Myopia with X-linked retinitis pigmentosa results from a novel gross deletion of RPGR gene

Clinical and genetic studies for a cohort of patients with Leber congenital amaurosis

PURPOSE

Leber congenital amaurosis (LCA) is a group of early-onset retinal degenerative disorders, resulting in blindness in children. This study aimed to describe the clinical and genetic characteristics of a cohort of patients with LCA and to investigate the retinal vascular characteristics in LCA patients.

METHODS

Fifty-two children with LCA were included in the study. All patients underwent detailed ocular examinations. Electroretinography (ERG) was used to evaluate the retinal function. Optical coherence tomography (OCT) was used to assess the structure change of the retina for those patients who were able to cooperate very well. Panel-based next-generation sequencing was performed to identify pathogenic variants in genes associated with LCA. Diameters of the retinal vessels were measured using the EVision AI screening system with an artificial intelligence (AI) technique. An ultrasound Doppler was used to evaluate hemodynamic parameters, including peak systolic velocity (PSV), resistive index (RI), and pulsatility index (PI), in the ophthalmic, central retinal, posterior ciliary, carotid, and internal carotid as well as external carotid arteries in 12 patients aged from 3 to 14 years.

RESULTS

We detected 75 pathogenic variants from ten genes of RPGRIP1, CEP290, GUCY2D, LCA5, AIPL1, CRB1, RPE65, CRX, RDH12, and TULP1, including 29 novel and 36 previously reported variants in 52 affected children with LCA, with the highest detective rate in RPGRIP1 (26.9%). Fundus appearance is diverse in patients with LCA, ranging from normal to severe peripheral or central retinopathy. Retinal vasculature was evaluated in 12 patients with different gene variants, showing narrowed arteries with an average diameter of 43.6 ± 3.8 μm compared to that of 51.7 ± 2.6 μm in the normal controls (P < 0.001, n = 12). Meanwhile, their hemodynamic parameters were changed as well in the ophthalmic artery (OA), with a decreased PSV (P = 0.0132, n = 12) and slightly increased PI (P = 0.0488, n = 12) compared to the normal controls. However, the hemodynamic parameters did not change significantly in the other vessels.

CONCLUSIONS

Blood supply to the eyeball is predicted to be reduced in patients with LCA, presumably due to photoreceptor cell degeneration. The novel identified variants will expand the spectrum of variants in LCA-related genes and be useful for studying the molecular mechanisms of LCA.

Female carrier of RPGR mutation presenting with high myopia

BACKGROUND

Inherited retinopathies can initially present with high refractive error in the first decade of life, before accompanying signs or symptoms are evident.

CASE PRESENTATION

A 4-year-old girl with high myopia (S-12.00 C-4.00 × 20 in the right and S-14.50 C-2.75 × 160 in the left eye), moderate visual acuity (0.3 logMAR in the right and 0.4 logMAR in the left eye), and left esotropia, presented with unremarkable past medical history and no family history of high refractive error or low vision. In optical coherence tomography imaging, macular thinning was evident, while morphology was normal. Full-field electroretinogram revealed normal implicit time recordings with reduced amplitudes in scotopic and photopic conditions. Fundus autofluorescence showed a radial pattern in both eyes. During a 5-year follow-up, significant myopia progression ensued (S-17.25 C-3.00 × 20 in the right and S-17.25 C-2.00 × 160 in the left eye), with a corresponding increase in axial length and an unchanged visual acuity. Whole-exome sequencing revealed a heterozygous termination codon variant c.212C>G (p.Ser71Ter) in RPGR, considered to be pathogenic. Segregation analysis precluded the variation in the mother and sister. A random pattern of X-chromosome inactivation was detected in the proband, without X-chromosome inactivation deviation.

CONCLUSION

This is the second report associating this specific RPGR mutation with high myopia and the first report to identify it in a female proband. This case provides additional evidence on the genotypic-phenotypic correlation between RPGR c.212C>G mutation and high myopia.

A pedigree with retinitis pigmentosa and its concomitant ophthalmic diseases

AIM

To characterize the ophthalmic clinical phenotype of a family with retinitis pigmentosa (RP) and closed-angle glaucoma and to detect pathogenic genes and mutation sites causing RP in this family.

METHODS

Ophthalmic clinic performance was examined in detail in 8 enrolled family members. Genomic DNA was extracted from the peripheral blood of 4 family members for whole-exome sequencing (WES) to select potential genetic mutations whose structures were identified by bioinformatics analysis. Then, Sanger sequencing was used in 12 family members and control group members to validate and confirm the disease-causing mutation loci, and we analyzed the genotype-phenotype relationships.

RESULTS

The known c.512C>T (p.P171L) mutation in the rhodopsin (RHO) gene was only found in afflicted family members and was confirmed by WES and Sanger sequencing as the pathogenic mutation in this family. In addition to being diagnosed with RP, family member III:4 was found to have bilateral closed-angle glaucoma, high myopia, and concurrent cataracts, and family members II:2 and II:4 had pathological changes of anterior chamber angle narrowing. Family members IV:3 and IV:4 were found to have retinoschisis.

CONCLUSION

Glaucoma and related pathological changes, such as retinoschisis, in family members are preliminarily considered RP complications caused by RHO mutation.

