Parkinson's disease

Degenerative disease of the brain characterized by a progressive loss of mobility, muscular rigidity, tremor, and speech difficulties. The condition is mainly seen in people over the age of 50.

Parkinson's disease destroys a group of cells called the substantia nigra (‘black substance’) in the upper part of the brainstem. These cells are concerned with the production of a neurotransmitter known as dopamine, which is essential to the control of voluntary movement. The almost total loss of these cells, and of their chemical product, produces the disabling effects. A defective gene responsible for 1 in 20 cases was identified in 1992.

The disease occurs in two forms: multiple system atrophy (MSA), which is a failure of the central nervous system and accounts for 1 in 5 cases; and pure autonomic failure (PAF), a deficit in the peripheral nerves. Symptoms, particularly in the early stages, can be identical. In 1997, an estimated 1.5 million Americans and over 120,000 Britons were suffering with Parkinson's.

The introduction of the drug L-dopa in the 1960s seemed at first the answer to Parkinson's disease. However, it became evident that long-term use brings considerable problems. At best, it postpones the terminal phase of the disease. Brain grafts with dopamine-producing cells were pioneered in the early 1980s, and attempts to graft Parkinson's patients with fetal brain tissue have been made. This experimental surgery brought considerable improvement to some PAF patients, but is ineffective in the MSA form. In 1989 a large US study showed that the drug deprenyl may slow the rate at which disability progresses in patients with early Parkinson's disease.

In 1997, the National Human Genome Research Institute at the National Institutes of Health in the USA announced that its scientists discovered a gene that causes Parkinson's disease. The gene produces a protein called alpha synuclein. When the instructions of the gene go wrong, the protein's structure is affected and this causes a buildup of deposits on brain cells that are usually seen in Parkinson's sufferers. According to 1999 research, however, there is strong evidence that environmental factors may also cause the disease in people aged 50 or over.