Proposal for updating the pseudoxanthoma elasticum classification system and a review of the clinical findings

The role of multimodal imaging in characterization and monitoring of choroidal neovascularization secondary to angioid streaks

BACKGROUND

To characterize and monitor choroidal neovascularisation (CNV) secondary to angioid streaks (AS) using multimodal imaging and to compare the results with conventional fluorescein angiography (FA).

METHODS

A total of 11 eyes with CNV secondary to AS were included in this retrospective study. Multimodal morphological and functional assessment, including spectral-domain optical coherence tomography (SD-OCT), spectral-domain optical coherence tomography angiography (SD-OCTA), and fundus autofluorescence (FAF), were used to assess for evidence of CNV activity and compared with conventional FA. Morphological features of CNV were analyzed and treatment was continuously monitored using SD-OCT and SD-OCTA.

RESULTS

Our results showed that SD-OCTA provided reliable results for the detection of secondary CNV in AS that were comparable to conventional FA. With SD-OCTA, a total of 13 CNVs were detected in 11 eyes and analyzed by means of outer retinal choriocapillaris depth (ORCC) segmentation and the corresponding B-scans. Twelve of the 13 CNVs were classified as active and therefore required treatment. For treatment monitoring during intravitreal therapy (IVT), SD-OCTA was found to be a valuable diagnostic tool over a mean follow-up of 76 weeks.

CONCLUSIONS

Our study demonstrates that SD-OCTA can be routinely used to identify ill-defined CNV without dye-based angiography, especially in cases of CNV secondary to AS, where Bruch's membrane (BM) defects limit the diagnostic value of FA. Our results showed that non-invasive multimodal imaging facilitates sufficient CNV monitoring and treatment guidance. Further studies are warranted to provide more evidence in this rare retinal disease.

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.

Mutational spectrum and deep phenotyping in Pseudoxanthoma Elasticum: Findings from a Portuguese cohort

INTRODUCTION

Pseudoxanthoma Elasticum (PXE) is a rare autosomal recessive disorder originated by disease-causing variants in ABCC6 gene. The purpose of this study was to characterize the genetic landscape, phenotypic spectrum and genotype-phenotype correlations in a Portuguese cohort of PXE patients.

METHODS

Multicentric cross-sectional study conducted in patients with a clinical and genetic diagnosis of PXE. Patients were identified using the IRD-PT registry (www.retina.com.pt). Genotypes were classified into 3 groups: (1) two truncating variants, (2) two non-truncating variants, or (3) mixed variants. Deep phenotyping comprised a comprehensive ophthalmologic and systemic evaluation using the updated Phenodex Score (PS).

RESULTS

Twenty-seven patients (23 families) were included. Sixteen different ABCC6 variants were identified, 7 of which are novel. The most prevalent variant was the nonsense variant c.3421C > T p.(Arg1141*) with an allele frequency of 18.5%. All patients exhibited ocular manifestations. Cutaneous manifestations were present in most patients (88.9%, n = 24/27). A PS score > E2 was strongly associated with worse visual acuity (B = -29.02; p = 0.001). No association was found between genotypic groups and cutaneous, vascular or cardiac manifestations.

CONCLUSIONS

This study describes the genetic spectrum of patients with PXE for the first time in a Portuguese cohort. A total of 16 different variants in ABCC6 were found (7 of which are novel), thus highlighting the genotypic heterogeneity associated with this condition and expanding its mutational spectrum. Still, no major genotype-phenotype associations could be established.

Increased Intracranial Arterial Pulsatility and Microvascular Brain Damage in Pseudoxanthoma Elasticum

BACKGROUND AND PURPOSE

Carotid siphon calcification might contribute to the high prevalence of cerebrovascular disease in pseudoxanthoma elasticum through increased arterial flow pulsatility. This study aimed to compare intracranial artery flow pulsatility, brain volumes, and small-vessel disease markers between patients with pseudoxanthoma elasticum and controls and the association between arterial calcification and pulsatility in pseudoxanthoma elasticum.

MATERIALS AND METHODS

Fifty patients with pseudoxanthoma elasticum and 40 age- and sex-matched controls underwent 3T MR imaging, including 2D phase-contrast acquisitions for flow pulsatility in the assessment of ICA and MCA and FLAIR acquisitions for brain volumes, white matter lesions, and infarctions. All patients with pseudoxanthoma elasticum underwent CT scanning to measure siphon calcification. Flow pulsatility (2D phase-contrast), brain volumes, white matter lesions, and infarctions (3D T1 and 3D T2 FLAIR) were compared between patients and controls. The association between siphon calcification and pulsatility in pseudoxanthoma elasticum was tested with linear regression models.

RESULTS

Patients with pseudoxanthoma elasticum (mean age, 57 [SD, 12] years; 24 men) had significantly higher pulsatility indexes (1.05; range, 0.94-1.21 versus 0.94; range, 0.82-1.04; P = .02), lower mean GM volumes (597 [SD, 53] mL versus 632 [SD, 53] mL; P < .01), more white matter lesions (2.6; range, 0.5-7.5 versus 1.1; range, 0.5-2.4) mL; P = .05), and more lacunar infarctions (64 versus 8, P = .04) than controls (mean age, 58 [SD, 11] years; 20 men). Carotid siphon calcification was associated with higher pulsatility indexes in patients with pseudoxanthoma elasticum (β = 0.10; 95% CI, 0.01-0.18).

CONCLUSIONS

Patients with pseudoxanthoma elasticum have increased intracranial artery flow pulsatility and measures of small-vessel disease. Carotid siphon calcification might underlie the high prevalence of cerebrovascular disease in pseudoxanthoma elasticum.

Plasma lipids in Pseudoxanthoma Elasticum (PXE) patients: A comparative study with population-based reference values and Non-PXE controls

Background and aims

- Pseudoxanthoma elasticum (PXE) is a rare genetic disease caused by pathogenic mutations in the ABCC6 gene, resulting in low values of inorganic pyrophosphate (PPi). While low PPi is thought to contribute to arterial calcification, it remains unclear whether this fully explains premature calcification in PXE. It has been hypothesized that the ABCC6 gene could be related to dyslipidemia, which could contribute to vascular calcification seen in PXE. The aim of this study is to evaluate the relation between PXE and plasma lipid concentrations in a large cohort of PXE patients compared with reference values for the general population and compared with non-PXE controls.

Methods

- The plasma concentrations of total cholesterol, HDL-cholesterol, tiglycerides, and LDL-cholesterol of 312 PXE patients were compared to age- and sex-matched modeled data of the general Dutch population. Differences in median lipid levels were compared with Mann-Whitney-U test. Secondly, plasma lipid concentrations of 44 PXE patients were compared to 44 not-genetically related relatives (spouses or friends), with linear models adjusted for age, sex and BMI.

Results

- Total cholesterol in PXE patients was 5.6 [IQR 4.6-6.4] mmol/L versus 5.3 [IQR 4.7-6.0] mmol/L (p < 0.01) in the general population; triglycerides were 1.1 [IQR 0.9-1.7] mmol/L versus 1.0 [0.7-1.4] mmol/L (p < 0.01); HDL-c was 1.4 [IQR 1.2-1.7] mmol/L versus 1.5 [IQR 1.2-1.8] mmol/L (p = 0.03) and LDL-c was 3.3 [IQR 2.7-4.1] mmol/L versus 3.2 [IQR 2.7-3.8] mmol/L (p = 0.01). In the patient control analysis with 44 pairs and age, sex and BMI adjusted, comparison with the non-PXE controls only triglycerides were significantly different (mean difference: 0.38 (0.13-0.63)).

Conclusion

-The lipid profiles of PXE patients are marginally different from the general population or compared to a matched control group, but the differences are unlikely to be clinically relevant. It is therefore unlikely that plasma lipids contribute to the premature vascular calcifications in PXE patients.

