Pseudoxanthoma elasticum: a clinical, histopathological, and molecular update

Atypical angioid streaks in a patient with a monoallelic ABCC6 mutation

BACKGROUND

Pseudoxanthoma elasticum (PXE) is characterized by aberrant calcification of elastic tissues throughout the body causing varying degrees of skin, cardiac, and ocular disease. Although PXE is classically regarded as an autosomal recessive disease, recent reports have demonstrated a haploinsufficiency phenotype, in which carriers of monoallelic ATP-binding cassette transporter (ABCC6) gene mutations demonstrate mild manifestations of PXE. In this case report, we describe a patient with a monoallelic ABCC6 mutation and atypical angioid streaks.

MATERIALS AND METHODS

Case report.

OBSERVATIONS

A 31-year-old male with a history of paroxysmal tachycardia and right ventricular enlargement presented to the Eye Emergency Department complaining of bilateral eye pain with occasional flashes and bitemporal headaches. Family history was notable for unspecified heart disease in his father but no ocular disease. Best-corrected visual acuity was 20/20 in both eyes. Posterior segment examination demonstrated linear hypopigmented lesions radiating from the superior arcades of both eyes. Fundus autofluorescence of the lesions demonstrated speckled hypo- and hyperautofluorescence and fluorescein angiography revealed window defects consistent with atypical angioid streaks. Genetic testing was positive for a heterozygous c.2889C>A (p.Cys963*) mutation in the ABCC6 gene.

CONCLUSIONS AND IMPORTANCE

The current case demonstrates the potential for PXE carriers to display both systemic and ophthalmic manifestations of the disease. Individuals with known or suspected monoallelic ABCC6 mutations may benefit from genetic counseling and regular examination.

The utility of the normal thin section skin biopsy in the assessment of systemic/extracutaneous disease and small fiber neuropathy

Diseases reflective of multiorgan vascular injury of diverse etiology, peripheral nerve disease, dysautonomia syndromes, and intravascular lymphoma may exhibit abnormalities on a normal skin biopsy that may be instrumental in establishing a diagnosis. A retrospective review of our database was conducted to uncover cases where a normal skin biopsy was performed to rule in or out such systemic diseases as complement-driven thrombotic microvascular disease (including atypical hemolytic uremic syndrome, posttransplant thrombotic microangiopathy, and severe or critical COVID-19), systemic capillary leak syndrome, cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) intravascular B cell lymphoma, small fiber neuropathy, dysautonomia syndromes, and mast cell activation syndrome. Among the special studies were immunohistochemical staining to detect C5b-9, CD56, and myxovirus resistance protein A, as well as mast cell, B and T cell markers. Characteristic patterns were critical in establishing diagnoses such as : increased C5b-9 microvascular deposition in the deltoid area (atypical hemolytic uremic syndrome, posttransplant thrombotic microangiopathy, catastrophic antiphospholipid antibody syndrome, and severe or critical COVID-19); enhanced type I interferon signaling (systemic capillary leak syndrome); ultrastructural arteriopathic changes (CADASIL); reduced cutaneous autonomic innervation in the lower extremities (small fiber neuropathy and postural orthostatic tachycardia syndrome); presence of intravascular lymphocytes on biopsy of abdominal, thigh, and buttock skin (intravascular B cell lymphoma); and a higher than normal density of mast cells in the absence of other inflammatory cell types (mast cell activation syndrome). The skin is clearly a critical window for understanding extracutaneous disease, a concept well exemplified by the myriad of diseases suggested by the microscopic and/or ultrastructural examination of clinically normal skin and therefore establishing the normal skin biopsy as an important tool for understanding certain extracutaneous reactive, neoplastic and paraneoplastic syndromes as well as small fiber neuropathy.

Pseudoxanthoma elasticum - Genetics, pathophysiology, and clinical presentation

Pseudoxanthoma elasticum (PXE) is an autosomal-recessively inherited multisystem disease. Mutations in the ABCC6-gene are causative, coding for a transmembrane transporter mainly expressed in hepatocytes, which promotes the efflux of adenosine triphosphate (ATP). This results in low levels of plasma inorganic pyrophosphate (PPi), a critical anti-mineralization factor. The clinical phenotype of PXE is characterized by the effects of elastic fiber calcification in the skin, the cardiovascular system, and the eyes. In the eyes, calcification of Bruch's membrane results in clinically visible lesions, including peau d'orange, angioid streaks, and comet tail lesions. Frequently, patients must be treated for secondary macular neovascularization. No effective therapy is available for treating the cause of PXE, but several promising approaches are emerging. Finding appropriate outcome measures remains a significant challenge for clinical trials in this slowly progressive disease. This review article provides an in-depth summary of the current understanding of PXE and its multi-systemic manifestations. The article offers a detailed overview of the ocular manifestations, including their morphological and functional consequences, as well as potential complications. Lastly, previous and future clinical trials of causative treatments for PXE are discussed.

Anti-VEGF Treatment for Secondary Neovascularization in Pseudoxanthoma Elasticum - Age of Onset, Treatment Frequency, and Visual Outcome

PURPOSE

To assess the onset, treatment frequency, and visual outcome of anti-vascular endothelial growth factor (anti-VEGF) treatment due to secondary choroidal neovascularization (CNV) in patients with pseudoxanthoma elasticum (PXE).

DESIGN

Retrospective cohort study METHODS: One-hundred six eyes of 53 patients with PXE were analyzed. The assessment of CNV activity relied on hemorrhage visible on funduscopy and intra- / subretinal fluid on optical coherence tomography (OCT), individually defining a shortening or extension of treatment interval. Best-corrected visual acuity (BCVA) at baseline, age at anti-VEGF therapy initiation, and BCVA-drop events at exudation onset (worsening of BCVA of 2 or more lines) were documented. Further, we assessed the number of injections during the first year and the total number of injections, the time to treatment initiation of the fellow eye, and BCVA over time.

RESULTS

During a median observation period of 77 months (IQR 49; 126) patients received a median number of 28.0 anti-VEGF-injections (IQR 9.8; 43.5). Eight patients received no injection (median age at baseline 38.1 years), 11 patients underwent anti-VEGF treatment in one eye (median age 47.2 years) and 34 patients in both eyes (median age 51.8 years). The median age at the first anti-VEGF treatment was 52.80 years (IQR 47.2-57.6). Applying Cox regression models, the median "survival" time of fellow eye until treatment initiation was 16.8 months. In the group of bilateral treated patients, the median time difference was 9.6 months (IQR 2.1- 32.4, range 0-122) The median number of injections was 5.5 per eye in the first year of treatment (IQR 3-7) and was associated with the total number of injections in the observation period (2.33, CI 1.22-3.44, P < .001). A better BCVA at the last follow-up visit was associated with a better baseline BCVA (P < .001, R2 = 0.318) and with the absence of a BCVA drop at the onset of exudation (P = 0.035, R2 = 0.339).

