Pseudoxanthoma elasticum: clinical phenotypes, molecular genetics and putative pathomechanisms

Pseudoxanthoma elasticum (PXE), a prototype of heritable multisystem disorders, is characterised by pathologic mineralisation of connective tissues, with primary clinical manifestations in the skin, eyes and the cardiovascular system. The causative gene was initially identified as ABCC6 which encodes an ABC transporter protein (ABCC6) expressed primarily in the liver and the kidneys. The critical role of ABCC6 in ectopic mineralisation has been confirmed by the development of Abcc6(-/-) knock-out mice which recapitulate the features of connective tissue mineralisation characteristic of PXE. Over 300 distinct loss-of-function mutations representative of over 1000 mutant alleles in ABCC6 have been identified by streamlined mutation detection strategies in this autosomal recessive disease. More recently, missense mutations in the GGCX gene, either in compound heterozygous state or digenic with a recurrent ABCC6 nonsense mutation (p.R1141X), have been identified in patients with PXE-like cutaneous findings and vitamin K-dependent coagulation factor deficiency. GGCX encodes a carboxylase which catalyses gamma-glutamyl carboxylation of coagulation factors as well as of matrix gla protein (MGP) which in fully carboxylated form serves as a systemic inhibitor of pathologic mineralisation. Collectively, these observations suggest the hypothesis that a consequence of loss-of-function mutations in the ABCC6 gene is the reduced vitamin K-dependent gamma-glutamyl carboxylation of MGP, with subsequent connective tissue mineralisation. Further progress in understanding the detailed pathomechanisms of PXE should provide novel strategies to counteract, and perhaps cure, this complex heritable disorder at the genome-environment interface.

Complementary angiographic and autofluorescence findings in pseudoxanthoma elasticum

Pseudoxanthoma elasticum (PXE) is a systemic disease with characteristic findings on fundus examination. The fundus findings may be difficult to detect with ophthalmoscopy. A case report is described as follows. A PXE patient had subtle retinal findings on fundoscopy that were more prominently seen using a combination of both fundus autofluorescence (FAF) imaging and indocyanine green (ICG) angiography. The fundus features visualized using each of these two modalities appeared different from each other. FAF imaging and ICG angiography may be able to more prominently detect pathology at the level of the retinal pigment epithelium and Bruch's membrane, respectively. The use of these imaging modalities together may be complementary and useful in the evaluation of patients with PXE.

Non-vascular vision loss in pseudoxanthoma elasticum

Pseudoxanthoma elasticum patients with angioid streaks are well-known to have acute vision loss due to choroidal bleeding. However, chronic vision loss due to macular atrophy is less well characterized. We describe a patient with sub-acute vision loss in one eye due to loss of macular retinal pigment epithelium function. Autofluorescence and pattern electroretinogram were useful adjuncts to help diagnose the source of her vision loss.

Placental calcification in pseudoxanthoma elasticum

INTRODUCTION

Pseudoxanthoma elasticum (PXE) is an inherited multisystem disorder of the elastic tissue and the objective of this case report is to correlate ultrasonographic and histological appearances of placental calcification in PXE.

CLINICAL PICTURE

We report a case of a 37-year-old white woman with PXE, whose antenatal imaging showed a markedly echogenic placenta due to extensive calcification confirmed on postpartum placental histology.

OUTCOME

There were no maternal or fetal complications in the antenatal period. A healthy baby of appropriate maturity and weight was delivered via Caesarean section and remained well at 6 months.

CONCLUSION

The majority of cases of PXE is caused by mutations in the ABCC6 gene. Serious complications in pregnancy can include gastrointestinal haemorrhage, congestive heart failure and cardiac arrhythmia but has not been shown to be associated with markedly increased fetal loss or adverse reproductive outcomes as reported in previous literature. Apart from the cosmetic deterioration of the abdominal skin, there were few serious complications and most have normal pregnancies. Obstetric prognosis is dependent on the vascular damage caused by the illness. There is no basis for advising women with PXE to avoid becoming pregnant, and most pregnancies in PXE are uncomplicated.

Pseudoxanthoma elasticum

Pseudoxanthoma elasticum (PXE) is an autosomal recessive disorder of connective tissue, characterized by elastic fibers mineralization and fragmentation, and affects the skin, eyes, cardiovascular system, and gastrointestinal system. PXE is caused by mutations in the ABCC6 gene, located on chromosome 16p13.1. We investigated clinical and laboratory three patients with pseudoxanthoma elasticum. All the patients present on dermatological examination yellowish papules, located especially on the neck and axillary area. In case no. 2 the patient presents "cutis laxa" in the axillary area. In case no. 3 the patient presents hyperpigmented spot on right forearm and another maculo-pigmented oval spot located at the base of the left posterior hemithorax. In two cases, the ophthalmologic examination shows angioid streaks. The modifications of elastic fibers (thickened or fragmented) are present in all cases.

