NRF1 and fleck corneal dystrophy: These findings build upon our previous studies, which demonstrated RFC upregulation at the BBB by PQQ under FS conditions through PGC-1α/NRF-1 signaling [21] and reveal for the first time that PQQ can also upregulate RFC and PCFT gene expression under FD conditions, providing new insight into how PQQ modulates folate transport at the BBB in conditions associated with CFD.