Late-Onset Stargardt Disease Due to Mild, Deep-Intronic ABCA4 Alleles

PURPOSE. To investigate the role of two deep-intronic ABCA4 variants, that showed a mild splice defect in vitro and can occur on the same allele as the low penetrant c.5603A>T, in Stargardt disease (STGD1). METHODS. Ophthalmic data were assessed of 18 STGD1 patients who harbored c.769-784C>T or c.4253+43G>A in combination with a severe ABCA4 variant. Subjects carrying c.[769784C>T; 5603A>T] were clinically compared with a STGD1 cohort previously published carrying c.5603A>T noncomplex. We calculated the penetrances of the intronic variants using ABCA4 allele frequency data of the general population and investigated the effect of c.769-784C>T on splicing in photoreceptor progenitor cells (PPCs). RESULTS. Mostly, late-onset, foveal-sparing STGD1 was observed among subjects harboring c.769-784C>T or c.4253+43G>A (median age of onset, 54.5 and 52.0 years, respectively). However, ages of onset, phenotypes in fundo, and visual acuity courses varied widely. No significant clinical differences were observed between the c.[769-784C>T; 5603A>T] cohort and the c.4253+43G>A or the c.5603A>T cohort. The penetrances of c.769-784C>T (20.5%-39.6%) and c.4253+43G>A (35.8%-43.1%) were reduced, when not considering the effect of yet unidentified or known factors in cis, such as c.5603A>T (identified in 7/7 probands with c.769-784C>T; 1/8 probands with c.4253+43G>A). Variant c.769-784C>T resulted in a pseudo-exon insertion in 15% of the total mRNA (i.e., similar to 30% of the c.769-784C>T allele alone). CONCLUSIONS. Two mild intronic ABCA4 variants could further explain missing heritability in late-onset STGD1, distinguishing it from AMD. The observed clinical variability and calculated reduced penetrance urge research into modifiers within and outside of the ABCA4 gene

Stargardt disease:monitoring incidence and diagnostic trends in the Netherlands using a nationwide disease registry

PURPOSE: To assess the incidence of Stargardt disease (STGD1) and to evaluate demographics of incident cases. METHODS: For this retrospective cohort study, demographic, clinical and genetic data of patients with a clinical diagnosis of STGD1 were registered between September 2010 and January 2020 in a nationwide disease registry. Annual incidence (2014-2018) and point prevalence (2018) were assessed on the basis of this registry. RESULTS: A total of 800 patients were registered, 56% were female and 83% were of European ancestry. The incidence was 1.67-1.95:1,000,000 per year and the point prevalence in 2018 was approximately 1:22,000-1:19,000 (with and without 10% of potentially unregistered cases). Age at onset was associated with sex (p = 0.027, Fisher's exact); 1.9x more women than men were observed (140 versus 74) amongst patients with an age at onset between 10 and 19 years, while the sex ratio in other age-at-onset categories approximated one. Late-onset STGD1 (≥45 years) constituted 33% of the diagnoses in 2014-2018 compared to 19% in 2004-2008. Diagnostic delay (≥2 years between the first documentation of macular abnormalities and diagnosis) was associated with older age of onset (p = 0.001, Mann-Whitney). Misdiagnosis for age-related macular degeneration (22%) and incidental STGD1 findings (14%) was common in patients with late-onset STGD1. CONCLUSION: The observed prevalence of STGD1 in real-world data was lower than expected on the basis of population ABCA4 allele frequencies. Late-onset STGD1 was more frequently diagnosed in recent years, likely due to higher awareness of its phenotype. In this pretherapeutic era, mis- and underdiagnosis of especially late-onset STGD1 and the role of sex in STGD1 should receive special attention

The common ABCA4 variant p.Asn1868ile shows nonpenetrance and variable expression of stargardt disease when present in trans with severe variants

PURPOSE. To assess the occurrence and the disease expression of the common p.Asn1868Ile variant in patients with Stargardt disease (STGD1) harboring known, monoallelic causal ABCA4 variants. METHODS. The coding and noncoding regions of ABCA4 were sequenced in 67 and 63 STGD1 probands respectively, harboring monoallelic ABCA4 variants. In case p.Asn1868Ile was detected, segregation analysis was performed whenever possible. Probands and affected siblings harboring p.Asn1868Ile without additional variants in cis were clinically evaluated retrospe

