Modified GRCh38 genome with U2AF1 region fix

A modified version of the GRCh38 human reference genome that replaces the region chr21:6427259-6580181 with "N" characters. This creates a coordinate-compatible build that removes a problematic duplication region This duplicated sequence in the original reference causes mismapping or multimapping of reads to a locus that includes the genes <em>CBS</em>, <em>U2AF1</em>, <em>FRGCA</em>, and <em>CRYAA</em> and hinders variant detection in those genes. More details are available at https://www.ncbi.nlm.nih.gov/grc/human/issues/HG-2544 This reference is useful in applications where detection of <em>U2AF1</em> mutations is critical, including studies of hematological cancers, or studies of spliceosome dysfunction. A publication with more details is forthcoming.