Ctso, encoding Cathepsin O, is a cysteine proteinase from the papain superfamily. The gene consists of eight coding exons and seven introns, spanning more than 30 kb, and maps to chromosome 4q31-q32 [6]. Cathepsin O is likely involved in proteolytic processes and may play roles in various cellular functions related to protein degradation and turnover.

In recent research, Ctso has emerged as a potential biomarker in multiple disease contexts. In Prader-Willi syndrome, Ctso was among the proteins with differential expression in liver steatosis, showing a progressive increase from grade 1 to grade 3, and may be involved in related metabolic pathways [1]. In obese adolescents, Ctso was identified as a biomarker for liver steatosis, with its expression correlating with the steatosis degree [3]. In sepsis-associated ARDS, Ctso was expressed in immune cells, and along with HLA-DQA1, could potentially be used as core genes for predicting sepsis-related prognosis analysis [2]. Additionally, in ERα-positive breast cancer, SNPs near the Ctso gene were associated with tamoxifen sensitivity, as Ctso reduces the protein levels of BRCA1 through cysteine proteinase-mediated degradation, and the variant Ctso SNP genotypes confer resistance to tamoxifen [4]. A SNP near the Ctso gene was also found to be a poor prognostic factor in hormone receptor-positive breast cancer patients receiving adjuvant tamoxifen therapy [5].

In conclusion, Ctso, as a cysteine proteinase-encoding gene, shows its significance in various disease areas such as liver steatosis, sepsis-associated ARDS, and breast cancer. Studies related to Ctso, especially those on its SNP associations in breast cancer and its role as a biomarker in liver steatosis and sepsis-associated ARDS, provide valuable insights into disease mechanisms and potential diagnostic or prognostic strategies.