Personalized genetic counseling for Stargardt disease: Offspring risk estimates based on variant severity

Recurrence risk calculations in autosomal recessive diseases are complicated when the effect of genetic variants and their population frequencies and penetrances are unknown. An example of this is Stargardt disease (STGD1), a frequent recessive retinal disease caused by bi-allelic pathogenic variants in ABCA4. In this cross-sectional study, 1,619 ABCA4 variants from 5,579 individuals with STGD1 were collected and categorized by (1) severity based on statistical comparisons of their frequencies in STGD1-affected individuals versus the general population, (2) their observed versus expected homozygous occurrence in STGD1-affected individuals, (3) their occurrence in combination with established mild alleles in STGD1-affected individuals, and (4) previous functional and clinical studies. We used the sum allele frequencies of these severity categories to estimate recurrence risks for offspring of STGD1-affected individuals and carriers of pathogenic ABCA4 variants. The risk for offspring of an STGD1-affected individual with the "severe vertical bar severe"genotype or a "severe vertical bar mild with complete penetrance"genotype to develop STGD1 at some moment in life was estimated at 2.8%-3.1% (1 in 36-32 individuals) and 1.6%-1.8% (1 in 62-57 individuals), respectively. The risk to develop STGD1 in childhood was estimated to be 2-to 4-fold lower: 0.68%-0.79% (1 in 148-126) and 0.34%-0.39% (1 in 296-252), respectively. In conclusion, we established personalized recurrence risk calculations for STGD1-affected individuals with different combinations of variants. We thus propose an expanded genotype-based personalized counseling to appreciate the variable recurrence risks for STGD1-affected individuals. This represents a conceptual breakthrough because risk calculations for STGD1 may be exemplary for many other inherited diseases

The common ABCA4 variant p.Asn1868ile shows nonpenetrance and variable expression of stargardt disease when present in trans with severe variants

PURPOSE. To assess the occurrence and the disease expression of the common p.Asn1868Ile variant in patients with Stargardt disease (STGD1) harboring known, monoallelic causal ABCA4 variants. METHODS. The coding and noncoding regions of ABCA4 were sequenced in 67 and 63 STGD1 probands respectively, harboring monoallelic ABCA4 variants. In case p.Asn1868Ile was detected, segregation analysis was performed whenever possible. Probands and affected siblings harboring p.Asn1868Ile without additional variants in cis were clinically evaluated retrospectively. Two asymptomatic siblings carrying the same ABCA4 variants as their probands were clinically examined. The penetrance of p.Asn1868Ile was calculated using allele frequency data of ABCA4 variants in non-Finnish European individuals. RESULTS. The p.Asn1868Ile variant was found in cis with known variants in 14/67 probands. In 27/67 probands, we identified p.Asn1868Ile without additional variants in cis, in combination with known, mainly severe ABCA4 variants. In 23/27 probands, the trans configuration was established. Among 27 probands and 6/7 STGD1 siblings carrying p.Asn1868Ile, 42% manifested late-onset disease (>44 years). We additionally identified four asymptomatic relatives carrying a combination of a severe variant and p.Asn1868Ile; ophthalmologic examination in two persons did not reveal STGD1. Based on ABCA4 allele frequency data, we conservatively estimated the penetrance of p.Asn1868Ile, when present in trans with a severe variant, to be below 5%. CONCLUSIONS. A significant fraction of genetically unexplained STGD1 cases carries p.Asn1868Ile as a second variant. Our findings suggest exceptional differences in disease expression or even nonpenetrance of this ABCA4 variant, pointing toward an important role for genetic or environmental modifiers in STGD1

Deep-intronic ABCA4 variants explain missing heritability in Stargardt disease and allow correction of splice defects by antisense oligonucleotides