Pseudoxanthoma elasticum veiled as vasculitis: shedding light on an uncommon disorder and an in-depth review of the literature

Pseudoxanthoma Elasticum (PXE) is a rare genetic disorder caused by an autosomal recessive mutation in the ABCC6 gene. It manifests with distinctive clinical symptoms impacting the skin, eyes, and cardiovascular system, along with an elevated risk of cardiovascular diseases. We present a case of a 34-year-old male patient who was initially referred to the rheumatology clinic for evaluation due to suspected large vessel vasculitis. The patient's primary complaint was severe hemifacial pain radiating to the neck and upper limb. Radiological imaging studies unveiled substantial vascular narrowing and collateral vessel formation, prompting further investigation to exclude systemic vasculitis. Intriguingly, the patient also exhibited cutaneous manifestations, which were later confirmed via skin biopsy as consistent with PXE. An ophthalmological examination further revealed the presence of the classic PXE findings of angioid streaks. Given the rarity of PXE and its multifaceted clinical presentation, it can be particularly challenging to diagnose and manage. As such, cases like the one presented here may necessitate a referral to a rheumatologist for evaluation of potential systemic involvement. To provide a comprehensive perspective on PXE, we conducted a systematic review of case reports published in the past decade in English, collected from PubMed, Scopus, and the Directory of Open Access databases. The analysis of these cases will be discussed to shed light on the diversity of PXE's clinical features and the diagnostic and management dilemmas it poses and to facilitate ongoing exploration and research into this intricate condition, ultimately leading to improved care for individuals affected by PXE.

The Purinergic Nature of Pseudoxanthoma Elasticum

Pseudoxanthoma Elasticum (PXE) is an inherited disease characterized by elastic fiber calcification in the eyes, the skin and the cardiovascular system. PXE results from mutations in ABCC6 that encodes an ABC transporter primarily expressed in the liver and kidneys. It took nearly 15 years after identifying the gene to better understand the etiology of PXE. ABCC6 function facilitates the efflux of ATP, which is sequentially hydrolyzed by the ectonucleotidases ENPP1 and CD73 into pyrophosphate (PPi) and adenosine, both inhibitors of calcification. PXE, together with General Arterial Calcification of Infancy (GACI caused by ENPP1 mutations) as well as Calcification of Joints and Arteries (CALJA caused by NT5E/CD73 mutations), forms a disease continuum with overlapping phenotypes and shares steps of the same molecular pathway. The explanation of these phenotypes place ABCC6 as an upstream regulator of a purinergic pathway (ABCC6 → ENPP1 → CD73 → TNAP) that notably inhibits mineralization by maintaining a physiological Pi/PPi ratio in connective tissues. Based on a review of the literature and our recent experimental data, we suggest that PXE (and GACI/CALJA) be considered as an authentic "purinergic disease". In this article, we recapitulate the pathobiology of PXE and review molecular and physiological data showing that, beyond PPi deficiency and ectopic calcification, PXE is associated with wide and complex alterations of purinergic systems. Finally, we speculate on the future prospects regarding purinergic signaling and other aspects of this disease.

Do pseudoxanthoma elasticum patients have higher prevalence of kidney stones on computed tomography compared to hospital controls?

BACKGROUND

Pseudoxanthoma elasticum (PXE) is an autosomal recessive disease characterized by diminished inorganic plasma pyrophosphate (PPi), a strong calcification inhibitor. In addition to more typical calcification of skin, retina and arterial wall a diminished plasma PPi could lead to other ectopic calcification, such as formation of kidney stones.

OBJECTIVE

To compare the prevalence of kidney stones between PXE patients and hospital controls on computed tomography (CT).

METHOD

Low-dose CT images of PXE patients and controls were assessed by one radiologist, who was blinded for the diagnosis PXE. The number of kidney stones, and the size of the largest stone was recorded. Odds ratios (ORs) for having kidney stone were calculated using multivariable adjusted logistic regression.

RESULTS

Our study comprised 273 PXE patients and 125 controls. The mean age of PXE patients was 51.5 ± 15.9 years compared to 54.9 ± 14.2 in the control group (p = 0.04) and PXE patients more often were women (63 vs. 50%, p = 0.013). The prevalence of kidney stones on CT was similar: 6.9% in PXE patients, compared to 5.6% in controls (p = 0.6). In the multivariate analysis adjusting for age and sex, there was no significantly higher odds for PXE patients on having stones, compared to controls: OR 1.48 (95% CI 0.62-3.96).

CONCLUSION

There is no significant difference in the prevalence of incidental kidney stones on CT in PXE patients versus controls.

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.

Pseudoxanthoma Elasticum With Detailed Analyses of Coronary Artery Disease

A 60-year-old woman with pseudoxanthoma elasticum (PXE) underwent thorough coronary artery disease assessments. Intravascular imaging tests suggested fragmented and calcified elastic fibers in the internal elastic lamina, suggesting a possible pathophysiology of coronary artery disease in PXE. Our case report would allow clinicians to acknowledge the clinical picture of PXE. (Level of Difficulty: Intermediate.).

Pseudoxanthoma-elasticum-like changes on the soft palate

Pseudoxanthoma elasticum (PXE) is an autosomal recessive genetic disorder characterized by aberrant fragmentation and calcification of elastic fibers, leading to characteristic cutaneous, ophthalmic, and cardiovascular manifestations. PXE demonstrates significant phenotypic variability; involvement of the oral mucosa may be the only clue to the diagnosis. Reports on mucous membrane involvement in PXE are scarce. Here, we present a case of PXE-like changes in the oral cavity. A 70-year-old male patient presented with a painless leukoplakic lesion on the soft palate. Biopsy revealed numerous degenerated fibers in the lamina propria. Verhoeff-van Gieson and von Kossa staining confirmed their identity as calcified elastic fibers. A histopathological diagnosis of PXE-like changes was made; the patient was referred to ophthalmology where angioid streaks were visualized fundoscopically. PXE-like changes in the absence of the characteristic genetic mutation have also been reported with or without systemic manifestations. Furthermore, PXE-like changes have been reported in up to 10% of oral biopsy specimens undertaken without clinical suspicion for PXE. Therefore, the significance of such changes in isolation is unclear. Clinicians and pathologists should be aware of the potential oral manifestations of PXE to facilitate prompt diagnosis and subspecialist referral.

Pseudoxanthoma elasticum is associated with cardiocirculatory inefficiency

Pseudoxanthoma elasticum (PXE) is a rare, genetic, metabolic disease characterized by dystrophic calcification of elastic fibres in the skin, retina and vascular wall. Data on cardiac involvement are inconsistent. Hence, we aimed to evaluate cardiorespiratory response to incremental cardiopulmonary exercise testing (CPET) in PXE. A total of 30 PXE patients (54.0 ± 11.2 years, 40.0% male) and 15 matched controls underwent symptom-limited incremental CPET. PXE patients presented an impaired peak work rate as compared to controls (84.2 ± 16.0% vs. 94.7 ± 10.4%, p = 0.03) that was accompanied by a lower peak oxygen uptake (in % predicted and mL/min/kg), reduced increments in oxygen uptake per increments of work rate (ΔV´O₂/ΔWR, 8.4 ± 3.0 mL/min/W vs. 11.3 ± 4.9 mL/ min/W, p = 0.02), lower peak oxygen pulse (78.0 ± 12.3% vs. 90.6 ± 19.6%, p = 0.01) and reduced minute ventilation at peak exercise (V´E, 66.2 ± 16.8% vs. 82.9 ± 25.2%, p = 0.02). To summarize, we presently observed impairment in mainly cardiocirculatory parameters, whilst no substantial ventilatory limitation was detected. The potential implications of this finding for PXE management warrant further study.

Genetic Causes of Cerebral Small Vessel Diseases: A Practical Guide for Neurologists

Cerebral small vessel disease (CSVD) includes various entities affecting the brain and, often, systemic small arteries, arterioles, venules, and capillaries. The underlying causes of CSVD are different, and some of them are genetic. Monogenic CSVDs are responsible for 1%-5% of all strokes and for several other disturbances. Despite many genes being involved, the phenotypes of monogenic CSVD partly overlap. Given that the genetic testing for different diseases can be challenging and time-consuming, the practicing neurologist should be adequately informed of the genetic background of CSVD and should be able to select patients to undergo genetic assessment and the genes to be analyzed. The purpose of this review was to summarize clinical, neurologic and non-neurologic, and neuroimaging features of monogenic CSVD and to provide a flowchart to be used in clinical practice to guide neurologists in this field. The proposed flowchart and the relative tables can be applied to 3 different settings, depending on the presentation: (1) ischemic stroke and/or transient ischemic attack, (2) cerebral hemorrhage, and (3) other neurologic, non-neurologic, and/or neuroimaging features of monogenic CSVD, in the absence of stroke syndromes because of infarction or hemorrhage.

