Characterising splicing defects of ABCA4 variants within exons 13-50 in patient-derived fibroblasts.

The ATP-binding cassette subfamily A member 4 gene (ABCA4)-associated retinopathy, Stargardt disease, is the most common monogenic inherited retinal disease. Given the pathogenicity of numerous ABCA4 variants is yet to be examined and a significant proportion (more than 15%) of ABCA4 variants are categorized as splice variants in silico, we therefore established a fibroblast-based splice assay to analyze ABCA4 variants in an Australian Stargardt disease cohort and characterize the pathogenic mechanisms of ABCA4 variants. A cohort of 67 patients clinically diagnosed with Stargardt disease was recruited. Genomic DNA was analysed using a commercial panel for ABCA4 variant detection and the consequences of ABCA4 variants were predicted in silico. Dermal fibroblasts were propagated from skin biopsies, total RNA was extracted and the ABCA4 transcript was amplified by RT-PCR. Our analysis identified a total of 67 unique alleles carrying 74 unique variants. The most prevalent splice-affecting complex allele c.[5461-10T>C; 5603A>T] was carried by 10% of patients in a compound heterozygous state. ABCA4 transcripts from exon 13 to exon 50 were readily detected in fibroblasts. In this region, aberrant splicing was evident in 10 out of 57 variant transcripts (18%), carried by 19 patients (28%). Patient-derived fibroblasts provide a feasible platform for identification of ABCA4 splice variants located within exons 13-50. Experimental evidence of aberrant splicing contributes to the pathogenic classification for ABCA4 variants. Moreover, identification of variants that affect splicing processes provides opportunities for intervention, in particular antisense oligonucleotide-mediated splice correction.

SIBLING CONCORDANCE IN SYMPTOM ONSET AND ATROPHY GROWTH RATES IN STARGARDT DISEASE USING ULTRA-WIDEFIELD FUNDUS AUTOFLUORESCENCE.

PURPOSE: To investigate concordance in symptom onset, area of dark autofluorescence (DAF), and growth rate (GR) between Stargardt disease siblings at an age-matched time point. METHODS: In this retrospective longitudinal study of sibling pairs with identical biallelic ABCA4 variants, age at symptom onset, best-corrected visual acuity, atrophy area, and effective radius of DAF on ultra-widefield fundus autofluorescence were recorded. Absolute intersibling differences for both eyes were compared with absolute interocular differences using the Mann-Whitney test. RESULTS: Overall 39 patients from 19 families were recruited. In 16 families, age-matched best-corrected visual acuity and DAF were compared between siblings. In 8 families, DAF GR was compared. The median (range) absolute difference in age at symptom onset between siblings was 3 (0-35) years. Absolute intersibling differences in age-matched best-corrected visual acuity were greater than interocular differences ( P = 0.01). Similarly, absolute intersibling differences in DAF area and radius were greater than interocular differences ( P = 0.04 for area and P = 0.001 for radius). Differences between absolute interocular and intersibling GR were not statistically significant ( P = 0.44 for area GR and P = 0.61 for radius GR). CONCLUSION: There was significant discordance in age-matched best-corrected visual acuity and DAF beyond the expected limits of interocular asymmetry. Lack of significant intersibling differences in GR warrants further investigation.

A novel phenotype in a family with autosomal dominant retinal dystrophy due to c.1430A > G in retinoid isomerohydrolase (RPE65) and c.37C > T in bestrophin 1 (BEST1).

