ProQR Therapeutics has received Fast Track designation from the Food and Drug Administration (FDA) for QR-421a.    QR-421a is a first-in-class investigational RNA-based oligonucleotide designed to address the underlying cause of the vision loss associated with Usher syndrome type 2 and non-syndromic retinitis pigmentosa (RP) due to mutations in exon 13 of the USH2A gene. Fast Track designation is granted by FDA to drugs that are under development for serious conditions and have th...