Novel Mutations in the ABC6 Gene of German Patients with Pseudoxanthoma Elasticum

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Abstract
Pseudoxanthoma elasticum (PXE) is a heritable disorder of the connective tissue affecting the skin, eyes, and cardiovascular system. Recently, the PXE candidate gene ABCC6 was identified and a limited number of ABCC6 mutations were observed in different PXE cohorts. To identify novel PXE-causing ABCC6 mutations in German patients with PXE, we investigated a cohort of 54 German PXE patients and 23 family members from 49 apparently nonconsanguineous families. From the mutational analysis we found 27 different ABCC6 sequence variations. Among these, 11 were polymorphisms or neutral alterations and 16 were PXE-causing mutations. The most common mutation in our PXE cohort was the nonsense mutation p.R1141X, which occurred with an allele frequency of 25.9%. Furthermore, we found nine missense, one additional nonsense, and two putative splice site mutations as well as three single-nucleotide deletions. Most of these mutations were unique and occurred in cytoplasmic regions of the MRP6 protein; these mutations are proposed to be critical for the physiological function of the MRP6 protein. In these regions we also found the three novel PXE-causing mutations p.R1114C, p.Y1239H, and p.G1311E, which were identified in three alleles from patients with PXE and were absent in 200 healthy control subjects. In addition, the first genotype-phenotype correlation was observed. By obtaining these genetic mutation data, we are contributing to an overview of all ABCC6 mutations leading to PXE and the pathogenetics of this disease.