Loss of smell can be an early sign of Parkinson's Disease

The sooner we recognize signs of neurodegeneration and intervene to reduce the underlying causes the better. A valuable presentation was offered at the recent European Human Genetics Conference 2010 describing research advancing the early diagnosis of Parkinson's Disease.

"Dr. Nuber and colleagues from Germany, Switzerland, and the UK, decided to study transgenic mice with high levels of human alpha-synuclein, a protein known to be crucial in the development of PD...“The mice expressed alpha-synuclein primarily in neurons of the olfactory bulb”, said Dr. Nuber, “and we therefore expected to find alterations in smell-related behaviour in these animals. Since one of the earliest symptoms in PD patients is a reduction in the sense of smell, we felt that these mice could mimic the early stages of the disease.”"

Abnormal dopamine signaling is a fundamental characteristic of Parkinson's Disease. The investigators demonstrated that impairment of dopamine function in olfactory pathways was apparent well before degradation of motor control.

"The nigrostriatal pathway is one of the major dopamine pathways in the brain, and is particularly involved in the control of movements. Loss of dopaminergic neurons in the substantia nigra, a structure located in the midbrain, is one of the main features of PD, but the motor symptoms of the disease do not show themselves until more than half of the dopamine function has been lost. Being able to identify the early stages of dopaminergic dysfunction is therefore particularly important both for diagnosis and treatment of PD."

They studied transgenic mice with high levels of human alpha-synuclein, a substance that accumulates in PD.

“The mice expressed alpha-synuclein primarily in neurons of the olfactory bulb”, said Dr. Nuber, “and we therefore expected to find alterations in smell-related behaviour in these animals. Since one of the earliest symptoms in PD patients is a reduction in the sense of smell, we felt that these mice could mimic the early stages of the disease.”

Having resolved the mechanism by which smell is impaired at an early stage of PD...

"The researchers say that it would be worthwhile to develop some standardised tests for testing smell function. “Based on what we know now, the clinical definition for the diagnosis of PD should not rely solely on the diagnosis of motor symptoms. It would be helpful to test the ability of olfactory detection and learning."

Of course PD or other expressions of accelerated neurodegeneration are not the only causes of impaired smell. But because it is so important to protect against loss of brain health before it advances, be aware that diminished function of any of the senses can be similar to declining memory and motor function in their implications.