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When a parent or grandparent develops Alzheimer's Disorder it is understandable to worry that you may inherit the illness, or pass it on to your own children. Here we explore the genetic indicators and whether Alzheimer's Disorder is hereditary. Which genes are linked to Alzheimer's Disorder? There has been a great deal of research into Alzheimer's Disorder, and geneticists have found two types of genes that affect whether or not a person might develop alzheimer`s disease. These are identified as 'risk genes' and 'deterministic genes'. The risk genes for Alzheimer's Disorder have been identified on chromosomes 1, 14, 19 and 21. It is the apolipoprotein E-e4 – or APOE-e4 – gene which has specifically been linked to late-onset Alzheimer's Disorder. This gene is found on chromosome 19, and is found in most people with the disease. Inheritance of this gene from one parent increases the risk of developing late-onset Alzheimer's disease. Inheriting from both parents increases the risk again.

I have the APOE-e4 gene – will I definitely develop Alzheimer's Disorder? The APOE-e4 gene is found in most people with Alzheimer's Disorder, and inheriting it does put you at a greater risk of developing the illness. However; having the gene does not mean that you will definitely develop Alzheimer's – simply that your risk of developing the disease is greater than that of someone without the gene. Many people who have the APOE-e4 gene do not go on to develop Alzheimer's Disorder. Conversely, there are many people without the gene who do develop AD. So though this gene has been identified as a genetic marker for the disease it is inconsistent, and only potentially increases the risks. Essentially, there are some genetic links found in people with Alzheimer's Disorder, but as yet no definitive answers as to whether late-onset Alzheimer's is hereditary. Some people are more at risk that others, but developing the illness isn't a certainty, and it's believed that environmental factors play a part in the illness developing, though there is less conclusive evidence of these. True familial Alzheimer's Disorder. As well as the APOE-e4 gene – which is the 'risk gene', as explained – there is conclusive proof of a 'deterministic gene' found in true familial Alzheimer's Disorder. This gene identifying familial neurology – or 'hereditary' Alzheimer's – is found in a very small proportion of those with the illness. Some studies record the gene in less than 5% of cases with the disease, other sources claim it is as low as 1%. These cases usually present as early-onset Alzheimer's Disorder, with symptoms occurring as early as a person's 30s or 40s, and many members of the family, across multiple generations, are affected. The chromosome on which these abnormalities have been identified is chromosome 21, and there are variants in the proteins amyloid precursor protein (APP) presenilin-1 (PS-1) and presenilin-2 (PS2). Cases of people with these genes are very rare compared to those with the risk gene. However, when these genes are found, the individual will definitely develop Alzheimer's Disorder, most probably early-onset AD. A parent or grandparent developing Alzheimer's Disorder does not mean that their children and grandchildren will definitely develop the disease. There are some indicators that make it more likely, but true familial Alzheimer's is rare.