PURPOSE: The c.1430A > G (Asp477Gly) variant in RPE65 has been reported in Irish and Scottish families with either an autosomal dominant retinal dystrophy (adRD) that resembles choroideremia, a vitelliform macular dystrophy or an isolated macular atrophy. We report novel features on multimodal imaging and the natural history of a family harbouring this variant in combination with the BEST1 c.37C > T (Arg13Cys) variant. METHODS: Members of a family with an adRD were examined clinically to ascertain phenotype and underwent genetic testing. Multimodal imaging included widefield colour fundus photography, quantitative autofluorescence (qAF) and spectral domain optical coherence tomography. Electrophysiology and microperimetry were also performed. RESULTS: Vision loss was attributed to foveal atrophy in the proband and choroidal neovascularisation and a vitello-eruptive lesion in one affected son. Peripheral retinal white dots corresponding to subretinal deposits were seen in three patients. The median qAF8 values in the proband (I:1) were low (40 and 101 in OD and OS) at age 79. Similarly, the qAF8 values for the middle son (II:2) were also low (100 and 87 in ODS and OS) at age 60. Electrophysiology showed disproportionate reduction in Arden ratio prior to the gradual loss of full-field responses. Microperimetry demonstrated an enlarging scotoma in the proband. CONCLUSIONS: The coexistence of the pathogenic BEST1 c.37C > T variant may modify clinical features observed in RPE65 adRD. This study expands our understanding of RPE65 adRD as a retinoid cycle disorder supported by the reduced qAF, fine white retinal dots and corresponding subretinal deposits on OCT in affected members.

CLASSIFYING ABCA4 MUTATION SEVERITY USING AGE-DEPENDENT ULTRA-WIDEFIELD FUNDUS AUTOFLUORESCENCE-DERIVED TOTAL LESION SIZE.

PURPOSE: To establish a mutation-specific age-dependent ultra-widefield fundus autofluorescence (UWF-FAF) trajectory in a large Stargardt disease (STGD1) cohort using total lesion size (TLS) and to develop a clinical method for variant classification. METHODS: A retrospective study of patients with biallelic ABCA4 mutations that were evaluated with UWF-FAF. Boundaries of TLS, defined by stippled hyper/hypoautofluorescence, were outlined manually. Pathogenicity was assessed according to ACMG/AMP criteria, and mutation severities were classified based on the current literature. Age-dependent trajectories in TLS were examined in patients with nullizygous, mild, and intermediate mutations. Mutations of uncertain severities were classified using a clinical criterion based on age of symptom onset and TLS. RESULTS: Eighty-one patients with STGD1 (mean age = 42 ± 20 years and mean visual acuity = 20/200) were recruited from 65 unrelated families. Patients with biallelic null/severe variants (n = 6) demonstrated an increase in TLS during their second decade reaching a mean ± SD of 796 ± 29 mm2 by age 40. Those harboring mild mutations c.5882G>A or c.5603A>T had lesions confined to the posterior pole with a mean ± SD TLS of 30 ± 39 mm2. Intermediate mutations c.6079C>T or c.[2588G>C;5603A>T] in trans with a null/severe mutation had a mean ± SD TLS of 397 ± 29 mm2. Thirty-two mutations were predicted to cause severe (n = 22), intermediate (n = 6), and mild (n = 5) impairment of ABCA4 function based on age of symptom onset and TLS. CONCLUSION: Age-dependent TLS showed unique ABCA4 mutation-specific trajectories. Our novel clinical criterion using age of symptom onset and TLS to segregate ABCA4 mutations into three severity groups requires further molecular studies to confirm its validity.

Resolving the dark matter of ABCA4 for 1054 Stargardt disease probands through integrated genomics and transcriptomics.

PURPOSE: Missing heritability in human diseases represents a major challenge, and this is particularly true for ABCA4-associated Stargardt disease (STGD1). We aimed to elucidate the genomic and transcriptomic variation in 1054 unsolved STGD and STGD-like probands. METHODS: Sequencing of the complete 128-kb ABCA4 gene was performed using single-molecule molecular inversion probes (smMIPs), based on a semiautomated and cost-effective method. Structural variants (SVs) were identified using relative read coverage analyses and putative splice defects were studied using in vitro assays. RESULTS: In 448 biallelic probands 14 known and 13 novel deep-intronic variants were found, resulting in pseudoexon (PE) insertions or exon elongations in 105 alleles. Intriguingly, intron 13 variants c.1938-621G>A and c.1938-514G>A resulted in dual PE insertions consisting of the same upstream, but different downstream PEs. The intron 44 variant c.6148-84A>T resulted in two PE insertions and flanking exon deletions. Eleven distinct large deletions were found, two of which contained small inverted segments. Uniparental isodisomy of chromosome 1 was identified in one proband. CONCLUSION: Deep sequencing of ABCA4 and midigene-based splice assays allowed the identification of SVs and causal deep-intronic variants in 25% of biallelic STGD1 cases, which represents a model study that can be applied to other inherited diseases.

