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Pseudoxanthoma elasticum (PXE) is a heritable multisystem ectopic calcification disorder. The gene responsible for PXE, ABCC6, encodes ABCC6, a hepatic efflux transporter regulating extracellular inorganic pyrophosphate (PPi), a potent endogenous calcification inhibitor. Recent studies demonstrated that in addition to the deficiency of plasma PPi, the activated DDR/PARP signaling in calcified tissues provides an additional possible mechanism of ectopic calcification in PXE. This study examined the effects of etidronate (ETD), a stable PPi analog, and its combination with minocycline (Mino), a potent inhibitor of DDR/PARP, on ectopic calcification in an Abcc6-/- mouse model of PXE. Abcc6-/- mice, at 4 weeks of age, before the development of ectopic calcification, were treated with ETD, Mino, or both for 18 weeks. Micro-computed tomography, histopathologic examination, and quantification of the calcium content in Abcc6-/- mice treated with both ETD and Mino revealed further reduced calcification than either treatment alone. The effects were associated with reduced serum alkaline phosphatase activity without changes in plasma PPi concentrations. These results suggest that ETD and Mino combination therapy might provide an effective therapeutic approach for PXE, a currently intractable disease.

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 M to 0.41 0.16 M (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.

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 M to 0.41 0.16 M (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.

Pseudoxanthoma elasticum (PXE) and generalized arterial calcification of infancy (GACI) are clinically distinct genetic entities of ectopic calcification associated with differentially reduced circulating levels of inorganic pyrophosphate (PPi), a potent endogenous inhibitor of calcification. Variants in ENPP1, the gene mutated in GACI, have not been associated with classic PXE. Here we report the clinical, laboratory, and molecular evaluations of ten GACI and two PXE patients from five and two unrelated families registered in GACI Global and PXE International databases, respectively. All patients were found to carry biallelic variants in ENPP1. Among ten ENPP1 variants, one homozygous variant demonstrated uniparental disomy inheritance. Functional assessment of five previously unreported ENPP1 variants suggested pathogenicity. The two PXE patients, currently 57 and 27 years of age, had diagnostic features of PXE and had not manifested the GACI phenotype. The similarly reduced PPi plasma concentrations in the PXE and GACI patients in our study correlate poorly with their disease severity. This study demonstrates that in addition to GACI, ENPP1 variants can cause classic PXE, expanding the clinical and genetic heterogeneity of heritable ectopic calcification disorders. Furthermore, the results challenge the current prevailing concept that plasma PPi is the only factor governing the severity of ectopic calcification.

Pseudoxanthoma elasticum, a heritable multisystem ectopic mineralization disorder, is caused by inactivating mutations in the ABCC6 gene. The encoded protein, ABCC6, a transmembrane transporter, has a specialized efflux function in hepatocytes by contributing to plasma levels of inorganic pyrophosphate, a potent inhibitor of mineralization in soft connective tissues. Reduced plasma inorganic pyrophosphate levels underlie the ectopic mineralization in pseudoxanthoma elasticum. In this study, we characterized the pathogenicity of three human ABCC6 missense variants using an adenovirus-mediated liver-specific ABCC6 transgene expression system in an Abcc6

Inactivating mutations in ABCC6 underlie the rare hereditary mineralization disorder pseudoxanthoma elasticum. ABCC6 is an ATP-binding cassette (ABC) integral membrane protein that mediates the release of ATP from hepatocytes into the bloodstream. The released ATP is extracellularly converted into pyrophosphate, a key mineralization inhibitor. Although ABCC6 is firmly linked to cellular ATP release, the molecular details of ABCC6-mediated ATP release remain elusive. Most of the currently available data support the hypothesis that ABCC6 is an ATP-dependent ATP efflux pump, an un-precedented function for an ABC transporter. This hypothesis implies the presence of an ATP-binding site in the substrate-binding cavity of ABCC6. We performed an extensive mutagenesis study using a new homology model based on recently published structures of its close homolog, bovine Abcc1, to characterize the substrate-binding cavity of ABCC6. Leukotriene C4 (LTC4), is a high-affinity substrate of ABCC1. We mutagenized fourteen amino acid residues in the rat ortholog of ABCC6, rAbcc6, that corresponded to the residues in ABCC1 found in the LTC4 binding cavity. Our functional characterization revealed that most of the amino acids in rAbcc6 corresponding to those found in the LTC4 binding pocket in bovine Abcc1 are not critical for ATP efflux. We conclude that the putative ATP binding site in the substrate-binding cavity of ABCC6/rAbcc6 is distinct from the bovine Abcc1 LTC4-binding site.

