Sorting out co-occurrence of rare monogenic retinopathies: Stargardt disease co-existing with congenital stationary night blindness

Nanotechnology Lighting the Way for Gene Therapy in Ophthalmopathy: From Opportunities toward Applications

Hereditary ophthalmopathy is a well-described threat to human visual health affecting millions of people. Gene therapy for ophthalmopathy has received widespread attention with the increasing understanding of pathogenic genes. Effective and safe delivery of accurate nucleic acid drugs (NADs) is the core of gene therapy. Efficient nanodelivery and nanomodification technologies, appropriate targeted genes, and the choice of drug injection methods are the guiding lights of gene therapy. Compared with traditional drugs, NADs can specifically change the expression of specific genes or restore the normal function of mutant genes. Nanodelivery carriers can improve targeting and nanomodification can improve the stability of NADs. Therefore, NADs, which can fundamentally solve pathogeny, hold great promise in the treatment of ophthalmopathy. This paper reviews the limitations of ocular disease treatment, discusses the classification of NADs in ophthalmology, reveals the delivery strategies of NADs to improve bioavailability, targeting, and stability, and summarizes the mechanisms of NADs in ophthalmopathy.

Simultaneous expression of two pathogenic genes in four Chinese patients affected with inherited retinal dystrophy

AIM

To describe the complex, overlapping phenotype of four Chinese patients with inherited retinal dystrophies (IRDs) who harbored two pathogenic genes simultaneously.

METHODS

This retrospective study included 4 patients affected with IRDs. Medical and ophthalmic histories were obtained, and clinical examinations were performed. A specific Hereditary Eye Disease Enrichment Panel (HEDEP) based on exome capture technology was used for genetic screening.

RESULTS

Four patients were identified to harbor disease-causing variants in two different genes. Patient retinitis pigmentosa (RP) 01-II:1 exhibited both classical ABCA4-induced Stargardt disease (STGD) 1 and USH2A-associated RP, patient RP02-III:2 exhibited both classical ABCA4-induced STGD1 and CDH23-associated RP, patient RP03-II:1 exhibited both USH2A-induced autosomal recessive retinitis pigmentosa (arRP) syndrome and SNRNP200-induced autosomal dominant retinitis pigmentosa (adRP), and patient RP04-II:2 exhibited USH2A-induced arRP syndrome and EYS-induced arRP at the same time.

CONCLUSION

Our study demonstrates that genotype-phenotype correlations and comprehensive genetic screening is crucial for diagnosing IRDs and helping family planning for patients suffering from the disease.

Coexistence of GNAT1 and ABCA4 variants associated with Nougaret-type congenital stationary night blindness and childhood-onset cone-rod dystrophy

PURPOSE

A single variant (p.G38D) in the GNAT1 gene, encoding the rod-specific transducin α-subunit in phototransduction, has been reported only in one French family with Nougaret-type autosomal dominant congenital stationary night blindness (CSNB). We identified a Japanese family with Nougaret-type CSNB and cone-rod dystrophy (CORD).

METHODS

Five patients with CSNB and two patients with childhood-onset CORD were recruited. We performed a comprehensive ophthalmic examination including electroretinography (ERG). Disease-causing variants were identified by whole exome sequencing, with candidates confirmed by Sanger sequencing in nine family members.

RESULTS

The GNAT1 variant (p.G38D) was identified in all four CSNB patients, whereas the two CORD patients carried biallelic truncated known ABCA4 variants as well as the GNAT1 variant. Clinically, no remarkable findings were observed in fuduscopy, fundus autofluorescence, or optical coherence tomography images from the CSNB patients. No response was detectable by rod ERG. The a-waves of standard and bright flash ERG were delayed and broadened rather than biphasic, and b/a-wave amplitude ratio was negative. Cone and 30-Hz flicker responses were normal, and overall, the ERG findings were compatible with previous descriptions of Nougaret-type CSNB. ERG of the CORD patients with macular atrophy showed non-recordable rod response and severely decreased standard flash, cone and 30-Hz flicker responses.

CONCLUSIONS

This is the second report of a Nougaret-type CSNB family with the GNAT1 variant. Our novel findings suggest that coexistence of the GNAT1 and biallelic ABCA4 variants is associated with an overlapping phenotype with both Nougaret-type CSNB and CORD.