Inner retinal degeneration associated with optic nerve head drusen in pseudoxanthoma elasticum

BACKGROUND/AIMS

To determine the association of age, presence of optic nerve head drusen (ONHD) and number of previous intravitreal anti-vascular endothelial growth factor (anti-VEGF) injections with inner retinal layer thicknesses in patients with pseudoxanthoma elasticum (PXE).

METHODS

In this retrospective case-control study, longitudinal spectral-domain optical coherence tomography imaging data from patients with PXE were compared with controls. A custom deep-learning-based segmentation algorithm was trained and validated to quantify the retinal nerve fibre layer (RNFL) and ganglion cell layer (GCL). The association of age, number of anti-VEGF injections and ONHD with the RNFL and GCL thickness in the outer ETDRS subfields as dependent variables was investigated using mixed model regression.

RESULTS

Fourty-eight eyes of 30 patients with PXE were compared with 100 healthy eyes. The mean age was 52.5±12.9 years (range 21.3-68.2) for patients and 54.2±18.7 years (range 18.0-84.5) for controls. In patients, ONHD were visible in 15 eyes from 13 patients and 31 eyes had received anti-VEGF injections. In the multivariable analysis, age (-0.10 µm/year, p<0.001), the diagnosis of PXE (-2.03 µm, p=0.005) and an interaction term between age and the presence of ONHD (-0.20 µm/year, p=0.001) were significantly associated with the GCL thickness. Including the number of intravitreal injections did not improve the model fit. The RNFL thickness was not significantly associated with any of these parameters.

CONCLUSIONS

This study demonstrates a significant association of ageing and ONHD with GCL thinning in patients with PXE, but not with the number of anti-VEGF injections. Given the severity of inner retinal degeneration in PXE, a clinical trial investigating neuroprotective therapy warrants consideration.

Lansoprazole Increases Inorganic Pyrophosphate in Patients with Pseudoxanthoma Elasticum: A Double-Blind, Randomized, Placebo-Controlled Crossover Trial

Pseudoxanthoma elasticum (PXE) is characterized by low levels of inorganic pyrophosphate (PPi) and a high activity of tissue-nonspecific alkaline phosphatase (TNAP). Lansoprazole is a partial inhibitor of TNAP. The aim was to investigate whether lansoprazole increases plasma PPi levels in subjects with PXE. We conducted a 2 × 2 randomized, double-blind, placebo-controlled crossover trial in patients with PXE. Patients were allocated 30 mg/day of lansoprazole or a placebo in two sequences of 8 weeks. The primary outcome was the differences in plasma PPi levels between the placebo and lansoprazole phases. 29 patients were included in the study. There were eight drop-outs due to the pandemic lockdown after the first visit and one due to gastric intolerance, so twenty patients completed the trial. A generalized linear mixed model was used to evaluate the effect of lansoprazole. Overall, lansoprazole increased plasma PPi levels from 0.34 ± 0.10 µM to 0.41 ± 0.16 µM (p = 0.0302), with no statistically significant changes in TNAP activity. There were no important adverse events. 30 mg/day of lansoprazole was able to significantly increase plasma PPi in patients with PXE; despite this, the study should be replicated with a large number of participants in a multicenter trial, with a clinical end point as the primary outcome.

Plasma Level of Pyrophosphate Is Low in Pseudoxanthoma Elasticum Owing to Mutations in the ABCC6 Gene, but It Does Not Correlate with ABCC6 Genotype

BACKGROUND

Pseudoxanthoma elasticum (PXE), a monogenic disorder resulting in calcification affecting the skin, eyes and peripheral arteries, is caused by mutations in the ABCC6 gene, and is associated with low plasma inorganic pyrophosphate (PP_i). It is unknown how ABCC6 genotype affects plasma PP_i.

METHODS

We studied the association of ABCC6 genotype (192 patients with biallelic pathogenic ABCC6 mutations) and PP_i levels, and its association with the severity of arterial and ophthalmological phenotypes. ABCC6 variants were classified as truncating or non-truncating, and three groups of the 192 patients were formed: those with truncating mutations on both chromosomes (n = 121), those with two non-truncating mutations (n = 10), and a group who had one truncating and one non-truncating ABCC6 mutation (n = 61). The hypothesis formulated before this study was that there was a negative association between PP_i level and disease severity.

RESULTS

Our findings confirm low PP_i in PXE compared with healthy controls (0.53 ± 0.15 vs. 1.13 ± 0.29 µM, p < 0.01). The PP_i of patients correlated with increasing age (β: 0.05 µM, 95% CI: 0.03-0.06 per 10 years) and was higher in females (0.55 ± 0.17 vs. 0.51 ± 0.13 µM in males, p = 0.03). However, no association between PP_i and PXE phenotypes was found. When adjusted for age and sex, no association between PP_i and ABCC6 genotype was found.

CONCLUSIONS

Our data suggest that the relationship between ABCC6 mutations and reduced plasma PP_i may not be as direct as previously thought. PP_i levels varied widely, even in patients with the same ABCC6 mutations, further suggesting a lack of direct correlation between them, even though the ABCC6 protein-mediated pathway is responsible for ~60% of this metabolite in the circulation. We discuss potential factors that may perturb the expected associations between ABCC6 genotype and PP_i and between PP_i and disease severity. Our findings support the argument that predictions of pathogenicity made on the basis of mutations (or on the structure of the mutated protein) could be misleading.

Peripheral Interventions in Patients with Pseudoxanthoma Elasticum (PXE)

OBJECTIVE

Pseudoxanthoma elasticum (PXE) is an autosomal recessive metabolic disorder that may be associated with a high prevalence of peripheral artery disease (PAD) and related symptoms. However, the evidence supporting this association is weak, as only small cohort studies are available. Furthermore, limited data are available on the outcome of lower limb peripheral arterial interventions (PAI) in patients with PXE. It was the aim of this study to clarify the prevalence of PAD, and the occurrence and outcome of PAI in patients with PXE.

METHODS

This was a retrospective review of prospectively collected data from the Dutch Expertise Centre for PXE database. Clinical data of consecutive patients with a definitive diagnosis of PXE were examined. The primary endpoint was the prevalence of PAD (defined as an ankle brachial index of < 0.9). The secondary endpoint was to report an overview of PAI and target lesion revascularisations.

RESULTS

In 285 PXE patients (median age 58 years), 50.9% of patients (n = 145) met the criteria for PAD. Seventeen patients underwent a PAI, mostly for intermittent claudication, at a median age of 51 years. The incidence of PAI was 2.25 per 1 000 patient years in patients with PAD and PXE. A total of 58 interventions was recorded, of which 35 were target lesion revascularisations in nine patients. Twenty one revascularisations were performed within a year following the primary intervention, in 16 cases due to an acute occlusion.

CONCLUSION

Within a well phenotyped and large PXE cohort, the diagnosis of PAD was prevalent in one in two patients. The observed rate of peripheral interventions was low, while the re-intervention rate was unfavourable after endovascular or bypass surgical procedures, with over half of these re-interventions indicated within a year.

Incidence and Risk Factors of Visual Impairment in Patients with Angioid Streaks and Macular Neovascularization

OBJECTIVE

To estimate the incidence and risk factors of visual impairment and complications in eyes with macular neovascularization (MNV) because of angioid streaks (ASs).

DESIGN

Longitudinal multicenter retrospective cohort study.

SUBJECTS

Patients with AS-associated MNV treated with anti-VEGF agents and a follow-up of > 3 months.

METHODS

Clinical and MNV characteristics were collected at baseline. Visual acuity (VA) values and the presence of atrophy or fibrosis were collected at each visit.

MAIN OUTCOME MEASURES

Rate of VA change over time and associated factors; the incidence rate of moderate-to-severe visual impairment (MSVI) and blindness and hazard ratio (HR) of candidate risk factors for MSVI; the incidence rate of fibrosis and macular atrophy.