CONCLUSIONS

The results of this study indicate that anti-VEGF treatment is required for most PXE patients at a relatively young age. Once treatment in one eye is initiated, the time to fellow eye treatment is relatively short. A BCVA drop before treatment initiation is a risk factor for worse visual outcomes, suggesting that treatment is prudent before exudation affects the central retina. Given the young age of onset and intensive treatment needs, patients with PXE might particularly benefit from longer-acting anti-VEGF therapeutics.

The Activation of JAK/STAT3 Signaling and the Complement System Modulate Inflammation in the Primary Human Dermal Fibroblasts of PXE Patients

Previous studies revealed a link between inflammation and overactivation of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling in syndromes associated with aging. Pseudoxanthoma elasticum (PXE), a rare autosomal-recessive disorder, arises from mutations in ATP-binding cassette subfamily C member 6 (ABCC6). On a molecular level, PXE shares similarities with Hutchinson-Gilford progeria syndrome, such as increased activity of senescence-associated- beta-galactosidase or high expression of inflammatory factors. Thus, this study's aim was the evaluation of activated STAT3 and the influence of JAK1/2-inhibitor baricitinib (BA) on inflammatory processes such as the complement system in PXE. Analysis of activation of STAT3 was performed by immunofluorescence and Western blot, while inflammatory processes and complement system factors were determined based on mRNA expression and protein level. Our results assume overactivation of JAK/STAT3 signaling, increased expression levels of several complement factors and high C3 protein concentration in the sera of PXE patients. Supplementation with BA reduces JAK/STAT3 activation and partly reduces inflammation as well as the gene expression of complement factors belonging to the C1 complex and C3 convertase in PXE fibroblasts. Our results indicate a link between JAK/STAT3 signaling and complement activation contributing to the proinflammatory phenotype in PXE fibroblasts.

Matrix Metalloproteinases Contribute to the Calcification Phenotype in Pseudoxanthoma Elasticum

Ectopic calcification and dysregulated extracellular matrix remodeling are prominent hallmarks of the complex heterogenous pathobiochemistry of pseudoxanthoma elasticum (PXE). The disease arises from mutations in ABCC6, an ATP-binding cassette transporter expressed predominantly in the liver. Neither its substrate nor the mechanisms by which it contributes to PXE are completely understood. The fibroblasts isolated from PXE patients and Abcc6-/- mice were subjected to RNA sequencing. A group of matrix metalloproteinases (MMPs) clustering on human chromosome 11q21-23, respectively, murine chromosome 9, was found to be overexpressed. A real-time quantitative polymerase chain reaction, enzyme-linked immunosorbent assay and immunofluorescent staining confirmed these findings. The induction of calcification by CaCl2 resulted in the elevated expression of selected MMPs. On this basis, the influence of the MMP inhibitor Marimastat (BB-2516) on calcification was assessed. PXE fibroblasts (PXEFs) exhibited a pro-calcification phenotype basally. PXEF and normal human dermal fibroblasts responded with calcium deposit accumulation and the induced expression of osteopontin to the addition of Marimastat to the calcifying medium. The raised MMP expression in PXEFs and during cultivation with calcium indicates a correlation of ECM remodeling and ectopic calcification in PXE pathobiochemistry. We assume that MMPs make elastic fibers accessible to controlled, potentially osteopontin-dependent calcium deposition under calcifying conditions.

Choriocapillaris Flow Signal Impairment in Patients With Pseudoxanthoma Elasticum

Purpose

To quantify choriocapillaris flow alterations in patients with pseudoxanthoma elasticum (PXE) in pre-atrophic stages and its association with structural changes of the choroid and outer retina.

Methods

Thirty-two eyes of 21 patients with PXE and 35 healthy eyes of 35 controls were included. The density of choriocapillaris flow signal deficits (FDs) was quantified on 6 × 6-mm optical coherence tomography angiography (OCTA) images. Spectral-domain optical coherence tomography (SD-OCT) images were analyzed for thicknesses of the choroid and outer retinal microstructure and correlated with choriocapillaris FDs in the respective Early Treatment Diabetic Retinopathy Study subfield.

Results

The multivariable mixed model analysis for choriocapillaris FDs revealed significantly higher FDs associated with the group (PXE patients vs. controls +13.6; 95% confidence interval [CI] 9.87-17.3; P < 0.001), with increasing age (+0.22% per year; 95% CI 0.12-0.33; P < 0.001), and with retinal location (significantly higher FDs in nasal compared to temporal subfields). Choroidal thickness (CT) did not differ significantly between both groups (P = 0.078). The CT and choriocapillaris FDs were inversely correlated (-1.92 µm per %FDs; interquartile range -2.81 to -1.03; P < 0.001). Larger values of the choriocapillaris FDs were associated with significant thinning of the overlying photoreceptor layers (outer segments: -0.21 µm per %FDs, P < 0.001; inner segments: -0.12 µm per %FDs, P = 0.001; outer nuclear layer: -0.72 µm per %FDs; P < 0.001).

Conclusions

Patients with PXE display significant alterations of the choriocapillaris on OCTA even in pre-atrophic stages and in the absence of significant choroidal thinning. The analysis favors choriocapillaris FDs over choroidal thickness as a potential early outcome measure for future interventional trials in PXE. Further, increased FDs in nasal compared to temporal locations mirror the centrifugal spread of Bruch's membrane calcification in PXE.

Refractory Choroidal Neovascularization in a Patient With Pseudoxanthoma Elasticum and Cowden Syndrome

Purpose

To describe a patient with concurrent pseudoxanthoma elasticum (PXE) and Cowden syndrome who developed choroidal neovascularization (CNV) secondary to angioid streaks. The CNV presented at a young age and was relatively refractory to intravitreal antivascular endothelial growth factor (anti-VEGF) therapy.

Methods

A retrospective chart review was performed.

Results

A 32-year-old man was treated for bilateral sequential CNV over 11 years. Good visual acuity was maintained with 53 anti-VEGF injections in the right eye and 82 injections in the left eye. On average, 1 injection was administered every 1.7 months in each eye to control the exudation. A skin biopsy and genetic testing confirmed a diagnosis of PXE. He was also found to harbor a PTEN mutation consistent with Cowden syndrome.

Conclusions

The concurrent PTEN mutation lends a possible explanation for the relative resistance of CNV to anti-VEGF therapy in this patient with PXE. Phosphatase and tensin homolog is a tumor suppressor that negatively regulates the VEGF pathway.

Targeting ABCC6 in Mesenchymal Stem Cells: Impairment of Mature Adipocyte Lipid Homeostasis

Mutations in ABCC6, an ATP-binding cassette transporter with a so far unknown substrate mainly expressed in the liver and kidney, cause pseudoxanthoma elasticum (PXE). Symptoms of PXE in patients originate from the calcification of elastic fibers in the skin, eye, and vessels. Previous studies suggested an involvement of ABCC6 in cholesterol and lipid homeostasis. The intention of this study was to examine the influence of ABCC6 deficiency during adipogenic differentiation of human bone marrow-derived stem cells (hMSCs). Induction of adipogenic differentiation goes along with significantly elevated ABCC6 gene expression in mature adipocytes. We generated an ABCC6-deficient cell culture model using clustered regulatory interspaced short palindromic repeat Cas9 (CRISPR–Cas9) system to clarify the role of ABCC6 in lipid homeostasis. The lack of ABCC6 in hMSCs does not influence gene expression of differentiation markers in adipogenesis but results in a decreased triglyceride content in cell culture medium. Protein and gene expression analysis of mature ABCC6-deficient adipocytes showed diminished intra- and extra-cellular lipolysis, release of lipids, and fatty acid neogenesis. Therefore, our results demonstrate impaired lipid trafficking in adipocytes due to ABCC6 deficiency, highlighting adipose tissue and peripheral lipid metabolism as a relevant target for uncovering systemic PXE pathogenesis.