Pseudoxanthoma elasticum-like papillary dermal elastolysis developed in early middle age

Pseudoxanthoma elasticum-like papillary dermal elastolysis is a rare acquired elastolytic disorder characterized by papules that resemble pseudoxanthoma elasticum, and it typically affects elderly women. Histopathological examination shows atrophic epidermis and band-like loss of elastic tissue in the papillary dermis. The pathogenesis is assumed to be related to intrinsic aging because it affects elderly people and shows the loss of elastic tissue. We report a case of pseudoxanthoma elasticum-like papillary dermal elastolysis in early middle age presenting typical clinical and histopathological findings. The patient was a 41-year-old woman who had had her lesions for 10 years. We propose that younger patients, hitherto unknown, can be affected by this disorder and suggest that mechanisms other than intrinsic aging are involved in its pathogenesis.

INTRAVITREAL BEVACIZUMAB FOR THE MANAGEMENT OF CHOROIDAL NEOVASCULARIZATION IN PSEUDOXANTHOMA ELASTICUM

PURPOSE

To determine the results of intravitreal bevacizumab injections for the management of choroidal neovascularization (CNV) in patients with pseudoxanthoma elasticum (PXE)-associated angioid streaks.

METHODS

A consecutive series of patients with PXE and CNV were managed with intravitreal bevacizumab injection (1.25 mg per 0.05 cc). The main outcome measures were visual acuity and greatest lesion height as measured by optical coherence tomography (OCT).

RESULTS

Nine eyes of nine consecutive patients received intravitreal bevacizumab (1.25 mg/0.05 mL) injections. The mean follow-up time was 6 months, during which eyes received an average of 1.8 injections. The baseline visual acuity was a mean of 20/368 and improved to 20/289 at the last visit (P = 0.056). Visual acuity either improved or stabilized in all 9 eyes (100%). Serial OCT measurements in 8 eyes showed a mean of 353 microm at baseline, which decreased to 201 mum at the last visit (P = 0.012). No complications were noted.

CONCLUSIONS

These short-term results support the use of intravitreal bevacizumab for the management of CNV in patients with PXE. Continued experience with intravitreal bevacizumab in this population will help establish its longer-term efficacy and better define the potential need for serial injections to maintain these results.

Pseudoxanthoma elasticum with cerebrovascular accident

A 65-year-old male presented with right hemiparesis and skin lesions. On examination, the patient had multiple, discrete, skin-colored papules on the neck and upper chest with wrinkling of the skin. The lateral part of the trunk and medial aspect of both upper arms showed atrophic plaques. A computerized tomography scan of the head showed dilatation of the basilar artery with a frontoparietal infarct. Funduscopic examination showed characteristic angioid streaks. Skin biopsy of the papule and atrophic plaques showed epidermal atrophy, calcium deposits in the mid-dermis and basophilic clumped and fragmented elastic fibers in the mid- and lower dermis, all findings consistent with pseudoxanthoma elasticum. We are reporting here a case of pseudoxanthoma elasticum with cerebrovascular accident.

Pseudoxanthoma elasticum-like phenotypes: more diseases than one

The classic pseudoxanthoma elasticum (PXE) phenotype derives from mutations in ABCC6. PXE-like phenotypes have been observed in a number of disorders, with no evidence of mutations in ABCC6. Vanakker et al. report PXE-like skin findings in patients with mutations in GGCX critical for gamma-carboxylation of gla-proteins. This report expands the clinical spectrum of PXE-like conditions and also provides potential insights into the ectopic mineralization process.

