STRA6 and schizophrenia: Using a highly sensitive HPLC-based method [50, 73] we were able to identify significantly reduced at-RA as well as ROL serum levels, reduced at-RA/ROL ratios as well as reduced expression of the RA-inducible and RA-metabolizing CYP26A and the RA-inducible protein stimulated by retinoic acid 6 (STRA6) in schizophrenia patients without clozapine treatment (Fig. 4).