RESULTS

Overall, 84 eyes of 66 patients (39 men, 58%) with a mean (standard deviation) age of 55.7 (13.8) years were followed for a mean (standard deviation) of 67.7 (48.5) months. The median number of anti-VEGF doses per eye was 13. The average rate (95% confidence interval [CI]) of visual loss was +0.04 (0.02-0.06) logarithm of the minimum angle of resolution/year (P < 0.001); the visual loss was faster in nonnaive eyes (P = 0.007) and those with better baseline VA (P < 0.001); it was slower in eyes with pattern dystrophy-like features (P = 0.04). The incidence rates (95% CI) of MSVI and blindness were 10.4 (6.88-15)/100-eye-years and 2.33 (1.12-4.29)/100-eye-years. A higher number of injections (HR [95% CI] = 0.45 [0.19-0.94] for receiving ≥ 13 injections vs. < 13; P = 0.03) was protective against MSVI. The incidence rates (95% CI) of fibrosis and macular atrophy were 24.1 (17.5-32.3)/100-eye-years and 14.3 (10.1-19.6)/100-eye-years.

CONCLUSIONS

Eyes with MNV-related AS had a high rate of visual impairment and propensity to macular fibrosis and atrophy. A higher number of injections yielded better chances of maintaining good VA, suggesting the need for intensive treatment.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

Various vascular malformations are prevalent in Finnish pseudoxanthoma elasticum (PXE) patients: a national registry study

Background

Pseudoxanthoma elasticum (PXE, OMIM# 264800) is an inborn error of metabolism causing ectopic soft tissue calcification due to low plasma pyrophosphate concentration. We aimed to assess the prevalence of PXE in Finland and to characterize the Finnish PXE population. A nationwide registry search was performed to identify patients with ICD-10 code Q82.84. Information was gathered from available medical records which were requisitioned from hospitals and health centers. Misdiagnosed patients and patients with insufficient records were excluded.

Results

The prevalence of PXE in Finland was 1:260,000 with equal sex distribution. Patients with high conventional cardiovascular risk had more visual and vascular complications than patients with low risk. Four patients (19%) had at least one vascular malformation. A high proportion (33%) of ABCC6 genotypes were of the common homozygous c.3421C > T, p.Arg1141Ter variant. Nine other homozygous or compound heterozygous allelic variants were found.

Conclusions

The prevalence of diagnosed PXE appears to be lower in Finland than in estimates from other countries. Decreased visual acuity is the most prevalent complication. We suggest that various vascular malformations may be an unrecognized feature of PXE.

Relationships between Plasma Pyrophosphate, Vascular Calcification and Clinical Severity in Patients Affected by Pseudoxanthoma Elasticum

Pseudoxanthoma elasticum (PXE; OMIM 264800) is an autosomal recessive metabolic disorder characterized by progressive calcification in the skin, the Bruch’s membrane, and the vasculature. Calcification in PXE results from a low level of circulating pyrophosphate (PPi) caused by ABCC6 deficiency. In this study, we used a cohort of 107 PXE patients to determine the pathophysiological relationship between plasma PPi, coronary calcification (CAC), lower limbs arterial calcification (LLAC), and disease severity. Overall, our data showed a deficit in plasma PPi in PXE patients compared to controls. Remarkably, affected females showed higher PPi levels than males, but a lower LLAC. There was a strong correlation between age and PPi in PXE patients (r = 0.423, p < 0.0001) but not in controls (r = 0.059, p = 0.828). A weak correlation was found between PPi and CAC (r = 0.266, p < 0.02); however, there was no statistically significant connection with LLAC (r = 0.068, p = 0.518) or a severity score (r = 0.077, p = 0.429). Surprisingly, we found no significant correlation between plasma alkaline phosphatase activity and PPi (r = 0.113, p = 0.252) or between a 10-year cardiovascular risk score and all other variables. Multivariate analysis confirmed that LLAC and CAC were strongly dependent on age, but not on PPi. Our data showed that arterial calcification is only weakly linked to circulating PPi levels and that time (i.e., age) appears to be the major determinant of disease severity and calcification in PXE. These data are important to better understand the natural history of this disease but also for the follow-up and management of patients, and the design of future clinical trials. Our results also show that PPi is not a good biomarker for the evaluation of disease severity and progression.

Neurovascular Syndromes

Patients with cerebrovascular syndromes are at risk for additional concerns associated with their syndrome. A wide variety of syndromes are associated with cerebrovascular diseases. Multidisciplinary care is helpful to ensure comprehensive evaluation and management. Precise diagnosis and appreciation for the underlying syndrome is critical for effective cerebrovascular and broader care. This text focuses on these conditions with a focus on underlying pathophysiology and associated genetics, presentation, diagnosis, and management of each disease.

Vascular uptake on 18F-sodium fluoride positron emission tomography: precursor of vascular calcification?

BACKGROUND

Microcalcifications cannot be identified with the present resolution of CT; however, 18F-sodium fluoride (18F-NaF) positron emission tomography (PET) imaging has been proposed for non-invasive identification of microcalcification. The primary objective of this study was to assess whether 18F-NaF activity can assess the presence and predict the progression of CT detectable vascular calcification.

METHODS AND RESULTS

The data of two longitudinal studies in which patients received a 18F-NaF PET-CT at baseline and after 6 months or 1-year follow-up were used. The target to background ratio (TBR) was measured on PET at baseline and CT calcification was quantified in the femoral arteries at baseline and follow-up. 128 patients were included. A higher TBR at baseline was associated with higher calcification mass at baseline and calcification progression (β = 1.006 [1.005-1.007] and β = 1.002 [1.002-1.003] in the studies with 6 months and 1-year follow-up, respectively). In areas without calcification at baseline and where calcification developed at follow-up, the TBR was .11-.13 (P < .001) higher compared to areas where no calcification developed.

CONCLUSION

The activity of 18F-NaF is related to the amount of calcification and calcification progression. In areas where calcification formation occurred, the TBR was slightly but significantly higher.

Pulsatility Attenuation along the Carotid Siphon in Pseudoxanthoma Elasticum

We compared velocity pulsatility, distensibility, and pulsatility attenuation along the intracranial ICA and MCA between 50 patients with pseudoxanthoma elasticum and 40 controls. Patients with pseudoxanthoma elasticum had higher pulsatility and lower distensibility at all measured locations, except for a similar distensibility at C4. The pulsatility attenuation over the siphon was similar between patients with pseudoxanthoma elasticum and controls. This finding suggests that other disease mechanisms are the main contributors to increased intracranial pulsatility in pseudoxanthoma elasticum.

Clinical Characterization of Korean Patients with Pseudoxanthoma Elasticum and Angioid Streaks

This study aimed to characterize Korean patients with pseudoxanthoma elasticum (PXE) presenting with angioid streaks. Retinal phenotypes were longitudinally evaluated by multimodal ophthalmic imaging, and targeted gene panel sequencing for inherited retinal diseases was conducted. Seven subjects from unrelated families (median age, 51.2 years) were enrolled and followed for a median of 3.2 years. Four asymptomatic patients were significantly younger than three symptomatic patients with decreased visual acuity at presentation (mean age; 38.1 vs. 61.5 years, p = 0.020). The asymptomatic patients maintained good vision (20/32 or better) and had no choroidal neovascularization (CNV) over the observation period. The symptomatic patients showed additional reduction in visual acuity and bilateral CNV occurrence during the longitudinal follow-up. Pathogenic ABCC6 variants were identified in all patients, leading to a diagnosis of PXE. Heterozygous monoallelic variants were identified in four patients and compound heterozygous variants were detected in three patients. Nine ABCC6 variants were identified, including one novel variant, c.2035G>T [p.Glu679Ter]. This is the first genetic study of Korean patients with PXE.