Contribution ofABCC6 genomic rearrangements to the diagnosis of pseudoxanthoma elasticum in French patients

Pseudoxanthoma elasticum (PXE) is an autosomal recessive disorder of connective tissues, which manifests with cutaneous, ophthalmologic and cardiovascular findings. PXE is caused by mutations in ABCC6 encoding a multidrug resistance protein (ABCC6, also known as MRP6). ABCC6 mutation detection rate ranges from 55% to 97% and it has been suggested that some of the remaining unidentified mutant alleles could correspond to large genomic rearrangements. In our cohort of 65 French PXE patients analysed for ABCC6 mutations, we identified two novel homozygous ABCC6 exonic deletions (deletions of exons 9-10 and exons 24-27). In order to systematically search for heterozygous genomic rearrangements, we have developed a quantitative multiplex PCR of short fluorescent fragments (QMPSF) approach that screens the 31 exons of ABCC6. We used QMPSF to analyse 13 PXE carrying at least one unidentified mutant, corresponding to 18 unidentified mutated alleles. This led to the detection of three large ABCC6 deletions, and two deletions of a single exon (exon 1 and exon 21). Thus QMPSF identified the causative mutation in 28% (5/18) of the uncharacterized ABCC6 mutant alleles in this cohort.

[Optic nerve drusen and angioid streaks in pseudoxanthoma elasticum]

The clinical study presents the association between optic disc drusen and angioid streaks in the context of pseudoxanthoma elasticum, in 8.5% (4 from 47) of the cases. The values are significantly higher compared to those from the normal population (0.34%). This result can be the consequence of pathogenic correlations between the two diseases, in which a role is attributed to the metabolic changes within the pseudoxanthoma elasticum. The starting point seems to be the accumulation of polyanions in the elastin of the cribriform plate, followed by disruption of axonal transport, mitochondrial extrusion and subsequent formation of optic disc drusen.

Pseudoxanthoma elasticum-like phenotype with cutis laxa and multiple coagulation factor deficiency represents a separate genetic entity

Data on six patients with a Pseudoxanthoma Elasticum (PXE)-like phenotype, characterized by excessive skin folding (resembling cutis laxa) and a deficiency of the vitamin K-dependent clotting factors (II, VII, IX, and X) are presented. A comparison is made between the clinical, ultrastructural, and molecular findings in these patients and those seen in classic PXE and cutis laxa, respectively. Clinical overlap with PXE is obvious from the skin manifestations of yellowish papules or leathery plaques with dot-like depressions at presentation, angioid streaks and/or ocular peau d'orange, and fragmentation and calcification of elastic fibers in the dermis. Important phenotypic differences with PXE include much more severe skin laxity with spreading toward the trunk and limbs with thick, leathery skin folds rather than confinement to flexural areas, and no decrease in visual acuity. Moreover, detailed electron microscopic analyses revealed that alterations of elastic fibers as well as their mineralization were slightly different from those in classic PXE. Molecular analysis revealed neither causal mutations in the ABCC6 gene (ATP-binding cassette subfamily C member 6), which is responsible for PXE, nor in VKORC1 (vitamin K 2,3 epoxide reductase), known to be involved in vitamin K-dependent factor deficiency. However, the GGCX gene (gamma-glutamyl carboxylase), encoding an enzyme important for gamma-carboxylation of gla-proteins, harbored mutations in six out of seven patients analyzed. These findings all support the hypothesis that the disorder indeed represents a separate clinical and genetic entity, the molecular background of which remains to be unraveled.

Pseudoxanthoma elasticum: evaluation of diagnostic criteria based on molecular data

BACKGROUND

Pseudoxanthoma elasticum (PXE) is a genetic disorder due to mutations in the gene encoding the transmembrane transporter protein adenosine triphosphate binding cassette (ABC)-C6, resulting in calcification of elastic fibres in the skin, eyes and cardiovascular system.

OBJECTIVES

To evaluate the diagnostic criteria for PXE based on molecular data.

METHODS

Of 10 families with a positive history of PXE 142 subjects were investigated for clinical symptoms, histological findings and genetic haplotype analysis.

RESULTS

Of these, 25 subjects were haplotypic homozygous for PXE and 23 had typical clinical and histopathological manifestations. Two of the 25 patients showed such marked solar elastosis and macular degeneration that PXE could not be confirmed clinically. Sixty-seven subjects were haplotypic heterozygous carriers and 50 were haplotypic homozygous unaffected. Of these 117 subjects, 116 showed no cutaneous or ophthalmological signs of PXE. In one of the 50 haplotypic homozygous unaffected patients important solar elastosis and scarring of the retina mimicked PXE lesions. Only four of the 67 haplotypic heterozygous carriers had biopsies of nonlesional skin; all were histopathologically normal.

CONCLUSIONS

In our patients, PXE presents as an autosomal recessive genodermatosis. Correlation of haplotype and phenotype confirmed actual major diagnostic criteria. In patients with marked solar elastosis and/or severe macular degeneration clinical diagnosis can be impossible and molecular testing is needed to confirm the presence of PXE. To the best of our knowledge our large study compares for the first time clinical findings with molecular data.