Analysis of the ABCA4 c.[2588G>C;5603A>T] Allele in the Australian Population.

Inherited retinal diseases (IRDs) are genetically and phenotypically diverse, and they cause significant morbidity worldwide. Importantly, IRDs may be amenable to precision medicine strategies, and thus the molecular characterisation of causative variants is becoming increasingly important with the promise of personalised therapies on the horizon. ABCA4, involved in the translocation of visual cycle derivatives, is a well-established, frequent cause of IRDs worldwide, with pathogenic variants implicated in phenotypically diverse diseases. Identification of causative ABCA4 variants in some individuals, however, has been enigmatic, and resolution of this issue is currently a hotbed of research. Recent evidence has indicated that hypomorphic alleles, which cause disease under certain conditions, may account for some of the missing causal variants. It has been postulated that the ABCA4 c.5603A>T (p.Asn1868Ile) variant, previously considered benign, be reclassified as hypomorphic when in cis configuration with c.2588G>C (p.Gly863Ala/Gly863del), a variant previously considered to be pathogenic in its own right. We are exploring this relationship within an Australian cohort to test this theory.

Maternal uniparental isodisomy of chromosome 6 unmasks a novel variant in TULP1 in a patient with early onset retinal dystrophy.

Purpose: Inherited retinal dystrophies are a clinically and genetically heterogeneous group of disorders. Molecular diagnosis has proven utility for affected individuals. In this study, we report an individual enrolled in the Australian Inherited Retinal Disease Registry and DNA Bank diagnosed with clinical features overlapping between Leber congenital amaurosis and retinitis pigmentosa. Methods: DNA from the proband was sequenced using a gene panel for inherited retinal disorders, and a single nucleotide polymorphism (SNP) array was conducted to detect the presence of deletions and uniparental disomy. Results: We identified a novel homozygous variant (c.524dupC, p.(Pro176ThrfsTer7)) in TULP1 resulting from maternal uniparental isodisomy of chromosome 6. The patient had clinical features consistent with biallelic pathogenic variants in TULP1, including congenital nystagmus, night blindness, non-recordable electroretinogram, mild myopia, and mild peripheral pigmentary changes in the fundus. Conclusions: This is the first report of uniparental disomy 6 and a homozygous variant in TULP1 associated with a rod-cone dystrophy. Molecular diagnosis of inherited retinal dystrophies is essential to inform the mode of transmission and clinical management, and to identify potential candidates for future gene-specific therapies.

Genetic analysis of choroideremia families in the Australian population.

BACKGROUND: Choroideremia is an X-linked inherited chorioretinal disease known to be caused by mutations in the CHM gene. In this study, Australian families clinically diagnosed with choroideremia were genetically analysed for mutations in the CHM gene. DESIGN: The Australian Inherited Retinal Disease Register and DNA Bank (AIRDR) was investigated to identify a cohort of choroideremia-affected families for genetic analysis. PARTICIPANTS: Participants were sourced from the AIRDR. Thirty-two participants (15 affected, 10 carriers, 7 unaffected) sourced from 11 unrelated families having at least one member clinically diagnosed with choroideremia were included in the study. METHODS: We performed sequence analysis of the CHM gene on the DNA of nine probands. We received the direct sequencing results of two probands by other means. Targeted analysis was subsequently performed for all 32 participants to confirm the direct sequencing results in the 11 probands and to establish the presence or absence of the implicated mutation in the remaining 21 affected, carrier or unaffected family members. MAIN OUTCOME MEASURES: Genetic characterisation of 11 choroideremia families in the Australian population. RESULTS: A CHM mutation was detected in all 11 families. Each family had a different mutation. Mutations segregated within each family according to disease status. Five mutations were novel and six have been previously reported. CONCLUSIONS: Six previously reported and five novel CHM mutations were detected in 11 Australian families clinically diagnosed with choroideremia. We anticipate that this work will facilitate access for AIRDR participants and their progeny to CHM gene therapy trials.

