softening of the characteristic excitations at Hc. A combined neutron scattering, specific heat, and magnetic susceptibility study reveals a novel non-MF critical scaling of the classical phase transition, belonging to the 2DXY /h4 universality class. In accord with this, the quantum phase transition at Hc exhibits a three-dimensional classical behavior. The effective dimensional reduction may be a consequence of the intrinsic anisotropic nature of the dipolar interaction. Four-fold anisotropy and degeneracy breaking could be due to the "order-by-disorder" phenomena, which could open a gap in dispersion of the magnetic excitations

A clinical and molecular characterisation of CRB1-associated maculopathy

To date, over 150 disease-associated variants in CRB1 have been described, resulting in a range of retinal disease phenotypes including Leber congenital amaurosis and retinitis pigmentosa. Despite this, no genotype–phenotype correlations are currently recognised. We performed a retrospective review of electronic patient records to identify patients with macular dystrophy due to bi-allelic variants in CRB1. In total, seven unrelated individuals were identified. The median age at presentation was 21 years, with a median acuity of 0.55 decimalised Snellen units (IQR = 0.43). The follow-up period ranged from 0 to 19 years (median = 2.0 years), with a median final decimalised Snellen acuity of 0.65 (IQR = 0.70). Fundoscopy revealed only a subtly altered foveal reflex, which evolved into a bull’s-eye pattern of outer retinal atrophy. Optical coherence tomography identified structural changes—intraretinal cysts in the early stages of disease, and later outer retinal atrophy. Genetic testing revealed that one rare allele (c.498_506del, p.(Ile167_Gly169del)) was present in all patients, with one patient being homozygous for the variant and six being heterozygous. In trans with this, one variant recurred twice (p.(Cys896Ter)), while the four remaining alleles were each observed once (p.(Pro1381Thr), p.(Ser478ProfsTer24), p.(Cys195Phe) and p.(Arg764Cys)). These findings show that the rare CRB1 variant, c.498_506del, is strongly associated with localised retinal dysfunction. The clinical findings are much milder than those observed with bi-allelic, loss-of-function variants in CRB1, suggesting this in-frame deletion acts as a hypomorphic allele. This is the most prevalent disease-causing CRB1 variant identified in the non-Asian population to date

Biallelic sequence and structural variants in RAX2 are a novel cause for autosomal recessive inherited retinal disease.

Purpose RAX2 encodes a homeobox-containing transcription factor, in which four monoallelic pathogenic variants have been described in autosomal dominant cone-dominated retinal disease. Methods Exome sequencing in a European cohort with inherited retinal disease (IRD) (n = 2086) was combined with protein structure modeling of RAX2 missense variants, bioinformatics analysis of deletion breakpoints, haplotyping of RAX2 variant c.335dup, and clinical assessment of biallelic RAX2-positive cases and carrier family members. Results Biallelic RAX2 sequence and structural variants were found in five unrelated European index cases, displaying nonsyndromic autosomal recessive retinitis pigmentosa (ARRP) with an age of onset ranging from childhood to the mid-40s (average mid-30s). Protein structure modeling points to loss of function of the novel recessive missense variants and to a dominant-negative effect of the reported dominant RAX2 alleles. Structural variants were fine-mapped to disentangle their underlying mechanisms. Haplotyping of c.335dup in two cases suggests a common ancestry. Conclusion This study supports a role for RAX2 as a novel disease gene for recessive IRD, broadening the mutation spectrum from sequence to structural variants and revealing a founder effect. The identification of biallelic RAX2 pathogenic variants in five unrelated families shows that RAX2 loss of function may be a nonnegligible cause of IRD in unsolved ARRP cases

Differentiating drusen:Drusen and drusen-like appearances associated with ageing, age-related macular degeneration, inherited eye disease and other pathological processes

Drusen are discussed frequently in the context of their association with age-related macular degeneration (AMD). Some types may, however, be regarded as a normal consequence of ageing; others may be observed in young age groups. They also occur in a number of inherited disorders and some systemic conditions. Whilst drusen are classically located external (sclerad) to the retinal pigment epithelium, accumulations of material internal (vitread to) this layer can display a drusen-like appearance, having been variously termed pseudodrusen or subretinal drusenoid deposits. This review first briefly presents an overview of drusen biogenesis and subclinical deposit. The (frequently overlapping) subtypes of clinically detectable deposit, seen usually in the context of ageing or AMD, are then described in more detail, together with appearance on imaging modalities: these include hard and soft drusen, cuticular drusen, reticular pseudodrusen and “ghost drusen”. Eye disorders other than AMD which may exhibit drusen or drusen-like features are subsequently discussed: these include monogenic conditions as well as conditions with undefined inheritance, the latter including some types of early onset drusen such as large colloid drusen. A number of systemic conditions in which drusen-like deposits may be seen are also considered. Throughout this review, high resolution images are presented for most of the conditions discussed, particularly the rarer ones, providing a useful reference library for images of the range of conditions associated with drusen-like appearances. In the final section, some common themes are highlighted, as well as a brief discussion of some future avenues for research

Early Patterns of Macular Degeneration in ABCA4-Associated Retinopathy.

PurposeTo describe the earliest features of ABCA4-associated retinopathy.DesignCase series.ParticipantsChildren with a clinical and molecular diagnosis of ABCA4-associated retinopathy without evidence of macular atrophy.MethodsThe retinal phenotype was characterized by color fundus photography, OCT, fundus autofluorescence (FAF) imaging, electroretinography, and in 2 patients, adaptive optics scanning laser ophthalmoscopy (AOSLO). Sequencing of the ABCA4 gene was performed in all patients.Main outcome measuresVisual acuity, OCT, FAF, electroretinography, and AOSLO results.ResultsEight children with ABCA4-associated retinopathy without macular atrophy were identified. Biallelic variants in ABCA4 were identified in all patients. Four children were asymptomatic, and 4 reported loss of VA. Patients were young (median age, 8.5 years; interquartile range, 6.8 years) with good visual acuity (median, 0.155 logarithm of the minimum angle of resolution [logMAR]; interquartile range, 0.29 logMAR). At presentation, the macula appeared normal (n = 3), had a subtly altered foveal reflex (n = 4), or demonstrated manifest fine yellow dots (n = 1). Fundus autofluorescence identified hyperautofluorescent dots in the central macula in 3 patients, 2 of whom showed a normal fundus appearance. Only 1 child had widespread hyperautofluorescent retinal flecks at presentation. OCT imaging identified hyperreflectivity at the base of the outer nuclear layer in all 8 patients. Where loss of outer nuclear volume was evident, this appeared to occur preferentially at a perifoveal locus. Longitudinal split-detector AOSLO imaging in 2 individuals confirmed that the greatest change in cone spacing occurred in the perifoveal, and not foveolar, photoreceptors. Electroretinography showed a reduced B-wave-to-A-wave ratio in 3 of 5 patients tested; in 2 children, recordings clearly showed electronegative results.ConclusionsIn childhood-onset ABCA4-associated retinopathy, the earliest stages of macular atrophy involve the parafovea and spare the foveola. In some cases, these changes are predated by tiny, foveal, yellow, hyperautofluorescent dots. Hyperreflectivity at the base of the outer nuclear layer, previously described as thickening of the external limiting membrane, is likely to represent a structural change at the level of the foveal cone nuclei. Electroretinography suggests that the initial site of retinal dysfunction may occur after phototransduction