Gene panel sequencing in Brazilian patients with retinitis pigmentosa

Background

Retinal dystrophies constitute a group of diseases characterized by clinical variability and pronounced genetic heterogeneity. Retinitis pigmentosa is the most common subtype of hereditary retinal dystrophy and is characterized by a progressive loss of peripheral field vision (Tunnel Vision), eventual loss of central vision, and progressive night blindness. The characteristics of the fundus changes include bone-spicule formations, attenuated blood vessels, reduced and/or abnormal electroretinograms, changes in structure imaged by optical coherence tomography, and subjective changes in visual function. The different syndromic and nonsyndromic forms of retinal dystrophies can be attributed to mutations in more than 250 genes. Molecular diagnosis for patients with retinitis pigmentosa has been hampered by extreme genetic and clinical heterogeneity between retinitis pigmentosa and other forms of retinal dystrophies. Next generation sequencing (NGS) technologies are among the most promising techniques to identify pathogenic variations in retinal dystrophies.

Purpose

The purpose of this study was to discover the molecular diagnosis for Brazilian patients clinically diagnosed with a retinitis pigmentosa pattern of inheritance by using NGS technologies.

Materials and methods

Sixteen patients with the clinical diagnosis of retinitis pigmentosa were included in the study. Their DNA was sequenced in a panel with 132 genes related to retinal dystrophies using the Illumina^® platform. Sequence analysis and variation calling was performed using Soft Genetics^®, NextGene, and Geneticist Assistant software. The criteria for pathogenicity analysis were established according to the results of prediction programs (Polyphen 2, Mutation taster and MetaCore™) and comparison of pathogenic variations found with databases.

Results

The identified potentially pathogenic variations were all confirmed by Sanger sequencing. There were 89 variations predicted as pathogenic, but only 10 of them supported the conclusion of the molecular diagnosis. Five of the nine patients were autosomal dominant RP (56%), two (22%) were autosomal recessive RP, and two (22%) were X-linked RP. Nine of the 16 patients (56%) had probably positive or positive results.

Conclusion

The Next Generation Sequencing used in this study allowed the molecular diagnosis to be confirmed in 56% of the patients and clarified the inheritance pattern of the patient’s retinal dystrophies.

Electronic supplementary material

The online version of this article (doi:10.1186/s40942-017-0087-6) contains supplementary material, which is available to authorized users.

Simultaneous Expression of ABCA4 and GPR143 Mutations: A Complex Phenotypic Manifestation

Purpose

To describe the complex, overlapping phenotype expressed in a two generation family harboring pathogenic mutations in the ABCA4 and GPR143 genes.

Methods

Clinical evaluation of a two generation family included quantitative autofluorescence imaging (qAF, 488-nm excitation) using a modified confocal scanning laser ophthalmoscope equipped with an internal fluorescent reference to account for varying laser power detector sensitivity, spectral-domain optical coherence tomography, and full-field ERG testing. Complete sequencing of the ABCA4 and GPR143 genes was carried out in each individual.

Results

Affected individuals presented with bull's eye lesions and qAF levels above the 95% confidence interval for healthy eyes; full-field ERG revealed no generalized rod dysfunction but mild implicit time delays in cone responses. Complete sequencing of the ABCA4 gene revealed two disease-causing mutations, p.L541P and p.G1961E; and mutational phase was confirmed in each unaffected parent. Further examination in the affected patients revealed a peripheral “mud-splattered” pattern of hypopigmented RPE after which sequencing of GPR143 revealed a novel missense variant, p.Y157C. The GPR143 variant segregated from the father who did not exhibit any indications of retinal disease with the exception of an abnormal near-infrared autofluorescence (NIR-AF) signal distribution in the macula.

Conclusions

An individual carrying both ABCA4 and GPR143 disease-causing mutations can express a complex, overlapping phenotype associated with both Stargardt disease and X-linked ocular albinism (OA1). The absence of OA1-related disease changes (with the exception of NIR-AF changes associated with melanin distribution) in the father may be indicative of mild expressivity or variable gene penetrance.

