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Parkinson’s disease: What goes wrong?

Written by Girish Khera on

Early signs of Parkinson’s disease are mild and may go unnoticed. No single one of these signs means that you should worry. But if your loved one shows more than one sign from the following, you must take them to a doctor:

  • Tremor or shaking of a limb, hand or fingers. An important characteristic of Parkinson's disease is a tremor of hand when it is at rest.
  • Bradykinesia or slowed movement. Steps become shorter when you walk, getting out of a chair becomes difficult.
  • Rigid muscles. As a result of dragging, muscle stiffness may occur in any part of your body, further limiting the range of motion and causing pain.
  • Impaired posture and balance
  • Loss of automatic movements. Performing unconscious movements, like blinking or swinging arms while walking, becomes difficult.
  • Speech changes. Speech may become more of a monotone rather than with the usual inflections because of Parkinson’s disease.
  • Writing changes. Handwriting may become smaller and it may become hard to write.
  • Loss of smell. Trouble smelling foods like bananas, dill pickles or licorice may indicate the onset of PD.

The above symptoms are usually caused as a result of abnormal brain activity due to loss of dopamine-producing neurons in the brain.

What causes Parkinson’s Disease?

Parkinson’s Disease (PD) doesn’t always have a non-genetic etiology. Single genes linked to heritable forms of the disease have been discovered and analyses of individuals with mutations in these genes have greatly advanced the knowledge of preclinical, clinical, morphological, as well as pathological symptoms of PD.

Most cases of Parkinson’s disease probably result from a complex interaction of environmental and genetic factors. These cases are classified as sporadic and occur in people with no apparent history of the disorder in their family. The cause of these sporadic cases remains unclear.

Parkinson’s disease
A visual comparison of a normal neuron with a Parkinson’s affected neuron in the brain

Let’s understand what goes wrong at the molecular level.

The affected genes identified are:

SNCA

The SNCA gene provides instructions for making a small protein called alpha-synuclein. Studies suggest that the protein plays an important role in maintaining an adequate supply of synaptic vesicles in presynaptic terminals. It may also help regulate the release of dopamine that is critical for controlling the start and stop of voluntary and involuntary movements.

When the genetic profiles of one large Italian family and three Greek families with familial Parkinson’s Disease were studied by researchers, it was found that their disease was related to a mutation in this gene. Later, a second alpha-synuclein mutation was found in a German family with the disease. . These findings prompted the researchers to explore the role played by alpha-synuclein in PD, which led to the discovery that Lewy bodies seen in all cases of PD contain alpha-synuclein protein.

This discovery revealed the link between hereditary and sporadic forms of the disease.

Later, the researchers discovered that the disease in one large family was caused by a triplication of the normal alpha-synuclein gene on one copy of chromosome 4. This triplication caused people in the affected family to produce too much of the normal alpha-synuclein. This study showed that an excess of the normal form of synuclein could result in Parkinson’s disease, just as the abnormal form does.

Parkin

The parkin gene is translated into a protein that normally helps cells break down and recycle proteins.

DJ-1

DJ-1 normally helps regulate gene activity and protect cells from oxidative stress.

PINK1

PINK1 codes for a protein active in mitochondria. The protein apparently protects mitochondria from malfunctioning during periods of cellular stress, such as unusually high energy demands. Mutations in this gene appear to increase susceptibility to cellular stress.

Both DJ-1 and PINK1 cause rare, early-onset forms of Parkinson’s disease.

LRRK2

Mutations in LRRK2 were originally identified in several English and Basque families as a cause of a late-onset PD. Subsequent studies have identified mutations of this gene in other families with PD as well as in some people with apparently sporadic PD. LRRK2 mutations are a major cause of PD in North Africa and the Middle East.

GBA gene

The gene codes for the enzyme glucocerebrosidase, which is active in lysosomes, which are structures inside cells that act as recycling centers. Mutations in both GBA genes cause Gaucher disease (in which fatty acids, oils, waxes, and steroids accumulate in the brain), but different changes in this gene are associated with an increased risk for Parkinson’s disease as well. Investigators seek to understand what this association can tell us about PD risk factors and potential treatments.

How is Parkinson’s diagnosed?

No specific tests exist to diagnose PD. A neurologist only analyses the medical history of the patient, the signs and symptoms, and conducts a normal physical examination. Blood tests and imaging tests such as MRI, PET scan or brain’s ultrasound are often used to help rule out other suspected disorders.

Parkinson’s Disease Treatment

Although there’s no cure for PD, there are medications that can help manage the symptoms. In advanced stages, surgery may also be sometimes advised. Certain lifestyle changes, especially aerobic exercises, physical therapy that focuses on balance and stretching, and speech therapy ease the difficult symptoms.

Dopamine agonist drugs that do not release, but mimic dopamine effects in the brain, are used as medication.

Deep Brain Stimulation (DBS) surgery is offered to those with advanced PD and have unstable medication responses. In this, electrodes are implanted into a specific part of the brain and are connected to a generator implanted in the chest near the collarbone that sends electrical impulses to the brain.

DBS can stabilize medication fluctuations, reduce or halt involuntary movements, tremor and rigidity and aid in improving movement. However the surgery involves risks, including infections, stroke or brain hemorrhage.

References:

  1. Genetics and Parkinson's Disease
  2. Parkinson's Disease: Hope Through Research
  3. Parkinson Health Conditions
  4. The genetics of Parkinson disease: implications for neurological care

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