Pathology of hereditary retinal degeneration associated with hypobetalipoproteinemia

Autosomal Dominant Gyrate Atrophy-Like Choroidal Dystrophy Revisited: 45 Years Follow-Up and Association with a Novel C1QTNF5 Missense Variant

We present a long-term follow-up in autosomal dominant gyrate atrophy-like choroidal dystrophy (adGALCD) and propose a possible genotype/phenotype correlation. Ophthalmic examination of six patients from two families revealed confluent areas of choroidal atrophy resembling gyrate atrophy, starting in the second decade of life. Progression continued centrally, reaching the fovea at about 60 years of age. Subretinal deposits, retinal pigmentation or choroidal neovascularization as seen in late-onset retinal degeneration (LORD) were not observed. Whole genome sequencing revealed a novel missense variant in the C1QTNF5 gene (p.(Q180E)) which was found in heterozygous state in all affected subjects. Haplotype analysis showed that this variant found in both families is identical by descent. Three-dimensional modeling of the possible supramolecular assemblies of C1QTNF5 revealed that the p.(Q180E) variant led to the destabilization of protein tertiary and quaternary structures, affecting both the stability of the single protomer and the entire globular head, thus exerting detrimental effects on the formation of C1QTNF5 trimeric globular domains and their interaction. In conclusion, we propose that the p.(Q180E) variant causes a specific phenotype, adGALCD, that differs in multiple clinical aspects from LORD. Disruption of optimal cell-adhesion mechanisms is expected when analyzing the effects of the point mutation at the protein level.

Quantifying microstructural changes in retinitis pigmentosa using spectral domain - optical coherence tomography

Background

Most patients of established retinitis pigmentosa (RP) have subnormal peripheral vision and heavily rely on central vision for their daily activities. Central visual acuity is dependent on photoreceptor survival at the macula. Identification of structural changes that precede visual loss is essential. The aim of this study was to correlate the Spectral Domain-Optical Coherence Tomography (SD-OCT) characteristics with visual acuity in patients with typical RP.

Methods

This was a retrospective, observational case series of 224 eyes of 113 RP patients conducted a tertiary eye care center. SD-OCT imaging was done for all eyes. Central retinal thickness (CRT), photoreceptor outer segment length (PROS), foveal outer segment pigment epithelial thickness (FOSPET) and ellipsoid zone (EZ) extent were measured. A new variable, FOSPET-PROS ratio (FPR), obtained by dividing FOSPET by PROS is defined and correlated to corrected distance visual acuity (CDVA) in logMAR using linear regression.

Results

Out of 113 patients, 71 were males and 42 females. Mean age of the patients was 35.4 ± 15.1 years. Mean CDVA was 0.33 ± 0.25 logMAR with no difference between the genders. Mean CRT (218.74 ± 83.5 μm) and FPR (1.63 ± 0.22) significantly correlated to CDVA with a correlation coefficient of r = − 0.139 (p = 0.048) and r = 0.842 (p = 0.0001), respectively. FOSPET (mean = 71.15 ± 13.8 μm) and PROS (mean = 44.85 ± 12.5 μm) did not show a significant correlation to CDVA, independent of FPR.

Conclusions

Retinal microstructural changes on SD-OCT, especially the FPR, can be used as a surrogate marker to monitor disease progression in the central retina in degenerative diseases like RP.

An in silico model of retinal cholesterol dynamics (RCD model): insights into the pathophysiology of dry AMD

We developed an in silico mathematical model of retinal cholesterol (Ch) dynamics (RCD) to quantify the physiological rate of Ch turnover in the rod outer segment (ROS), the lipoprotein transport mechanisms by which Ch enters and leaves the outer retina, and the rates of drusen growth and macrophage-mediated clearance in dry age-related macular degeneration. Based on existing experimental data and mechanistic hypotheses, we estimated the Ch turnover rate in the ROS to be 1–6 pg/mm²/min, dependent on the rate of Ch recycling in the outer retina, and found comparable rates for LDL receptor-mediated endocytosis of Ch by the retinal pigment epithelium (RPE), ABCA1-mediated Ch transport from the RPE to the outer retina, ABCA1-mediated Ch efflux from the RPE to the choroid, and the secretion of 70 nm ApoB-Ch particles from the RPE. The drusen growth rate is predicted to increase from 0.7 to 4.2 μm/year in proportion to the flux of ApoB-Ch particles. The rapid regression of drusen may be explained by macrophage-mediated clearance if the macrophage density reaches ∼3,500 cells/mm². The RCD model quantifies retinal Ch dynamics and suggests that retinal Ch turnover and recycling, ApoB-Ch particle efflux, and macrophage-mediated clearance may explain the dynamics of drusen growth and regression.

