Dementia is a clinical syndrome involving cognitive impairment that is generally caused by disease. There are various types of dementia, including Alzheimer’s disease, vascular dementia, Lewy body dementia, and frontotemporal dementia. In most cases, dementia is not strictly hereditary, but the disease underlying dementia is usually caused by a combination of various genetic and environmental factors. However, there are a few cases of familial dementia, where dementia is inherited and caused by genetic mutations.
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Dementia and Genetics
Is dementia genetic? Most forms of dementia have multiple risk factors, with genetics being only one of them. Alzheimer’s disease accounts for 60% to 80% of all dementia cases, and it is caused by a mixture of genetic, environmental and social factors.
Possessing certain gene variants can increase the risk of developing dementia. Gene variants are genes that determine the same trait (eye color) but exist in different forms (blue, brown, etc.). Gene variants, in other words, are functional genes that are not abnormal or mutated. Possessing certain gene variants can increase the risk of dementia, but it depends on their interaction with certain environmental and social factors. In this way, dementia and genetics are related.
Familial dementia refers to cases where dementia is caused by the inheritance of genes. Mutations in certain genes (faulty genes) are responsible for familial dementia. In most cases, receiving a single copy of the mutated gene from either parent is enough to develop the disease (dominant inheritance). In other cases, receiving a mutated gene from both parents is necessary for developing the disease (recessive inheritance). Most forms of familial dementia develop between the ages of 30 to 65 and are referred to as early-onset dementia.
Genetic testing for dementia may be undertaken to assess an individual’s risk of developing the condition, especially when they have a blood relative diagnosed with dementia. Because of the absence of a cure, genetic testing can cause anxiety and emotional distress. To help prevent this, counseling is advised before testing.
Alzheimer’s disease is the most common form of dementia. Age, rather than genetics, is Alzheimer’s disease’s largest risk factor, with the risk of dementia doubling every five years after 65 years of age. In the case of twins, if one has Alzheimer’s disease, the risk of the other twin developing it is only 40% to 50%. This indicates there is a significant role played by environmental factors.
Although a close family member suffering from dementia increases the risk in their relatives, dementia is usually not inherited by the next generation. This shows that Alzheimer’s disease is not a hereditary disease, but possessing certain genes may increase the risk of developing it.
There are, however, a small number of cases (less than 5%) where Alzheimer’s disease is hereditary. This familial form of Alzheimer’s disease generally results in early-onset dementia that develops between the ages of 30 to 60 years. Mutations in three genes have been identified as being responsible for early-onset familial Alzheimer’s disease (eFAD). Possessing a single copy of any of those mutated genes is enough to develop this form of familial dementia.
Except for a few rare types, vascular dementia is not hereditary. Vascular dementia is caused by damage to blood vessels in the brain, often after a stroke. The risk factors for vascular dementia are similar to risk factors for stroke, high blood pressure, atherosclerosis (disease of blood vessels) and diabetes. These risks show that vascular dementia is genetic to an extent. Genes that increase the risk of developing any of these conditions are also likely to increase the risk of developing vascular dementia.
Lewy Body Dementia
Only two decades have passed since Lewy body dementia has been recognized as a separate disease. Because of its relatively new status, there is a lack of substantial data regarding the prevalence of sporadic and familial Lewy body dementia.
Lewy body dementia genetic factors have not been fully characterized, and only a small number (about 10%) of cases of Lewy body dementia are hereditary. Like Alzheimer’s disease, a family history of Lewy body dementia can increase the risk of developing dementia. For example, the siblings of Lewy body dementia patients have twice the risk of developing dementia.
Frontotemporal dementia (FTD) is a type of dementia involving neuronal degeneration in the frontal or temporal lobes of the brain. Frontotemporal dementia is one of the leading causes of early-onset dementia, with only 25% of all frontotemporal dementia cases being late-onset. But is frontal lobe dementia hereditary?
Frontotemporal dementia is hereditary in 40% to 50% of the cases. Mutations in five genes are responsible for familial frontotemporal dementia, with the inheritance of these genes leading to this form of dementia in all cases. This means frontotemporal dementia is genetic. In the remaining cases where FTD is sporadic, trauma and thyroid disease are major risk factors.
Family History of Dementia
Individuals with a family history of dementia may be at a higher risk of developing dementia. However, this may be due to the inheritance of gene variants that increase susceptibility to dementia rather than cause it directly. In such cases, chances of getting dementia are also influenced by social and environmental factors as well as lifestyle choices.
In the case of familial dementia, genetic testing may be useful. Such genetic testing is available for genes involved in Alzheimer’s disease (three genes) and frontotemporal dementia (six genes). This can help people to be vigilant about the signs and symptoms of dementia and increase awareness about available tests and treatments. Although there are no cures available for dementia, individuals may participate in ongoing clinical trials.
Reducing Your Risk of Developing Dementia
As mentioned earlier, genes increase the risk of dementia but do not cause it in most cases. There are multiple risk factors associated with dementia, including cardiovascular diseases, diabetes, and smoking, that can be managed to help in preventing dementia. Maintaining a healthy lifestyle with physical exercise, a balanced Mediterranean diet, low levels of alcohol intake and abstinence from smoking can help in reducing the risk of dementia.
Individuals with substance use disorders are often at an increased risk of developing dementia. In addition, family members of an individual with dementia may turn to substances to deal with the stress of caring for their loved one. If you or a loved one suffers from a substance use disorder, The Recovery Village can help. Contact us today to learn about specialized treatment programs that can work well for your situation.
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Alzheimer’s Association. “What is Alzheimer’s?” 2019. Accessed June 18, 2019.
McCullagh, C.D., Craig, D., McIlroy, S.P., Passmore, A.P. “Risk factors for dementia. Advances in psychiatric treatment.” Advances in Psychiatric Treatment, January 2001. Accessed June 18, 2019.
van der Flier, W.M., Scheltens, P. “Epidemiology and risk factors of dementia.” Journal of Neurology, Neurosurgery & Psychiatry, December 2005. Accessed June 18, 2019.
Cohn‐Hokke, P.E., Elting, M.W., Pijnenburg, Y.A., van Swieten, J.C. “Genetics of dementia: update and guidelines for the clinician.” American Journal of Medical Genetics Part B: Neuropsychiatric Genetics, September 2012. Accessed June 18, 2019.
Alzheimer’s Research UK. “What is vascular dementia?” January 2015. Accessed June 18, 2019.
Neary, D., Snowden, J., Mann, D. “Frontotemporal dementia.” The Lancet Neurology, November 2005. