There are multiple definitions:

1. uridine 5'-diphosphate(English)

   • Abbreviation may be used in Am. Soc. Physiol. journals without definition.
   • Biochemistry, Physiology

2. Undiagnosed Diseases Program(English)

   • IRUD, NGS, RD, UDN
   • Diagnostics
   • https://doi.org…al.pone.0265847