A new kid on the block: Facial Onset Sensory Motor Neuropathy Syndrome

Modern medicine knows about thousands and thousands of diseases. The body is a temple which can be ruined in an endless number of ways. But now there's a new kid on the block. A new disease has entered the medical lexicon. I am talking about Facial Onset Sensory Motor Neuropathy Syndrome (FOSMN). Not that there is anything strange about new diseases. It happens all the time. Sometimes because of a change in the world we live in, such as when a new virus strikes, causing anything from the common cold to a deadly wide-spread pandemic. Sometimes because of a change in how we interact with the world, such as when a prion disease spread from person to person on New Guinea through ritual cannibalism, and from infected cattle to other cattle (being forced to cannibalism) to humans during the "mad cow" prion epidemic. And sometimes the cause is unknown, such as with the fascinating but strange dancing mania that plagued Europe from time to time during the medieval ages.

Sometimes a rare constellation of features- a syndrome - is noticed by the medical profession for the first time. The syndrome may of course have existed for a long time, only escaping naming, but it may also have appeared just now, perhaps due to a novel mutation in the human genome, a novel infection, or a change in lifestyle making us susceptible in a new way. Anyway, if the syndrome is characterized well enough, doctors will feel certain that it represents a new disease. And then, there most likely will be a cure, someday. Because a disease has a cause, and a cause can be tackled. That is a paradigm of biological medicine. Of course, when there will be a cure is another matter.

In 2006 a group of researchers from Australia identified the first known cases of Facial Onset Sensory Motor Neuropathy Syndrome (FOSMN). And since then several research groups have reported patients from all over the world with this new disease. Still, there are probably less than 100 known patients world-wide. Nevertheless, it has a very clear history of symptoms. It always begins with a feeling of numbness on one side of the face. This is due to engagement of the trigeminal nerve, which provides sensation to the face. Over the years the feeling of numbness spreads to the rest of the face, including the tongue which causes the patient to bite herself involuntarily, and then downwards to other parts of the body. Eventually the disease involves both sensation and motor functions. It is intriguing that the trigeminal nerve is always the first structure to be affected. Does this imply that the disease exploits a particular weakness of this nerve or its nuclei in the brain stem? Or is it related to an infection (herpes viruses resides in the ganglion of the trigeminal nerve) or some other exposure to the face?

In fact, many neurodegenerative diseases are characterized by having a distinct point of origin in the nervous system. But as they progress the different diseases tend to converge, since they engage more and more overlapping regions of the nervous system. An import insight in neurology is that many of the neurodegenerative diseases form a continuum where they partly share pathological mechanisms. The development of symptoms in FOSMN makes it likely that the disease spreads from neuron to neuron, first within the brainstem and then to more distal parts of the central nervous system. Thus, it may be a prion disease, which is characterized by the spread of malformed proteins, similar to what is believed to occur in many other neurodegenerative diseases. In fact, FOSMN seems "related" to amytrophic lateral sclerosis, only that it also affects sensory functions.

Through comparing different neurodegenerative diseases, researchers may reveal mechanisms that are common and shared between diseases. This gives important clues to the development of treatments. Patients who participate in research may therefore help to understand and treat not only their own disease, but also other diseases of the brain.