We thank Ellen Blokland, Lonneke Duijkers, Duaa Elmelik, Anita Hoogendoorn, Marlie Jacobs-Camps, Saskia van der Velde-Visser, and Marijke Zonneveld-Vrieling for technical assistance. We thank Sabine Defoort, Hélène Dollfus, Isabelle Drumare, Christian P. Hamel, Karsten Hufendiek, Cord Huchzermeyer, Herbert Jägle, Ulrich Kellner, Philipp Rating, Klaus Rüther, Eric Souied, Georg Spital, and Xavier Zanlonghi for their cooperation and ascertaining STGD1 cases. This work was supported by the FP7-PEOPLE-2012-ITN programme EyeTN, agreement 317472 (to F.P.M.C.); the Macula Vision Research Foundation (to F.P.M.C.); the Foundation Fighting Blindness USA, grant no. PPA-0517-0717-RAD (to A.G., C.B.H., F.P.M.C., R.W.J.C., and S.A.); the RP Fighting Blindness UK (RetinaUK), grant no. GR591 (to F.P.M.C. and S.A.); the Rotterdamse Stichting Blindenbelangen, the Stichting Blindenhulp, and the Stichting tot Verbetering van het Lot der Blinden (to F.P.M.C. and S.A.); and by the Landelijke Stichting voor Blinden en Slechtzienden, Macula Degeneratie fonds, and the Stichting Blinden-Penning, which contributed through Uitzicht 2016-12 (to F.P.M.C. and S.A.). This work was also supported by the Algemene Nederlandse Vereniging ter Voorkoming van Blindheid, Stichting Blinden-Penning, Landelijke Stichting voor Blinden en Slechtzienden, Stichting Oogfonds Nederland, Stichting Macula Degeneratie Fonds, and Stichting Retina Nederland Fonds, which contributed through UitZicht 2015-31, together with the Rotterdamse Stichting Blindenbelangen, Stichting Blindenhulp, Stichting tot Verbetering van het Lot der Blinden, Stichting voor Ooglijders, and Stichting Dowilvo (to A.G. and R.W.J.C.); the Stichting Macula Degeneratie Fonds; and the Stichting A.F. Deutman Researchfonds Oogheelkunde (to C.B.H.). This work was also supported by the Algemene Nederlandse Vereniging ter Voorkoming van Blindheid and Landelijke Stichting voor Blinden en Slechtzienden, which contributed through UitZicht 2014-13, together with the Rotterdamse Stichting Blindenbelangen, Stichting Blindenhulp, and the Stichting tot Verbetering van het Lot der Blinden (to F.P.M.C.), the Ghent University Research Fund (BOF15/GOA/011), the Research Foundation Flanders (FVO) G0C6715N, and the Hercules Foundation AUGE/13/023 and JED Foundation to E.D.B. M.B. was PhD fellow of the FWO and recipient of a grant of the funds for Research in Ophthalmology (FRO). E.D.B. is Senior Clinical Investigator of the FWO (1802215N). This work was also supported by the National Institute for Health Research (NIHR) Biomedical Centre at Moorfields and UCL Institute of Ophthalmology (to A.W.), UK NIHR Rare Disease Translational Research Consortium (to G.A. and A.W.), NIHR for the NIHR BioResource (RG65966) (to F.L.R.) by grants from the Federal Ministry of Education and Research (BMBF) (ref. IDs 01GM0851 and 01GM1108B) (to B.H.F.W.). G.A. is supported by a Fight for Sight UK Early Career Investigator Award. The funding organizations had no role in the design or conduct of this research, and provided unrestricted grants. This study made use of data generated by the Genome of the Netherlands Project. Funding for the project was provided by the Netherlands Organization for Scientific Research under award number 184021007, dated 9 July 2009 and made available as a Rainbow Project of the Biobanking and Biomolecular Research Infrastructure Netherlands (BBMRI-NL). Samples where contributed by LifeLines (http://lifelines.nl/lifelines-research/general), the Leiden Longevity Study (http://www.healthy-ageing.nl; http://www.langleven.net), the Netherlands Twin Registry (NTR: http://www.tweelingenregister.org), the Rotterdam studies (http://www.erasmus-epidemiology.nl/rotterdamstudy), and the Genetic Research in Isolated Populations program (http://www.epib.nl/research/geneticepi/research.html#gip). The sequencing was carried out in collaboration with the Beijing Institute for Genomics (BGI).Peer reviewedPublisher PD