Background Polar bears are uniquely adapted to an Arctic existence. Since their relatively recent divergence from their closest living relative, brown bears, less than 500,000 years ago, the species has evolved an array of novel traits suited to its Arctic lifestyle. Previous studies sought to uncover the genomic underpinnings of these unique characteristics, and disclosed the genes showing the strongest signal of positive selection in the polar bear lineage. Here, we survey a comprehensive dataset of 109 polar bear and 33 brown bear genomes to investigate the genomic variants within these top genes present in each species. Specifically, we investigate whether fixed homozygous variants in polar bears derived from selection on standing variation in the ancestral gene pool or on de novo mutation in the polar bear lineage. Results We find that a large number of sites fixed in polar bears are biallelic in brown bears, suggesting selection on standing variation. Moreover, we uncover sites in which polar bears are fixed for a derived allele while brown bears are fixed for the ancestral allele, which we suggest may be a signal of de novo mutation in the polar bear lineage. Conclusions Our findings suggest that, among other mechanisms, natural selection acting on changes in genes derived from a combination of variation already in the ancestral gene pool, and from de novo missense mutations in the polar bear lineage, may have enabled the rapid adaptation of polar bears to their new Arctic environment.

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.

Epidemiological studies indicate that elevated alkaline phosphatase activity is associated with increased cardiovascular disease risk. Other epidemiological data demonstrate that mothers giving multiple childbirths (multipara) are also at increased risk of developing late-onset cardiovascular disease. We hypothesized that these two associations stem from a common cause, the insufficient plasma level of the ectopic mineralization inhibitor inorganic pyrophosphate, which is a substrate of alkaline phosphatase. As alkaline phosphatase activity is elevated in pregnancy, we hypothesized that pyrophosphate concentrations decrease gestationally, potentially leading to increased maternal vascular calcification and cardiovascular disease risk in multipara. We investigated plasma pyrophosphate kinetics pre- and postpartum in sheep and at term in humans and demonstrated its shortage in pregnancy, mirroring alkaline phosphatase activity. Next, we tested whether multiparity is associated with increased vascular calcification in pseudoxanthoma elasticum patients, characterized by low intrinsic plasma pyrophosphate levels. We demonstrated that these patients had increased vascular calcification when they give birth multiple times. We propose that transient shortages of pyrophosphate during repeated pregnancies might contribute to vascular calcification and multiparity-associated cardiovascular disease risk threatening hundreds of millions of healthy women worldwide. Future trials are needed to assess if gestational pyrophosphate supplementation might be a suitable prophylactic treatment to mitigate maternal cardiovascular disease risk in multiparous women.

Background Polar bears are uniquely adapted to an Arctic existence. Since their relatively recent divergence from their closest living relative, brown bears, less than 500,000 years ago, the species has evolved an array of novel traits suited to its Arctic lifestyle. Previous studies sought to uncover the genomic underpinnings of these unique characteristics, and disclosed the genes showing the strongest signal of positive selection in the polar bear lineage. Here, we survey a comprehensive dataset of 109 polar bear and 33 brown bear genomes to investigate the genomic variants within these top genes present in each species. Specifically, we investigate whether fixed homozygous variants in polar bears derived from selection on standing variation in the ancestral gene pool or on de novo mutation in the polar bear lineage. Results We find that a large number of sites fixed in polar bears are biallelic in brown bears, suggesting selection on standing variation. Moreover, we uncover sites in which polar bears are fixed for a derived allele while brown bears are fixed for the ancestral allele, which we suggest may be a signal of de novo mutation in the polar bear lineage. Conclusions Our findings suggest that, among other mechanisms, natural selection acting on changes in genes derived from a combination of variation already in the ancestral gene pool, and from de novo missense mutations in the polar bear lineage, may have enabled the rapid adaptation of polar bears to their new Arctic environment.