Clinical and molecular characterization of females affected by X-linked retinoschisis.

BACKGROUND: X-linked retinoschisis (XLRS) is a leading cause of juvenile macular degeneration associated with mutations in the RS1 gene. XLRS has a variable expressivity in males and shows no clinical phenotype in carrier females. DESIGN: Clinical and molecular characterization of male and female individuals affected with XLRS in a consanguineous family. PARTICIPANTS: Consanguineous Eastern European-Australian family METHODS: Four clinically affected and nine unaffected family members were genetically and clinically characterized. Deoxyribonucleic acid (DNA) analysis was conducted by the Australian Inherited Retinal Disease Register and DNA Bank. MAIN OUTCOME MEASURES: Clinical and molecular characterization of the causative mutation in a consanguineous family with XLRS. RESULTS: By direct sequencing of the RS1 gene, one pathogenic variant, NM_000330.3: c.304C > T, p. R102W, was identified in all clinically diagnosed individuals analysed. The two females were homozygous for the variant, and the males were hemizygous. CONCLUSION: Clinical and genetic characterization of affected homozygous females in XLRS affords the rare opportunity to explore the molecular mechanisms of XLRS and the manifestation of these mutations as disease in humans.

Rapid Variant Pathogenicity Analysis by CRISPR Activation of CRB1 Gene Expression in Patient-Derived Fibroblasts.

Inherited retinal diseases (IRDs) are a heterogeneous group of blinding genetic disorders caused by pathogenic variants in genes expressed in the retina. In this study, we sought to develop a method for rapid evaluation of IRD gene variant pathogenicity by inducing expression of retinal genes in patient-derived fibroblasts using CRISPR-activation (CRISPRa). We demonstrate CRISPRa of CRB1 expression in fibroblasts derived from patients with retinitis pigmentosa, enabling investigation of pathogenic mechanisms associated with specific variants. We show the CRB1 c.4005 + 1G>A variant caused exon 11 skipping in CRISPR-activated fibroblasts and retinal organoids (ROs) derived from the same RP12 patient. The c.652 + 5G>C variant was shown to enhance exon 2 skipping in CRISPR-activated fibroblasts and differentially affected CRB1 isoform expression in fibroblasts and ROs. Our study demonstrates an accessible platform for transcript screening of IRD gene variants in patient-derived fibroblasts, which can potentially be applied for rapid pathogenicity assessments of any gene variant.

Establishment of an induced pluripotent stem cell line LEIi019-A from an early-onset retinal dystrophy patient with the autosomal dominant OTX2 c.259G>A variant.

The human induced pluripotent stem cell (iPSC) line LEIi019-A was generated from a patient with early-onset pattern dystrophy caused by a heterozygous mutation NM_001270525.1:c.259G>A (p.Glu87Lys) in OTX2. Patient-derived dermal fibroblasts were reprogrammed using episomal plasmids containing reprogramming factors OCT4, SOX2, KLF4, MYCL, LIN28, TP53 shRNA and miR-302/367. The iPSC line expressed pluripotency markers, displayed a normal 46,XY karyotype and demonstrated the ability to differentiate into the three primary germ layers, retinal organoids and retinal pigment epithelial cells.

Analysis of the Outer Retinal Bands in ABCA4 and PRPH2-Associated Retinopathy using OCT.

