LAS1L (LAS1 like ribosome biogenesis factor) is an X-linked gene essential for ribosome biogenesis, specifically required for 60S ribosomal subunit synthesis and 28S rRNA maturation 1. The protein functions as an endoribonuclease that, together with NOL9 polynucleotide kinase, forms the ITS2 pre-rRNA endonuclease-kinase machinery responsible for cleaving internal transcribed spacer 2 (ITS2) and marking it for degradation during ribosome assembly 2. LAS1L localizes to the nucleolus where it undergoes critical post-translational modifications, including SUMOylation at lysine 565 by USP36, which is essential for its ITS2 processing function 3. Disease-causing mutations in LAS1L are associated with severe phenotypes including X-linked intellectual disability 1 and congenital lethal motor neuron disease with respiratory insufficiency resembling spinal muscular atrophy with respiratory distress (SMARD) 4. The protein is also elevated in triple-negative breast cancer, where it contributes to tumor growth and invasive properties 5. Functional validation studies using zebrafish models demonstrate that LAS1L deficiency causes early lethality and disruption of muscle and peripheral nerve architecture, confirming its critical role in development 4.