Pseudoxanthoma elasticum (PXE) is an autosomal recessive disorder characterized by atypical elastic fibers that causes connective tissue abnormalities of the skin, eyes, and heart, among other organs. The disorder is rare, with a classic presentation of yellow-orange cobblestone-like papules on flexural areas, lax skin, ocular degeneration, and moribund vasculature in multiple organs. There is wide variability in the presentation of the affected organs [1]. We present two sisters with classic cutaneous findings of PXE with the additional unusual findings of numerous open comedones on the neck. To our knowledge, this is the first report of numerous open comedones in familial PXE.

Pseudoxanthoma elasticum (PXE) is an autosomal recessive disorder characterized by atypical elastic fibers that causes connective tissue abnormalities of the skin, eyes, and heart, among other organs. The disorder is rare, with a classic presentation of yellow-orange cobblestone-like papules on flexural areas, lax skin, ocular degeneration, and moribund vasculature in multiple organs. There is wide variability in the presentation of the affected organs [1]. We present two sisters with classic cutaneous findings of PXE with the additional unusual findings of numerous open comedones on the neck. To our knowledge, this is the first report of numerous open comedones in familial PXE.

A 50-year-old woman presented with a 2-year history of a yellowish plaque studded with red brown keratotic papules in the periumbilical region. Histopathological examination from the yellow plaque showed curled and granular elastic fibers in the mid and lower dermis. Histopathological examination from a keratotic papule showed pathological elastic fibers and dense chronic inflammatory cells around areas of perforation. Clinicopathological correlation established periumbilical perforating pseudoxanthoma elasticum as the final diagnosis.

Purpose - To present en face optical coherence tomography (OCT) images generated by graph-search theory algorithm-based custom software and examine correlation with other imaging modalities. Methods - En face OCT images derived from high density OCT volumetric scans of 3 healthy subjects and 4 patients using a custom algorithm (graph-search theory) and commercial software (Heidelberg Eye Explorer software (Heidelberg Engineering)) were compared and correlated with near infrared reflectance, fundus autofluorescence, adaptive optics flood-illumination ophthalmoscopy (AO-FIO) and microperimetry. Results - Commercial software was unable to generate accurate en face OCT images in eyes with retinal pigment epithelium (RPE) pathology due to segmentation error at the level of Bruch’s membrane (BM). Accurate segmentation of the basal RPE and BM was achieved using custom software. The en face OCT images from eyes with isolated interdigitation or ellipsoid zone pathology were of similar quality between custom software and Heidelberg Eye Explorer software in the absence of any other significant outer retinal pathology. En face OCT images demonstrated angioid streaks, lesions of acute macular neuroretinopathy, hydroxychloroquine toxicity and Bietti crystalline deposits that correlated with other imaging modalities. Conclusions - Graph-search theory algorithm helps to overcome the limitations of outer retinal segmentation inaccuracies in commercial software. En face OCT images can provide detailed topography of the reflectivity within a specific layer of the retina which correlates with other forms of fundus imaging. Our results highlight the need for standardization of image reflectivity to facilitate quantification of en face OCT images and longitudinal analysis.

A 50-year-old woman presented with a 2-year history of a yellowish plaque studded with red brown keratotic papules in the periumbilical region. Histopathological examination from the yellow plaque showed curled and granular elastic fibers in the mid and lower dermis. Histopathological examination from a keratotic papule showed pathological elastic fibers and dense chronic inflammatory cells around areas of perforation. Clinicopathological correlation established periumbilical perforating pseudoxanthoma elasticum as the final diagnosis.