PURPOSE: To evaluate the outer retinal bands using OCT in ABCA4- and PRPH2-associated retinopathy and develop a novel imaging biomarker to differentiate between these 2 genotypes. DESIGN: Multicenter case-control study. PARTICIPANTS: Patients with a clinical and genetic diagnosis of ABCA4- or PRPH2-associated retinopathy and an age-matched control group. METHODS: Macular OCT was used to measure the thickness of the outer retinal bands 2 and 4 by 2 independent examiners at 4 retinal loci. MAIN OUTCOME MEASURES: Outcome measures included the thicknesses of band 2, band 4, and the band 2/band 4 ratio. Linear mixed modeling was used to make comparisons across the 3 groups. Receiver operating characteristic (ROC) analysis determined the optimal cutoff for the band 2/band 4 ratio to distinguish PRPH2- from ABCA4-associated retinopathy. RESULTS: We included 45 patients with ABCA4 variants, 45 patients with PRPH2 variants, and 45 healthy controls. Band 2 was significantly thicker in patients with PRPH2 compared with ABCA4 (21.4 vs. 15.9 µm, P < 0.001) variants, whereas band 4 was thicker in patients with ABCA4 variants than those with PRPH2 variants (27.5 vs. 21.7 µm, P < 0.001). Similarly, the band 2/band 4 ratio was significantly different (1.0 vs. 0.6 for PRPH2 vs. ABCA4, P < 0.001). The area under the ROC curve was 0.87 for either band 2 (> 18.58 µm) or band 4 (< 26.17 µm) alone and 0.99 (95% confidence interval: 0.97-0.99) for the band 2/band 4 ratio with a cutoff threshold of 0.79, providing 100% specificity. CONCLUSIONS: We report an altered outer retinal band profile whereby the band 2/band 4 ratio was able to discriminate between PRPH2- and ABCA4-associated retinopathy. This may have future clinic utility in predicting the genotype and provide further insight into the anatomic correlate of band 2. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Retinal characteristics of female choroideremia carriers: Multimodal imaging, microperimetry and genetics.

PURPOSE: Describe visual function and retinal features of female carriers of choroideremia (CHM), using multimodal imaging and microperimetry. DESIGN: Cross-sectional cohort study PARTICIPANTS AND CONTROLS: CHM carriers seen in Australia (Melbourne or Perth) or United Kingdom (Oxford or Cambridge) between 2012 and 2023. Healthy age-matched controls seen in Melbourne, Australia, between 2022 and 2023. METHODS: Participants had visual acuity, fundus-tracked microperimetry, optical coherence tomography (OCT), and fundus autofluorescence (FAF) imaging performed. CHM carriers were either genetically and/or clinically confirmed (i.e., obligate carriers). CHM carriers were grouped according to their retinal phenotype and compared to healthy controls. Statistical analyses were performed on StataBE (v18.0). MAIN OUTCOME MEASURES: Best-corrected visual acuity (BCVA), low-luminance visual acuity (LLVA), average retinal sensitivity, volume of macular hill of vision (HoV), inner retinal thickness (IRT), and photoreceptor complex (PRC) thickness. RESULTS: Eighty-six eyes of 43 CHM carriers and 60 eyes of 30 healthy controls were examined using multimodal imaging and microperimetry. Median age was 54 and 48.5 years for CHM carriers and controls, respectively (p=0.18). Most CHM carriers (86%) were genetically confirmed. CHM carriers and controls had strong inter-eye correlation between eyes for BCVA and average retinal sensitivity (p<0.001). LLVA and macular HoV tests were sensitive tests to detect changes in CHM carriers with mild phenotypes (i.e., fine and coarse). CHM carriers with geographic and/or male pattern phenotypes had reduced BCVA, LLVA, retinal sensitivity, and retinal thinning, compared to healthy controls. Retinal thickening of the inner retina was observed in the central 1 degree, despite generalised thinning of the PRC in the central 7 degrees, indicating retinal remodelling in CHM carriers, compared to controls. There were no genotype-phenotype correlations observed. CONCLUSIONS: Female carriers of CHM with severe retinal phenotypes (i.e., geographic or male pattern) have significantly decreased visual function and retinal structural changes, when compared to age-matched controls and those carriers with milder phenotypes. LLVA and volumetric measures of the macular HoV were found to be the most sensitive functional tests to detect milder retinal disease (fine and coarse phenotypes) in CHM carriers.

Retinal Dystrophies Associated With Peripherin-2: Genetic Spectrum and Novel Clinical Observations in 241 Patients.

