ASS1 and acute lymphoblastic leukemia: Inter-individual differences in ASNS expression levels and ALL sensitivity to ASNase were noted, which might be explained by a change in expression of ASNS gene itself, or genes coding for the regulators of its expression [e.g., The basic region leucine zipper activating transcription factor 5 (ATF5); and arginosuccinate synthase 1 (ASS1)].