Brain

Parkinson’s Disease

Affecting neurons in the mid-brain that control body movement, this disease shows its ugly head with signs of weakness or stiffness in a limb or a trembling sensation in a hand when it is at rest. As the disease progresses, the shaking worsens and the muscles become more stiff leading to body’s imbalance. This makes the patients incapable of doing day-to-day tasks, as the tremors or shakiness limits the ability to even stand or walk. Depression and other mental or emotional problems are also common in the victims.

Parkinson’s disease is more common in men and it normally affects individuals in the age group 50-65 years. The part of mid-brain called the ‘basal ganglia’ is affected, whose cells require a proper balance of two neurotransmitters called ‘dopamine’ and ‘acetylcholine’. The specific area of this part of brain where deterioration of nerves occurs is called ‘substantia nigra’. Actually the cells that produce dopamine begin to degenerate and this disturbs the balance of these two neurotransmitters. Basically, dopamine acts as a chemical messenger between the substantia nigra and another area of the brain called ‘corpus striatum’, and this communication is crucial for coordinating smooth and balanced muscle movement.

Although the exact reason for the occurrence of this disease is not clear, it is known to have a genetic link. Scientists also believe that certain toxins may selectively destroy the specific neurons causing Parkinson’s disease. Toxins that may be linked to Parkinson’s include manganese, carbon monoxide, carbon disulfide and some pesticides. Certain drugs such as anti-psychotics used to treat severe paranoia and schizophrenia can also cause a person to experience symptoms that resemble Parkinson’s disease.

Treatment normally includes drug therapy and/or surgery that reduces the symptoms. Besides, a diet rich in fruits and vegetables, high-fibre foods, fish, and omega-3 rich oils have a protective effect against Parkinson’s disease.

Huntington’s Chorea

It is a degenerative, age-onset disorder of the brain that results in loss of body’s response to various sensations and total mental incapacitation. The disease appears late in life, only after child-bearing years. It is named after George Huntington, an American physician who first described the inherited nature of this disease.

Huntington’s Chorea is a genetic disorder where a single copy of the defective gene inherited from either parent is sufficient to spell disaster. Individuals with two copies of the faulty gene show the same degree of illness. It is, therefore, an autosomal dominant disorder. The faulty, culprit gene causing this brain disorder was identified in 1983 by scientists led by James Gusella, a Harvard molecular geneticist. Further, a marker DNA sequence linked to the faulty gene in Huntington’s chorea was identified by Gusella, based on which a diagnostic test was developed which is being used at the Massachusetts General Hospital in Boston and the John Hopkins Hospital in Baltimore.

In an interesting study Nancy Wexler, a psychologist at the Columbia University and president of the Hereditary Disease Foundation has traced the inheritance of this disease in the world’s largest family of Huntingtons’ victims composed of about 9000 members, at Lake Maracaibo, Venezuela, Residing on chromosome 4, the defective gene has been linked to a repeat sequence comprising three nucleotides namely, CAG (Cytosine-Adenine-Guanine).

These nucleotides repeats are formed as a result of mutations that occur during DNA copying. The insertion of extra nucleotides increases the repeat number. However, a minimum number of 36 CAG repeats is the threshold length supposed to cause the disease. This linked marker for the faulty gene acts like a flag for tracing the defect through successive generations of a family. Unfortunately, Wexler, one of the top researchers in this field too carries this ill-fated gene!

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