Inclusion criteria with patients iOD:

• Age 55 -75 years of age
• Slowly progressing and non-fluctuating iOD
• Able to give informed consent and to cooperate as evaluated by the PI

Exclusion criteria with patients iOD:

• Diagnosed with a neurodegenerative disease or major neurological/psychiatric condition.
• Anosmia/hyposmia caused by sino-nasal disease (including chronic rhinitis and allergy), after trauma, infection, congenial, olfactory dysfunction due to surgery, or toxins/drugs affecting the olfactory function.
• Olfactory dysfunction with response to systemic or local corticosteroids if tried
• Severe nasal cavity abnormalities or infections.
• Overt signs of dementia or PD
• Current alcohol or drug abuse
• Terminal illness
• Diagnosed with neurodegenerative disease or major neurological/psychiatric condition.

Inclusion criteria controls:

• Age 55 -75 years of age
• Able to give informed consent
• Able to cooperate as evaluated by the PI

Exclusion criteria controls:

• Olfactory dysfunction on clinical test
• Overt signs of dementia or PD
• Severe nasal cavity abnormalities or infections.
• Current alcohol or drug abuse
• Diagnosed with neurodegenerative disease or major neurological/psychiatric condition.