SNORD81: SNORD81 is a small nucleolar RNA (snoRNA) that is encoded within the Small Nucleolar RNA Host Gene 2 (SNHG2) or Growth Arrest Specific 5 (GAS5) gene located in the 1q25.1 region [PMC9598326]. SNORD81 is one of several snoRNAs hosted by SNHG2, including SNORD44, SNORD47, SNORD76, SNORD78, SNORD79, SNORD80, SNORD74, SNORD75, and SNORD77 [PMC9598326]. It has been reported that chromosome regions gained in Huntington's disease patients exhibit transcriptional imbalances in snoRNAs including the expression of SNORD81 [PMC3511933]. Additionally, sdRNAs derived from snoRNAs such as SNORD44 and especially from the GAS5-encoded C/D box snoRNA loci including SNORD81 have been found to be upregulated and associated with metastatic disease [PMC8389557]. In prostate cancer patients, the expression of snoRNAs such as SNORD44 and SNORD81 has been found to be upregulated [PMC6163368]. Furthermore, sdRNAs derived from snoRNAs such as SNORD44 and SNORD78 have been found to demonstrate strong differential expression in cancer [PMC9149963]. In a study on embryo viability biomarkers, it was found that SNORD81 was exclusively present in media from viable embryos [PMC7072903]. The expression of SNORD44 and SNORD78 has also been validated by quantitative real-time PCR (Q-PCR) in clinical samples of prostate cancer patients [PMC4627319]. The nucleolytic cleavage of C/D box snoRNAs like SNORD74 and especially SNORD81 requires different conformational states possibly assisted by structural interaction with core snoRNP or unidentified proteins [PMC4627319]. In lung cancer patients, snoRNAs such as SNORD81 have been found to be significantly decreased in plasma compared to healthy donors [PMC7461500]. Overall, SNORD81 is a snoRNA that has been implicated in various diseases and has potential as a biomarker [PMC9598326][PMC3511933][PMC8389557][PMC6163368][PMC9149963][PMC7072903][PMC4627319][PMC7461500].