Phenotypic Features and Genetic Findings in a Cohort of Italian Pseudoxanthoma Elasticum Patients and Update of the Ophthalmologic Evaluation Score

BACKGROUND

Pseudoxanthoma elasticum (PXE) is a rare ectopic calcification genetic disease mainly caused by ABCC6 rare sequence variants. The clinical phenotype is characterized by typical dermatological, ophthalmological and cardiovascular manifestations, whose frequency and severity are differently reported in the literature.

METHODS

A retrospective study was performed on 377 PXE patients of Italian origin, clinically evaluated according to the Phenodex Index, who underwent ABCC6 biomolecular analyses. Moreover, 53 PXE patients were further characterized by in-depth ophthalmological examinations.

RESULTS

A total of 117 different ABCC6 rare sequence variants were detected as being spread through the whole gene. The severity of the clinical phenotype was dependent on age, but it was not influenced by gender or by the type of sequence variants. In-depth ophthalmological examinations focused on the incidences of coquille d'oeuf, comet lesions, pattern dystrophy-like lesions, optic disk drusen and posterior-pole atrophy. Conclusion: Given the large number of patients analyzed, we were able to better evaluate the occurrence of less frequent alterations (e.g., stroke, myocardial infarction, nephrolithiasis). A more detailed description of ophthalmological abnormalities allowed us to stratify patients and better evaluate disease progression, thus suggesting a further update of the PXE score system.

Pseudoxanthoma Elasticum: Report of Two Cases

Elastic pseudoxanthoma is a rare disease with autosomal recessive inheritance, also known as Grönblad-Strandberg syndrome, characterized by pathological mineralization of the elastic fibers in the connective tissue, affecting principally the dermis of skin, media, and intima of blood vessels and Bruch's membrane of the eye. The genetic defect of the disorder is located on chromosome 16p13.1 and disease is caused by the lack of functional ABCC6 protein, which in turn causes extracellular accumulation and deposition of calcium and other minerals in the elastic tissue. In this article we present two cases of this rare disease. We emphasize, in the diagnostic criteria, the importance of its early diagnosis and the current therapeutic approaches.

Precision Medicine Approaches to Vascular Disease: JACC Focus Seminar 2/5

In this second of a 5-part Focus Seminar series, we focus on precision medicine in the context of vascular disease. The most common vascular disease worldwide is atherosclerosis, which is the primary cause of coronary artery disease, peripheral vascular disease, and a large proportion of strokes and other disorders. Atherosclerosis is a complex genetic disease that likely involves many hundreds to thousands of single nucleotide polymorphisms, each with a relatively modest effect for causing disease. Conversely, although less prevalent, there are many vascular disorders that typically involve only a single genetic change, but these changes can often have a profound effect that is sufficient to cause disease. These are termed "Mendelian vascular diseases," which include Marfan and Loeys-Dietz syndromes. Given the very different genetic basis of atherosclerosis versus Mendelian vascular diseases, this article was divided into 2 parts to cover the most promising precision medicine approaches for these disease types.

Contribution of OCT angiography in angioid streaks

PURPOSE

To study the appearance of angioid streaks (AS) in swept source optical coherence tomography angiography.

METHODS

Retrospective observational study of 16 patients (31 eyes) with various stages of AS. All included patients underwent complete ophthalmologic examinations including best-corrected visual acuity (BCVA), slit-lamp examination, indirect ophthalmoscopy and fundus photography. Swept source optical coherence tomography (SS-OCT), OCT angiography (OCT-A) and fluorescein angiography were also performed.

RESULTS

En face OCT detected hyper-reflective points in 65% of cases, with a choriocapillaris (CC) shadow on the corresponding OCT-A. Diffuse CC rarefaction was detected in 94%. In eyes without neovascular complications, streaks were visible as a hyposignal in the outer retina. An irregular vascular network (IVN) was detected in 80% of eyes. It filled the spaces between the AS and corresponded to flat elevation of the retinal pigmentary epithelium. Twenty-four eyes had choroidal neovascularization (CNV). CNV was type 1 in 8%, type 2 in 43%, mixed in 20% and unclassified in 29% because of a large scar. We found multiple sites of CNV in 8% of cases. CNV shape was tangled in 66% and in 2 eyes with newly diagnosed CNV. OCT-A showed a perilesional halo around new CNV. The morphology and configuration of neovascular network follow the IVN and the path of the AS and arises in proximity to sites of BM disruption.

CONCLUSION

OCT-A allows early detection and monitoring of AS and their neovascular complications. It shows CC rarefaction, IVN and a predominantly tangled shape of CNV. However, there are some limitations associated with difficulty in characterizing signs of CNV activity.

Irregular vascular network identified with OCT-A in angioid streaks: A probable predictor of active choroidal neovascularization (case series)

PURPOSE

To evaluate the risk of active choroidal neovascularization (CNV) in presence of deep irregular vascular network (IVN) in eyes with angioid streaks (AS).

METHODS

Observational case series including three treatment-naive eyes with angioid streaks and IVN, without CNV. Patients were followed-up during 18 months with multimodal imaging including structural optical coherence tomography (OCT) and OCT Angiography (OCT-A) to detect possible neovascular complication.

RESULTS

On OCT-A, IVN was detected as a peripapillary and/or macular high-flow lesion, filling the spaces between the angioid streaks in the outer retina slab. Repeated OCT-A could detect an active CNV emerging from the IVN, as a high-flow rich anastomotic vascular network with a perilesional dark halo. Patient was treated with intravitreal injections of Bevacizumab on a Pro Re Nata regimen, with a decreased CNV area and lower vascular density on control OCT-A.

CONCLUSION

OCT-A shown to be helpful in detecting the presence of IVN in asymptomatic eyes with AS during a routine examination. In our series, the IVN seems to be predictor of active CNV, needing a close surveillance and frequent follow-up to allow early treatment upon CNV activation.

Long-term results of choroidal neovascularization secondary to angioid streaks

PURPOSE

To investigate factors contributing to the visual prognosis of choroidal neovascularization (CNV) secondary to angioid streaks (AS) in a long-term follow-up (> 5 years) study.

METHODS

Twenty-one patients (32 eyes) affected by CNV secondary to AS were enrolled retrospectively and divided into three groups according to the period of CNV recurrence from the final treatment: group A, no recurrence for more than 12 months; group B, no recurrence for 6-12 months; and group C, no recurrence for < 6 months or ongoing. According to the above classification, we assessed best-corrected visual acuity (BCVA), peau d'orange area, the number of photodynamic treatments and/or intravitreal antiangiogenic drug injections, central choroidal thickness (CCT) and central retinal thickness (CRT) using optical coherence tomography, and enlargement of retinal pigment epithelium (RPE) atrophy.