Genetic analysis of 10 pedigrees with inherited retinal degeneration by exome sequencing and phenotype-genotype association

Our purpose was to identify causative mutations and characterize the phenotype associated with the genotype in 10 unrelated families with autosomal recessive retinal degeneration. Ophthalmic evaluation and DNA isolation were carried out in 10 pedigrees with inherited retinal degenerations (IRD). Exomes of probands from eight pedigrees were captured using Nimblegen V2/V3 or Agilent V5+UTR kits, and sequencing was performed on Illumina HiSeq. The DHDDS gene was screened for mutations in the remaining two pedigrees with Ashkenazi Jewish ancestry. Exome variants were filtered to detect candidate causal variants using exomeSuite software. Segregation and ethnicity-matched control sample analysis were performed by dideoxy sequencing. Retinal histology of a patient with DHDDS mutation was studied by microscopy. Genetic analysis identified six known mutations in ABCA4 (p.Gly1961Glu, p.Ala1773Val, c.5461-10T>C), RPE65 (p.Tyr249Cys, p.Gly484Asp), PDE6B (p.Lys706Ter) and DHDDS (p.Lys42Glu) and ten novel potentially pathogenic variants in CERKL (p.Met323Val fsX20), RPE65 (p.Phe252Ser, Thr454Leu fsX31), ARL6 (p.Arg121His), USH2A (p.Gly3142Ter, p.Cys3294Trp), PDE6B (p.Gln652Ter), and DHDDS (p.Thr206Ala) genes. Among these, variants/mutations in two separate genes were observed to segregate with IRD in two pedigrees. Retinal histopathology of a patient with a DHDDS mutation showed severe degeneration of retinal layers with relative preservation of the retinal pigment epithelium. Analysis of exome variants in ten pedigrees revealed nine novel potential disease-causing variants and nine previously reported homozygous or compound heterozygous mutations in the CERKL, ABCA4, RPE65, ARL6, USH2A, PDE6B, and DHDDS genes. Mutations that could be sufficient to cause pathology were observed in more than one gene in one pedigree.

The current status of molecular diagnosis of inherited retinal dystrophies

PURPOSE OF REVIEW

We are witnessing lightning-fast advances in the molecular diagnosis of inherited retinal dystrophies, mainly due to the widespread use of next-generation sequencing technologies. The purpose of this review is to highlight the breadth of findings from this in-depth testing approach, and to propose changes to our traditional testing and diagnostic paradigms. Lessons learned from modern molecular testing suggest that the previous concept of inherited retinal dystrophies as a group of 'single gene diseases' may require a significant update.

RECENT FINDINGS

All of the known retinal dystrophies genes can now be sequenced. In many cases, this nonhypothesis driven testing strategy is uncovering mutations in unsuspected genes, generating data that challenges established concepts of genetic mechanisms and provides insights regarding genes previously thought to be exclusively related to syndromic disease. Recent advances in testing have improved not only the breadth, but also the depth of genetic data. For example, deep intronic sequencing has uncovered many novel intronic mutations/variations in the ABCA4 gene.

SUMMARY

Currently, in approximately 50-60% of patients with nonsyndromic retinal dystrophy, the disease mechanism can be identified. The presence of pathogenic alleles in more than one gene is not uncommon. Retinal dystrophy, with relatively defined clinical presentations and a large but limited number of genes involved, is becoming a model for the next-generation study of molecular disease mechanisms.

Genetic and clinical analysis of ABCA4-associated disease in African American patients

Autosomal recessive Stargardt disease (STGD1) is caused by hundreds of mutations in the ABCA4 gene, which are often specific to racial and ethnic groups. Here, we investigated the ABCA4 variation and their phenotypic expression in a cohort of 44 patients of African American descent, a previously under-characterized racial group. Patients were screened for mutations in ABCA4 by next-generation sequencing and array-comparative genomic hybridization (aCGH), followed by analyses for pathogenicity by in silico programs. Thorough ophthalmic examination was performed on all patients. At least two (expected) disease-causing alleles in the ABCA4 gene were identified in 27 (61.4%) patients, one allele in 11 (25%) patients, and no ABCA4 mutations were found in six (13.6%) patients. Altogether, 39 different disease-causing ABCA4 variants, including seven new, were identified on 65 (74%) chromosomes, most of which were unique for this racial group. The most frequent ABCA4 mutation in this cohort was c.6320G>A (p.(R2107H)), representing 19.3% of all disease-associated alleles. No large copy number variants were identified in any patient. Most patients reported later onset of symptoms. In summary, the ABCA4 mutation spectrum in patients of West African descent differs significantly from that in patients of European descent, resulting in a later onset and "milder" disease.