The man alone also carried novel heterozygous missense variants within two additional genes that condition mineral homeostasis and are the basis for autosomal recessive disorders: CYP27B1 underlying vitamin D dependent rickets, type 1, and ABCC6 underlying both generalized arterial calcification of infancy, type 2 and pseudoxanthoma elasticum (PXE).
Overlap has been reported between the inherited PXE phenotype associated with ENPP1, ABCC6 or NT5E mutations and acquired PXE clinical manifestations associated with haemoglobinopathies induced by HBB mutations.
It was recently shown that the absence of ABCC6-mediated adenosine triphosphate release from the liver and, consequently, reduced inorganic pyrophosphate levels underlie the pathogenesis of PXE.
This way, we aim to better understand the up- and down-stream signaling of TGF-βs and BMPs in PXE and we demonstrate that ANKH deficiency can be an additional mechanism contributing to decreased serum PPi levels in PXE patients.
To identify genetic modifiers, we performed quantitative trait locus analysis in inbred mouse strains that carry the same hypomorphic allele in Abcc6 yet with highly variable ectopic mineralization phenotypes of pseudoxanthoma elasticum.
Dark adaptation thresholds were significantly higher, and adaptation periods were prolonged in patients with pseudoxanthoma elasticum (n = 35; 33 with 2 ABCC6 mutations) compared with controls (n = 35).
The carrier frequency of ABCC6 was 0.60% for c.3421C > T, 0.17% for c.4182delG, 0.05% for c.3775delT and 0.03% for c.2787+1G > T. The prevalence of PXE based upon the allele frequencies of these four mutations was estimated as 1 per 56,000 (95%CI 1 per 35,000-97,000).
ABCC6 is a member of the C subfamily of ATP-binding cassette transporters whose mutations are correlated to Pseudoxanthoma elasticum, an autosomal recessive, progressive disorder characterized by ectopic mineralization and fragmentation of elastic fibers.
This case suggests that ABCC6 testing is warranted for sickle cell disease patients with the PXE-like phenotype and that the pathogenesis of PXE manifestations in beta-thalassemia and sickle cell disease may differ.
These results suggest that adenovirus-mediated ABCC6 gene delivery, when initiated early, is a promising prevention therapy for pseudoxanthoma elasticum and generalized arterial calcification of infancy, diseases that currently lack preventive or therapeutic options.
The two siblings were trans-compound heterozygous pseudoxanthoma elasticum (PXE) patients with the same genotype (c.3703C>T and c.1177-2A>G for ABCC6) but different phenotypes.
Pseudoxanthoma elasticum (PXE) is a rare autosomal recessive disorder caused by mutations in the ABCC6 gene, resulting in various retinal lesions, among other systemic manifestations.
We studied the impact of ABCC6 deficiency on blood levels of adenosine triphosphate and related metabolites and on soluble nucleotidase activities in PXE patients and Abcc6<sup>-/-</sup> mice.
Using CRISPR/Cas9 methodology, van Gils et al. generated knockout zebrafish for abcc6a, the orthologue of human ABCC6 that is mutated in pseudoxanthoma elasticum.
These results suggest that a significant fraction of PXE-associated mutations located in NBD1 causes changes in its structural properties and that these mutation-induced alterations directly affect the maturation of the full-length ABCC6 protein.