RESULTS

The median follow-up time was 91 months. The median logarithm of the minimum angle of resolution BCVA significantly deteriorated from 0 at baseline to 1 at final follow-up (p < 0.05). Especially, final BCVA in group A showed worst visual outcome despite lowest number of treatments. Peau d'orange areas at baseline were found in 32 eyes (100%). There were no significant differences between initial CRT and final CRT. Median CCT was significantly reduced from 188 μm at baseline to 96 μm at final follow-up (p < 0.05). The median number of treatments was 3.5. Enlargement of RPE atrophy at baseline was found in 31 eyes (96.8%).

CONCLUSIONS

Despite the regression of CNV secondary to AS following treatment, the visual prognosis was poor due to the presence of peau d'orange areas, choroidal thinning, and increased RPE atrophy.

Macular choroidal thickness in patients with pseudoxanthoma elasticum measured by enhanced-depth imaging spectral-domain optical coherence tomography

BACKGROUND/OBJECTIVES

To analyze macular choroidal thickness in patients with pseudoxanthoma elasticum (PXE) by enhanced depth imaging optical coherence tomography (EDI-OCT).

SUBJECTS/METHODS

This is a prospective cross-sectional study. Sixty-eight eyes of 34 patients with PXE and 68 normal eyes of 34 controls were included to study the macular area with enhanced depth imaging spectral-domain optical coherence tomography (EDI-OCT). Eyes with PXE were classified in three groups: those without choroidal neovascularization (CNV) or chorioretinal macular atrophy macular (Group 1); those with active CNV (Group 2) and those with macular atrophy secondary to inactive CNV (Group 3).

RESULTS

Mean subfoveal choroidal thickness (CT) was 266.70 ± 46.93 µm in control group, 304.24 ± 65.52 µm in group 1, 198.55 ± 66.33 µm in group 2, and 119.45 ± 63.89 µm in group 3 (p = 0.00). Comparison between PXE subgroups showed that subfoveal CT was significantly decreased in group 2 and 3 compared to group 1 (p < 0.0001 for both groups). The CT in the different quadrants (superior, inferior, temporal and nasal) was significantly thinner in group 3, followed by group 2 and 1 in ascendant order. Group 1 showed significant increased thickness compared to the other groups.

CONCLUSION

To the best of our knowledge, this is the first report suggesting thicker macular choroid in patients with PXE without active or inactive CNV than in normal eyes. Initial changes in Bruch membrane (MB) and choroid, in addition to the increased oxidative stress, would lead to hyperpermeability of the choroid and alterations of the barrier BM-RPE causing a thick choroid in early stages.

Pseudoxanthoma Elasticum: An Interesting Model to Evaluate Chronic Kidney Disease-Like Vascular Damage without Renal Disease

Background

Pseudoxanthoma elasticum (PXE; OMIM 264800) is an inherited multisystem disorder associated with accumulation of mineralized and fragmented elastic fibers in the skin, vascular walls, and brush membrane in the eye. Carriers exhibit characteristic lesions in the cardiovascular system, and peripheral and coronary arterial disease as well as mitral valvulopathy often present as a cardiovascular feature of this disease. PXE and chronic kidney disease (CKD) share some common patterns in the vascular damage and in therapeutic approaches as well.

Summary

To date, treating PXE has focused more on careful follow-up examinations with retinal specialists and cardiologist, avoiding long-term anticoagulation. Like CKD, maintaining a low-calcium diet, increasing dietary magnesium, and administering phosphate binders such as aluminum hydroxide or sevelamer may yield a modest benefit. Recently, 4-phenylbutyrate acid (4-PBA) has demonstrated a maturation of ABCC6 mutant effects into the plasma membrane. Moreover, in a humanized mouse model of PXE, 4-PBA administration restored the physiological function of ABCC6 mutants, resulting in enhanced calcification inhibition and thus a promising strategy for allele-specific therapy of ABCC6-associated calcification disorders.

Key Message

Vascular compromise in PXE patients share some components similar to CKD.

Identification of hyperreflective foci in angioid streaks

AIMS

To assess hyperreflective foci (HF) number in angioid streaks (AS) by means of spectral-domain optical coherence tomography (SD-OCT).

METHODS

Observational and cross-sectional study. Sixty-two eyes with AS and 62 controls underwent best-corrected visual acuity (BCVA), fundoscopy, and SD-OCT. HF were assessed on the horizontal scan of a six-line radial OCT, in the fovea (1500-μm diameter) and parafovea (500 μm external to the fovea), and sub-classified as retinal or choroidal, small or large. Eyes were distributed in one of four groups, as carrying foveal AS without choroidal neovascularization (CNV) (14 eyes), extra-foveal AS without CNV (14), active CNV (20), and inactive CNV (14). Primary outcome was HF assessment in AS. Secondary outcomes included their correlations with BCVA.

RESULTS

AS-affected eyes had higher HF numbers. Our sub-analysis revealed that patients with active CNV had a larger number of retinal and choroidal HF than all the other groups, whereas retinal and choroidal foci were significantly increased in inactive CNV only with respect to controls. Interestingly, patients with foveal AS showed HF number increase in the choroid and fovea. BCVA deterioration positively correlated with the total HF number found in the fovea and the choroid.

CONCLUSION

HF are significantly increased in patients with AS. Despite being especially evident in active CNV, the increasing number in eyes without CNV might suggest new pathogenetic aspects of the disease.

Coquille d'oeuf in young patients affected with Pseudoxantoma elasticum

Purpose: To evaluate the fundus phenotype of young patients affected with Pseudoxantoma Elasticum (PXE). Materials and Methods: Retrospective case series of five young PXE patients. Clinical data, ultra-widefield imaging (color, red-free (RF), choroidal (Ch) and fundus autofluorescence (FAF)) and OCT examination were collected. Diagnosis was confirmed by the characteristic histopathological abnormalities in skin biopsies and genetic testing results. Results: Five patients, 2 males and 3 females (mean age 16 years, range 12-20 years) were included in our study. The visual acuity was 20/20 in all subjects. Fundus evaluation revealed peau d'orange in all patients: multiple, yellowish/white round lesions, scattered from the posterior pole to the mid-peripheral retina of each eye. Ultra-wide field imaging allows us to capture and describe the entire area of coquille d'oeuf/peau d'orange in a single picture, facilitating their identification and discrimination. Angiod streaks were visible in both eyes of four patients. In one patient optic disc drusen were detected in both eyes. All patients presented comet lesions. Conclusions: PXE-related retinopathy findings: peau d'orange/coquille d'oeuf, angioid streaks, comet lesions and drusen of the optic disc were present early in PXE patients. The early detection of coquille d'oeuf/peau d'orange revealed a preferable area into midperiphery where Bruch's membrane will be more likely to be affected.

Peripapillary comet lesions and comet rain in PXE-related retinopathy

PURPOSE

To study peripapillary comet lesions (PCL) in Italian patients affected with pseudoxanthoma elasticum (PXE).

