Tag Archives: smell

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

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European Human Genetics ConferenceThe 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.

How well can you smell: autoimmunity & neuropsychiatric disorders

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Clinical ImmunologyThere is a connection between how well you can smell, brain damage from autoimmune inflammation, and psychiatric disease. Consider this fascinating paper published in the journal Clinical Immunology in which the authors discuss the “inter-relationship between olfactory impairment, autoimmunity and neurological/psychiatric symptoms in several diseases affecting the central nervous system (CNS) such as Parkinson, Alzheimer’s disease, autism, schizophrenia, multiple sclerosis and neuropsychiatric lupus erythematosus. We suggest that common manifestations are not mere coincidences. Current data from animal models show that neuropsychiatric manifestations are intimately associated with smell impairment, and autoimmune dysregulation, via autoantibodies…”

Autoimmunity ReviewsIn another paper published in the journal Autoimmunity Reviews the authors note that “Research in the field of immunology as well as in various brain illnesses is beginning to indicate the increasing relevance of smell in pathophysiology.” They further state “…evidence exists that there may be something unique about the olfactory system that is inextricably related to immunological function. In addition, accumulating evidence confirms the existence of olfactory dysfunction in brain disease, much of which appears at early stages including multiple sclerosis, Alzheimer’s Disease, Parkinson’s Disease, schizophrenia and depression…under certain circumstances, olfactory abnormalities may be associated with autoimmune conditions. Since the organization of the olfactory system is so sensitive, impairment may be noted at an early stage. This may become important in the prediction of certain brain illnesses.”

International Journal of NeuroscienceThis paper recently published in the International Journal of Neuroscience focuses specifically on the link between olfaction, autoimmunity and Parkinson’s Disease. They first describe “the immune alterations observed in PD patients…the increase in the innate immune components including complement and cytokines within their substantia nigra and cerebrospinal fluid (CSF). These alterations extended to the adaptive immune response with the elevation of T cells and autoantibodies…in the peripheral blood and CSF of PD patients.” (Just the kinds of things we test for in the functional medicine approach.) They then describe the link between PD, autoimmunity and olfaction: “Smell deficit is one of the earliest signs of PD and a unique observation suggesting olfactory declines to be a consequence of autoimmune mechanisms.”

AutoimmunityAnd the authors of this study published recently in the journal Autoimmunity observe that “Psychiatric diseases are often associated with mild alterations in immune functions (e.g., schizophrenia) as well as autoimmune features. Recent evidence suggests that autoimmune diseases (AD) demonstrate a higher prevalence of psychiatric disorders, such as depression and psychosis, than in the normal population. Patients with AD often have an olfactory impairment as well, based on smell studies… ” They report that olfactory gene receptors have brain functions in addition to smell, and go on to describe the genetic polymorphisms (variations) that link autoimmunity, psychiatric disorders and smell impairment.

Israel Medical Association JournalThe paper that concludes this post is tantalizingly entitled Olfaction—A Window to the Mind. Published not long ago in The Israel Medical Association Journal, it is available here in its entirety. The authors comment that “The sense of smell can provide a natural window to the brain. This window provides an opportunity to examine neural mechanisms and brain function in a non-invasive way.” They then undertake a fascinating review of the field of olfactory studies encompassing aspects ranging from autoimmunity and neuropsychiatric disease to sexual function, addiction, social behavior and the discrimination of self from non-self. Their conclusion is worth bearing in mind: “…assessment of the sense of smell and olfactory impairments is usually overlooked by patients and their clinicians. Given the clinical data reviewed here, clinicians should be encouraged to screen for olfactory impairments, which can help in the early diagnosis of CNS diseases such as Parkinson, dementia and schizophrenia, as well as CNS-autoimmune diseases such as neuropsychiatric lupus.”