Huntington's Disease (HD) is a hereditary illness that causes damage in a certain part of the brain. This stops the brain and body from working as well as they used to, and affects a person's movements, thoughts and behaviour. People generally start to develop symptoms of HD between the ages of 30 and 50.

The part of the brain that is affected is called the basal ganglia (say: bay-sul gang-lee-ah). This is a very important part of the brain that co-ordinates a lot of the information that's whizzing around, and makes sure it gets to the right part of the brain. HD causes brain cells in the basal ganglia to deteriorate and die. This means that it can no longer co-ordinate information as efficiently, so the messages being passed through the brain don't always get to the right place, or get lost along the way.

Think of your mobile phone, sometimes you get a signal, no problem. But at other times, the signal gets cut off halfway through, just when you were getting to the good part of the gossip! At other times, you cannot get a signal at all.

Having HD is a bit like this, sometimes the messages get through and other times they only get a little of the way through. Other times they just don't get through at all. So some days are better than others. Some things affect the messages getting through, for example, if the person is feeling stressed this makes it harder for the messages to get through and things may become worse at times of stress.

The brain cells in the basal ganglia deteriorate over a long period of time, 15-20 years, and during this time the affected person slowly loses different skills and abilities. This happens gradually and they can be reasonably well for a long time.

For more info on how the brain works, check out www.kidshealth.org

 and http://faculty.washington.edu/chudler/neurok.html

When someone has HD they may change and behave differently. They may not be able to walk and talk as well as before, and they may be more forgetful. Sometimes they may be more bad-tempered and get angry about little things. These changes take a long time and you might not notice them at first.

You might have more than one person in your family who has HD. This is because HD runs in families – it is hereditary. This means it can be passed from parents to their children. People might say that you look like other people in your family – this is because of your genes. Genes are passed to you from your parents – that’s why you might have freckles like your dad, or brown eyes like your mum. You have about 30,000 different genes in your body.

Genes are sections of DNA carried on your chromosomes. These genes are all different, and are programmed with different information. They decide things like the colour of your hair and your eyes, how tall you are, etc. They are like a recipe book - your genes are the ingredients that make you uniquely you. Everyone has a different recipe - that’s why we’re all different shapes and sizes. Most cells in your body have 23 pairs of chromosomes. Each parent gives you 1 chromosome in each pair. Our genes are strung out along our chromosomes and there are 100s of genes in each chromosome. We have 2 copies of each gene as well – one from each parent.

People can be identified because of the differences in their genes and the DNA that makes them. DNA can be extracted from one cell of our body, such as a single skin or blood cell, or even a hair root. That’s why on your fave crime dramas, they search the crime scene for DNA evidence. People can then be identified by their DNA.

For more info on genes and genetics, check out www.kidshealth.org and www.gslc.genetics.utah.edu

Sometimes genes don’t work properly. In people with HD,a faulty gene causes things to go wrong in the brain. If a parent has HD, they have 1 copy of the faulty gene and 1 good copy. They may pass either of these on to their children. Their children therefore have a 1 in 2, or 50 chance of inheriting the faulty gene. You may hear people saying you are “at risk” – this just means you have the 50chance of inheriting the faulty gene. If your grandparent has HD that means your parent is at 50risk. If they do not have the faulty gene, then you are no longer at risk.

The specific gene that causes HD was identified in 1993. It is located on chromosome 4. No-one knows exactly how this faulty gene causes HD and there is a lot of research going on all over the world to try and find out. Somehow having the faulty gene causes the build up of a protein (a type of body chemical) called Huntingtin in some of the brain cells which makes them deteriorate and die. Once we know how this works, then we can try and find a way to stop it happening or at least slow it down. We know a lot more about the HD gene now than ever before and different medications and approaches are being tested. So the future looks positive!