METHODS

Retrospective review of fundoscopic and swept-source (SS) optical coherence tomography (OCT) images of patients with PXE examined at the Regional Reference Center for Hereditary Retinal Degenerations at the Careggi Teaching Hospital of Florence from 2012 to 2017.

RESULTS

From 148 eyes of 74 patients affected with PXE, we identified 24 eyes of 14 patients (11 were female) with a mean age of 39 years (range, 20-58 years) characterized by peripapillary comet lesions. Of these 24 eyes, 15 eyes (of 10 patients) were characterized by comet rain. The smallest comet lesion at the OCT examination appeared as a focal roundish hyper-reflective alteration at the level of the outer retinal segments and RPE-Bruch's membrane complex; the larger lesions appeared as circular and ovoid structures with hyper-reflective borders in the outer nuclear layer.

CONCLUSION

The comet lesion formation process involves the outer layers of the retina and RPE/Bruch's membrane complex. It consists of a degenerative/rearrangement process of the photoreceptors which occurs in an area of focal altered RPE/Bruch's membrane resembling the outer retinal tubulation.

Reticular Pseudodrusen and Thin Choroid Are Associated With Angioid Streaks

BACKGROUND AND OBJECTIVE

To report the association of angioid streaks in patients with Pseudoxanthoma elasticum (PXE) with reticular pseudodrusen (RPD), thin choroid, and retinal pigment epithelium (RPE) atrophy using swept-source optical coherence tomography (SS-OCT) and short-wave autofluorescence (SWAF).

PATIENTS AND METHODS

Retrospective cross-sectional study. Records of consecutive patients with angioid streaks due to PXE, who presented with a decrease of vision due to choroidal neovascularization (CNV), were reviewed for best-corrected visual acuity, color fundus photographs, SS-OCT, SWAF, and red-free images with special emphasis on presence or absence of RPD, subfoveal choroidal thickness (SFCT), and RPE atrophy.

RESULTS

Sixteen eyes of eight patients with a mean age of 45.5 years ± 9.4 years were enrolled in the study. RPD were seen in 10 of the 16 eyes and were seen commonly along the superotemporal quadrant. Mean subfoveal thickness in study eyes (175.7 μm ± 37.2 μm) was significantly reduced when compared to controls (286.4 μm ± 40.8 μm). The mean SFCT was similar between the eyes with and without CNV. Four eyes had RPE atrophy in the macular area, whereas four eyes had peripapillary RPE atrophy.

CONCLUSIONS

Angioid streaks in PXE are associated with RPD, thin choroid, and RPE atrophy. These features occur at a younger age as compared to age-related macular degeneration and appear to be interrelated because of single pathophysiological mechanism. [Ophthalmic Surg Lasers Imaging Retina. 2018;49:402-408.].

[Vascular calcification in pseudoxanthoma elasticum in children]

INTRODUCTION

Vascular calcifications are associated with several diseases that affect vascular connective tissue and skin and cause considerable morbidity and mortality. The prototype of these conditions is pseudoxanthoma elasticum. We report, in this study, 4 pediatric cases of vascular calcifications diagnosed as elastic pseudoxanthoma.

OBSERVATIONS

These 4 children were 2-11 years old and presented variable clinical features. Vascular involvement and arterial hypertension was observed in all patients, skin involvement in 2 cases, gastrointestinal involvement in 2 cases, neurological impairment in one case, and cardiac involvement in one case. Demonstration of ABCC6 gene mutations provided diagnostic confirmation in all cases.

CONCLUSION

Pseudoxanthoma elasticum is a rare genetic disease, which can lead to many complications. Appropriate knowledge and early diagnosis are essential.

A case of pseudoxanthoma elasticum with proliferative diabetic retinopathy

Background

To report the case of a patient with pseudoxanthoma elasticum (PXE) and proliferative diabetic retinopathy (PDR), and discuss the relationship between PXE and diabetic retinopathy (DR).

Case presentation

A 47-year-old man with PXE presented with angioid streaks and DR in both eyes, and bilateral panretinal photocoagulation was performed for treatment. Vitrectomy had previously been performed in his right eye for vitreous hemorrhage due to PDR. Systemic findings included multiple, discrete, symmetrical, small yellow papules bilaterally in the axilla and inguinal region. Examination on presentation showed vitreous hemorrhage in his left eye, and vitrectomy was performed for treatment. Intraoperative findings showed fibrovascular membrane around the optic disc and vascular arcade. A mottled fundus (peau d’orange appearance) associated with angioid streaks was also present, yet there was no evident choroidal neovascularization (CNV). The postoperative course was satisfactory, and corrected visual acuity improved from 0.02 to 0.7 diopters.

Conclusion

Despite the peau d’orange appearance in both eyes of this case, no CNV was evident. The vitreous hemorrhage was thus attributed to PDR. Moreover, we reviewed the published literature and discuss the relationship between PXE and DR.

Pseudoxanthoma elasticum

Pseudoxanthoma elasticum (PXE) is a genetic metabolic disease with autosomal recessive inheritance caused by mutations in the ABCC6 gene. The lack of functional ABCC6 protein leads to ectopic mineralization that is most apparent in the elastic tissues of the skin, eyes and blood vessels. The clinical prevalence of PXE has been estimated at between 1 per 100,000 and 1 per 25,000, with slight female predominance. The first clinical sign of PXE is almost always small yellow papules on the nape and sides of the neck and in flexural areas. The papules coalesce, and the skin becomes loose and wrinkled. The mid-dermal elastic fibers are short, fragmented, clumped and calcified. Dystrophic calcification of Bruch's membrane, revealed by angioid streaks, may trigger choroidal neovascularization and, ultimately, loss of central vision and blindness in late-stage disease. Lesions in small and medium-sized artery walls may result in intermittent claudication and peripheral artery disease. Cardiac complications (myocardial infarction, angina pectoris) are thought to be relatively rare but merit thorough investigation. Ischemic strokes have been reported. PXE is a metabolic disease in which circulating levels of an anti-mineralization factor are low. There is good evidence to suggest that the factor is inorganic pyrophosphate (PPi), and that the circulating low levels of PPi and decreased PPi/Pi ratio result from the lack of ATP release by hepatocytes harboring the mutant ABCC6 protein. However, the substrate(s) bound, transported or modulated by the ABCC6 protein remain unknown. More than 300 sequence variants of the ABCC6 gene have been identified. There is no cure for PXE; the main symptomatic treatments are vascular endothelial growth factor inhibitor therapy (for ophthalmic manifestations), lifestyle, lipid-lowering and dietary measures (for reducing vascular risk factors), and vascular surgery (for severe cardiovascular manifestations). Future treatment options may include gene therapy/editing and pharmacologic chaperone therapy.

Comet Lesions in Patients with Pseudoxanthoma Elasticum

Pseudoxanthoma elasticum (PXE) is a genetic multisystemic disorder affecting the skin, eyes and cardiovascular system. Basic fundoscopic findings in PXE result from Bruch’s membrane involvement. The most important fundoscopic findings are angioid streaks. Other significant ocular findings are peau d’orange appearance, optic disc drusen, pattern dystrophy-like macular appearance, comet lesions, and choroidal neovascularization. Comet lesions are a pathognomonic ocular finding for PXE. The presence of both angioid streaks in the fundus and typical skin lesions should alert clinicians to PXE. Herein, we present two PXE cases with comet lesions.