The function of the ATP-binding cassette transporter MRP6 is unknown but mutations in its gene cause pseudoxanthoma elasticum. We have investigated the membrane topology of the N-terminal transmembrane domain TMD0 of MRP6 and the membrane integration and orientation propensities of its transmembrane segments (TMs) by glycosylation mapping. Results demonstrate that TMD0 has five TMs, an Nout-Cin topology and that the less hydrophobic TMs have strong preference for their orientation in the membrane that affects the neighboring TMs. Two disease-causing mutations changing the number of positive charges in the loops of TMD0 did not affect the membrane insertion efficiencies of the adjacent TMs.

Pseudoxanthoma elasticum (PXE), an autosomal recessive disorder characterized by ectopic mineralization, is caused by mutations in the ABCC6 gene. We examined clinically 29 Chinese PXE patients from unrelated families, so far the largest cohort of Asian PXE patients. In a subset of 22 patients, we sequenced ABCC6 and another candidate gene, ENPP1, and conducted pathogenicity analyses for each variant. We identified a total of 17 distinct mutations in ABCC6, 15 of them being, to our knowledge, previously unreported, including 5 frameshift and 10 missense variants. In addition, a missense mutation in combination with a recurrent nonsense mutation in ENPP1 was discovered in a pediatric PXE case. No cases with p.R1141X or del23-29 mutations, common in Caucasian patient populations, were identified. The 10 missense mutations in ABCC6 were expressed in the mouse liver via hydrodynamic tail-vein injections. One mutant protein showed cytoplasmic accumulation indicating abnormal subcellular trafficking, while the other nine mutants showed correct plasma membrane location. These nine mutations were further investigated for their pathogenicity using a recently developed zebrafish mRNA rescue assay. Minimal rescue of the morpholino-induced phenotype was achieved with eight of the nine mutant human ABCC6 mRNAs tested, implying pathogenicity. This study demonstrates that the Chinese PXE population harbors unique ABCC6 mutations. These genetic data have implications for allele-specific therapy currently being developed for PXE.

OBJECTIVE: Mutations in ABCC6 underlie the ectopic mineralization disorder pseudoxanthoma elasticum (PXE) and some forms of generalized arterial calcification of infancy, both of which affect the cardiovascular system. Using cultured cells, we recently showed that ATP-binding cassette subfamily C member 6 (ABCC6) mediates the cellular release of ATP, which is extracellularly rapidly converted into AMP and the mineralization inhibitor inorganic pyrophosphate (PPi). The current study was performed to determine which tissues release ATP in an ABCC6-dependent manner in vivo, where released ATP is converted into AMP and PPi, and whether human PXE ptients have low plasma PPi concentrations.APPROACH AND RESULTS: Using cultured primary hepatocytes and in vivo liver perfusion experiments, we found that ABCC6 mediates the direct, sinusoidal, release of ATP from the liver. Outside hepatocytes, but still within the liver vasculature, released ATP is converted into AMP and PPi. The absence of functional ABCC6 in patients with PXE leads to strongly reduced plasma PPi concentrations.CONCLUSIONS: Hepatic ABCC6-mediated ATP release is the main source of circulating PPi, revealing an unanticipated role of the liver in systemic PPi homeostasis. Patients with PXE have a strongly reduced plasma PPi level, explaining their mineralization disorder. Our results indicate that systemic PPi is relatively stable and that PXE, generalized arterial calcification of infancy, and other ectopic mineralization disorders could be treated with PPi supplementation therapy.

