Successful Pedal Bypass in a Patient With Pseudoxanthoma Elasticum

OBJECTIVES

Pseudoxanthoma elasticum (PXE) is a rare metabolic disease, causing calcification in the arterial media layer and further peripheral artery disease (PAD). A high rate of failure has been reported after endovascular and open surgical management of PAD among patients with PXE. Critical limb ischemia (CLI) rarely develops in PXE, and there are only few reports of its treatment.

METHODS

We present a case report of a 57 year-old female diagnosed with pseudoxanthoma elasticum (PXE). She presented with critical limb ischemia (CLI) and was successfully treated with pedal bypass using the great saphenous vein.

RESULTS

Despite obtaining suboptimal outcomes through the initial approach of percutaneous transluminal angioplasty to treat critical limb ischemia, the subsequent bypass operation proved to be a success. At the first follow-up appointment at 1 month, the patient was asymptomatic and the ulceration had almost healed. The patient underwent an ultrasound examination at 3, 6, 12, and 24 months after discharge, and the surveillance was uncomplicated.

CONCLUSIONS

With a clear indication for surgery, limb-threatening ischemia can be successfully treated with distal bypass, if necessary, in patients with PXE similarly to atherosclerotic PADs. Appropriate diagnostic and surveillance imaging and the utilization of a multidisciplinary team are key components for effective management of PAD in patients with PXE.

The PROPHECI trial: a phase II, double-blind, placebo-controlled, randomized clinical trial for the treatment of pseudoxanthoma elasticum with oral pyrophosphate

BACKGROUND

/aims. Pseudoxanthoma Elasticum (PXE, OMIM 264800) is an autosomal, recessive, metabolic disorder characterized by progressive ectopic calcification in the skin, the vasculature and Bruch's membrane. Variants in the ABCC6 gene are associated with low plasma pyrophosphate (PPi) concentration. There is currently no reference treatment for this chronic debilitating disease.

METHODS

PROPHECI (PyROphosPHate supplementation to fight ECtopIc calcification in PseudoXanthoma Elasticum) is the first phase II, randomized, double-blind, placebo-controlled clinical trial (NTC 04868578) to evaluate the efficacy and safety of a daily oral PPi salt supplementation to attenuate and/or stabilize the progression of ectopic calcification in PXE patients. The primary endpoint is the change in arterial calcification volume quantified by non-contrast CT scan between baseline and 12 months of treatment. Secondary endpoints include the safety and efficacy of daily oral PPi administration on ocular and skin lesions and the evaluation of patients' quality of life.

DISCUSSION

The PROPHECI trial aims to provide safety and efficacy data on the use of daily oral PPi to reduce or stabilize ectopic calcification in PXE. It also aims to validate the best markers to include in the design of future trials for the treatment of PXE and other parent diseases.

TRIAL REGISTRATION

Trial registration number: NCT04868578. References can be found on the ClinicalTrials.gov website: https://clinicaltrials.gov/study/NCT04868578?cond=Pseudoxanthoma%20Elasticum&intr=pyrophosphate&rank=2.

Novel Human Induced Pluripotent Stem Cell-Based Model for Retinal Pigment Epithelial Cells to Reveal Possible Disease Mechanisms for Macular Degeneration in Pseudoxanthoma Elasticum

Pseudoxanthoma elasticum (PXE) is a rare metabolic disease with autosomal recessive inheritance. The manifestation in PXE is represented by retinal complications, pseudoxanthomas of the skin folding areas, and arterial calcification. The retinal complications are caused by the calcification of Bruch's membrane beneath retinal pigment epithelial cells (RPE) that can lead to retinal macular degeneration. The exact mechanism for the retinal pathophysiology is not known, and patients have variable symptoms and findings. Two induced pluripotent stem cell (hiPSC) lines from a patient carrying the common homozygous mutation c.3421C > T, p.Arg1141X in the ATP-binding cassette transporter gene (ABCC6; OMIM264800) were established and fully characterized. Then, RPE cells were differentiated, and molecular and functional characterization was conducted as a comparison to healthy controls. Data demonstrated that PXE-specific high-quality hiPSC lines can be established from a skin biopsy regardless of the skin-related disease phenotype and disease-specific RPE differentiation is feasible. The molecular and functional assessment of the PXE-specific RPE indicated increased pigmentation and reduced epithelial barrier functions as well as phagocytosis activity as compared to healthy controls. Although preliminary data, this indicates possible RPE-dependent factors that might explain the individual vulnerability of the retinas for macular degeneration in PXE. Future validation of the novel findings with additional PXE patients will be important.

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.

Therapeutics Development for Pseudoxanthoma Elasticum and Related Ectopic Mineralization Disorders: Update 2020

Pseudoxanthoma elasticum (PXE), the prototype of heritable ectopic mineralization disorders, manifests with deposition of calcium hydroxyapatite crystals in the skin, eyes and arterial blood vessels. This autosomal recessive disorder, due to mutations in ABCC6, is usually diagnosed around the second decade of life. In the spectrum of heritable ectopic mineralization disorders are also generalized arterial calcification of infancy (GACI), with extremely severe arterial calcification diagnosed by prenatal ultrasound or perinatally, and arterial calcification due to CD73 deficiency (ACDC) manifesting with arterial and juxta-articular mineralization in the elderly; the latter disorders are caused by mutations in ENPP1 and NT5E, respectively. The unifying pathomechanistic feature in these three conditions is reduced plasma levels of inorganic pyrophosphate (PPi), a powerful endogenous inhibitor of ectopic mineralization. Several on-going attempts to develop treatments for these conditions, either with the goal to normalize PPi plasma levels or by means of preventing calcium hydroxyapatite deposition independent of PPi, are in advanced preclinical levels or in early clinical trials. This overview summarizes the prospects of treatment development for ectopic mineralization disorders, with PXE, GACI and ACDC as the target diseases, from the 2020 vantage point.