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Secret is in the genes

Developing countries such as South Africa, India and Brazil have a growing problem: a rapidly ageing population. In South Africa we are familiar with the enormous problem of infectious diseases such as tuberculosis and HIV. However, illnesses such as Alzheimer’s and Parkinson’s disease will become increasingly important given the large number of people who are affected by these conditions.

Parkinson’s disease, a devastating and complex illness that starts at about the age of retirement, potentially affects everyone and becomes much commoner as you get older. Actor Michael J Fox and boxer Muhammad Ali have it, as did cricketer Basil D’Oliveira and Pope John Paul II. 

In this illness, certain groups of cells in the brainstem — the part of the brain that lies between the spinal cord and the brain itself — start functioning poorly and stop producing a major neurotransmitter, dopamine. We can treat this, usually quite effectively for a while, but as time goes on other cells die and people with Parkinson’s face an increasingly uphill battle against a host of disabilities that can range from physical to mental.

Our major research interest is trying to find out the cause of Parkinson’s. It is not just intellectually important, but an absolutely crucial step to finding a cure. Until the 20th century, most medicines were discovered by accident, but thereafter the process has largely been a scientifically rigorous one of testing multiple drugs based on existing hypotheses of how diseases work. Of course, what we need for Parkinson’s is not really more drugs but a cure, something that will stop the illness in its tracks as soon as the tremors start. Since the revolution in human genetics there have been spectacular advances in identifying what causes Parkinson’s. The illness was traditionally believed to be caused by unknown factors in the environment, but now at least 10 genes have been found that trigger the disease, some of them common, some of them found only in a few individuals. Certain genetic mutations result in enzymes working less efficiently, especially in the battery that powers human cells, the mitochondrion. Others seem to be associated with a build-up of abnormal protein in the cell, which is associated with the cell gradually losing function and ultimately in cells dying.

Unexpected events
Interestingly, this accumulation of protein in cells can quite often be seen in people who died without ever having been known to have Parkinson’s in life. 

We know that about 80% of the dopamine cells in the human brain have been lost by the time someone shows their first signs of Parkinson’s. It is becoming clearer that the process takes much longer than we thought and the cell damage starts at the base of the brainstem and gradually moves up through it towards the brain. It explains many rather unexpected events that can be associated with the disease and may occur several years before tremors start. Thus, many who will develop this illness can lose their sense of smell and some will have odd episodes during sleep, frequently shouting or acting out dreams because of damage to the brainstem areas that control rapid eye movement sleep.

What it adds up to is that increasingly we may be able to identify healthy people who are at risk for developing Parkinson’s later in life. It could be from genetic studies in which family members are found to carry a gene, or one could cast the net wider and investigate people with loss of smell and sleep disturbances. Traditionally, the diagnosis of Parkinson’s has rested entirely on the expertise of the neurologist, but this has changed and a dopamine scan is now available at Tygerberg Academic Hospital. Such a scan can indicate early on whether the illness is present or not.

Of course, there is not much point to identifying Parkinson’s early unless we can offer a cure, which is not available yet. However, even though genes are unlikely to be the cause of Parkinson’s, they offer new insights into and novel approaches to understanding the illness. The cure is going to be a medicine and it will probably be found as a result of new gene discoveries that identify targets for research and drug trials.

Professor Jonathan Carr is head of the neurology division at Tygerberg Academic Hospital and Stellenbosch University

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Jonathan Carr
chief executive at lgiu: tweeting (very occasionally) local democracy, culture, politics and random mini thoughts Jonathan Carr has over 1051 followers on Twitter.

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