The Curious Tale of Narcolepsy and Dementia: Discovering the Cause

Previously, I introduced you to a rare familial disorder baptized Autosomal Dominant Cerebellar Ataxia, Deafness and Narcolepsy or ADCA-DN, first described in a small Swedish family by the Scandinavian Neurologist Dr. Atle Melberg in 1995. This terrible disease -- characterized by narcolepsy evolving into neuropsychiatric problems and dementia -- stayed in my mind until 2010, when Dr. Guiseppe Plazzi called me to ask my opinion regarding a specific case. Dr. Plazzi directs the sleep program at Bologna University, the oldest medical university of the world, and a rival to Stanford for its pioneering work in sleep medicine and narcolepsy. This particular day, Dr. Plazzi was very much worried about a patient he just saw, who had narcolepsy and had just developed cerebellar ataxia. Upon mentioning this case, I asked if the patient was also deaf and, as he was, it was fairly certain that it was the same disorder. Most interestingly in this case, however, while the patient was in his 40s, both parents were in their 70s and doing well, suggesting that it could not be a familial form like in the Swedish family.

The occurrence of such a "sporadic case" with the same syndrome can mean two possible things. First, it is possible that the same disorder has several causes, some related to genetics and others not, explaining the two possible variants. Second, the "sporadic" instance can be the result of a new or "de novo" mutation that appeared in the same gene in the father or mother germ line of the patient. In this instance, we are witnessing the appearance of a new genetic mutation that will thereafter be transmitted to future generations. Although it was impossible at the time to distinguish between these possibilities, two additional factors made us decide to pursue and seek the cause of the syndrome through genetic analysis.

First, at about the same time, I was also made aware of a second family that had the same syndrome in Minnesota. After talking to the daughter of one of the affected people, I became convinced that the same problem was also striking another family, this time in the United States. Second, a new technique called "exome sequencing" had just been invented by genetic researchers and seemed ideal to use in this case. The technique, now almost routine in genetic research, is the result of many years of rapid improvements in DNA sequencing technology.

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Author of the article: 
By Dr. Emmanuel Mignot
Source: 
The Huffington Post