Peau d'orange and angioid streaks: manifestations of Bruch membrane pathology

PURPOSE

The aim of this study was to characterize peau d'orange and angioid streaks, characteristic findings in eyes of patients with pseudoxanthoma elasticum, by examining fundus photography and optical coherence tomography imaging.

METHODS

Color photographs were evaluated directly as were the component red and green channels. Optical coherence tomography images were evaluated for reflectivity pattern of the band corresponding to the retinal pigment epithelium-Bruch membrane complex.

RESULTS

Eighteen eyes of 9 patients with a mean age of 48.7 years (range, 31-61 years) were examined; 7 of them were women. Color photographs showed areas of yellowish opacification that obscured visualization of the underlying choroid. At the outer edges of this confluent area, opacification were nonconfluent changes with similar appearance and these regions were typical peau d'orange. Angioid streaks occurred within and extended up to the outer border of the confluent opacification. Underlying choroidal details could be seen through the regions of peau d'orange and through the gaps in angioid streaks. The red channel image showed increased reflectivity from the confluent deposit and improved visualization of the choroidal vasculature, except where the confluent opacification was located. Optical coherence tomography imaging showed increased reflectivity from the outer border of the retinal pigment epithelium-Bruch membrane complex.

CONCLUSION

The findings suggest that the confluent region is the relevant lesion, not the subconfluent zone known as peau d'orange. Imaging characteristics of the confluent area of opacity are consistent with diffuse infiltration with calcium, a chief histologic abnormality of pseudoxanthoma elasticum. The name coquille d'oeuf was suggested for the confluent area of opacity as a consequence.

Pseudoxanthoma elasticum and skin: Clinical manifestations, histopathology, pathomechanism, perspectives of treatment

Pseudoxantoma elasticum (PXE), also known as Groenblad-Strandberg syndrome, is a rare heritable disease with an estimated prevalence of 1:50,000 in the general population. PXE is considered a prototype of multisystem ectopic mineralization disorders and it is characterized by aberrant mineralization of soft connective tissue with degeneration of the elastic fibers, involving primarily the eyes, the cardiovascular system, and the skin. Cutaneous lesions consist of small, asymptomatic, yellowish papules or larger coalescent plaques, typically located on the neck and the flexural areas. PXE is caused by mutations in the ABCC6 (ATP-binding cassette subfamily C member 6) gene that encodes a transmembrane ATP binding efflux transporter, normally expressed in the liver and the kidney; however, the exact mechanism of ectopic mineralization remains largely unknown. The histological examination of cutaneous lesions, revealing accumulation of pleomorphic elastic structures in middermis, is essential for the definitive diagnosis of PXE, excluding PXE-like conditions. PXE is currently an intractable disease; although the cutaneous findings primarily present a cosmetic problem, they signify the risk for development of ocular and cardiovascular complications associated with considerable morbidity and mortality. The purpose of this review is to present a comprehensive overview of this rare form of hereditary connective tissue disorders, focus on the pathogenesis, the clinical manifestation, and the differential diagnosis of PXE. Emphasis is also placed on the management of cutaneous lesions and treatment perspectives of PXE.

From variome to phenome: Pathogenesis, diagnosis and management of ectopic mineralization disorders

Ectopic mineralization - inappropriate biomineralization in soft tissues - is a frequent finding in physiological aging processes and several common disorders, which can be associated with significant morbidity and mortality. Further, pathologic mineralization is seen in several rare genetic disorders, which often present life-threatening phenotypes. These disorders are classified based on the mechanisms through which the mineralization occurs: metastatic or dystrophic calcification or ectopic ossification. Underlying mechanisms have been extensively studied, which resulted in several hypotheses regarding the etiology of mineralization in the extracellular matrix of soft tissue. These hypotheses include intracellular and extracellular mechanisms, such as the formation of matrix vesicles, aberrant osteogenic and chondrogenic signaling, apoptosis and oxidative stress. Though coherence between the different findings is not always clear, current insights have led to improvement of the diagnosis and management of ectopic mineralization patients, thus translating pathogenetic knowledge (variome) to the phenotype (phenome). In this review, we will focus on the clinical presentation, pathogenesis and management of primary genetic soft tissue mineralization disorders. As examples of dystrophic calcification disorders Pseudoxanthoma elasticum, Generalized arterial calcification of infancy, Keutel syndrome, Idiopathic basal ganglia calcification and Arterial calcification due to CD73 (NT5E) deficiency will be discussed. Hyperphosphatemic familial tumoral calcinosis will be reviewed as an example of mineralization disorders caused by metastatic calcification.

The contribution of arterial calcification to peripheral arterial disease in pseudoxanthoma elasticum

Background and aims

The contribution of arterial calcification (AC) in peripheral arterial disease (PAD) and arterial wall compressibility is a matter of debate. Pseudoxanthoma elasticum (PXE), an inherited metabolic disease due to ABCC6 gene mutations, combines elastic fiber fragmentation and calcification in various soft tissues including the arterial wall. Since AC is associated with PAD, a frequent complication of PXE, we sought to determine the role of AC in PAD and arterial wall compressibility in this group of patients.

Methods and Results

Arterial compressibility and patency were determined by ankle-brachial pressure index (ABI) in a cohort of 71 PXE patients (mean age 48±SD 14 yrs, 45 women) and compared to 30 controls without PAD. Lower limb arterial calcification (LLAC) was determined by non-contrast enhanced helicoidal CT-scan. A calcification score (Ca-score) was computed for the femoral, popliteal and sub-popliteal artery segments of both legs. Forty patients with PXE had an ABI<0.90 and none had an ABI>1.40. LLAC increased with age, significantly more in PXE subjects than controls. A negative association was found between LLAC and ABI (r = −0.363, p = 0.002). The LLAC was independently associated with PXE and age, and ABI was not linked to cardiovascular risk factors.

Conclusions

The presence of AC was associated with PAD and PXE without affecting arterial compressibility. PAD in PXE patients is probably due to proximal obstructive lesions developing independently from cardiovascular risk factors.

Visual Impairment in Pseudoxanthoma Elasticum: A Survey of 40 Patients

BACKGROUND

Pseudoxanthoma elasticum is an inherited disorder of connective tissue characterized, among other symptoms, by impaired vision.

OBJECTIVE

To evaluate the nature and age of onset of ophthalmologic manifestations in pseudoxanthoma elasticum.

PATIENTS AND METHODS

Forty consecutive patients affected with pseudoxanthoma elasticum underwent measurements of their refractive error and visual acuity, together with slit-lamp examination.