Genetic spectrum, retinal phenotype, and peripapillary RNFL thickness in RPGR heterozygotes

PURPOSE

Phenotypic heterogeneity with variable severity has been reported in female carriers of retinitis pigmentosa GTPase regulator (RPGR) mutations, including a male-type phenotype. A phenomenon not fully understood is peripapillary retinal nerve fiber layer (pRNFL) thickening in male patients with RPGR-associated X-linked retinitis pigmentosa, especially in the temporal sector. We aim to describe the genetic spectrum, retinal phenotypes, and pRNFL thickness in a cohort of Caucasian RPGR-mutation heterozygotes.

METHODS

A cross-sectional study was conducted at an inherited retinal degeneration (IRD) reference center in Portugal. Female patients heterozygous for clinically significant RPGR variants were identified using the IRD-PT registry. A complete ophthalmologic examination was performed, complemented by macular and peripapillary spectral domain optical coherence tomography (SD-OCT), ultra-widefield color fundus photography (UW-CFP), and ultra-widefield fundus autofluorescence (UW-FAF). The retinal phenotypes were graded according to previously described classifications. The pRNFL thickness across the superior, inferior, nasal, and temporal quadrants was compared to the Spectralis® RNFL age-adjusted reference database.

RESULTS

Forty-eight eyes from 24 females (10 families) were included in the study. Genetic analysis yielded 8 distinct clinically significant frameshift variants in RPGR gene, 3 of which herein reported for the first time. No association was found between mutation location and best-corrected visual acuity (BCVA) or retinal phenotype. Age was associated with worse BCVA and more advanced phenotypes on SD-OCT, UW-CFP, and UW-FAF. Seven women (29.17%) presented a male-type phenotype on UW-FAF in at least one eye. An association was found between UW-FAF and pRNFL thickness in the temporal sector (p = 0.003), with the most advanced fundus autofluorescence phenotypes showing increased pRNFL thickness in this sector.

CONCLUSION

This study expands the genetic landscape of RPGR-associated disease by reporting 3 novel clinically significant variants. We have shown that clinically severe phenotypes are not uncommon among female carriers. Furthermore, we provide novel insights into pRNFL changes observed in RPGR heterozygotes that mimic what has been reported in male patients.

Profiling of visual acuity and genotype correlations in RP2 patients: a cross-sectional comparative meta-analysis between carrier females and affected males

BACKGROUND

X-linked retinitis pigmentosa (XLRP) is the most severe form of retinitis pigmentosa (RP) and accounts for 15-20% of all RP cases. In this study, we investigated the progression of visual acuity loss across age groups in female carriers and compared it to affected males.

METHODS

A PubMed literature search was conducted, and RP2 cases were included based on specific inclusion criteria. Visual acuity (VA), refractive error spherical equivalent (SE), and retinal findings were recorded. Cross-sectional analyses investigated the relationship between VA and age in carrier females and affected males. Genotype-phenotype VA correlations were studied using t-tests.

RESULTS

35 carrier females and 28 affected males with confirmed RP2 mutations were collected from 13 studies. The mean age and logMAR VA of carrier females were 44.2 ± 17.4 years, and 0.5 ± 0.5, respectively. 78.8% of carrier females showed abnormal XLRP-related fundus findings and had significantly reduced VA compared to those with normal fundi (0.6 ± 0.5 vs. 0.1 ± 0.1; p = 0.03). Compared to affected males, no statistical correlation was found between logMAR VA and advancing age in carrier females (p = 0.75). Statistically significant linear correlations were found between logMAR VA and SE in each of carrier females (p = 0.01). There were no observed differences in logMAR VA based on mutation type (p = 0.97) or mutation location (p = 0.83). Anisometropia was observed in 38% of carrier females and 68% of affected males; these prevalence numbers are statistically significant between the two groups (1.7 ± 0.3 vs. 3.9 ± 10.9 dioptres; p = 0.03).

CONCLUSIONS

RP2 carrier females generally maintain good VA throughout their lifetime, as opposed to affected males, whose vision progressively declines. Our study provides important VA prognostic data that is crucial for patient counseling.

Next-Generation Sequencing Applications for Inherited Retinal Diseases

Inherited retinal diseases (IRDs) represent a collection of phenotypically and genetically diverse conditions. IRDs phenotype(s) can be isolated to the eye or can involve multiple tissues. These conditions are associated with diverse forms of inheritance, and variants within the same gene often can be associated with multiple distinct phenotypes. Such aspects of the IRDs highlight the difficulty met when establishing a genetic diagnosis in patients. Here we provide an overview of cutting-edge next-generation sequencing techniques and strategies currently in use to maximise the effectivity of IRD gene screening. These techniques have helped researchers globally to find elusive causes of IRDs, including copy number variants, structural variants, new IRD genes and deep intronic variants, among others. Resolving a genetic diagnosis with thorough testing enables a more accurate diagnosis and more informed prognosis and should also provide information on inheritance patterns which may be of particular interest to patients of a child-bearing age. Given that IRDs are heritable conditions, genetic counselling may be offered to help inform family planning, carrier testing and prenatal screening. Additionally, a verified genetic diagnosis may enable access to appropriate clinical trials or approved medications that may be available for the condition.