CHIT1 (chitotriosidase 1) is a chitinase enzyme that degrades chitin-containing compounds and functions as a biomarker for immune activation and disease progression. The enzyme is predominantly expressed by activated macrophages and microglia, particularly in inflammatory conditions 1. CHIT1 serves as a defense mechanism against chitin-containing pathogens, including parasites and fungi 23. The gene contains a common 24bp duplication polymorphism that reduces enzyme activity, with frequencies varying across populations 4. Clinically, elevated CHIT1 levels in cerebrospinal fluid serve as predictive biomarkers for faster disability progression in multiple sclerosis, correlating with microglial activation in active lesions 1. The enzyme also shows diagnostic utility in amyotrophic lateral sclerosis, with increased CSF levels distinguishing ALS from other neurodegenerative diseases 5. Additionally, CHIT1 expression correlates with gastric inflammation and Helicobacter pylori infection 6, and decreases following anti-inflammatory treatments like dupilumab in atopic dermatitis 7. The 24bp duplication polymorphism may influence susceptibility to parasitic infections, particularly filarial diseases 2. CHIT1 represents a valuable biomarker for monitoring immune activation, disease progression, and therapeutic responses across multiple inflammatory and neurodegenerative conditions 8.