Association of Sex With Frequent and Mild ABCA4 Alleles in Stargardt Disease

IMPORTANCE The mechanisms behind the phenotypic variability and reduced penetrance in autosomal recessive Stargardt disease (STGD1), often a blinding disease, are poorly understood. Identification of the unknown disease modifiers can improve patient and family counseling and provide valuable information for disease management. OBJECTIVE To assess the association of incompletely penetrant ABCA4 alleles with sex in STGD1. DESIGN, SETTING, AND PARTICIPANTS Genetic data for this cross-sectional study were obtained from 2 multicenter genetic studies of 1162 patients with clinically suspected STGD1. Unrelated patients with genetically confirmed STGD1 were selected. The data were collected from June 2016 to June 2019, and post hoc analysis was performed between July 2019 and January 2020. MAIN OUTCOMES AND MEASURES Penetrance of reported mild ABCA4 variants was calculated by comparing the allele frequencies in the general population (obtained from the Genome Aggregation Database) with the genotyping data in the patient population (obtained from the ABCA4 Leiden Open Variation Database). The sex ratio among patients with and patients without an ABCA4 allele with incomplete penetrance was assessed. RESULTS A total of 550 patients were included in the study, among which the mean (SD) age was 45.7 (18.0) years and most patients were women (311 [57%]). Five of the 5 mild ABCA4 alleles, including c.5603A>T and c.5882G>A, were calculated to have incomplete penetrance. The women to men ratio in the subgroup carrying c.5603A>T was 1.7 to 1; the proportion of women in this group was higher compared with the subgroup not carrying a mild allele (difference, 13%; 95% CI, 3%-23%; P=.02). The women to men ratio in the c.5882G>A subgroup was 2.1 to 1, and the women were overrepresented compared with the group carrying no mild allele (difference, 18%; 95% CI, 6%-30%; P=.005). CONCLUSIONS AND RELEVANCE This study found an imbalance in observed sex ratio among patients harboring a mild ABCA4 allele, which concerns approximately 25% of all patients with STGD1, suggesting that STGD1 should be considered a polygenic or multifactorial disease rather than a disease caused by ABCA4 gene mutations alone. The findings suggest that sex should be considered as a potential disease-modifying variable in both basic research and clinical trials on STGD1

