The Worst Disease You Can Get: Fatal Familial Insomnia and the I-Function
Pierluigi Gambetti, one of the discoverers of the condition known as fatal familial insomnia (FFI), claims that it is "the worst disease you can get." (5) Given the vast number of diseases in the world, Gambetti's claim seems farfetched at first glance, maybe even selfish; who wouldn't want to take credit for discovering one of the worst diseases in the world? But a quick overview of the disease presents solid evidence in favor of the claim- and some interesting insights about the many tasks of the I-function.
FFI has been discovered in only 28 families worldwide; it is an autosomal dominant gene mutation, meaning that a parent with the disease has a fifty percent chance of passing it on to his or her child (2). That much is predictable. But every other aspect of the disease is wildly unpredictable, forcing family members to make difficult decisions. If parents have such a high chance of passing on the disease, one might ask, why don't they simply choose not to have children? The answer: FFI , unlike many other fatal genetic conditions, doesn't appear until the victim is middle-aged, and tests to see whether parents carry the FFI mutation only recently became available (1). Here the first questions of the I-function, and the first paradoxes of the disease, appear. If this disease occurred in childhood, natural selection would have long ago done away with it. Because it does not strike until middle age, however, parents who may be carriers must make difficult decisions about childbirth. Paradoxically, it is in the parents' best interest to have more children, in order to ensure that at least some live FFI free into old age. More children, however, also means more potential FFI cases- a tough paradox for the I-function to work through.
Next, the symptoms. FFI baffled investigators for years, because certain symptoms resemble encephalitis, end-stage alcoholism, and dementia, among other conditions (1). But the hallmark of FFI, which the aforementioned conditions don't necessarily show, is the complete inability to sleep. The brain wave patterns that appear on FFI patients' EEGs go up and down wildly, in a pattern completely unlike the normal sleep-wake cycle; they may still show patterns indicative of REM sleep at night, but they do not pass through the sleep stages that typically precede REM, and they can still move while in the REM stage (5). There are also unbelievable highs in pulse and blood pressure, excessive sweating and an eventual loss of coordination and other gross motor skills (including speech) before the victim finally falls into a coma-like state and dies (1). But, most horribly, the thinking portions of the I-function remain intact, even as the rest of the body deteriorates (4). Because FFI is invariably fatal, patients understand that they will die, can talk and write freely about their coordination deteriorates and understand their fate up until their death (5). Some diseases, like Alzheimer's disease, are tragic because their victims lose the ability to describe their decline; in these diseases, the I-function deteriorates along with the physical body. But FFI is tragic for precisely the opposite reason; it leaves the I-function intact, even when its victims are clearly in physical agony.
Even the agent that causes FFI defies conventions. It is a prion, a form of infectious protein. Humans naturally produce thousands of intricately folded proteins, and the vast majority of them are harmless. But if one protein happens to misfold in a harmful way, it can trigger a chain reaction, leading other proteins to produce similarly harmful forms; the immune system cannot counteract the chain, since it does not see the proteins as infectious agents (4). The exact mechanisms behind this process, and the reasons why it should be fatal, aren't well understood. The effects of prions on the brains of FFI victims, however, are well-documented. In most areas of the brain, FFI victims show remarkably little damage. The thalamus, however, is utterly destroyed, full of holes (3). Given this evidence, one might try to make the argument that the I-function cannot be located in the thalamus; after all, FFI victims remain completely able to think and comprehend the world, even as the prions destroy that part of the brain. However, the I-function isn't limited to one section of the brain, and it does not only control thinking and speech. Indeed the sleep-wake cycle, so damaged in FFI victims, is also regulated in part by the I-function; people simply tend to forget this fact, because sleep feels like such a natural part of our existence. Only in unusual cases, like the severe insomnia of FFI, do we remember the I-function's role in this cycle.
FFI, then, presents yet another example of why it's useless to try to pin down one precise area where the I-function lies. One can see from FFI victims that the parts of the I-function that have to do with language use and comprehension, with naming people and objects in the world, probably aren't located in the thalamus. But the thalamus must play some role in the sleep-wake cycle, judging from FFI victims' brain damage, and the I-function aids in sleep-wake cycles as well; one cannot give an exact location for a function that performs so many diverse tasks.
1) Case Study: Fatal Familial Insomnia; Location: Venice, Italy; To Sleep No More
2) Dying for Sleep: Researchers Track the Cause of a Rare but Fatal form of Insomnia
3) Fatal Familial Insomnia
4) Biofundamentals: Protein Folding and Turnover
1) The Family That Couldn't Sleep: A Medical Mystery, by D.T. Max. Random House Publications, New York, 2006.