Purpose: To describe the clinical, electrophysiological and genetic spectrum of inherited retinal diseases associated with variants in the PRPH2 gene. Methods: A total of 241 patients from 168 families across 15 sites in 9 countries with pathogenic or likely pathogenic variants in PRPH2 were included. Records were reviewed for age at symptom onset, visual acuity, full-field ERG, fundus colour photography, fundus autofluorescence (FAF), and SD-OCT. Images were graded into six phenotypes. Statistical analyses were performed to determine genotype-phenotype correlations. Results: The median age at symptom onset was 40 years (range, 4-78 years). FAF phenotypes included normal (5%), butterfly pattern dystrophy, or vitelliform macular dystrophy (11%), central areolar choroidal dystrophy (28%), pseudo-Stargardt pattern dystrophy (41%), and retinitis pigmentosa (25%). Symptom onset was earlier in retinitis pigmentosa as compared with pseudo-Stargardt pattern dystrophy (34 vs 44 years; P = 0.004). The median visual acuity was 0.18 logMAR (interquartile range, 0-0.54 logMAR) and 0.18 logMAR (interquartile range 0-0.42 logMAR) in the right and left eyes, respectively. ERG showed a significantly reduced amplitude across all components (P < 0.001) and a peak time delay in the light-adapted 30-Hz flicker and single-flash b-wave (P < 0.001). Twenty-two variants were novel. The central areolar choroidal dystrophy phenotype was associated with 13 missense variants. The remaining variants showed marked phenotypic variability. Conclusions: We described six distinct FAF phenotypes associated with variants in the PRPH2 gene. One FAF phenotype may have multiple ERG phenotypes, demonstrating a discordance between structure and function. Given the vast spectrum of PRPH2 disease our findings are useful for future clinical trials.

Establishment and evolution of the Australian Inherited Retinal Disease Register and DNA Bank.

BACKGROUND: Inherited retinal disease represents a significant cause of blindness and visual morbidity worldwide. With the development of emerging molecular technologies, accessible and well-governed repositories of data characterising inherited retinal disease patients is becoming increasingly important. This manuscript introduces such a repository. DESIGN: Participants were recruited from the Retina Australia membership, through the Royal Australian and New Zealand College of Ophthalmologists, and by recruitment of suitable patients attending the Sir Charles Gairdner Hospital visual electrophysiology clinic. PARTICIPANTS: Four thousand one hundred ninety-three participants were recruited. All participants were members of families in which the proband was diagnosed with an inherited retinal disease (excluding age-related macular degeneration). METHODS: Clinical and family information was collected by interview with the participant and by examination of medical records. In 2001, we began collecting DNA from Western Australian participants. In 2009 this activity was extended Australia-wide. Genetic analysis results were stored in the register as they were obtained. MAIN OUTCOME MEASURES: The main outcome measurement was the number of DNA samples (with associated phenotypic information) collected from Australian inherited retinal disease-affected families. RESULTS: DNA was obtained from 2873 participants. Retinitis pigmentosa, Stargardt disease and Usher syndrome participants comprised 61.0%, 9.9% and 6.4% of the register, respectively. CONCLUSIONS: This resource is a valuable tool for investigating the aetiology of inherited retinal diseases. As new molecular technologies are translated into clinical applications, this well-governed repository of clinical and genetic information will become increasingly relevant for tasks such as identifying candidates for gene-specific clinical trials.

Driving with retinitis pigmentosa.