Cutaneous and Vascular Deposits of 18F-NaF by PET/CT in the Follow-Up of Patients with Pseudoxanthoma Elasticum

Active microcalcification of elastic fibers is a hallmark of pseudoxanthoma elasticum and it can be measured with the assessment of deposition of 18F-NaF using a PET/CT scan at the skin and vascular levels. It is not known whether this deposition changes over time in absence of specific therapy. We repeated in two years a PET/CT scan using 18F-NaF as a radiopharmaceutical in patients with the disease and compared the deposition at skin and vessel. Furthermore, calcium score values at the vessel wall were also assessed. Main results indicate in the vessel walls that calcification progressed in each patient; by contrast, the active microcalcification, measured and target-to-background ratio showed reduced active deposition. By contrast, at skin levels (neck and axillae) the uptake of the pharmaceutical remains unchanged. In conclusion, because calcification in the arterial wall is not specific for pseudoxanthoma elasticum condition, the measurement of the deposition of 18F-NaF in the neck might be potentially used as a surrogate marker in future trials for the disease.

Pseudoxanthoma elasticum overlaps hereditary spastic paraplegia type 56

PURPOSE

Pseudoxanthoma elasticum (PXE) is a recessive disorder involving skin, eyes and arteries, mainly caused by ABCC6 pathogenic variants. However, almost one fifth of patients remain genetically unsolved despite extensive genetic screening of ABCC6, as illustrated in a large French PXE series of 220 cases. We searched for new PXE gene(s) to solve the ABCC6-negative patients.

METHODS

First, family-based exome sequencing was performed, in one ABCC6-negative PXE patient with additional neurological features, and her relatives. CYP2U1, involved in hereditary spastic paraplegia type 56 (SPG56), was selected based on this complex phenotype, and the presence of two candidate variants. Second, CYP2U1 sequencing was performed in a retrospective series of 46 additional ABCC6-negative PXE probands. Third, six additional SPG56 patients were evaluated for PXE skin and eye phenotype. Additionally, plasma pyrophosphate dosage and functional analyses were performed in some of these patients.

RESULTS

6.4% of ABCC6-negative PXE patients (n = 3) harboured biallelic pathogenic variants in CYP2U1. PXE skin lesions with histological confirmation, eye lesions including maculopathy or angioid streaks, and various neurological symptoms were present. CYP2U1 missense variants were confirmed to impair protein function. Plasma pyrophosphate levels were normal. Two SPG56 patients (33%) presented some phenotypic overlap with PXE.

CONCLUSION

CYP2U1 pathogenic variants are found in unsolved PXE patients with neurological findings, including spastic paraplegia, expanding the SPG56 phenotype and highlighting its overlap with PXE. The pathophysiology of ABCC6 and CYP2U1 should be explored to explain their respective role and potential interaction in ectopic mineralization.

Genotype-phenotype correlation in pseudoxanthoma elasticum

BACKGROUND AND AIMS

Pseudoxanthoma elasticum (PXE) is caused by variants in the ABCC6 gene. It results in calcification in the skin, peripheral arteries and the eyes, but has considerable phenotypic variability. We investigated the association between the ABCC6 genotype and calcification and clinical phenotypes in these different organs.

METHODS

ABCC6 sequencing was performed in 289 PXE patients. Genotypes were grouped as two truncating, mixed, or two non-truncating variants. Arterial calcification mass was quantified on whole body, low dose CT scans; and peripheral arterial disease was measured with the ankle brachial index after treadmill test. The presence of pseudoxanthoma in the skin was systematically scored. Ophthalmological phenotypes were the length of angioid streaks as a measure of Bruchs membrane calcification, the presence of choroidal neovascularizations, severity of macular atrophy and visual acuity. Regression models were built to test the age and sex adjusted genotype-phenotype association.

RESULTS

158 patients (median age 51 years) had two truncating variants, 96 (median age 54 years) a mixed genotype, 18 (median age 47 years) had two non-truncating variants. The mixed genotype was associated with lower peripheral (β: 0.39, 95%CI:-0.62;-0.17) and total (β: 0.28, 95%CI:-0.47;-0.10) arterial calcification mass scores, and lower prevalence of choroidal neovascularizations (OR: 0.41 95%CI:0.20; 0.83) compared to two truncating variants. No association with pseudoxanthomas was found.

CONCLUSIONS

PXE patients with a mixed genotype have less severe arterial and ophthalmological phenotypes than patients with two truncating variants in the ABCC6 gene. Research into environmental and genetic modifiers might provide further insights into the unexplained phenotypic variability.

The Natural History of Bruch’s Membrane Calcification in Pseudoxanthoma Elasticum

Purpose

To describe the natural history of Bruch’s membrane (BM) calcification in patients with pseudoxanthoma elasticum (PXE).

Design

Retrospective cohort study.

Participants

Both eyes of 120 PXE patients younger than 50 years, 78 of whom had follow-up imaging after more than 1 year.

Methods

All patients underwent multimodal imaging, including color fundus photography, near-infrared reflectance (NIR) imaging, and late phase indocyanine green angiography (ICGA). We determined the distance from the optic disc to the central and temporal border of peau d’orange on NIR, expressed in horizontal optic disc diameter (ODD). The length of the longest angioid streak was classified into 5 zones.

Main Outcome Measures

Age-specific changes of peau d’orange, angioid streaks, and ICGA hypofluorescence as surrogate markers for the extent of BM calcification.

Results

In cross-sectional analysis, longer angioid streaks were associated with increasing age (P < 0.001 for trend). The temporal border of peau d’orange showed a weak association with increasing age (β = 0.02; 95% confidence interval [CI], 0.00–0.04), whereas the central border showed a strong association (β = 0.12; 95% CI, 0.09–0.15). Longitudinal analysis revealed a median shift of the central border to the periphery of 0.08 ODD per year (interquartile range [IQR], 0.00–0.17; P < 0.001). This shift was more pronounced in patients younger than 20 years (0.12 ODD per year [IQR, 0.08–0.28]) than in patients older than 40 years (0.07 ODD per year [IQR, –0.05 to 0.15]). The temporal border did not shift during follow-up (P = 0.69). New or growing angioid streaks were detected in 39 of 156 eyes (25%). The hypofluorescent area on ICGA was visible only in the fourth or fifth decade and correlated with longer angioid streaks.

Conclusions

In PXE patients, the speckled BM calcification slowly confluences during life. The location of the temporal border of peau d’orange remains rather constant, whereas the central border shifts to the periphery. This suggests the presence of a predetermined area for BM calcification. A larger ICGA hypofluorescent area correlates with older age and longer angioid streaks, which implies that it depends on the degree of BM calcification.

Mesopic and Scotopic Light Sensitivity and Its Microstructural Correlates in Pseudoxanthoma Elasticum

Importance

Correlates for Bruch membrane alterations are needed for interventional trials targeting the Bruch membrane in pseudoxanthoma elasticum (PXE).

Objectives

To quantify mesopic and scotopic light sensitivity and identify its microstructural correlates associated with a diseased Bruch membrane in patients with PXE.

Design, Setting, and Participants

A prospective, single-center, cross-sectional case-control study was conducted at a tertiary referral center from January 31, 2018, to February 20, 2020. Twenty-two eyes of 22 patients with PXE and 40 eyes of 40 healthy individuals were included. Data analysis was completed March 15, 2020.

Exposures

Mesopic and dark-adapted 2-color fundus-controlled perimetry (microperimetry) and multimodal retinal imaging including spectral-domain optical coherence tomography (SD-OCT) and OCT angiography were performed. Perimetry thresholds were analyzed using mixed models, and structure-function correlation with SD-OCT data was performed using machine learning.

Main Outcomes and Measures

Observed dark-adapted cyan sensitivity loss as measure of rod photoreceptor dysfunction, as well as mean absolute error between predicted and observed retinal sensitivity to assess the accuracy of structure-function correlation.

