Parkinson's disease is caused by the loss of brain cells that produce a chemical called dopamine. This results in low levels of the chemical in the brain.

This matters because dopamine is a chemical messenger, a neurotransmitter, that makes other parts of your brain that are responsible for coordinating movement, work properly. The level of dopamine in the brain is balanced with the levels of other chemicals, including one called acetylcholine. Low levels of dopamine and changes in other chemicals, including acetylcholine, are the cause of the symptoms of Parkinson's disease.

You might be surprised as I was to know that Parkinson's disease affects around one to two out of 100 people over 65. It's slightly more common in men than in women. Most people develop the condition at around the age of 65, but around one in 12 people with Parkinson's disease start having symptoms before the age of 40 and this is known as early-onset Parkinson's disease.

Yes the symptoms of Parkinson's often start on one side of the body first and then go on to affect both sides. The main symptoms are:

Shaking (muscle tremor) is usually one of the first symptoms and this affects most people with Parkinson's disease. It often starts in the hand and describes a circular movements - as if rolling a pebble between your thumb and forefinger. It usually affects the arms and legs, but sometimes also it can affect the head and jaw although this may mean you have another kind of tremor and you should never assume anything. The tremor is most obvious when an affected person is at rest, and is reduced when the person is moving or in sleep.

There will be stiffness that will make limbs feel difficult to move.
Slow movement or an inability to move are common in people with Parkinson's disease. People with Parkinson's disease often walk with a slow shuffle

I know a few people who have had this disease and their experience was that as different muscles become affected they developed:
problems with posture and balance - you may have falls and have difficulty turning in bed or getting out of a chair, their speech changed, becoming quiet or rapid, making it hard for others to understand them. Some had loss of facial expression they seemed to smile less, frown more and blink slowly and also wrote very small!

Some of the other symptoms seem not to be related to movement so much and can include:
mental health problems, including depression, loss of memory, difficulty reasoning, increased anxiety and changes in behaviour. Sometimes also bowel and bladder problems such as constipation and the need to urinate often. Problems with swallowing and weight loss, impotence as well as low blood pressure on standing, increased saliva and sweating sleep problems and tiredness. I know the list is pretty general and will have us all thinking we have the disease but if in any doubt, see the doc!

I met a doctor on a plane once who specialised in this condition. I asked him what the causes of Parkinson's were and he told me that the exact reasons why people develop Parkinson's disease are not fully understood at present, but he did say that inherited factors seem to play a role.

A family history is more common in the kind of Parkinson's disease that starts earlier in life. He said that certain chemicals in the environment that might be harmful to the brain, called neurotoxins, have also been linked to Parkinson's disease. It's possible that people who are exposed to more of these neurotoxins are more likely to develop the condition. He did say that e research on possible environmental risk factors for Parkinson's disease was on going. I suppose that it does make sense that anyhting that disturbs the fine balance of the brain might cause such a disease.

Having given those very useful details of symptoms it would be noted that these symptoms aren't always due to Parkinson's disease but if you have them, you should visit your GP.

In diagnosing the condition your GP will ask you about your symptoms and examine you. He or she may also ask you about your medical history. If there is a chance you have Parkinson's disease, your GP will refer you to a neurologist (a doctor who specialises in conditions of the nervous system) or a pediatrician (a doctor who specialises in treating older people).

There is no definitive single test for Parkinson's disease. Diagnosis is based on you having Parkinson's disease symptoms and by ruling out other conditions that cause similar symptoms. You may need to have a blood test or an MRI scan or you may need a further test called a SPECT (single photon emission computed tomography) scan to help your doctor distinguish between Parkinson's disease and another condition called essential tremor.

Symptoms similar to Parkinson's disease - known as parkinsonism - can be a side-effect of some medications, including those used to treat mental illness. If this is the case, changing your medication may reduce your symptoms.
If you have been diagnosed with Parkinson's disease, you should see your specialist doctor every six to 12 months for a review.