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

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.Fil: Khan, Mubeen. Radboud University Nijmegen Medical Centre; Países BajosFil: Cornelis, Stéphanie S.. Radboud University Nijmegen Medical Centre; Países BajosFil: Del Pozo Valero, Marta. Hospital Universitario Fundación Jiménez Díaz; España. Radboud University Nijmegen Medical Centre; Países BajosFil: Whelan, Laura. Trinity College; Estados UnidosFil: Runhart, Esmee H.. Radboud University Nijmegen Medical Centre; Países BajosFil: Mishra, Ketan. Radboud University Nijmegen Medical Centre; Países BajosFil: Bults, Femke. Radboud University Nijmegen Medical Centre; Países BajosFil: AlSwaiti, Yahya. St John of Jerusalem Eye Hospital Group; Palestina (ANP)Fil: AlTalbishi, Alaa. St John of Jerusalem Eye Hospital Group; Palestina (ANP)Fil: De Baere, Elfride. University of Ghent; BélgicaFil: Banfi, Sandro. Seconda Universita Degli Studi Di Napoli; ItaliaFil: Banin, Eyal. The Hebrew University of Jerusalem; IsraelFil: Bauwens, Miriam. University of Ghent; BélgicaFil: Ben Yosef, Tamar. The Ruth And Bruce Rappaport Faculty Of Medicine; IsraelFil: Boon, Camiel J. F.. Leiden University. Leiden University Medical Center; Países BajosFil: van den Born, L. Ingeborgh. Rotterdam Ophthalmic Institute; Países BajosFil: Defoort, Sabine. Universite Lille; FranciaFil: Devos, Aurore. Universite Lille; FranciaFil: Dockery, Adrian. Trinity College; Estados UnidosFil: Dudakova, Lubica. Charles University and General University Hospital; República ChecaFil: Fakin, Ana. Charles University and General University Hospital; República ChecaFil: Farrar, G. Jane. Trinity College; Estados UnidosFil: Ferraz Sallum, Juliana Maria. Universidade Federal de Sao Paulo; BrasilFil: Fujinami, Kaoru. UCL Institute of Ophthalmology; Reino UnidoFil: Gilissen, Christian. Radboud University Nijmegen Medical Centre; Países BajosFil: Glavac, Damjan. University of Ljubljana; EsloveniaFil: Gorin, Michael B.. University of California at Los Angeles. School of Medicine; Estados UnidosFil: Greenberg, Jacquie. University of Cape Town; SudáfricaFil: Hayashi, Takaaki. The Jikei University School of Medicine; JapónFil: Hettinga, Ymkje M.. Bartiméus Diagnostic Center for Complex Visual Disorders; Países BajosFil: Hoischen, Alexander. Radboud University Nijmegen Medical Centre; Países BajosFil: Hoyng, Carel B.. Radboud University Nijmegen Medical Centre; Países BajosFil: Hufendiek, Karsten. University Eye Hospital Hannover Medical School; AlemaniaFil: Jägle, Herbert. University Regensburg; AlemaniaFil: Kamakari, Smaragda. OMMA Ophthalmological Institute of Athens; GreciaFil: Karali, Marianthi. Seconda Universita Degli Studi Di Napoli; ItaliaFil: Kellner, Ulrich. No especifíca;Fil: Klaver, Caroline C. W.. Radboud University Nijmegen Medical Centre; Países BajosFil: Kousal, Bohdan. Charles University and General University Hospital; República ChecaFil: Lamey, Tina M.. University of Western Australia; AustraliaFil: MacDonald, Ian M.. University of Alberta; CanadáFil: Matynia, Anna. University of California at Los Angeles. School of Medicine; Estados UnidosFil: McLaren, Terri L.. University of Western Australia; AustraliaFil: Mena, Marcela D.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Meunier, Isabelle. Université Montpellier II; FranciaFil: Miller, Rianne. Radboud University Nijmegen Medical Centre; Países BajosFil: Newman, Hadas. Universitat Tel Aviv; IsraelFil: Ntozini, Buhle. University of Cape Town; SudáfricaFil: Oldak, Monika. No especifíca;Fil: Pieterse, Marc. Radboud University Nijmegen Medical Centre; Países BajosFil: Podhajcer, Osvaldo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Puech, Bernard. Universite Lille; FranciaFil: Ramesar, Raj. University of Cape Town; SudáfricaFil: Rüther, Klaus. No especifíca;Fil: Salameh, Manar. No especifíca;Fil: Salles, Mariana Vallim. Universidade de Sao Paulo; BrasilFil: Sharon, Dror. The Hebrew University of Jerusalem; IsraelFil: Simonelli, Francesca. Seconda Universita Degli Studi Di Napoli; ItaliaFil: Spital, Georg. No especifíca;Fil: Steehouwer, Marloes. Radboud University Nijmegen Medical Centre; Países BajosFil: Szaflik, Jacek P.. No especifíca;Fil: Thompson, Jennifer A.. No especifíca;Fil: Thuillier, Caroline. Universite Lille; FranciaFil: Tracewska, Anna M.. No especifíca;Fil: van Zweeden, Martine. Radboud University Nijmegen Medical Centre; Países BajosFil: Vincent, Andrea L.. University of Auckland; Nueva ZelandaFil: Zanlonghi, Xavier. No especifíca;Fil: Liskova, Petra. Charles University and General University Hospital; República ChecaFil: Stöhr, Heidi. Universitat Regensburg; AlemaniaFil: De Roach, John N.. University of Western Australia; AustraliaFil: Ayuso, Carmen. Hospital Universitario Fundación Jiménez Díaz; EspañaFil: Roberts, Lisa. University of Cape Town; SudáfricaFil: Weber, Bernhard H. F.. Universitat Regensburg; AlemaniaFil: Dhaenens, Claire Marie. Universite Lille; FranciaFil: Cremers, Frans P. M.. Radboud University Nijmegen Medical Centre; Países Bajo