Results

Of the 22 patients with PXE included in this study, 15 were women (68%); median age was 56.5 years (interquartile range, 50.4-61.2). These patients exhibited mesopic (estimate, 5.13 dB; 95% CI, 2.89-7.38 dB), dark-adapted cyan (estimate, 9.08 dB; 95% CI, 6.34-11.82 dB), and dark-adapted red (estimate, 7.05 dB; 95% CI, 4.83-9.27 dB) sensitivity losses. This sensitivity loss was also evident in 9 eyes with nonneovascular PXE (mesopic: estimate, 3.21 dB; 95% CI, 1.28-5.14 dB; dark-adapted cyan: 5.93 dB; 95% CI, 3.59-8.27 dB; and dark-adapted red testing: 4.84 dB; 95% CI, 2.88-6.80 dB), showing a distinct centrifugal pattern of sensitivity loss with preserved function toward the periphery. Retinal function could be predicted from microstructure with high accuracy (mean absolute errors, of 4.91 dB for mesopic, 5.44 dB for dark-adapted cyan, and 4.99 dB for dark-adapted red). The machine learning-based analysis highlighted an association of a thinned inner retina and putative separation of the pigment-epithelium-photoreceptor complex with sensitivity loss.

Conclusions and Relevance

In this study, among 22 patients with PXE, those with and without choroidal neovascularization exhibited reductions of retinal sensitivity being most pronounced in dark-adapted cyan testing. This finding suggests that pathologic characteristics of this Bruch membrane disease may be dominated by rod photoreceptor degeneration and/or dysfunction. A putative pigment-epithelium-photoreceptor separation may further impair rod function, while inner retinal abnormalities appear to be correlated with overall dysfunction.

Autofluorescence Imaging of the Skin Is an Objective Non-Invasive Technique for Diagnosing Pseudoxanthoma Elasticum

Pseudoxanthoma elasticum (PXE) is a rare multisystemic autosomal recessive connective tissue disease. In most cases, skin manifestations of PXE are the first to develop, followed later by severe ocular and cardiovascular complications. In our present study, in addition to dermoscopy, we introduced novel techniques, autofluorescence (AF) and diffuse reflectance (DR) imaging for the assessment of affected skin sites of five PXE patients. PXE-affected skin areas in most skin sites showed a previously observed pattern upon dermoscopic examination. With the novel imaging, PXE-affected skin lesions displayed high AF intensity. During our measurements, significantly higher mean, minimum and maximum AF intensity values were found in areas of PXE-affected skin when compared to uninvolved skin. Conversely, images acquired with the use of 660 and 940 nm illumination showed no mentionable difference. Our results demonstrate that AF imaging may be used in the in vivo diagnostics and quantification of the severity of the skin lesions of PXE patients. In addition, it is a safe, fast and cost-effective diagnostic method. AF imaging may be also used to objectively monitor the efficacy of the possible novel therapeutic approaches of PXE in the future.

Molecular Genetics and Modifier Genes in Pseudoxanthoma Elasticum, a Heritable Multisystem Ectopic Mineralization Disorder

In the past two decades, there has been great progress in identifying the molecular basis and pathomechanistic details in pseudoxanthoma elasticum (PXE), a heritable multisystem ectopic mineralization disorder. Although the identification of pathogenic variants in ABCC6 has been critical for understanding the disease process, genetic modifiers have been disclosed that explain the phenotypic heterogeneity of PXE. Adding to the genetic complexity of PXE are PXE-like phenotypes caused by pathogenic variants in other ectopic mineralization-associated genes. This review summarizes the current knowledge of the genetics and candidate modifier genes in PXE, a multifactorial disease at the genome-environment interface.

Kidney Stones are Prevalent in Individuals with Pseudoxanthoma Elasticum, a Genetic Ectopic Mineralization Disorder

Pseudoxanthoma elasticum (PXE) is a rare genetic disorder caused by loss-of-function mutations in the ABCC6 gene. While PXE is characterized by ectopic mineralization of connective tissues clinically affecting the skin, eyes, and cardiovascular system, kidney stones were reported in some individuals with PXE. The aim of this study is to determine whether kidney stones are an incidental finding or a frequent manifestation of PXE. We investigated the genetic basis of two siblings diagnosed with PXE. The younger patient presented with recurrent kidney stones since age 8. To address whether kidney stones are associated with PXE, the prevalence of kidney stones in a survey cohort of 563 respondents with PXE was compared to that of a general U.S. population survey, NHANES (National Health and Nutrition Examination Survey), with 28,629 participants. Genetic analysis in both patients identified compound heterozygous mutations in ABCC6, c.2787+1G>T and c.3774_3775insC. The analysis of participants aged 20 and older revealed that 23.4% of PXE patients had previously had a kidney stone, a significant increase compared to 9.2% in the general population. In addition, 17.8% of PXE patients reported their first kidney stone episode before age 18. PXE correlates with an increased risk of developing kidney stones with considerable morbidity and health-care cost.

Osteoarthritis in Pseudoxanthoma Elasticum Patients: An Explorative Imaging Study

Pseudoxanthoma elasticum (PXE) is a systemic disease affecting the skin, eyes, and cardiovascular system of patients. Cardiovascular disease is associated with osteoarthritis (OA), which is the most common cause of joint pain. There is a lack of systematic investigations on joint manifestations in PXE in the literature. In this explorative study, we aimed to investigate whether patients with PXE are more at risk for developing osseous signs of OA. Patients with PXE and hospital controls with whole-body low-dose CT examinations available were included. OA was assessed using the OsteoArthritis Computed Tomography (OACT)-score, which is a 4-point Likert scale, in the acromioclavicular (AC), glenohumeral (GH), facet, hip, knee, and ankle joints. Additionally, intervertebral disc degeneration was scored. Data were analyzed using ordinal logistic regression adjusted for age, body mass index (BMI), and smoking status. In total, 106 PXE patients (age 56 (48-64), 42% males, BMI 25.3 (22.7-28.2)) and 87 hospital controls (age 55 (43-67), 46% males, BMI 26.0 (22.5-29.2)) were included. PXE patients were more likely to have a higher OA score for the AC joints (OR 2.00 (1.12-3.61)), tibiofemoral joint (OR 2.63 (1.40-5.07)), and patellofemoral joint (2.22 (1.18-4.24)). For the other joints, the prevalence and severity of OA did not differ significantly. This study suggests that patients with PXE are more likely to have structural OA of the knee and AC joints, which needs clinical confirmation in larger groups and further investigation into the mechanism.

The Extent of Angioid Streaks Correlates With Macular Degeneration in Pseudoxanthoma Elasticum

PURPOSE

To investigate whether the extent of Bruch's membrane calcification is associated with choroidal neovascularization (CNV) and macular atrophy in patients with pseudoxanthoma elasticum (PXE) by using the extent of angioid streaks as a surrogate marker for the degree of Bruch's membrane calcification.

DESIGN

Retrospective cross-sectional study.

METHODS

We investigated 301 patients with PXE (median age, 52 years; range, 9-79 years) in a tertiary referral center. For both eyes, we graded the extent of angioid streaks, that is, their distance from the optic disc, into 5 groups. Imaging was systematically assessed for signs of CNV and macular atrophy. Associations between the extent of angioid streaks and CNV or macular atrophy were investigated using regression analysis.

RESULTS

CNV was present in 148 patients (49%) and retinal atrophy in 71 patients (24%). The extent of angioid streaks was associated with older age (P for trend = 1.92 × 10^-15) and a higher prevalence of CNV and/or macular atrophy (P for trend = 4.22 × 10^-10 and P for trend = 5.17 × 10^-6, respectively). In addition, the extent of angioid streaks was associated with the presence of CNV when adjusted for age and sex (odds ratio, 1.9; 95% confidence interval, 1.3-2.9) and with more severe macular atrophy (proportional odds ratio, 2.3; 95% confidence interval, 1.5-3.6).

CONCLUSIONS

In patients with PXE, longer angioid streaks are associated with an increased risk of CNV and macular atrophy, even after adjustment for age. These findings are relevant when counseling PXE patients on their visual prognosis.

