RNA expression variant 21U RNA expression variant 21U RNA expression abnormal WBPhenotype:0001759 C_elegans_phenotype_ontology piRNA expression abnormal Variations in the biogenesis or stability of the 21U-RNA class of molecules compared to control. Molecules are classified as 21U-RNA based on the presence of a 5'U and a conserved upstream motif, which may specify the production of these molecules, in addition these molecules are typically 21nt in length.