SNORD77: SNORD77 is a C/D box small nucleolar RNA (snoRNA) encoded by the GAS5 gene. It is predicted to regulate the 2'O-methylation of rRNA, facilitating RNA folding and interaction with ribosomes [PMC8658237]. SNORD77 is also involved in the diagnosis of lung cancer, as its coexpression with SNORD66 improves sensitivity and specificity [PMC9005336]. Mutations in SNORD77 have been observed, including a 11-nt deletion in the 5'-terminal area and a 1-nt insertion in the C-box-adjacent area [PMC6856654]. These mutations affect the spatial structure of SNORD77 and its interaction with snoRNA-associated proteins, leading to dysfunction [PMC6856654]. The downregulation of SNORD77 in certain cell lines indicates its altered function due to mutations [PMC6856654]. The presence of mutations in SNORD77 has been confirmed through T7 endonuclease I assay [PMC6856654]. It has been observed that mutant SNORD77 is expressed at a reduced level compared to wild-type, while mutant U74 RNA is not detected at all [PMC6856654]. Overall, SNORD77 plays a role in rRNA methylation and has implications for cancer diagnosis. It is encoded within GAS5 gene along with other snoRNAs such as SNORD74, SNORD75, and others [PMC9598326] [PMC9219770].