- The underlying physical cause of Parkinson’s
- Essential genetic knowledge needed to understand genetic disease
- How Parkinson’s is inherited
- The ways mutated genes cause Parkinson’s.
The cause of Parkinson’s disease
In 1817 Dr James Parkinson published the first formal description of the motor symptoms of what was then known as the “shaking palsy”. It wasn’t until the 1950s that the primary cause of Parkinson’s was discovered; sufferers have reduced numbers of nerve cells in a structure of the brain called the substantia nigra. Normally, these nerve cells release dopamine, which activates the motor cortex of the brain to initiate and control movement. Therefore, the loss of nerve cells causes a reduction in dopamine levels leading to impaired movement (and other symptoms).
Since the 1950s the main question in Parkinson’s research has been, why do substantia nigra nerve cells die?
Genes, DNA and Mutations
Nerve cells can die from external causes (such as environmental toxins) and internal causes (something going wrong inside nerve cells). Genes control the function of cells so an obvious place to start looking for the internal cause is in genes. Genes are made of the famous double helix molecule DNA, which comprises four different chemical subunits (A, T, C and G) arranged into two strands. In nearly every human cell there are 3 billion subunits of DNA encoding about 30,000 genes.
DNA is the key information-carrying molecule in all living things. DNA “expresses” this information by being transcribed into RNA and RNA is then translated into Protein (RNA is similar to DNA, but it is single stranded and Proteins are made up of amino acid subunits). An analogy might help to illustrate this process: DNA is like a set of handwritten instructions and specific paragraphs are typed up to form an RNA copy. RNA is the template for arranging amino acids in a specific order to make specific Proteins (a bit like a jelly mould to “set” the protein). Proteins form the structure, and control all the functions, of a cell.
Genes can malfunction when they become mutated. For example, gene TTATTCCGG becomes mutated at the third subunit; TTTTTCCGG. This mutation will get copied into RNA and the mutant RNA will fail to arrange the amino acids in the correct order; therefore making the protein faulty and unable to do its job properly.