Transmissible spongiform encephalopathies (TSEs) are diseases of the b

Transmissible spongiform encephalopathies (TSEs) are diseases of the brain, all of them invariably fatal. Multiple mammals are known to be susceptible, including humans. There are descriptions of TSE-like diseases dating back to the 5th century BCE, when Hippocrates wrote of a condition that caused damage to the brains of goats, but it was not until 1982 that Stanley Prusiner published an article giving name to what is now believed to be the cause of these diseases: prions.

Prions are created as a result of a mutation in the PRNP gene, which in normal form produces the prion protein PrPC. The mutation causes the gene to produce a misfolded form of the protein, often called PrPSc. Once this mutation occurs and one misfolded protein is present, it functions like a virus, spreading to other proteins, which then misfold as well. The misfolded proteins are not able to function, leading to progressive neurodegeneration and, ultimately, to death. TSEs may be acquired—cats are believed to have developed feline spongiform encephalitis after eating meat from cows infected with the bovine form of the disease—but they may also be inherited or sporadic, developing spontaneously for reasons not yet understood.

Fatal insomnia is a TSE that arises either through genetic inheritance (fatal familial insomnia) or spontaneously (sporadic fatal insomnia). As in other TSEs, symptoms include loss of coordination, involuntary movement, confusion, paranoia, hallucinations, and dementia, but fatal insomnia differs from the other prion diseases in that the thalamus is particularly impacted by the misfolded proteins. The thalamus is the part of the brain responsible for controlling sleep and wakefulness, and, as the name of the disorder implies, those suffering from fatal insomnia reach a point where they can no longer sleep due to thalamic damage. The closest they can get is hypnagogia, the semiconscious onset phase of sleep. They may exist in this state for months on end, able neither to progress into full sleep nor to wake up. As with all TSEs, the disease ultimately ends in death.

1. The primary purpose of the passage is to

(A) argue that despite the fact that the cause of TSEs is well established, there is a lack of scientific consensus over whether fatal insomnia is a TSE
(B) explain the cause of TSEs and use a specific TSE as an example to illustrate the effect of prions on the brain
(C) propose prions as a possible cause of TSEs and to describe a particular type of TSE in support of this hypothesis
(D) show that even though TSEs have been described since the 5th century BCE, at least one type of TSE continues to defy explanation
(E) use an explanation of a well-documented TSE to demonstrate that scientific understanding of such disorders remains incomplete

2. According to the passage, which of the following is true of the way in which TSEs are contracted?

(A) They are inherited via genetic mutations that originally occurred in the 5th century BCE.
(B) People who suffer from insomnia are more susceptible to spontaneous development of TSEs.
(C) They are most likely to appear in individuals who have consumed the brains of animals with TSEs.
(D) They occur due to a repeated folding and unfolding of prions that eventually damages these proteins.
(E) They may be acquired by some animals through interspecies contact.

3. The passage suggests that a physician would most likely diagnose a patient who has tested positive for abnormal prions with fatal insomnia if the patient has

(A) a history of eating beef from cows raised where bovine TSE is present
(B) an inability to perform tasks requiring fine motor skills
(C) a tendency to become disoriented and unreasonably fearful
(D) a symptom of damage to the thalamus such as altered body temperature
(E) a family history of age-related neurodegenerative diseases