- Otopetrin 2 (OTOP2)
- Otopetrin 1 (OTOP1)
- Otospiralin (OTOS)
- Osteocrin (OSTN)
- Osmosis Responsive Factor (OSRF)
- O-Sialoglycoprotein Endopeptidase (OSGEP)
- Ovary Specific Acidic Protein (OSAP)
- Oral Cancer Overexpressed Protein 1 (ORAOV1)
- Osteomodulin (OMD)
- Oligodendrocyte Myelin Glycoprotein (OMG)
- Olfactory Marker Protein (OMP)
- Oligodendrocyte Transcription Factor 3 (OLIG3)
- O-Linked-N-Acetylglucosamine Transferase (OGT)
- Opa Interacting Protein 5 (OIP5)
- Opioid Growth Factor Receptor (OGFR)
