Pseudoxanthoma elasticum (PXE) is a systemic heritable disorder that affects the elastic tissue in the skin, eye, and cardiovascular system. Mutations in the ABCC6 gene cause PXE. We performed a mutation screen in ABCC6 using haplotype analysis in conjunction with direct sequencing to achieve a mutation detection rate of 97%. This screen consisted of 170 PXE chromosomes in 81 families, and detected 59 distinct mutations (32 missense, eight nonsense, and six likely splice-site point mutations; one small insertion; and seven small and five large deletions). Forty-three of these mutations are novel variants, which increases the total number of PXE mutations to 121. While most mutations are rare, three nonsense mutations, a splice donor site mutation, and the large deletion comprising exons 23-29 (c.2996_4208del) were identified as relatively frequent PXE mutations at 26%, 5%, 3.5%, 3%, and 11%, respectively. Chromosomal haplotyping with two proximal and two distal polymorphic markers flanking ABCC6 demonstrated that most chromosomes that carry these relatively frequent PXE mutations have related haplotypes specific for these mutations, which suggests that these chromosomes originate from single founder mutations. The types of mutations found support loss-of-function as the molecular mechanism for the PXE phenotype. In 76 of the 81 families, the affected individuals were either homozygous for the same mutation or compound heterozygous for two mutations. In the remaining five families with one uncovered mutation, affected showed allelic compound heterozygosity for the cosegregating PXE haplotype. This demonstrates pseudo-dominance as the relevant inheritance mechanism, since disease transmission to the next generation always requires one mutant allelic variant from each parent. In contrast to other previous clinical and molecular claims, our results show evidence only for recessive PXE. This has profound consequences for the genetic counseling of families with PXE.

We recently published the precise chromosomal localization on chromosome 16p13.1 of the genetic defect underlying pseudoxanthoma elasticum (PXE), an inherited disorder characterized by progressive calcification of elastic fibers in skin, eye, and the cardiovascular system. Here we report the identification of mutations in the gene encoding the transmembrane transporter protein, ABC-C6 (also known as MRP-6), one of the four genes located in the region of linkage, as cause of the disease. Sequence analysis in four independent consanguineous families from Switzerland, Mexico, and South Africa and in one non-consanguineous family from the United States demonstrated several different mis-sense mutations to cosegregate with the disease phenotype. These findings are consistent with the conclusion that PXE is a recessive disorder that displays allelic heterogeneity, which may explain the considerable phenotypic variance characteristic of the disorder.

Pseudoxanthoma elasticum (PXE) is a classic inherited disorder of the elastic tissue characterized by progressive calcification of elastic fibers with a pathognomonic histological appearance. The clinical manifestations of PXE typically involve the skin, the eye and the cardiovascular system, resulting in skin lesions, decreased vision and vascular disease. Clinically, a more common autosomal recessive and a less common autosomal dominant pattern of inheritance, with high penetrance, have been described; the estimated prevalence of the disease is 1 in 70,000-100,000. Previous failure to link the disease to any of several candidate genes prompted us to conduct a genome-wide screen on a collection of 38 families with two or more affected siblings, using allele sharing algorithms. Excess allele sharing was found on the short arm of chromosome 16 and confirmed by conventional linkage analysis, localizing the disease gene under a recessive model with a maximum two point lod score of 21.27 on chromosome 16p13.1, an area so far devoid of any obvious candidate genes. Under a dominant transmission pattern linkage with a maximum two point lod score of 14.53 was observed to the same region. Linkage heterogeneity analysis predicted the presence of allelic heterogeneity with different variants of a single gene that resides in this chromosomal region accounting for recessive and dominant forms of PXE.

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.

We have recently mapped the genetic defect underlying pseudoxanthoma elasticum (PXE), an inherited disorder characterized by progressive calcification of elastic fibers in skin, eye, and cardiovascular system, to chromosome 16p 13.1. Here we report further data on the fine-mapping and genomic structure of this locus. Haplotype analysis of informative PXE families narrowed the locus to an interval of less than 500 kb located between markers D16B9621 and D16S764. Three overlapping YAC clones were found to cover this region through YAC-STS content mapping. An overlapping BAC contig was then constructed to cover this interval and the surrounding region. About 80% of this chromosomal region has been fully sequenced using the BAC shotgun technique. Gene content and sequence analysis predicted four genes (MRP1, MRP6, PM5, and a novel transcript) and two pseudogenes (ARA and PKDI) within this interval. By screening a somatic cell hybrid panel we were able to precision-map the breakpoint of Cy185 and the starting point of a chromosomal duplication within 20 kb of BAC A962B4. The present data further refine the localization of PXE, provide additional physical cloning resources, and will aid in the eventual identification of the genetic defect causing PXE.

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The pathophysiological basis of Liddle's syndrome, a rare autosomal dominant form of arterial hypertension, has been found to rest on missense mutations or truncations of the beta- and gamma-subunits of the epithelial sodium channel. The hypothesis has been advanced that molecular variants of these genes might also contribute to the common polygenic forms of hypertension. We tested this hypothesis by performing a cosegregation study in a reciprocal cross between the stroke-prone spontaneously hypertensive rat (SHRSPHD) and a Wistar-Kyoto rat (WKY-1HD) reference strain. We carried out genetic mapping and chromosomal assignment of the alpha-, beta-, and gamma-subunits of the epithelial sodium channel using both linkage analysis and fluorescent in situ hybridization techniques. We demonstrate that in the rat, the beta- and gamma-subunits, as in humans, are in close linkage; they map to rat chromosome 1 and cosegregate with systolic pressure after dietary NaCl (logarithm of the odds [LOD] score, 3.7), although the peak LOD score of 5.0 for this quantitative trait locus was detected 4.4 cM away from the beta-/gamma-subunit locus. The alpha-subunit was mapped to chromosome 4 and exhibited no linkage to blood pressure phenotype. Comparative analysis of the complete coding sequences of all three subunits in the SHRSPHD and WKY-1HD strains revealed no biologically relevant mutations. Furthermore, Northern blot comparison of mRNA levels for all three subunits in the kidney showed no differences between SHRSPHD and WKY-1HD. Our results fail to support a material contribution of the epithelial sodium channel genes to blood pressure regulation in this model of polygenic hypertension.