ALAS1 (5'-aminolevulinate synthase 1) catalyzes the pyridoxal 5'-phosphate-dependent condensation of succinyl-CoA and glycine to form aminolevulinic acid (ALA), the first and rate-limiting step of heme biosynthesis 1. This mitochondrial enzyme is essential for hemoglobin and heme production across non-erythroid tissues, with tissue-specific transcriptional regulation 2. Beyond its canonical role, ALAS1 exhibits a noncanonical cytoplasmic function as a heme-independent repressor of microRNA accumulation and Argonaute complex assembly 3. ALAS1 expression is negatively regulated by heme through decreased mRNA stability and altered protein processing 4. Dysregulation of ALAS1 is central to acute intermittent porphyria pathogenesis, where uncontrolled enzyme activity causes neurotoxic accumulation of ALA and porphobilinogen, triggering acute attacks 15. Lower baseline ALAS1 serum levels associate with increased susceptibility to anti-tuberculosis drug-induced liver injury 6. Clinically, givosiran, an FDA-approved siRNA targeting ALAS1, reduces porphyria attack rates by 74% and improves disease markers in acute hepatic porphyria patients, establishing ALAS1 inhibition as a therapeutic target 17. Additionally, ALAS1 suppression enhances siRNA therapeutic efficacy 3.