As an inhibitor of cysteine proteinases, this protein is thought to serve an important physiological role as a local regulator of this enzyme activity. Homodimer. Expressed in submandibular and sublingual saliva but not in parotid saliva (at protein level). Expressed in various body fluids, such as the cerebrospinal fluid and plasma. Expressed in highest levels in the epididymis, vas deferens, brain, thymus, and ovary and the lowest in the submandibular gland. The Thr-25 variant is O-glycosylated with a core 1 or possibly core 8 glycan. The signal peptide of the O-glycosylated Thr-25 variant is cleaved between Ala-20 and Val-21. The disease is caused by variants affecting the gene represented in this entry. Disease susceptibility is associated with variants affecting the gene represented in this entry. Potential cerebrospinal fluid marker for the diagnosis of Creutzfeldt-Jakob disease. Belongs to the cystatin family.