Huntington's Disease (HD) is a heritable genetic disease that is neurodegenerative in nature. It impacts every aspect of the human condition -- the physical (muscular), the mental (memory and cognition), and behavior (mood). The onset of the disease varies with the majority of cases appearing in adults. As it is a genetic disease that is caused when genes are inherited, all persons who have the defective gene in their bodies act as carriers and may pass it on to offspring. Thus, a copy of a defective Huntington gene is the culprit, and when genes are passed down through the generations, one defect is all that is needed in order for an individual to develop the disease. Once the gene is possessed, onset at some point is certain, as the "monogenetic etiology" consists of a single defective inherited gene that needs no other external factors or variants for causation (Lu, Yang, p. 964, 2012). This paper will discuss the nature of Huntington's Disease and the state of research on it today. The disease process usually onsets in middle age, with symptoms ranging from feelings of "clumsiness" to "balance trouble" (Margolis, Ross, 2003, p. 1726). These symptoms are typically accompanied by cognitive disruptions. Mood disorders are also commonly associated with the onset of HD. Once onset begins, the disease progresses and is fatal. Predisposing factors are simply the possession of the defective Huntington gene. There is currently no prophylaxis nor method of prevention for the disease as it is incurable. However, studies are being performed in which therapies are being tested for alleviation of symptoms (Lu, Yang, 2012). These studies include antisense therapy and the "sustained benefit of transient mHtt lowering" (Lu, Yang, 2012). While it is unknown why or how this therapy works, it is assessed that relief of the symptoms is the result.

HD is still a relatively mysterious phenomenon. The pathogenesis of HD is not exactly clear with various researchers offering different theories about how the disease progresses (Landles, Bates, 2004). However, the causative effects have been identified by Lu and Yang (2012) as beginning with a "CAG expansion encoding an elongated polyglutamine (polyQ) repeat near the N terminus of the Huntingtin (Htt) protein," though it is still uncertain how these molecules interact and function (p. 965). The temporal nature of the onset can be latent for many years and depends on the repetitions of the CAG, but it has been "seen in individuals with a juvenile onset" (Kojovic, Cordivari, Bhatia, 2011, p. 50). Once the disease is onset in the middle age, however, the temporal progress is acute, with precipitating factors being determined on a body by body basis, with the normal onset occurring around age 40, in men and women alike and irrespective of race (Lu, Yang, 2012)

The CAG trinucleotide repeat is the segment that is involved in the HTT gene that is defective and it consists of a DNA series that repeats over a number of times. In a normal CAG segment, the repeat is anywhere from 10 to 35 times. Huntington's Disease is characterized by a repeat that is anywhere from 36 to 120 times. Individuals with fewer repeats (in the 36 to 40 range) many not show or develop any signs or symptoms of HD, though individuals with over 40 repeats typically do show signs and symptoms of the disorder and impacted most heavily by it (Warby, Graham, Hayden, 2014).

The manifestations of Huntington's Disease include moodiness, irritability, inability to function normally, a loss of short-term memory, a fumbling of objections and a loss of coordination. Because it is a neurological disease that impacts the brain, the nervous system is affected as a result and degeneration of the body's ability to behave normally is the main manifestation. The condition worsens over time and it is expected that the patient will require care, usually being fed by a caretaker, washed, and overseen in this manner (Huntington's Disease, 2013).

According to Stoler and Meltzer (2013) HD "introduces a large and extrogenous risk of early mortality and morbidity" (p. 132). Complications ensue as the disease permeates the "motor, cognitive and psychiatric" processes of the body, thereby impacting virtually every aspect of the person, both in mind and physicality (Stoler, Meltzer, 2013, p. 133). It is thus a bioneurological disorder that has no reverse. The genetic possibility of obtaining Huntington's Disease from a parent who has the defective gene is 50%, as either a copy of the whole gene will be passed or a copy of the defective gene will be passed. As the disease progresses, disability...

In children (though less common than adult onset) the disease manifests and progresses acutely and early mortality is common. Adult onset is more gradual though it may also be defined as acute as it progresses steadily and there is no method of prevention. While scientists and researchers continue to attempt to understand the pathways of the disease and the way in which the cells regulate and respond to the expansion of the proteins involved, more light is shed on the nature of HD (Lu, Yang, 2012).
One "surprising and important finding" of researchers in recent years was the "sustained benefit of transient mHtt lowering" which is termed the Huntingtin Holiday because of the "transient relief of the primary insult" in tests using lab mice (Lu, Yang, 2012, p. 966). This research suggests that scientists may be closer to identifying at the very least a way to treat the symptoms of HD even if no cure remains in sight. However, with stem cell research underway, it is theorized that some form regenerative replacement can be identified. Thus, as researchers experiment on the CAG sequence using laboratory animals, possible treatments are being identified and tested for the purpose of providing relief.

Diagnostic tests of HD is made simply on how one answers questions given by a doctor, how one performs in a physical, and what one's family medical history reveals (this is sometimes the most direct route) plus the current neurological and psychiatric tests used to assess the individual's mental state (Huntington's Disease, 2013).

The purpose of the neurological tests which can be conducted in a doctor's office, are to measure the patient's motor skills and to see if there are any motor signs or symptoms of the disease. Thus, reflexes, muscle tone, balance, strength, and coordination are all tested. Sensory signs and symptoms are also examined -- such as vision/eye movement, hearing, and touch sensitivity. Psychiatric testing is performed to gauge mood imbalance and the state of the mental capacities. Neuropsychological testing is performed to gauge the condition of the individual's memory, ability to reason, the ability to communicate using spoken language, and so on. A psychiatric evaluation can also be conducted that will indicate the individual's emotional state and ability to cope with normal, everyday life. Signs of cognitive disorder are noted. Brain imaging can also be conducted (Margolis, Ross, 2003; Huntington's Disease, 2013).

Genetic counseling is one of the strongest diagnostic tests because it can confirm HD diagnosis, so long as the family medical history is available. Predictive genetic testing is also available for individuals who are aware of the disease within the family and want to see if they themselves are a carrier of the defective gene. This test is not recommended for everyone primarily because of the stress that can be involved if results are found to be positive and the person is indeed a carrier (Margolis, Ross, 2003; Huntington's Disease, 2013).

It is estimated that 3 to 7 persons for every 100,000 people of Anglo-Saxon/European ancestry are affected by HD. In the Eastern cultures, the disease is less common, though it is unknown if this is just a matter of it not being reported and/or identified or if the HD defect is simply a Western phenomenon (Huntington Disease, 2013).

In summation, Huntington's Disease is a hereditary genetic disorder that is caused by a single defective gene. It is still unclear to researcher's how and why it begins its onset, although it is known that CAG segment repetitions are related to the onset and the more frequently they occur, the more likely symptoms are to occur. Why some individuals only have a few segments and others do not is unknown (Lu, Yang, 2012). At the same time there is no known cure for this disease and it is fatal. Yet there has been evidence that relief of the symptoms is possible by lowering the mHtt levels in the patient (Lu, Yang, 2012). Diagnosis depends upon identification of symptoms as well as assessment of family medical history. Huntington's Disease is rare, fatal, and most commonly found in Western (as opposed to Eastern) societies. For this reason, researchers are attempting to understand whether the genetic make-up of these populations…