Assessment of Inflammation and Calcification in Pseudoxanthoma Elasticum Arteries and Skin with 18F-FluroDeoxyGlucose and 18F-Sodium Fluoride Positron Emission Tomography/Computed Tomography Imaging: The GOCAPXE Trial

Background: Pseudoxanthoma elasticum (PXE) is an inherited metabolic disease characterized by elastic fiber fragmentation and ectopic calcification. There is growing evidence that vascular calcification is associated with inflammatory status and is enhanced by inflammatory cytokines. Since PXE has never been considered as an inflammatory condition, no incidence of chronic inflammation leading to calcification in PXE has been reported and should be investigated. In atherosclerosis and aortic stenosis, positron emission tomography combined with computed tomographic (PET-CT) imaging has demonstrated a correlation between inflammation and calcification. The purpose of this study was to assess skin/artery inflammation and calcification in PXE patients. Methods: 18F-FluroDeoxyGlucose (18F-FDG) and 18F-Sodium Fluoride (18F-NaF) PET-CT, CT-imaging and Pulse wave velocity (PWV) were used to determine skin/vascular inflammation, tissue calcification, arterial calcium score (CS) and stiffness, respectively. In addition, inorganic pyrophosphate, high-sensitive C-reactive protein and cytokines plasma levels were monitored. Results: In 23 PXE patients, assessment of inflammation revealed significant 18F-FDG uptake in diseased skin areas contrary to normal regions, and exclusively in the proximal aorta contrary to the popliteal arteries. There was no correlation between 18F-FDG uptake and PWV in the aortic wall. Assessment of calcification demonstrated significant 18F-NaF uptake in diseased skin regions and in the proximal aorta and femoral arteries. 18F-NaF wall uptake correlated with CS in the femoral arteries, and aortic wall PWV. Multivariate analysis indicated that aortic wall 18F-NaF uptake is associated with diastolic blood pressure. There was no significant correlation between 18F-FDG and 18F-NaF uptake in any of the artery walls. Conclusion: In the present cross-sectional study, inflammation and calcification were not correlated. PXE would appear to more closely resemble a chronic disease model of ectopic calcification than an inflammatory condition. To assess early ectopic calcification in PXE patients, 18F-NaF-PET-CT may be more relevant than CT imaging. It potentially constitutes a biomarker for disease-modifying anti-calcifying drug assessment in PXE.

Non-exudative macular neovascularization in pseudoxanthoma elasticum

PURPOSE

To characterize morphological changes in the retina and to report the frequency and natural history of non-exudative macular neovascularization (MNV) in a cohort of pseudoxanthoma elasticum (PXE).

METHODS

A single-center, retrospective study was complemented by a cross-sectional examination. Consecutive patients with a definitive genetic and/or clinical diagnosis of PXE, visiting our department between January 2019 and December 2019, and with a minimum follow-up of 6 months were recruited. Baseline data were retrieved from each patient file. Additionally, a cross-sectional examination comprising color fundus photography, spectral-domain optical coherence tomography (SD-OCT), OCT-Angiography (OCT-A), and fundus autofluorescence was performed. The presence of typical PXE-related findings, as well as related complications, was multimodally evaluated. The prevalence and natural history of non-exudative MNV were assessed. All images were graded by two independent graders.

RESULTS

Forty-eight eyes from 24 patients (mean age 59.11 ± 18.14) with a median follow-up of 53.00 months were included. Angioid streaks and peau d'orange were observed in 46/48 and 42/48 eyes, while MNV was present in 75.00% of the cohort. The prevalence of non-exudative MNV was 33.33% (6/18). In the 2 eyes that developed exudation, time to conversion was 9.50 ± 4.95 months. No significant difference in visual acuity was found between eyes with non-exudative MNV and those with no signs of MNV.

CONCLUSION

We have shown that non-exudative MNV is a frequent finding in PXE but the majority of eyes did not develop exudation during follow-up. Our results are a clear evidence of the utility of OCT-A in the management of PXE.

The effect of etidronate on choroidal neovascular activity in patients with pseudoxanthoma elasticum

Aim

To assess the effect of the bisphosphonate etidronate on choroidal neovascular (CNV) activity in patients with pseudoxanthoma elasticum (PXE).

Methods

This is an ancillary study in a single center, randomized, double-blind placebo-controlled trial (RCT) in which 74 patients with PXE were assigned to either one-year etidronate or placebo treatment. Spectral domain optical coherence tomography (SD-OCT) imaging and color fundus photography were performed every three months for one year and were systematically assessed on signs of CNV activity.

Results

In the etidronate group, 11 (30%) of the patients had CNV activity at baseline, compared to 25 (67%) of the patients in the placebo group (P = 0.005). The proportion of eyes with CNV activity during the study ranged from 18–33% in the etidronate group and 42–56% in the placebo group and no significant difference in improvement or worsening of CNV activity was found (P = 0.168). Using a generalized mixed model for repeated measures, there was a protective effect of etidronate in crude analysis (RR 0.86, 95% CI 0.75–0.98) that disappeared when adjusting for baseline CNV activity (RR 0.97, 95% CI 0.84–1.13).

Conclusion

In this post-hoc RCT analysis we did not observe a protecting or deteriorating effect of etidronate on CNV activity in patients with PXE after adjustment for baseline CNV.

Late-onset Pseudoxanthoma Elasticum Associated with a Hypomorphic ABCC6 Variant

PURPOSE

To describe patients with late-onset pseudoxanthoma elasticum (PXE) associated with a likely hypomorphic ABCC6 variant.

DESIGN

Retrospective observational case series.

METHODS

Clinical evaluation, multimodal retinal imaging, genetic testing, and molecular modeling.

RESULTS

Three patients, in whom vision symptoms first arose at 80 years of age or later, showed age-related macular degeneration (AMD)-like fundus changes. However, features characteristic of PXE, including discrete angioid streaks and reduced fluorescence on late-phase indocyanine green angiography, prompted genetic testing which revealed the c.1171A>G variant in combination with a large deletion in the ABCC6 gene in each case. None of the patients had obvious skin changes or cardiovascular disease atypical for their age. Comparative molecular modeling supported the hypothesis that the c.1171A>G_ABCC6 variant acted as a hypomorphic variant.

CONCLUSIONS

Late-onset PXE extends the spectrum of ectopic calcification disorders caused by mutations in ABCC6 and may clinically be limited to the eye, mimicking AMD. Patients may be identified based on specific ocular changes, whereas skin and cardiovascular changes may remain ambiguous. The study provides evidence for a role for hypomorphic ABCC6 variants in the pathogenesis of PXE.

Increased Elastin Degradation in Pseudoxanthoma Elasticum Is Associated with Peripheral Arterial Disease Independent of Calcification

Pseudoxanthoma elasticum (PXE) results in extensive fragmentation and calcification of elastin fibers in the peripheral arteries, which results in peripheral arterial disease (PAD). Current research focuses on the role of calcifications in the pathogenesis of PXE. Elastin degradation and calcification are shown to interact and may amplify each other. This study aims to compare plasma desmosines, a measure of elastin degradation, between PXE patients and controls and to investigate the association between desmosines and (1) arterial calcification, (2) PAD, and (3) PAD independent of arterial calcification in PXE. Plasma desmosines were quantified with liquid chromatography-tandem mass spectrometry in 93 PXE patients and 72 controls. In PXE patients, arterial calcification mass was quantified on CT scans. The ankle brachial index (ABI) after treadmill test was used to analyze PAD, defined as ABI < 0.9, and the Fontaine classification was used to distinguish symptomatic and asymptomatic PAD. Regression models were built to test the association between desmosines and arterial calcification and arterial functioning in PXE. PXE patients had higher desmosines than controls (350 (290–410) ng/L vs. 320 (280–360) ng/L, p = 0.02). After adjustment for age, sex, body mass index, smoking, type 2 diabetes mellitus, and pulmonary abnormalities, desmosines were associated with worse ABI (β (95%CI): −68 (−132; −3) ng/L), more PAD (β (95%CI): 40 (7; 73) ng/L), and higher Fontaine classification (β (95%CI): 30 (6; 53) ng/L), but not with arterial calcification mass. Lower ABI was associated with higher desmosines, independent from arterial calcification mass (β (95%CI): −0.71(−1.39; −0.01)). Elastin degradation is accelerated in PXE patients compared to controls. The association between desmosines and ABI emphasizes the role of elastin degradation in PAD in PXE. Our results suggest that both elastin degradation and arterial calcification independently contribute to PAD in PXE.

Is arterial stiffness in the carotid artery associated with choroidal thinning in patients with pseudoxanthoma elasticum or controls?