BACKGROUND: To establish the proportion of patients with retinitis pigmentosa (RP) meeting the Australian fitness to drive (FTD) visual standards. METHODOLOGY: A prospective consecutive case series of patients with a clinical or genetic diagnosis of RP. Data on age at symptom onset, current driving status, inheritance pattern, better eye visual acuity (BEVA), binocular Esterman visual field (BEVF) parameters, genotype and ability to meet the driving standards based on BEVA and BEVF were collected. Outcome measures included the proportion of RP patients overall meeting the standards and clinical predictors for passing. A sub-analysis was performed on those RP patients who reported to drive. Change in BEVA and BEVF parameters across age in specific genotype groups was assessed. RESULTS: Overall, 228 patients with RP had a BEVF assessment. Only 39% (89/228) met the driving standards. Younger age at the time of testing was the only significant predictor (p < 0.01) for passing. Of the 55% of RP patients who reported to drive, 52% (65/125) met the standards, decreasing to 14% in the 56- to 65-year-old age group. RP patients harbouring mutations in HK1 or RHO genes may have slower rates of decline in their VF parameters. CONCLUSION: Nearly 40% of RP patients met the driving standards. However, almost 50% of RP drivers were unaware of their failure to meet the current standards. BEVF testing is essential in the assessment of RP patients who are still driving. Phenotype and genotype predictors for passing the standards warrant further investigation.Abbreviation: FTD, fitness to drive; IRD, inherited retinal disease; RP, retinitis pigmentosa; RHO, rhodopsin; HK1, hexokinase 1; PRPF31 pre-mRNA processing factor 31; RPGR, retinitis pigmentosa GTPase regulator; VF, visual field; BEVA, better eye visual acuity; BEVF, binocular Esterman visual field.

Longitudinal Analysis of Functional and Structural Outcome Measures in PRPH2-Associated Retinal Dystrophy.

PURPOSE: To establish disease progression rates in total lesion size (TLS), decreased autofluorescence (DAF) area, total macular volume (TMV), and mean macular sensitivity (MMS) in PRPH2-associated retinal dystrophy. DESIGN: Single-center, retrospective chart review. PARTICIPANTS: Patients with heterozygous pathogenic or likely pathogenic PRPH2 variants. METHODS: Patients who underwent serial ultrawide-field (UWF) fundus autofluorescence (FAF), OCT, and Macular Integrity Assessment microperimetry with at least 1 year of follow-up were included. Linear correlation was performed in eyes of all patients to determine the rate of change over time. MAIN OUTCOME MEASURES: Outcome measures included changes in TLS, DAF area, TMV, and MMS. RESULTS: Twelve patients (mean age, 55) from 10 unrelated families attended 100 clinic visits, which spanned over a mean (SD) of 4.7 (2.0) years. Mean (SD) TLS and DAF radius expansion were 0.14 (0.12) and 0.10 (0.08) mm/year, respectively. Mean (SD) TMV change was -0.071 (0.040) mm3/year with no interocular difference (P = 0.20) and strong interocular correlation (r2 = 0.88, P < 0.01). Mean (SD) MMS change was -0.10 (1.25) dB/year. Mean macular sensitivity declined in 4 and improved in 6 patients. Mean macular sensitivity was subnormal despite a TMV within the normal range. CONCLUSIONS: Serial measurements of UWF-FAF-derived TLS and DAF showed slow expansion. Total macular volume might be a more sensitive measure than MMS in detecting disease progression.

Microperimetry and Adaptive Optics Imaging Reveal Localized Functional and Structural Changes in Asymptomatic RPGR Mutation Carriers.

Purpose: Female carriers of RPGR mutations demonstrate no significant retinal dysfunction or structural change despite a characteristic tapetal-like reflex. In this study, we examined localized changes of pointwise sensitivity (PWS) and cone density (CD) using microperimetry (MP) and adaptive optics (AO) imaging in female carriers of RPGR mutations. Methods: In this cross-sectional case-control study, MP (MAIA, 10-2 test grid) and AO imaging (rtx1) were performed in female carriers of RPGR mutations and unrelated age-matched healthy controls. PWS at 68 loci located 1 degree to 9 degrees away from the preferred retinal locus and CD at 12 loci located 1 degree to 3 degrees away from the foveal center were measured. Severity of defect was defined by standard deviation (SD) from age-matched healthy control means: normal (<1 SD from normal average), moderate defect (1-2 SD from normal average), and severe defect (>2 SD from normal average). Results: Twelve patients from seven unrelated families were enrolled. Seven patients were asymptomatic, 5 of whom had visual acuity 20/20 or better in both eyes. PWS and CD were available in 12 and 8 patients, respectively. Severe PWS and CD defect in at least 1 test location was observed in 10 of 12 patients and 7 of 8 patients, respectively. Among the five asymptomatic patients who had normal visual acuity, severe PWS and CD defects were observed in three of five and four of five patients, respectively. Conclusions: MP and AO imaging revealed early functional and structural changes in asymptomatic RPGR mutation carriers and should be considered in clinical assessment of these patients.

