Excellent sources of information and advice on Huntington’s disease are provided within a number of recognised professional organisations including the Huntington’s Disease Association (HDA) and the Hereditary Disease Foundation (HDF). Below is a brief summary providing information

PREVALENCE
Huntington’s disease affects approximately 5-7 per 100, 000 individuals in Western countries. However, there are different prevalence rates across the world. For instance, in Venezuela which has one of the highest prevalence rates for Huntington’s disease, it is estimated the disease affects 700 per 100, 000 individuals.

THE HUNTINGTON GENE
The gene for Huntington’s disease is located on chromosome 4. The normal gene produces the huntingtin protein, the exact role of which is not fully understood. However, we do know that if we did not have the gene, we would probably not survive embryonic development so it clearly has an essential role in the very early stages of life.
Each of our genes is made up of different batches of codes (nucleotides) which program a gene to produce particular proteins (protein synthesis).The section of the gene for Huntington’s disease which is expanded (i.e. mutated) has more repetitions of one piece of code than usual. This expansion causes Huntington’s disease. We know that the expansion causes huntingtin protein with an extra long stretch of one particular part of the protein to be produced, and this somehow triggers a cascade of damaging events in cells, eventually giving rise to the onset and progression of the disease.

INHERITANCE
Huntington’s disease is an inherited neurodegenerative disease caused by an expanded mutation to the Huntington’s disease gene. Here, we refer to the normal-sized gene as h, and the mutated (i.e expanded) gene as H. We each carry two copies of the huntingtin gene. However, the general population carry two normal-sized copies (hh), whereas individuals with Huntington’s disease carry one mutated copy and one normal-sized copy (Hh). For instance, if one of your parents carries the mutation, the likelihood you will inherit the mutated copy of this gene is 50 %. The risk of not inheriting the mutated gene is therefore, also 50%. Risk of inheritance is the same for each offspring; it does not mean that only 50% of offspring will inherit the mutation. Risk of inheritance is not affected by whether you are male or female or whether it is passed on by your mother or father.

Here you can see that each parent has two copies of the huntingtin gene. One of the mother’s copies is mutated (H).  The risk that their offspring will inherit the mutation set at 50%. n is 50%.

DIAGNOSIS
Huntington’s disease is formally diagnosed when there is both overt movement symptoms and a confirmed genetic diagnosis for carrying the mutation. Presymptomatic testing can be carried out in individuals who believe they are at risk of inheriting the disease but who are not showing any overt signs of the disease onset.

THE HUNTINGTON’S DISEASE BRAIN
The main part of the brain affected by Huntington’s disease is the basal ganglia. This part of the brain is essential for the proper control and execution of movement. The brain structures that are specifically targeted are the caudate nucleus and the putamen. One particular type of cell, called the medium spiny neuron, makes up the majority of the cells in these areas is particularly vulnerable to damage. Exactly why these cells are singled out and damaged remains unknown, but it is the result of a cascade of events originally brought about by the mutated gene.
As the caudate and putamen degenerate, disruption occurs to crucial circuitry in specific areas of the brain. These circuits become damaged leading to a number of movement, cognitive and behavioural/emotional changes known to occur in Huntington’s disease