PURPOSE

Patients with pseudoxanthoma elasticum (PXE) develop calcification of Bruch's membrane (BM) and choroidal thinning, as well as calcification of intracranial arteries, leading to arterial stiffness. We investigated whether arterial stiffness is associated with choroidal thinning in PXE patients, besides the presumed effect of BM calcification.

METHODS

Cross-sectional study with 75 PXE patients and 40 controls. Macular choroidal thickness was measured using optical coherence tomography scans. Functional magnetic resonance imaging was used to calculate the pulsatility index (PI) of the carotid siphon as a measure of arterial stiffness. Associations between PI and choroidal thickness were investigated using linear mixed effects models adjusted for age and ocular axial length. Furthermore, we investigated choroidal thickness in relation to the presence of retinal pigment epithelium (RPE) atrophy, its topographical distribution and age.

RESULTS

Median age was 58 years (IQR 53-66) in PXE patients and 62 years (IQR 56-67) in controls (p = 0.08). Pseudoxanthoma elasticum (PXE) patients had a thinner choroid than controls (138 μm versus 248 μm, p < 0.01). No association was observed between PI and choroidal thickness in PXE patients (β = -1.6, 95% CI -59.4 to 54.5) nor in controls (β =-47.6, 95% CI -129.7 to 31.9). In PXE patients, RPE atrophy was associated with a thinner choroid (p < 0.01). Also, the nasal choroid was thinner than the temporal choroid, and choroidal thickness already decreased with age in PXE eyes without RPE atrophy.

CONCLUSION

There was no independent association between measures of arterial stiffness and choroidal thinning in PXE patients and controls. Probably, changes in BM lead to choroidal thinning in PXE.

A Reflectivity Measure to Quantify Bruch's Membrane Calcification in Patients with Pseudoxanthoma Elasticum Using Optical Coherence Tomography

Purpose

Progressive calcification of Bruch's membrane (BM) causes considerable visual morbidity in patients with pseudoxanthoma elasticum (PXE). Since calcification is hyperreflective on optical coherence tomography (OCT), our aim was to measure BM calcification with OCT imaging.

Methods

Case-control study with 45 patients with PXE under 40 years (range, 11-39) and 25 controls (range, 14-39). Spectralis HRA-OCT imaging consisted of seven macular B-scans with 250-µm spacing. Retinal segmentation was performed with the IOWA Reference Algorithms. MATLAB was used to extract and average z-axis reflectivity profiles. Layer reflectivities were normalized to the ganglion cell and inner plexiform layers. Both median and peak layer reflectivities were compared between patients with PXE and controls. The discriminative value of the retinal pigment epithelium (RPE)-BM peak reflectivity was analyzed using receiver operating characteristic analysis.

Results

The reflectivity profile of patients with PXE differed from controls in the outer retinal layers. The normalized median RPE-BM reflectivity was 41.1 (interquartile range [IQR], 26.3-51.9) in patients with PXE, compared with 22.5 (IQR, 19.3-29.5) in controls (P = 2.09 × 10^-3). The normalized RPE-BM peak reflectivity was higher in patients with PXE (67.5; IQR, 42.1-84.2) than in controls (32.7; IQR, 25.7-38.9; P = 2.43 × 10^-5) and had a high discriminative value with an area under the curve of 0.85 (95% confidence interval, 0.76-0.95). In patients with PXE under 40 years, increasing age did not have a statistically significant effect on the RPE-BM peak reflectivity (patients under 20 years: 44.2 [IQR, 40.5-74.6]; 20-30 years: 66.0 [IQR, 45.1-83.8]; 30-40 years: 70.8 [IQR, 49.0-88.0], P = 0.47).

Conclusions

BM calcification can be measured as increased RPE-BM reflectivity in young patients with PXE and has a high discriminative value.

Translational Relevance

In patients with PXE, the OCT reflectivity of Bruch's membrane may be the first biomarker for Bruch's membrane calcification and a valuable ophthalmologic endpoint in clinical trials.

Cellular and Molecular Biomarkers Indicate Premature Aging in Pseudoxanthoma Elasticum Patients

The molecular processes of aging are very heterogenic and not fully understood. Studies on rare progeria syndromes, which display an accelerated progression of physiological aging, can help to get a better understanding. Pseudoxanthoma elasticum (PXE) caused by mutations in the ATP-binding cassette sub-family C member 6 (ABCC6) gene shares some molecular characteristics with such premature aging diseases. Thus, this is the first study trying to broaden the knowledge of aging processes in PXE patients. In this study, we investigated aging associated biomarkers in primary human dermal fibroblasts and sera from PXE patients compared to healthy controls. Determination of serum concentrations of the aging biomarkers eotaxin-1 (CCL11), growth differentiation factor 11 (GDF11) and insulin-like growth factor 1 (IGF1) showed no significant differences between PXE patients and healthy controls. Insulin-like growth factor binding protein 3 (IGFBP3) showed a significant increase in serum concentrations of PXE patients older than 45 years compared to the appropriate control group. Tissue specific gene expression of GDF11 and IGFBP3 were significantly decreased in fibroblasts from PXE patients compared to normal human dermal fibroblasts (NHDF). IGFBP3 protein concentration in supernatants of fibroblasts from PXE patients were decreased compared to NHDF but did not reach statistical significance due to potential gender specific variations. The minor changes in concentration of circulating aging biomarkers in sera of PXE patients and the significant aberrant tissue specific expression seen for selected factors in PXE fibroblasts, suggests a link between ABCC6 deficiency and accelerated aging processes in affected peripheral tissues of PXE patients.

Skin and Arterial Wall Deposits of 18F-NaF and Severity of Disease in Patients with Pseudoxanthoma Elasticum

Pseudoxanthoma elasticum (PXE) is a genetic disease characterized by the calcification of elastin fibers. Our aim was to quantify vascular calcification in the arteries and the deposition of 18F-sodium-fluoride (18F-NaF) in the skin and vessel walls with positron emission tomography/computed tomography. This was an observational study including 18 patients with PXE. Vascular calcification was measured in Agatston units, and deposition in the skin and vessel walls was shown using target-to-background ratio (TBR). Severity of the disease was scored by Phenodex. We found higher vascular calcification in the popliteal, femoral, and aortic arch vessels compared to other vascular regions; however, the uptake of radiotracer was the highest in the aorta and femoral arteries. In the skin, the highest uptake was observed in the neck and the axillae. There was no significant association between 18F-NaF deposition in the arteries or skin and the global Phenodex score. In contrast, the Phenodex score was significantly associated in univariate analyses with the averaged vascular calcium score (p < 0.01). In the neck, patients with higher skin Phenodex scores exhibited higher radiotracer uptake. As a conclusion, because vascular calcification is physiological, our data suggested that the detection of cutaneous (neck) 18F-NaF deposits might serve to monitor the calcification process in the short-term for patients with PXE.

Nonlinear optical microscopy is a novel tool for the analysis of cutaneous alterations in pseudoxanthoma elasticum

Pseudoxanthoma elasticum (PXE, OMIM 264800) is a rare autosomal recessive disorder with ectopic mineralization and fragmentation of elastin fibers. It is caused by mutations of the ABCC6 gene that leads to decreased serum levels of inorganic pyrophosphate (PPi) anti-mineralization factor. The occurrence of severe complications among PXE patients highlights the importance of early diagnosis so that prompt multidisciplinary care can be provided to patients. We aimed to examine dermal connective tissue with nonlinear optical (NLO) techniques, as collagen emits second-harmonic generation (SHG) signal, while elastin can be excited by two-photon excitation fluorescence (TPF). We performed molecular genetic analysis, ophthalmological and cardiovascular assessment, plasma PPi measurement, conventional histopathological examination, and ex vivo SHG and TPF imaging in five patients with PXE and five age- and gender-matched healthy controls. Pathological mutations including one new variant were found in the ABCC6 gene in all PXE patients and their plasma PPi level was significantly lower compared with controls. Degradation and mineralization of elastin fibers and extensive calcium deposition in the mid-dermis was visualized and quantified together with the alterations of the collagen structure in PXE. Our data suggests that NLO provides high-resolution imaging of the specific histopathological features of PXE-affected skin. In vivo NLO may be a promising tool in the assessment of PXE, promoting early diagnosis and follow-up.