Abstract 19822: Ldlr Splice-Site Mutation (ivs9-1g>A) Identified by Whole-Exome Sequencing in an Extended Family with Myocardial Infarction

Abstract

Introduction: Large genome-wide association studies have identified a number of chromosomal loci for CAD and MI, which display clear significance yet weak absolute effects for disease manifestation. Combined, these loci explain only a small fraction of the expected heritability. Aim: Here we analyzed a rare extended family with clustering of MI/CAD by means of whole-exome-sequencing (WES) to reveal rare disease-causing variants, which may provide new insights in the cause of the disease. Methods: Primarily, we analyzed three affected cousins of a German MI family with 13 affected and 56 unaffected family members by WES using the Agilent SureSelect 38 Mb Kit. Variants were validated by Sanger re-sequencing. Results and Discussion: We identified 19,870 variants shared by all three sequenced family members. Of these, 17,268 variants were found in dbSNP with a frequency >1%. Of the remaining 2,602 variants, 935 are conserved (46 Way) and again 728 are located outside of regions of segmental duplication. To identify function-altering variants we filtered all variants based on avsift score >0.05 and ,,HIGH“ effect predicted by Annovar and SNPEFF, respectively. Due to the relative large number of potentially disease causing variants, we focused on the variants not known in dbSNP. This approach left three variants. One variant, a single base-pair substitution (G>A) in intron 9 of the LDLR gene, was validated by Sanger re-sequencing. This variant lies in the acceptor splice-site of exon 10 (c.855-1G>A) and leads the loss of exon 10 (loss of 76 AA) in the LDLR domain class B repeat. We sequenced all family members available for genetic analysis and found that the variant co-segregates with MI. Mutation carriers had -on average- elevated LDL cholesterol (LDLC) levels (211 vs 141mg/dL), but with variable plasma levels (116-274mg/dL), such that severe hypercholesterolaemia was not observed in our index patient. Conclusion: Using WES we identified the disease-causing variant for this familial form of MI in the LDLR . Interestingly, highly varying LDLC levels initially impeded the diagnosis of heterozygous familial hypercholesterolaemia. This work clearly show the power of systematic WES approaches for identification of disease causing variants within families.