OBJECTIVE: Pseudoxanthoma elasticum is an inherited metabolic disorder resulting from ABCC6 gene mutations. It is characterized by progressive calcification and fragmentation of elastic fibers in the skin, retina, and the arterial wall. Despite calcium accumulation in the arteries of patients with pseudoxanthoma elasticum, functional consequences remain unknown. In the present study, we investigated arterial structure and function in Abcc6(-/-) mice, a model of the human disease.APPROACH AND RESULTS: Arterial calcium accumulation was evaluated using alizarin red stain and atomic absorption spectrometry. Expression of genes involved in osteochondrogenic differentiation was measured by polymerase chain reaction. Elastic arterial properties were evaluated by carotid echotracking. Vascular reactivity was evaluated using wire and pressure myography and remodeling using histomorphometry. Arterial calcium accumulation was 1.5- to 2-fold higher in Abcc6(-/-) than in wild-type mice. Calcium accumulated locally leading to punctuate pattern. Old Abcc6(-/-) arteries expressed markers of both osteogenic (Runx2, osteopontin) and chondrogenic lineage (Sox9, type II collagen). Abcc6(-/-) arteries displayed slight increase in arterial stiffness and vasoconstrictor tone in vitro tended to be higher in response to phenylephrine and thromboxane A2. Pressure-induced (myogenic) tone was significantly higher in Abcc6(-/-) arteries than in wild type. Arterial blood pressure was not significantly changed in Abcc6(-/-), despite higher variability.CONCLUSIONS: Scattered arterial calcium depositions are probably a result of osteochondrogenic transdifferentiation of vascular cells. Lower elasticity and increased myogenic tone without major changes in agonist-dependent contraction evidenced in aged Abcc6(-/-) mice suggest a reduced control of local blood flow, which in turn may alter vascular homeostasis in the long term.

OBJECTIVE: Pseudoxanthoma elasticum is an inherited metabolic disorder resulting from ABCC6 gene mutations. It is characterized by progressive calcification and fragmentation of elastic fibers in the skin, retina, and the arterial wall. Despite calcium accumulation in the arteries of patients with pseudoxanthoma elasticum, functional consequences remain unknown. In the present study, we investigated arterial structure and function in Abcc6(-/-) mice, a model of the human disease.APPROACH AND RESULTS: Arterial calcium accumulation was evaluated using alizarin red stain and atomic absorption spectrometry. Expression of genes involved in osteochondrogenic differentiation was measured by polymerase chain reaction. Elastic arterial properties were evaluated by carotid echotracking. Vascular reactivity was evaluated using wire and pressure myography and remodeling using histomorphometry. Arterial calcium accumulation was 1.5- to 2-fold higher in Abcc6(-/-) than in wild-type mice. Calcium accumulated locally leading to punctuate pattern. Old Abcc6(-/-) arteries expressed markers of both osteogenic (Runx2, osteopontin) and chondrogenic lineage (Sox9, type II collagen). Abcc6(-/-) arteries displayed slight increase in arterial stiffness and vasoconstrictor tone in vitro tended to be higher in response to phenylephrine and thromboxane A2. Pressure-induced (myogenic) tone was significantly higher in Abcc6(-/-) arteries than in wild type. Arterial blood pressure was not significantly changed in Abcc6(-/-), despite higher variability.CONCLUSIONS: Scattered arterial calcium depositions are probably a result of osteochondrogenic transdifferentiation of vascular cells. Lower elasticity and increased myogenic tone without major changes in agonist-dependent contraction evidenced in aged Abcc6(-/-) mice suggest a reduced control of local blood flow, which in turn may alter vascular homeostasis in the long term.

OBJECTIVE: Mutations in ABCC6 underlie the ectopic mineralization disorder pseudoxanthoma elasticum (PXE) and some forms of generalized arterial calcification of infancy, both of which affect the cardiovascular system. Using cultured cells, we recently showed that ATP-binding cassette subfamily C member 6 (ABCC6) mediates the cellular release of ATP, which is extracellularly rapidly converted into AMP and the mineralization inhibitor inorganic pyrophosphate (PPi). The current study was performed to determine which tissues release ATP in an ABCC6-dependent manner in vivo, where released ATP is converted into AMP and PPi, and whether human PXE ptients have low plasma PPi concentrations.APPROACH AND RESULTS: Using cultured primary hepatocytes and in vivo liver perfusion experiments, we found that ABCC6 mediates the direct, sinusoidal, release of ATP from the liver. Outside hepatocytes, but still within the liver vasculature, released ATP is converted into AMP and PPi. The absence of functional ABCC6 in patients with PXE leads to strongly reduced plasma PPi concentrations.CONCLUSIONS: Hepatic ABCC6-mediated ATP release is the main source of circulating PPi, revealing an unanticipated role of the liver in systemic PPi homeostasis. Patients with PXE have a strongly reduced plasma PPi level, explaining their mineralization disorder. Our results indicate that systemic PPi is relatively stable and that PXE, generalized arterial calcification of infancy, and other ectopic mineralization disorders could be treated with PPi supplementation therapy.

