Key Points:
Using transcriptome-wide association studies, we identified an association between splicing out of exon 27 of COL4A4 and hematuria.
We confirmed the presence of COL4A4 exon 27 splicing in an independent cohort.
Functional assays revealed that the COL4A4 transcript with exon 27 spliced out affects collagen IV trimer assembly and secretion.
Background: Hematuria is an established sign of glomerular disease and can be associated with kidney failure, but there has been limited scientific study of this trait.
Methods: Here, we combined genetic data from the UK Biobank with predicted gene expression and splicing from Genotype Tissue Expression kidney cortex samples (n=65) in a transcriptome-wide association study to identify additional potential biological mechanisms influencing hematuria.
Results: The transcriptome-wide association study using kidney cortex identified significant associations for five genes in expression and three significant splicing events. Notably, we identified an association between the skipping of COL4A4 exon 27, which is genetically predicted by intronic rs11898094 (minor allele frequency 13%), and hematuria. Association between this variant was also found with urinary albumin excretion. We found independent evidence supporting the same variant predicting this skipping event in glomeruli-derived mRNA transcriptomics data (n=245) from the Nephrotic Syndrome Study Network. The functional significance of loss of exon 27 was demonstrated using the split NanoLuc-based α3α4α5(IV) heterotrimer assay, in which type IV collagen heterotrimer formation was quantified by luminescence. The causal splicing variant for this skipping event is yet to be identified.
Conclusions: In summary, by integrating multiple data types, we identified a potential splicing event associated with hematuria and albuminuria.