Clinical and Molecular Characterization of a Patient with Generalized Arterial Calcification of Infancy Caused by Rare ABCC6 Mutation

Generalized arterial calcification of infancy (GACI) is a rare autosomal-recessive disease characterized by extensive arterial calcification in infancy, with clinical manifestations such as arterial stenoses and heart failure. The ENPP1 inactivation mutation has been identified as a potential defect in most of the cases of GACI, while mutations in ABCC6 are demonstrated in patients who are genotyped as pseudoxanthoma elasticum and only limited cases of GACI are reported. Whole-exome sequencing was applied for the detection of pathogenic variants. Copy-number variants of pathogenic genes were also evaluated through a bioinformatic process and were further validated by real-time quantitative PCR. In this report, we described the clinical information and treatment of a patient with extensive arterial calcification. We have identified the underlying cause as biallelic mutations in ABCC6 (NM_00117: exon30, c.4223_4227dupAGCTC p.(Leu1410Serfs*56)) and a unique exonic deletion that spans from the first to the fourth exons of ABCC6 (chr16:16313388-16330869)). This discovery was made by utilizing a combined genetic testing approach. With the review of previously reported GACI patients with ABCC6 mutation, our work contributed to enriching the mutation spectrum of GACI and providing further information on this rare form of inherited disorder.

Severe early-onset manifestations of generalized arterial calcification of infancy (mimicking severe coarctation of the aorta) with ABCC6 gene variant - Case report and literature review

Introduction

Generalized arterial calcification of infancy (GACI) is a rare cause of infantile heart failure and systemic hypertension with a poor prognosis, characterized by extensive calcification and proliferation of the intimal layer of large and medium sized arteries.

Case report

We present the first case report of successful surgical treatment of severe aortic arch obstruction by calcified plaques mimicking severe coarctation of the aorta and the outcome (of bisphosphonate therapy) in a newborn with GACI. Furthermore, we report the identification of a variant in ATP Binding Cassette Subfamily C, Member 6 (ABCC6) gene, possibly associated with severe early-onset manifestations of GACI.

Conclusion

This case report highlights the importance of considering GACI in an infant with heart failure, systemic hypertension, and evidence of increased echogenicity of the arterial vessels. We noted the favorable outcome in improving the aortic calcification in our patient after surgical treatment and bisphosphonates therapy. Early diagnosis and treatment improve the long-term prognosis. A better understanding of this rare genetic disease could lead to new therapeutic strategies.

A New Zebrafish Model for Pseudoxanthoma Elasticum

Calcification of various tissues is a significant health issue associated with aging, cancer and autoimmune diseases. There are both environmental and genetic factors behind this phenomenon and understanding them is essential for the development of efficient therapeutic approaches. Pseudoxanthoma elasticum (PXE) is a rare genetic disease, a prototype for calcification disorders, resulting from the dysfunction of ABCC6, a transport protein found in the membranes of cells. It is identified by excess calcification in a variety of tissues (e.g., eyes, skin, arteries) and currently it has no cure, known treatments target the symptoms only. Preclinical studies of PXE have been successful in mice, proving the usefulness of animal models for the study of the disease. Here, we present a new zebrafish (Danio rerio) model for PXE. By resolving some ambiguous assemblies in the zebrafish genome, we show that there are two functional and one non-functional paralogs for ABCC6 in zebrafish (abcc6a, abcc6b.1, and abcc6b.2, respectively). We created single and double mutants for the functional paralogs and characterized their calcification defects with a combination of techniques. Zebrafish deficient in abcc6a show defects in their vertebral calcification and also display ectopic calcification foci in their soft tissues. Our results also suggest that the impairment of abcc6b.1 does not affect this biological process.

Case Report: Pseudoxanthoma elasticum

Pseudoxanthoma elasticum (PXE) is a rare inherited disorder, characterised by a progressive mineralization and fragmentation of elastic fibres of the skin, retina and cardiovascular system. At an initial stage, the skin usually exhibits distinctive lesions and subsequently extra-dermal manifestations. The diagnosis is based on clinical manifestations, histological analysis of the lesions and genetic analysis.

This is a case report of a 12-year-old child complaining of painless, mildly itchy yellow papules in the cervical region with 1 year of evolution.

PXE is currently an incurable disease and has a favourable prognosis when cardiovascular and retinal complications are prevented and monitored.

[Vascular calcification in pseudoxanthoma elasticum in children]

INTRODUCTION

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

OBSERVATIONS

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

CONCLUSION

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

Visual Impairment in Pseudoxanthoma Elasticum: A Survey of 40 Patients

BACKGROUND

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

OBJECTIVE

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

PATIENTS AND METHODS

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

RESULTS

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

CONCLUSION

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

Pseudoxanthoma Elasticum: A Novel Mutation in the ABCC6 Gene That Affects Eye Manifestations of the Disease

PURPOSE

To determine whether a correlation between ABCC6 mutations and ocular phenotypic expressions exists.

METHODS

In this study, 28 relatives of a consultand with known pseudoxanthoma elasticum were recruited for evaluation of the ocular manifestations of the disease, including peau d'orange appearance, angioid streaks, choroidal neovascular membranes, peripapillary atrophy, and retinal drusen. Comprehensive eye examinations were documented for all patients, who were then evaluated for the presence of known mutations in the aforementioned ABCC6 gene.

RESULTS

Statistically significant correlations were noted between the gene and peau d'orange appearance (P  =  0.0016), angioid streaks (P < 0.0001), and choroidal neovascular membranes (P  =  0.0016).

CONCLUSIONS

A statistically significant association was documented between the R39G mutation of the ABCC6 protein and 3 of 6 known manifestations of pseudoxanthoma elasticum. Although mutations of this gene are clearly associated with angioid streaks, the mechanism by which the transporter affects development of this pathology is speculative.

ABCC6 Mutation in Patients with Angioid Streaks

Angioid streaks (AS) are hereditary eye conditions caused by breaks in the elastic layer of Bruch's membrane. Patients with AS are also frequently affected with pseudoxanthoma elasticum (PXE). The locus of PXE has been reported to exist in chromosome 16p13.1, and the ABCC6 gene in this locus has been identified as the causal gene of PXE. In this study we investigated the association of the ABCC6 gene and AS. Elucidation of the causal gene of AS will be useful for gene diagnosis in the future. Many mutations in patients with PXE are found in exons 24 and 27 of the ABCC6 gene in previous reports. Therefore, we examined exons 24 and 27 of the ABCC6 gene using the single-strand conformation polymorphism technique. There was no mutation or polymorphism in exon 24. The base substitution of G3803A was identified in exon 27, with a change in the amino acid from CGG to CAG (R1268Q). The genotype frequencies in patients with AS were G/G 52% (23/44), G/A 32% (14/44) and A/A 16% (14/44). In control subjects, the genotype frequencies were G/G 69% (107/154), G/A 29% (44/154) and A/A 2% (3/154). Highly significant differences were observed in both genotype and allele frequencies of R1268Q between patients with AS and control subjects (p<0.001, p<0.002; chi-square test). In conclusion, the missense mutation R1268Q in the ABCC6 gene is not a specific marker of PXE, but is associated with the disease state of AS.