BACKGROUND: Pseudoxanthoma elasticum (PXE) is a heritable ectopic mineralization disorder affecting cutaneous, ocular, and cardiovascular systems, caused by mutations in the ABCC6 gene. PXE presents with a marked clinical and genetic heterogeneity. Furthermore, heterozygous carriers may present with limited histopathological features. This study was conducted to investigate a patient with PXE and her family members clinically, histopathologically, and genetically. METHODS: Clinical and histopathological examinations and mutation analyses of ABCC6 gene were performed. RESULTS: Lesional skin biopsy of the patient with PXE demonstrated clumping and fragmentation of elastic fibers, and calcification in the dermis. Non-lesional axillary skin samples of the husband, daughter, and older son were histopathologically normal. The skin from a similar region of a younger son revealed elastic fibers with some fragmentation and clumping but no mineralization. The patient with PXE was homozygous for the R1141X mutation in the ABCC6 gene. The husband had wild-type alleles, while all children were heterozygous carriers. Daily treatment of antioxidant therapy with tocopherol acetate and ascorbic acid was prescribed to the patient with PXE. After one year, both clinical and histopathological regression of the lesions was observed; however, lesions began to progress during the additional 6-month period of treatment. CONCLUSION: The mutation analyses of ABCC6 gene are important to determine the genotype of both patients with PXE and putative heterozygous carriers, as histopathological features of carriers may differ even in the same family. The role of antioxidant therapy for PXE is unclear, and there is a need for controlled clinical trials.

Pseudoxanthoma elasticum (PXE), caused by mutations in the ABCC6 gene, demonstrates progressive build-up of calcium phosphate and proteoglycans in the skin, eye, and arteries, and is associated to myocardial infarctions, stroke, blindness, and elevated carotid intima-media thickness (CIMT). Although CIMT reduction with magnesium (Mg) has been documented in a mouse model for PXE (Abcc6(-/-) ), it is not clear if Mg is effective in humans with PXE to reduce CIMT. To examine this, we calculated the rate of change of CIMT (washout) in 15- and 12-month-old Abcc6(-/-) mice fed standard rodent diet with or without Mg supplementation for 2 months. Using means in untreated 15- and 12-month-old Abcc6(-/-) mice (145 and 120 μm, respectively), the rate of change was 8.3 μm/month. Using means in treated 15- and 12-month-old Abcc6(-/-) mice (118 and 104.6 μm, respectively), the rate of change was 4.5 μm. Compared to normal progression of CIMT in humans without PXE, PXE has advanced atherosclerosis and possibly a higher CIMT rate of change. This experiment may portend, at least in PXE, the rationale for a 1-year oral Mg CIMT clinical trial and may be useful for application in other progressive mineralizing disorders like atherosclerosis.

BACKGROUND: Pseudoxanthoma elasticum (PXE) is characterized by aberrant mineralization of connective tissues, causing considerable morbidity and mortality. The disease is typically of late onset, the skin manifestations first being noted in the teens or later. Another aberrant mineralization disorder, generalized arterial calcification of infancy (GACI), is present at birth and can demonstrate a phenotypic overlap with PXE. OBJECTIVES: A patient with PXE was noted to have skin findings as early as at 6 years of age, with cardiovascular involvement. The purpose of this study was to examine the genetic basis of this phenotypic presentation in the spectrum of PXE/GACI. METHODS: The patient's genotype was studied by sequencing ABCC6 and ENPP1, genes known to be associated with PXE and/or GACI. RESULTS: Screening of the ABCC6 gene revealed two pathogenetic mutations, p.R1141X and g.del23-29. Analysis of the ENPP1 gene failed to demonstrate the presence of mutations. CONCLUSIONS: This study demonstrates the presence of cutaneous findings of PXE in an 8-year-old paediatric patient, with cardiovascular involvement, illustrating the phenotypic spectrum of PXE.