Choroidal neovascularization in Bardet-Biedl syndrome

PURPOSE

To describe a case of choroidal neovascularization in a young patient with genetically-proven Bardet-Biedl syndrome.

METHODS

Case description with fundus and anatomical photography and optical coherence tomography.

PATIENTS

Single patient case description.

RESULTS

Fundus photography and optical coherence tomography reveal the presence of previously-active choroidal neovascularization. Anatomical, historical, and genetic evidence confirm Bardet-Biedl syndrome in this individual.

DISCUSSION

Choroidal neovascularization accompanying this syndrome has not been reported. Herein we describe the first published description of choroidal neovascularization in an individual with genetically-proven Bardet-Biedl syndrome.

A CTRP5 gene S163R mutation knock-in mouse model for late-onset retinal degeneration

Late-onset retinal macular degeneration (L-ORD) is an autosomal dominant inherited disorder caused by a single missense mutation (S163R) in the CTRP5/C1QTNF5 protein. Early phenotypic features of L-ORD include: dark adaptation abnormalities, nyctalopia, and drusen deposits in the peripheral macular region. Apart from posterior segment abnormalities, these patients also develop abnormally long anterior lens zonules. In the sixth decade of life the rod and cone function declines, accompanied by electroretinogram (ERG) abnormalities. Some patients also develop choroidal neovascularization and glaucoma. In order to understand the disease pathology and mechanisms involved in retinal dystrophy, we generated a knock-in (Ctrp5(+/-)) mouse model carrying the disease-associated mutation in the mouse Ctrp5/C1QTNF5 gene. These mice develop slower rod-b wave recovery consistent with early dark adaptation abnormalities, accumulation of hyperautofluorescence spots, retinal pigment epithelium abnormalities, drusen, Bruch's membrane abnormalities, loss of photoreceptors, and retinal vascular leakage. The Ctrp5(+/-) mice, which have most of the pathological features of age-related macular degeneration, are unique and may serve as a valuable model both to understand the molecular pathology of late-onset retinal degeneration and to evaluate therapies.

Apolipoprotein B-containing lipoproteins in retinal aging and age-related macular degeneration

The largest risk factor for age-related macular degeneration (ARMD) is advanced age. With aging, there is a striking accumulation of neutral lipids in Bruch's membrane (BrM) of normal eye that continues through adulthood. This accumulation has the potential to significantly impact the physiology of the retinal pigment epithelium (RPE). It also ultimately leads to the creation of a lipid wall at the same locations where drusen and basal linear deposit, the pathognomonic extracellular, lipid-containing lesions of ARMD, subsequently form. Here, we summarize evidence obtained from light microscopy, ultrastructural studies, lipid histochemistry, assay of isolated lipoproteins, and gene expression analysis. These studies suggest that lipid deposition in BrM is at least partially due to accumulation of esterified cholesterol-rich, apolipoprotein B-containing lipoprotein particles produced by the RPE. Furthermore, we suggest that the formation of ARMD lesions and their aftermath may be a pathological response to the retention of a sub-endothelial apolipoprotein B lipoprotein, similar to a widely accepted model of atherosclerotic coronary artery disease (Tabas, I., K. J. Williams, and J. Borén. 2007. Subendothelial lipoprotein retention as the initiating process in atherosclerosis: update and therapeutic implications. Circulation. 116:1832-1844). This view provides a conceptual basis for the development of novel treatments that may benefit ARMD patients in the future.

Late-onset retinal macular degeneration: clinical insights into an inherited retinal degeneration

AIM

This study describes, in detail, the phenotype of late-onset retinal macular degeneration (L-ORMD) an inherited condition affecting both the retina and anterior segment. A staging based on clinical characteristics is proposed, and the relevance of this condition to current understanding of age-related macular degeneration is discussed.

METHODS

A systematic review of the literature regarding this condition supports a detailed description of the natural history. Clinical experiences in identifying, monitoring and managing patients are also presented.

RESULTS

L-ORMD is a rare fully penetrant autosomal dominant condition resulting from a mutation in the C1QTNF5 gene on chromosome 11. Affected individuals develop bilateral loss of vision, dark-adaptation abnormalities, fundus drusen-like yellow spots, midperipheral pigmentation, choroidal neovascularisation, chorioretinal atrophy and long anteriorly inserted lens zonules. Patients may benefit from treatment with high-dose vitamin A.