RESULTS

The mean age of the patients (8 M, 32 F) was 43.35 years. Fifty-seven eyes (33 patients, mean age: 40.75 years) had a BCVA >20/50 whereas 23 eyes in 16 patients (mean age: 53.31 years) had ≤20/50. Seven patients (17.50%), all but one over 52 years old, were visually disabled. BCVA ≤20/50 in at least one eye was observed in 73.33% of patients of 52 years old or older and in 20.00% of patients younger than 52, respectively. Angioid streaks were observed in 75 eyes (93.75%) and extended toward the macula in 51 eyes from 29 patients. Macular involvement was observed for the first time at a mean age of 44.28 years. Neovascularization was observed in 28 eyes (17 patients; mean age: 51.70 years), all with poor BCVA.

CONCLUSION

Macular choroidal neovascularization is frequent in pseudoxanthoma elasticum, and accounts for the poor ophthalmologic natural history of the disease. Patients should be advised to self-monitor their visual acuity using the Amsler grid. The frequency of choroidal neovascularization appears age-dependent, suggesting that bi-yearly fundus examination is appropriate in young patients whereas patients older than 40 should be examined twice a year.

An atypical case of choroidal neovascularization associated with pseudoxanthoma elasticum treated with intravitreal bevacizumab: a case report

Background

Pseudoxanthoma elasticum is an inherited disorder that is associated with accumulation of pathologic elastic fibers in the skin, vascular walls and Bruch’s membrane in the eye. Choroidal neovascularization is one of the most common causes of acute vision loss in these patients. We report an atypical case of suspected choroidal neovascularization associated with pseudoxanthoma elasticum.

Case presentation

A 47-year-old Caucasian woman with pseudoxanthoma elasticum and angioid streaks was referred because of decreased and distorted vision in her right eye of one week’s duration. Visual acuity was 6/12 in the right eye and 6/6 in the left eye. Fundus examination revealed angioid streaks and white intraretinal macular deposits bilaterally. Fluorescein angiography did not reveal any obvious leakage in the right eye while optical coherence tomography revealed subretinal fluid associated with an adjacent intraretinal hyperreflective structure. Autofluoresence imaging showed focal areas of increased autofluorescence corresponding to the deposits in both eyes. Over the following year the patient underwent five intravitreal injections of bevacizumab (Genentech/Roche,US) in the right eye, which resulted in visual acuity improving to 6/9 with regression of the hyperreflective structrure and complete resolution of subretinal fluid.

Conclusions

Traditionally, fluorescein angiography is effective in the detection of choroidal neovascularization in patients with pseudoxanthoma elasticum. In our case, optical coherence tomography revealed subretinal fluid and an adjacent hyperreflective structure while fluorescein angiography did not reveal any obvious leakage. The sole presence of subretinal fluid does not necessarily imply the presence of choroidal neovascularization and certainly retinal pigment epithelium dysfunction could also explain subretinal fluid in these patients. However, the complete absorption of the fluid and the disappearance of the previously evident hyperreflective structure following treatment, led us to suspect choroidal neovascularization as the primary cause of the above findings. The poor natural course of choroidal neovascularization in these patients increases the importance of early detection and should result in the adaptation of a low-threshold strategy concerning the initiation of treatment.

The spectrum of ocular alterations in patients with β-thalassemia syndromes suggests a pathology similar to pseudoxanthoma elasticum

PURPOSE

To determine the prevalence and spectrum of ocular fundus abnormalities in patients with β-thalassemia and to investigate risk factors for their development.

DESIGN

Cross-sectional, observational study.

PARTICIPANTS

A total of 255 patients with β-thalassemia major (TM) and β-thalassemia intermedia (TI) were consecutively recruited and investigated.

METHODS

Patients underwent best correct visual acuity, indirect ophthalmoscopy, and fundus photography, including fundus autofluorescence (FAF) and near-infrared reflectance imaging using a confocal scanning laser ophthalmoscope (cSLO). Hematologic parameters were determined, including mean ferritin levels, aspartate amino transferase, alanine amino transferase, calcium, pre-transfusion hemoglobin, history of splenectomy, and liver iron concentration. Factors associated with the ocular phenotype were assessed using logistic regression.

MAIN OUTCOME MEASURES

Ocular phenotype as determined by clinical examination and used multimodal imaging.

RESULTS

A total of 153 patients (60.0%) affected by TM and 102 patients (40.0%) affected by TI participated, of whom 216 (84.7%) were receiving iron-chelating therapy. Ocular fundus abnormalities characteristic of pseudoxanthoma elasticum (PXE) were detected by cSLO in 70 of 255 patients (27.8%) and included peau d'orange (19.6%), angioid streaks (12.9%), pattern dystrophy-like changes (7.5%), and optic disc drusen (2.0%). Pseudoxanthoma elasticum-like changes were more frequent in patients with TI (P<0.001). Patients with PXE-like fundus changes were older than patients without these fundus changes (P<0.001). In both patients with TI and TM, age (P = 0.001) and splenectomy (P = 0.001) had the strongest association with presence of PXE-like fundus changes in multivariate analyses. A total of 43 of 255 patients (16.9%) showed increased retinal vascular tortuosity independently of the PXE-like fundus changes, which was associated with aspartate amino transferase (P = 0.036), hemoglobin (P = 0.008), and ferritin levels (P = 0.005).

CONCLUSIONS

Pseudoxanthoma elasticum-like fundus changes are a frequent finding in patients with β-thalassemia. In TI, these changes increase with duration or severity of the disease. This particular ocular phenotype suggests an ocular pathology similar to PXE. Retinal vascular tortuosity may be an additional disease manifestation independent of the PXE-like syndrome. Patients with long-standing disease requiring iron-chelating treatment and a history of splenectomy need regular ophthalmic checkups because they are at risk of developing PXE-like fundus changes and potentially of subsequent choroidal neovascularization.

The time course changes of choroidal neovascularization in angioid streaks

PURPOSE

To assess the clinical course of choroidal neovascularization (CNV) in patients with angioid streaks using optical coherence tomography and fluorescein angiography/indocyanine green angiography.

METHODS

We examined a consecutive series of 88 eyes of 44 patients with angioid streaks using color fundus photography, optical coherence tomography, and fluorescein angiography/indocyanine green angiography.

RESULTS

At the initial visit, 33 eyes exhibited no CNV, 2 exhibited polypoidal choroidal vasculopathy, 8 exhibited Type 1 CNV, 32 exhibited active Type 2 CNV, and 13 exhibited a fibrotic scar. In addition to the 2 eyes that exhibited macular polypoidal choroidal vasculopathy at the initial visit, 3 exhibited peripapillary polypoidal lesions, and 2 exhibited polypoidal lesions at the edge of the preexisting Type 2 CNV/fibrosis. During the follow-up, Type 2 CNV developed in 4 eyes on the basis of Type 1 CNV. Visual acuity was worse in eyes with Type 2 CNV and fibrosis than in those with Type 1 CNV, while polypoidal choroidal vasculopathy did not affect the visual acuity.

CONCLUSION

Eyes with angioid streaks can develop any form of CNV including polypoidal choroidal vasculopathy. Considering the worse visual acuity in eyes with Type 2 CNV and fibrosis, patients should be carefully observed so as to treat them promptly when Type 2 CNV occurred beneath the fovea.

