Molecular dynamics insights into novel and nano-rare <i>de novo</i> mutations in the ribosomal proteins S19 and L26 causing Diamond-Blackfan anemia in Iranian patients

Diamond-Blackfan anemia syndrome (DBAS) is a rare congenital ribosomopathy characterized by erythroid hypoplasia, congenital anomalies and increased malignancy risk. Although pathogenic variants in <i>RPS19</i> are the most frequent cause of DBAS, mutations in <i>RPL26</i> remain exceedingly rare. Here, we identified two novel <i>de novo</i> variants in unrelated Iranian patients: a frameshift mutation in <i>RPL26</i> (c.36_39del, p.Ser12Argfs*26) and a missense mutation in <i>RPS19</i> (c.184C > G, p.Arg62Gly). Both variants were absent from major population databases and classified as likely pathogenic/pathogenic according to ACMG guidelines. Conservation analyses highlighted functional importance at the affected residues, and segregation studies confirmed their <i>de novo</i> status. To gain mechanistic insights, we performed molecular dynamics (MD) simulations comparing wild-type and mutant proteins. The <i>RPL26</i> variant resulted in a truncated, shorter and more flexible protein with reduced solvent accessibility and compact conformation, consistent with impaired ribosome assembly and destabilized p53 regulatory signaling. In contrast, the <i>RPS19</i> variant induced a globally compact structure while preserving local flexibility and solvent exposure, suggesting altered rRNA binding as the primary pathogenic mechanism. Collectively, our findings expand the mutational spectrum of DBAS, underscore the critical role of <i>RPL26</i> and <i>RPS19</i> in ribosome biogenesis and demonstrate how MD simulations can provide decisive structural evidence supporting variant pathogenicity in rare ribosomopathies.