Pseudoxanthoma elasticum (PXE; OMIM 264800) manifests with characteristic skin lesions of yellowish papules which coalesce into plaques of inelastic and leathery skin on the predilection sites (1). The ocular findings consist of angioid streaks, choroidal neovascularization and subretinal hemorrhages resulting in loss of visual acuity and occasional blindness. Cardiovascular problems include hypertension, intermittent claudication, and occasional myocardial infarcts and stroke. The prevalence of PXE is estimated to be in the range of 1:50,000-70,000 and to be more frequent in females than in males. The diagnosis can be challenging to clinicians due to late-onset of clinical manifestations and considerable heterogeneity. PXE is associated with mutations in the ABCC6 gene which encodes a transmembrane efflux transporter expressed primarily in the liver and the kidneys (2). Consequently, PXE has been suggested to be a metabolic disorder with ectopic mineralization of the peripheral connective tissues. Recent studies have also suggested that cutaneous features of PXE can be found in patients with generalized arterial calcification of infancy due to mutations in the ENPP1 gene (3, 4). Previous studies, which have documented close to 600 distinct mutations in the ABCC6 gene, have suggested the presence of unique mutations affecting certain ethnic groups with different ancestral backgrounds (5, 6). In this study, we asked the specific question whether Brazilian patients of mixed European, Native Indian and African ancestry with PXE harbor unique ABCC6 mutations, and whether such mutations might be correlated with the clinical phenotypes in this population with particular reference to heterozygous carriers.

Pseudoxanthoma elasticum (PXE) is a heritable ectopic mineralization disorder caused by loss-of-function mutations in the ABCC6 gene which is primarily expressed in the liver. There is currently no effective treatment for PXE. In this study, we characterized bone marrow derived mesenchymal stem cells (MSCs) and evaluated their ability to contribute to liver regeneration, with the aim to rescue PXE phenotype. The MSCs, isolated from GFP-transgenic mice by magnetic cell sorting, were shown to have high potential for hepatic differentiation, with expression of Abcc6, in culture. These cells were transplanted into the livers of 4-week-old immunodeficient Abcc6⁻/⁻ mice by intrasplenic injection one day after partial hepatectomy, when peak expression of the stromal cell derived factor-1 (SDF-1) in the liver was observed. Fluorescent bioimaging analyses indicated that transplanted MSCs homed into liver between day 1 and 7, and significant numbers of GFP-positive cells were confirmed in the liver by immunofluorescence. Moreover, enhanced engraftment efficiency was observed with MSCs with high expression levels of the chemokine receptor Cxcr4, a receptor for SDF-1. These data suggest that purified MSCs have the capability of differentiating into hepatic lineages relevant to PXE pathogenesis and may contribute to partial correction of the PXE phenotype.

Pseudoxanthoma elasticum (PXE) is an autosomal recessive disorder in which calcification of connective tissue leads to pathology in skin, eye and blood vessels. PXE is caused by mutations in ABCC6. High expression of this transporter in the basolateral hepatocyte membrane suggests that it secretes an as-yet elusive factor into the circulation which prevents ectopic calcification. Utilizing our Abcc6-/-mouse model for PXE, we tested the hypothesis that this factor is vitamin K (precursor) (Borst et al. 2008, Cell Cycle). For 3 months, Abcc6-/-and wild-type mice were put on diets containing either the minimum dose of vitamin K required for normal blood coagulation or a dose that was 100 times higher. Vitamin K was supplied as menaquinone-7 (MK-7). Ectopic calcification was monitored in vivo by monthly micro-CT scans of the snout, as the PXE mouse model develops a characteristic connective tissue mineralization at the base of the whiskers. In addition, calcification of kidney arteries was measured by histology. Results show that supplemental MK-7 had no effect on ectopic calcification in Abcc6-/-mice. MK-7 supplementation increased vitamin K levels (in skin, heart and brain) in wild-type and in Abcc6-/-mice. Vitamin K tissue levels did not depend on Abcc6 genotype. In conclusion, dietary MK-7 supplementation increased vitamin K tissue levels in the PXE mouse model but failed to counteract ectopic calcification. Hence, we obtained no support for the hypothesis that Abcc6 transports vitamin K and that PXE can be cured by increasing tissue levels of vitamin K.

