microRNA Expression =================== The current ISB TCGA data pipeline uses a Perl script ``expression\_matrix\_mimat.pl`` provided by BCGSC which reads the isoform data files and outputs expression values for "mature microRNAs". This output matrix contains a consistent number of mature microRNAs, referred to using a combination of the microRNA gene name and the unique accession number, eg: "hsa-mir-21.MIMAT0000076". During ETL, this string is split into two parts and stored as separate columns in the BigQuery \ `table `_. The entire matrix is then melted into a flat structure (known as the tidy data format) and loaded into the table. Only the isoform files matching the pattern ``%.hg19.mirbase20.isoform.quantification.txt`` and containing hg19 data were used. The aliquot barcode information was obtained from the SDRF file associated with the Level-3 isoform data file. There is also a `table `_ with the expression data and corresponding tables reprocessed by the GDC against the HG38 genomic build for `isoform `_ and `expression `_