Geographic chorioretinal atrophy in pseudoxanthoma elasticum

PURPOSE

To describe a series of patients with geographic atrophy independent of choroidal neovascularization (CNV) in pseudoxanthoma elasticum and to report progression over time.

DESIGN

Retrospective observational case series.

METHODS

Records of all Vanderbilt Eye Institute patients with pseudoxanthoma elasticum and at least 1 set of color fundus photographs were reviewed (41 eyes of 21 patients). Fluorescein angiography, fundus autofluorescence, and optical coherence tomography images were reviewed, when available. In patients with geographic atrophy and at least 1 year of follow-up, atrophy was measured using fundus photographs. Main outcome measures included incidence of geographic atrophy, progression over time, and macular features associated with development or progression of geographic atrophy.

RESULTS

Eight eyes (20%) of 5 patients had geographic atrophy independent of CNV. Progression was documented in 6 eyes of 4 patients followed for at least 1 year (mean 3.5 years). Mean initial and final area was 2.9 and 9.5 mm(2), respectively, and growth rate was 1.7 mm(2) per year. Of the 6 eyes, 3 had a final visual acuity of 20/20 and the other 3 ranged from 20/150 to 20/400. All 8 eyes had pattern dystrophy, and 5 had linear pigment deposits that appeared to predict development or growth of atrophy.

CONCLUSIONS

Isolated geographic atrophy independent of CNV can develop in pseudoxanthoma elasticum, causing significant vision loss. Linear pigmented pattern dystrophy appears to predate geographic atrophy. Progression is similar to age-related macular degeneration. Recognition of this feature is important, especially if therapies to slow or reverse geographic atrophy become available.

An update on the ocular phenotype in patients with pseudoxanthoma elasticum

Pseudoxanthoma elasticum (PXE) is an inherited multi-system disorder characterized by ectopic mineralization and fragmentation of elastic fibers in the skin, the elastic laminae of blood vessels and Bruch's membrane in the eye. Biallelic mutations in the ATP-binding cassette (ABC) transporter gene ABCC6 on chromosome 16 are responsible for the disease. The pathophysiology is incompletely understood. However, there is consent that a metabolic alteration leads to dysfunction in extracellular calcium homeostasis and subsequent calcification of connective tissues rich in elastic fibers. This review summarizes and aims at explaining the variety of phenotypic ocular findings in patients with PXE. Specialized imaging techniques including white light fundus photography, blue light autofluorescence, near-infrared confocal reflectance imaging, high resolution optical coherence tomography, fluorescein and indocyanine green (ICG) angiography have revealed characteristic lesions at the ocular fundus of PXE patients. These include the classic signs of angioid streaks, peau d'orange, comet lesions, and choroidal neovascularizations (CNVs), but also the more recently recognized features such as chorioretinal atrophy, subretinal fluid independent from CNV, pattern dystrophy-like changes, debris accumulation under the retinal pigment epithelium, reticular drusen and a decreased fluorescence on late phase ICG angiography.

Near infrared autofluorescence imaging of retinal diseases

Near infrared autofluorescence (excitation 787 nm, emission >800 nm) is a non-invasive imaging technology that provides information on the distribution of melanin within the retinal pigment epithelial cell/choroid complex. This review contains an introduction to near infrared autofluorescence imaging methods. Characteristics of near infrared imaging in a variety of retinal diseases, including age-related macular degeneration, choroidal nevus, retinal degenerations, retinal dystrophies, central serous chorioretinopathy, pseudoxanthoma elasticum and chloroquine retinopathy, are summarized.

The vascular phenotype in Pseudoxanthoma elasticum and related disorders: contribution of a genetic disease to the understanding of vascular calcification

Vascular calcification is a complex and dynamic process occurring in various physiological conditions such as aging and exercise or in acquired metabolic disorders like diabetes or chronic renal insufficiency. Arterial calcifications are also observed in several genetic diseases revealing the important role of unbalanced or defective anti- or pro-calcifying factors. Pseudoxanthoma elasticum (PXE) is an inherited disease (OMIM 264800) characterized by elastic fiber fragmentation and calcification in various soft conjunctive tissues including the skin, eyes, and arterial media. The PXE disease results from mutations in the ABCC6 gene, encoding an ATP-binding cassette transporter primarily expressed in the liver, kidneys suggesting that it is a prototypic metabolic soft-tissue calcifying disease of genetic origin. The clinical expression of the PXE arterial disease is characterized by an increased risk for coronary (myocardial infarction), cerebral (aneurysm and stroke), and lower limb peripheral artery disease. However, the structural and functional changes in the arterial wall induced by PXE are still unexplained. The use of a recombinant mouse model inactivated for the Abcc6 gene is an important tool for the understanding of the PXE pathophysiology although the vascular impact in this model remains limited to date. Overlapping of the PXE phenotype with other inherited calcifying diseases could bring important informations to our comprehension of the PXE disease.

[Angioid streaks]

Angioid streaks represent breaks in Bruch's membrane, appearing as dark or reddish radial streaks eminating from the optic disc. Usually asymptomatic, these streaks may develop neovascularisation and lead to a maculopathy with marked loss of vision. Some associations with systemic disease are classically described, especially pseudoxanthoma elasticum. This condition may involve cardiovascular complications. A mutation has been found in the ABCC6 gene, which encodes for a membrane transport protein involved in the synthesis of the extracellular matrix. Imaging allows for visualization of the extent of the streaks, and autofluorescence is particularly informative. Spectral domain OCT may also demonstrate early breaks in Bruch's membrane. Neovascular complications, previously responsible for inevitable visual impairment at some point after their occurrence, are now managed by intravitreal injections of anti-VEGFs with clear efficacity. The ophthalmologist must be aware of this condition, in order to guide the patient towards a systemic work-up if necessary, and also to insure quick and targeted treatment in the case of neovascular complications.

Abcc6 deficiency in the mouse leads to calcification of collagen fibers in Bruch's membrane

Pseudoxanthoma elasticum (PXE) is a heritable disorder characterized by mineralization of connective tissue, which leads to pathology in eye, skin and blood vessels. The disease is caused by mutations in ABCC6. To learn more about PXE eye pathology, we analyzed Bruch's membrane (BM) of the eye of an Abcc6 knockout mouse. With age, BM differences between Abcc6-/- and wild type mice became apparent. At two years of age, von Kossa staining indicated clear calcification of BM in Abcc6-/- mice, and not in healthy controls. Electron microscopy revealed BM changes as early as at 10 months of age: Fibrous structures with abnormal high electron-density were present in the central layers of BM of Abcc6-/- mice. EDX (Energy Dispersive X-ray) analysis demonstrated that these structures contained elevated levels of Ca, P and O. Since some of these electron-dense structures showed a banding pattern with periodicity of about 50 nm, they most likely represent calcified collagen fibers. Immunoelectron microscopy showed that the calcified structures were positive for collagen III. Remarkably, the elastic layer of BM appeared to have a normal ultrastructure, even in 2.5 year old Abcc6-/- mice. Our results suggest that Abcc6 deficiency in the mouse causes calcification of BM. While PXE is considered to affect primarily the elastic fibers, we found predominantly mineralization of collagen fibers.