CONCLUSIONS

Raised awareness of L-ORMD should lead to earlier diagnosis and improved care for patients. New antivascular endothelial growth factor treatment may provide a new possibility for management. A deeper insight into molecular and genetic mechanisms of L-ORMD may suggest avenues to explore new treatments of this disorder.

Retinal morphology in patients with BBS1 and BBS10 related Bardet-Biedl Syndrome evaluated by Fourier-domain optical coherence tomography

Retinal dystrophy in Bardet-Biedl Syndrome (BBS) is caused by defective genes that are expressed within ciliated cells such as photoreceptors. The purpose of this study was to characterize and compare the retinal structure and lamination of two groups of patients, carrying mutations in BBS1 or BBS10. Eight patients with BBS (ages 11.9-28.5 years) and mutations in BBS1 (4/8) or BBS10 (4/8) were tested. A high-resolution hand-held probe Fourier-domain optical coherence tomography system (Fd-OCT) was used for retinal image acquisition. Macular scans were evaluated with respect to structure, retinal layering and photoreceptor integrity. Micro-structural in-vivo analysis showed abnormalities within retinal layers but preserved retinal lamination. Photoreceptor integrity was disrupted in all patients. Macular scans from patients with BBS10 mutations most often showed 'deposits' adjacent and anterior to Bruch's membrane. Age, genotype and presence of macular changes did not correlate with the structural changes observed. Retinal dystrophy in BBS is reflected by major changes in the outer retinal layers. This is the first report of in-vivo micro-structural analysis of retinal layers in patients with BBS. Mutations in different BBS genes seem to be associated with similar micro-structural changes in retinal layers.

Histopathologic-genotypic correlations in retinitis pigmentosa and allied diseases

This paper reviews the published histopathologic findings of patients with retinitis pigmentosa (RP) or an allied disease in whom the responsible gene defect was identified, including 10 cases with dominant RP (cases with mutations in RHO, PRPC8, and RP1), three with dominant spinocerebellar ataxia (SCA7), three X-linked RP carrier females (RPGR), two with congenital retinal blindness (AIPL1 and RPE65), two with mitochondrial encephalomyopathy overlap syndrome (MTTL1), and one case each with dominant cone degeneration (GCAP1), X-linked cone degeneration (RCP), enhanced S-cone syndrome (NR2E3), and dominant late-onset retinal degeneration (CTRP5). No histopathologic descriptions were found of the vast majority of genetically defined forms of retinal degeneration.

Differential gene expression in anatomical compartments of the human eye

DNA microarrays (representing approximately 30,000 human genes) were used to analyze gene expression in six different human eye compartments, revealing candidate genes for diseases affecting the cornea, lens and retina.

Background

The human eye is composed of multiple compartments, diverse in form, function, and embryologic origin, that work in concert to provide us with our sense of sight. We set out to systematically characterize the global gene expression patterns that specify the distinctive characteristics of the various eye compartments.

Results

We used DNA microarrays representing approximately 30,000 human genes to analyze gene expression in the cornea, lens, iris, ciliary body, retina, and optic nerve. The distinctive patterns of expression in each compartment could be interpreted in relation to the physiology and cellular composition of each tissue. Notably, the sets of genes selectively expressed in the retina and in the lens were particularly large and diverse. Genes with roles in immune defense, particularly complement components, were expressed at especially high levels in the anterior segment tissues. We also found consistent differences between the gene expression patterns of the macula and peripheral retina, paralleling the differences in cell layer densities between these regions. Based on the hypothesis that genes responsible for diseases that affect a particular eye compartment are likely to be selectively expressed in that compartment, we compared our gene expression signatures with genetic mapping studies to identify candidate genes for diseases affecting the cornea, lens, and retina.

Conclusion

Through genome-scale gene expression profiling, we were able to discover distinct gene expression 'signatures' for each eye compartment and identified candidate disease genes that can serve as a reference database for investigating the physiology and pathophysiology of the eye.

Mutation in a short-chain collagen gene, CTRP5, results in extracellular deposit formation in late-onset retinal degeneration: a genetic model for age-related macular degeneration

A primary feature of age-related macular degeneration (AMD) is the presence of extracellular deposits between the retinal pigment epithelium (RPE) and underlying Bruch's membrane, leading to RPE dysfunction, photoreceptor death and severe visual loss. AMD accounts for about 50% of blind registrations in Western countries and is a common, genetically complex disorder. Very little is known regarding its molecular basis. Late-onset retinal degeneration (L-ORD) is an autosomal dominant disorder with striking clinical and pathological similarity to AMD. Here we show that L-ORD is genetically heterogeneous and that a proposed founder mutation in the CTRP5 (C1QTNF5) gene, which encodes a novel short-chain collagen, changes a highly conserved serine to arginine (Ser163Arg) in 7/14 L-ORD families and 0/1000 control individuals. The mutation occurs in the gC1q domain of CTRP5 and results in abnormal high molecular weight aggregate formation which may alter its higher-order structure and interactions. These results indicate a novel disease mechanism involving abnormal adhesion between RPE and Bruch's membrane.

