Whole exome sequencing identified three ABCC6 variants in two Pakistani families with pseudoxanthoma elasticum phenotype

ABCC6 gene mutational spectrum and ocular features in Mexican patients with pseudoxanthoma elasticum-related angioid streaks

OBJECTIVE

Angioid streaks (AS) are uncommon retinal lesions associated with significant risk of vision loss due to choroidal neovascularization. About half of AS cases have a concurrent disease, most commonly pseudoxanthoma elasticum (PXE), a recessively inherited disorder that affects the skin, the eye, and vascular system and caused by biallelic mutations in the ABCC6 gene. In this work, we describe the ocular phenotype and the ABCC6 mutational profile in a cohort of 17 AS Mexican patients.

METHODS

17 unrelated AS probands, with or without concurrent dermatologic features were studied. ABCC6 mutational analysis was performed employing next-generation sequencing (NGS) gene panel or exome sequencing.

RESULTS

Biallelic pathogenic variants in ABCC6 were demonstrated in 10 out of 17 (~60%) AS patients confirming a PXE diagnosis. In 4 individuals, only heterozygous ABCC6 variants were recognized while in 3 cases no mutations in AS-related genes were identified. A total of 7 previously unpublished ABCC6 disease-causing variants were identified in our cohort, including 5 missense, 1 frameshift, and 1 intragenic deletion.

CONCLUSION

In most subjects from our cohort, AS were due to genetically confirmed PXE, as previously observed in other ethnic groups. We expanded the ABCC6-related mutational spectrum by recognizing 7 previously unpublished pathogenic variants.

Multidrug resistance proteins (MRPs): Structure, function and the overcoming of cancer multidrug resistance

ATP-binding cassette (ABC) transporters mediate the ATP-driven translocation of structurally and mechanistically distinct substrates against steep concentration gradients. Among the seven human ABC subfamilies namely ABCA-ABCG, ABCC is the largest subfamily with 13 members. In this respect, 9 of the ABCC members are termed "multidrug resistance proteins" (MRPs1-9) due to their ability to mediate cancer multidrug resistance (MDR) by extruding various chemotherapeutic agents or their metabolites from tumor cells. Furthermore, MRPs are also responsible for the ATP-driven efflux of physiologically important organic anions such as leukotriene C₄, folic acid, bile acids and cAMP. Thus, MRPs are involved in important regulatory pathways. Blocking the anticancer drug efflux function of MRPs has shown promising results in overcoming cancer MDR. As a result, many novel MRP modulators have been developed in the past decade. In the current review, we summarize the structure, tissue distribution, biological and pharmacological functions as well as clinical insights of MRPs. Furthermore, recent updates in MRP modulators and their therapeutic applications in clinical trials are also discussed.