Application of a high-throughput genotyping method for loci exclusion in non-consanguineous Australian pedigrees with autosomal recessive retinitis pigmentosa.

PURPOSE: Retinitis pigmentosa (RP) is the most common form of inherited blindness, caused by progressive degeneration of photoreceptor cells in the retina, and affects approximately 1 in 3,000 people. Over the past decade, significant progress has been made in gene therapy for RP and related diseases, making genetic characterization increasingly important. Recently, high-throughput technologies have provided an option for reasonably fast, cost-effective genetic characterization of autosomal recessive RP (arRP). The current study used a single nucleotide polymorphism (SNP) genotyping method to exclude up to 28 possible disease-causing genes in 31 non-consanguineous Australian families affected by arRP. METHODS: DNA samples were collected from 59 individuals affected with arRP and 74 unaffected family members from 31 Australian families. Five to six SNPs were genotyped for 28 genes known to cause arRP or the related disease Leber congenital amaurosis (LCA). Cosegregation analyses were used to exclude possible causative genes from each of the 31 families. Bidirectional sequencing was used to identify disease-causing mutations in prioritized genes that were not excluded with cosegregation analyses. RESULTS: Two families were excluded from analysis due to identification of false paternity. An average of 28.9% of genes were excluded per family when only one affected individual was available, in contrast to an average of 71.4% or 89.8% of genes when either two, or three or more affected individuals were analyzed, respectively. A statistically significant relationship between the proportion of genes excluded and the number of affected individuals analyzed was identified using a multivariate regression model (p<0.0001). Subsequent DNA sequencing resulted in identification of the likely disease-causing gene as CRB1 in one family (c.2548 G>A) and USH2A in two families (c.2276 G>T). CONCLUSIONS: This study has shown that SNP genotyping cosegregation analysis can be successfully used to refine and expedite the genetic characterization of arRP in a non-consanguineous population; however, this method is effective only when DNA samples are available from more than one affected individual.

Atrophy Expansion Rates in Stargardt Disease Using Ultra-Widefield Fundus Autofluorescence.

Purpose: To investigate atrophy expansion rate (ER) using ultra-widefield (UWF) fundus autofluorescence (FAF) in Stargardt disease (STGD1). Design: Retrospective, longitudinal study. Participants: Patients with biallelic ABCA4 mutations who were evaluated with UWF FAF and Heidelberg 30° × 30° and 55° × 55° FAF imaging. Methods: Patients with atrophy secondary to STGD1 were classified into genotype groups: group A, biallelic severe or null-like variants with early-onset disease; group B, 1 intermediate variant in trans with severe or null-like variant; and group C, 1 mild variant in trans with severe or null-like variant or late-onset disease. The boundaries of definitely decreased autofluorescence (DDAF) were outlined manually and areas (in square millimeters) were recorded at baseline and follow-up. Bland-Altman analysis was conducted to examine agreement between observers and devices. Linear mixed modeling was used to evaluate predictors of ER in DDAF area and square root area (SRA). Main Outcome Measures: Patient and ocular predictors of DDAF area ER and DDAF SRA ER included age at onset, duration of symptoms, genotype group, baseline visual acuity, and baseline atrophy size. Results: A total of 138 eyes from 69 patients (33 men [47%]; mean age ± standard deviation, 41 ± 20 years; range, 10-83 years) carrying 61 unique ABCA4 variants were recruited. Ultra-widefield FAF measurements were equivalent to Heidelberg 30° × 30° imaging. Baseline DDAF area was the only significant predictor of DDAF area ER (P < 0.001). Age at baseline and genotype group were predictors for DDAF SRA ER. Definitely decreased autofluorescence area ER ranged from 4.65 mm2/year (group A) to 0.62 mm2/year (group C). Conclusions: Ultra-widefield FAF is a feasible and reliable method for assessing atrophy ER in STGD1. The value of ABCA4 mutation severity in predicting atrophy ER warrants further investigation.