Carriers of X-linked recessive retinitis pigmentosa: investigation by vitreous fluorophotometry

The double-edged sword of inflammation in inherited retinal degenerations: Clinical and preclinical evidence for mechanistically and prognostically impactful but treatable complications

We present retrospective data from our clinical research efforts of the past several years alongside a review of past and current clinical and preclinical data independently by several investigators supporting our clinical evidence for the importance of inflammation in inherited retinal degenerations (IRDs). We show how inflammation is a complicating factor in IRDs but, if recognized and managed, also a great opportunity to mitigate disease severity immediately, improve patient prognosis and quality of life, extend the treatment windows for gene-specific and agnostic therapeutic approaches, mitigate the impact of inflammatory complications on the accurate estimate of vision changes in IRD natural history studies, improve the chances of safer outcomes following cataract surgery, and potentially reduce the likelihood of inflammatory adverse events and augment the efficacy of viral vector-based treatment approaches to IRDs. Manuscript contribution to the field. Inflammation has been suspected to be at play in IRDs since the beginning of the 1900s and became a research focus through the early 1990s but was then largely abandoned in favor of genetic-focused research. Thanks to regained cognizance, better research tools, and a more holistic approach to IRDs, the recent reappraisal of the role of inflammation in IRDs has brought back to the surface its importance. A potential confounder in natural history studies and a limiting factor in clinical trials if not accounted for, inflammation can be managed and often offers an opportunity for immediately improved prognosis and outcomes for IRD patients. We present our retrospective clinical evidence for connections with a measurable secondary autoimmune component that can develop in IRDs and contribute to vision loss but is at least in part treatable. We also present ample lines of evidence from the literature corroborating our clinical observations at the preclinical level.

Cellular imaging demonstrates genetic mosaicism in heterozygous carriers of an X-linked ciliopathy gene

X-linked retinitis pigmentosa (XLRP) is the least common genetic type of retinitis pigmentosa; however, it has extremely devastating consequences to patients' activities of daily living. RPGR and RP2 genes expressed in the photoreceptor sensory cilia are predominantly implicated in XLRP; however, the interpretation of genetic mutations and their correlation with clinical phenotypes remain unknown, and the role of these genes in photoreceptor cilia function is not completely elucidated. Therefore, we evaluated structural characteristics in five female obligate carriers of XLRP by using state-of-the-art non-invasive imaging methods, including adaptive optics (AO) scanning laser ophthalmoscopy (SLO). In all five carriers examined, qualitative and quantitative analyses by AO SLO imaging revealed a mosaic pattern of cone disruption, even in the absence of visual symptoms, normal visual acuity and normal macular thickness, on optical coherence tomography and mildly subnormal full-field cone electroretinographic findings. As the technique is sensitive to the level of a single cone, the ability to visualize the cone cells in vivo should be especially useful in other retinal diseases. In addition, further investigation of XLRP carriers may yield insight into how cone structures change over time and ultimately enable understanding of the role of RPGR and RP2 in cone cell survival.

Fundus changes in mesangiocapillary glomerulonephritis type II: vitreous fluorophotometry

We have described a complex abnormality of retinal pigment epithelium, Bruch's membrane, and choriocapillaris in mesangiocapillary glomerulonephritis (MCGN) type II. Patients with MCGN type II were examined by vitreous fluorophotometry which reveals that there is a breakdown of the blood retinal barrier (BRB) in those patients with the typical fundus lesions. The function of this barrier was calculated as a penetration ratio and was statistically greater in these patients when compared with a group of (a) normal persons, (b) patients with drusen, and (c) patients with other forms of glomerulonephritis.

Retinitis pigmentosa

Retinitis pigmentosa is a clinically and genetically heterogeneous group of hereditary disorders in which there is progressive loss of photoreceptor and pigment epithelial function. The prevalence of retinitis pigmentosa is between 1/3000 and 1/5000 making it one of the most common causes of visual impairment in all age groups. The natural history, differential diagnosis, diagnostic clinical and electrophysiologic findings are reviewed. Generalization about the different genetic subtypes of retinitis pigmentosa are reviewed along with the uses of DNA probes for linkage studies. Syndromes in which retinitis pigmentosa is a manifestation are summarized.

Carriers of X-linked retinitis pigmentosa. A fluorophotometric determination of the permeability of the blood-retinal barrier

The blood-retinal barrier permeability to fluorescein was studied in a single family with X-linked retinitis pigmentosa by an elaborate vitreous fluorophotometric method. Affected males showed a ten times increase of permeability compared with normals. In a group of seven obligate carriers the mean permeability was significantly increased by 45% compared with the mean permeability in a group of normals. Five of the seven carriers had permeabilities higher than the normal mean permeability + 2 SD, while two carriers had a permeability within the normal mean +/- 2 SD. Thus, this study supported that carriers of X-linked retinitis pigmentosa show deterioration of the blood-retinal barrier. However, the phenomenon is not present in all carriers and the permeability cannot be used as a completely safe indicator of the carrier state.

Clinical patterns and electrophysiological findings in retinal pigment epithelium diseases. Does a correlation exist?

At present it is difficult to distinguish those human chorioretinal diseases in which the retinal pigment epithelium (RPE) is the primary site of dysfunction. This difficulty is caused by several factors such as scarcity of biochemical and histological information and a lack of correlation of basic science information available with the clinical body of knowledge. In the present study we examined 134 eyes at early or late stages of hereditary diseases involving the RPE. We tried to distinguish primary RPE involvement by using standard ERG (a- and b-wave) and EOG testing. We conclude that in general primary RPE damage can be better assessed by current electrophysiology in those diseases which seem to remain localized at the RPE level for a long time.

Retinal histopathology of a carrier of X-chromosome-linked retinitis pigmentosa

Autopsy eyes were examined from a 79-year-old female carrier of X-chromosome-linked retinitis pigmentosa. At age 78 years, she had no visual symptoms but had intraretinal bone spicule pigmentation in the nasal and inferior periphery of both eyes. Rods, cones, and pigment epithelium in the central retina appeared normal. In the midperiphery, patches with advanced photoreceptor cell degeneration were observed overlying pigment epithelium containing melanolysosomes. Within these patches, rods and cones were reduced in number or absent, and pigment epithelial cells abutted the external limiting membrane. A precipitous decline in rod nuclei was observed in transitional zones between areas of apparently normal photoreceptors and areas of absent photoreceptors. In the far periphery, large areas lacked photoreceptors and pigment epithelium. Histopathologic findings in this elderly carrier are compared with those previously described in a 24-year-old man with X-chromosome-linked retinitis pigmentosa.