Activated microglia in human retinitis pigmentosa, late-onset retinal degeneration, and age-related macular degeneration

Many gaps exist in our knowledge of human retinal microglia in health and disease. We address the hypothesis that primary death of rod photoreceptors leads to activation of resident microglia in human retinas with retinitis pigmentosa (RP), late-onset retinal degeneration (L-ORD), or age-related macular degeneration (AMD). Regions of ongoing photoreceptor cell death were studied by immunocytochemistry with microglia- and other retinal cell-specific markers. In normal human retinas, quiescent microglia were small, stellate cells associated with inner retinal blood vessels. In retinas with RP, L-ORD, or AMD, numerous activated microglia were present in the outer nuclear layer in regions of ongoing rod cell death. These microglia were enlarged, amoeboid cells that contained rhodopsin-positive cytoplasmic inclusions. We conclude that activated microglia migrate to the outer nuclear layer and remove rod cell debris. In other central nervous system diseases such as stroke, activated microglia phagocytose debris from the primary injury and also secrete molecules that kill nearby normal neurons. By analogy with these diseases, we suggest that microglia activated by primary rod cell death may kill adjacent photoreceptors. Activated microglia may be a missing link in understanding why initial rod cell death in the human diseases RP, L-ORD, and AMD leads to death of the cones that are critical for high acuity daytime vision.

Dominant late-onset retinal degeneration with regional variation of sub-retinal pigment epithelium deposits, retinal function, and photoreceptor degeneration

PURPOSE

To clarify the pathogenesis of late-onset retinal degeneration (L-ORD), an autosomal dominant disorder characterized by thick deposits of lipid-rich material between the retinal pigment epithelium (RPE) and Bruch's membrane.

STUDY DESIGN

Comparative clinicopathologic case report and case series. TISSUES: Eyes of an 82-year-old L-ORD eye donor and an age-matched control.

SUBJECTS

Five descendants of the eye donor and his affected sister.

METHODS

The eyes were processed for histopathologic examination, including electron microscopy and immunohistochemistry. Family members were examined clinically and with retinal function tests.

RESULTS

The L-ORD eye had sub-RPE deposits that were positive for lipid, including esterified and unesterified cholesterol. The deposits were thinnest in the macula, which retained the highest percentage of photoreceptors. In the periphery, RPE thinning and photoreceptor loss correlated with thickness of the sub-RPE deposits. The eye donor was asymptomatic until his late 50s, when he developed problems with adapting to darkness. At age 68, the eye donor had normal acuity but a midperipheral scotoma and subnormal electroretinograms (ERGs); visual loss was progressive. The five descendants (at the time of examination ages 44-58) of the eye donor and his affected sister, who were at 50/50 risk of inheriting L-ORD, had normal ERGs, but four showed defects in dark adaptation. The dark adaptation abnormalities had a distribution similar to the thickness of the sub-RPE deposits in the eye donor, with slow kinetics in the midperiphery and normal kinetics centrally.

CONCLUSIONS

The L-ORD donor eye differed from a previous case in the regional distribution of sub-RPE deposits and photoreceptors. In the next generation of this L-ORD family, the first expression of disease, abnormal dark adaptation, mirrored the regional distribution of the deposits in the donor eye. The fine structure and staining characteristics of the sub-RPE deposits in L-ORD resemble those in age-related macular degeneration and Sorsby fundus dystrophy.

Diffuse fatty liver in familial heterozygous hypobetalipoproteinemia

A 34-year-old man had asymptomatic hepatomegaly, slightly increased serum alanine aminotransferase and gamma-glutamyl transpeptidase levels, and a sonographic pattern suggesting diffuse hepatic steatosis. Liver biopsy revealed fatty change in 25% to 50% of hepatocytes. The patient also had low serum levels of cholesterol and triglycerides and met clinical, biochemical, and familial diagnostic criteria of heterozygous hypobetalipoproteinemia. We could not relate his hepatic steatosis to any already known cause of fatty liver and could only attribute it to heterozygous hypobetalipoproteinemia. Familial heterozygous hypobetalipoproteinemia should be ruled out in patients with unexplained hepatic steatosis.