SLC25A15 and keratoconus: The genes identified in KC are involved in several amino acid metabolic processes such as catabolism of amino acids (AASS, ARG1, ASL, GOT1, HAL, SDS and TAT), amino acid transport (ARG1, IGF1, SLC16A10, SLC22A7, SLC25A15 and SLC7A2) and the urea cycle (ARG1 and ASL).