Pathogenic variants in the ABCC6 gene are associated with an increased risk for ischemic stroke

Abstract

Ischemic stroke causes a high mortality and morbidity worldwide. It results from a complex interplay of incompletely known environmental and genetic risk factors. We investigated the ABCC6 gene as a candidate risk factor for ischemic stroke because of the increased ischemic stroke incidence in the autosomal recessive disorder pseudoxanthoma elasticum, caused by biallelic pathogenic ABCC6 variants, the higher cardiovascular risk in heterozygous carriers and the established role of ABCC6 dysfunction in myocardial ischemia. We established segregation of a known pathogenic ABCC6 variant (p.[Arg1314Gln]) in 11/19 family members of an ischemic stroke patient in a large multigenerational family suffering from ischemic stroke and/or cardiovascular disease at a relatively young age. In an independent case-control study in 424 ischemic stroke patients and 250 healthy controls, pathogenic ABCC6 variants were 4.9 times more frequent (P = 0.036; 95% CI 1.11-21.33) in the ischemic stroke patient cohort. To study cellular consequences of ABCC6 deficiency in the brain, immunostaining of brain sections in Abcc6-deficient mice and wild-type controls were performed. An upregulation of Bmp4 and Eng and a downregulation of Alk2 was identified in Abcc6-/- mice, suggesting an increase in apoptosis and angiogenesis. As both of these processes are induced in ischemia, we propose that a pro-ischemic state may explain the higher risk to suffer from ischemic stroke in patients carrying a pathogenic ABCC6 variant, as this may lower the threshold to develop acute ischemic events in these patients. In conclusion, this study identified heterozygous ABCC6 variants as a risk factor for ischemic stroke. Further, dysregulation of Bmp (Bmp4, Alk2) and Tgfβ (Eng) signaling in the brain of Abcc6-/- mice could lead to a pro-ischemic state, lowering the threshold to develop acute ischemic events. These data demonstrate the importance of a molecular analysis of the ABCC6 gene in patients diagnosed with cryptogenic ischemic stroke.

Keywords: ABCC6; ischemia; pseudoxanthoma elasticum; stroke; susceptibility.

Figure 1

Pedigree of the investigated family with an apparent autosomal dominant segregation of cerebro‐ and cardiovascular disease. In generation II 5 out 7 siblings died due to a cerebro‐ or cardiovascular event. For family members II‐1, II‐2, II‐3 and II‐5 we were able to show segregation in generation III and/or IV, proving that they are obligate carriers of the pathogenic p.(Arg1314Gln) ABCC6 variant. For II‐4 segregation could not be confirmed. IV‐11 and IV‐12 were diagnosed with pseudoxanthoma elasticum, and inherited the pathogenic p.(Arg1314Gln) ABCC6 variant from their mother and the pathogenic multi‐exon 23‐29 deletion in the ABCC6 gene from their father.

Figure 2

Bmp4, Bmp9, Eng, Alk2 immunostaining in brain sections in Abcc6−/− and Abcc6 +/+ mice. The left panel shows the immunostaining results for each target with DAPI counterstaining (A) and the DAPI counterstaining only (B) in Abcc6−/− mice. On the right, the results are shown for brain sections of Abcc6 +/+ mouse. The DAPI counterstaining shows a homogeneous cellularity among the used samples. Abcc6 = ATP‐binding cassette subfamily C member 6, Alk2 = activin receptor‐like kinase, Bmp4 = bone morphogenetic protein 4, Bmp9 = bone morphogenetic protein 9, DAPI= 4′,6‐diamidino‐2‐phenylindole, Eng = endoglin.