Objective: Case report of a patient with angioid streaks, peau d'orange, comet tail lesions, choroidal neovascularisation and presumed pseudoxanthoma elasticum (PXE). PXE was confirmed by gene analysis but not by skin biopsies. Methods: Case report of a patient with angioid streaks identified at age 21 and follow-up till age 43 with repeated fluorescein angiography (FA) and optical coherence tomography (OCT). Dermatologic examination, skin biopsies and genetical analysis performed to confirm suspected diagnosis of PXE. Results: At age 43, no specific skin lesions were identified and 3 biopsies could not confirm PXE. Genetic analysis showed a homozygous mutation in the ABCC6 gene and confirmed the diagnosis of PXE. Conclusions: This case illustrates that in patients with angioid streaks having strong ocular indicators of PXE, confirmation of PXE can be obtained not only with dermatologic examination and skin biopsies, but also with genetic analysis. PXE associated mutations can be detected occasionally in biopsy negative patients and for this reason are extremely helpful in confirming a suspected diagnosis.

A 29-year-old woman affected by pseudoxanthoma elasticum gave birth to her second child in our department, thirteen months after the delivery of her first boy. Her care illustrates many of the potential risks of this rare autosomal systemic disorder. In order to detect any changes due to pregnancy, ophthalmologic and cardiologic screening examinations should be performed in the beginning of the pregnancy and repeated several weeks after the delivery. During labor, epidural anesthesia seems to be more advantageous.

This thesis describes research to elucidate the molecular pathology of pseudoxanthoma elasticum (PXE), from phenotype to genotype. PXE is an autosomally inherited disorder of connective tissue, affecting the skin, Bruch's membrane of the eye, and cardiovascular system. The most apparent clinical features of PXE is the skin manifestation. Ocular features include angioid streaks, peau d'orange, and comet-like streaks in the retina. Disability in PXE is usually the result of vascular complications, among which loss of visual acuity due to hemorrhage and scarring in the centre of the retina, the macula lutea. PXE is either sporadic or usually segregates as an recessive disorder. Also dominant inheritance has been described. PXE is caused by mutations in the ABCC6 (ATP-binding cassette, subfamily C, member 6) gene encoding a transmembrane protein. The aim of this thesis was outlined in a brief introduction on PXE in chapter 1.1. The history of PXE was described in chapter 1.2 in which we summarized clinical, histopathological, and molecular aspects of PXE by reviewing the literature over the period from 1966 to 2002.

We report the clinicopathological features of an old woman with a recent and progressive development of soft white-yellow papules of the neck and supraclavicular areas reminding of pseudoxanthoma elasticum without systemic involvement. The similarity of this entity with fibroelastopathic papular dermatoses of the neck is briefly discussed.

Pseudoxanthoma elasticum complicated by angioid streaks and various other vascular problems was described. The patient was a 69-year-old female and was found to be hypertensive with the left ventricular hypertrophy. Skin biopsies from bilateral sides of the neck disclosed a typical lesion indicating pseudoxanthoma elasticum. Subsequently, several complications were sorted out and hypertension has been well under control. Apart from angioid streaks and hypertension, the possibility of vascular Involvement, such as in the gastrointestinal tract, four extremities, lung and heart was cautioned. And, attention to this disorder, especially among internists, was aroused.

We examined a patient with central retinal artery occlusion (CRAO) who was diagnosed as having pseudoxanthoma elasticum and exhibited angioid streaks. Echocardiography revealed stenosis and plaques of the right carotid artery. Magnetic resonance imaging (MRI) showed multiple cerebral infarctions, which were considered to be the result of vascular-endothelial abnormalities associated with pseudoxanthoma elasticum. Systemic examination of any plaque which may cause CRAO is recommended.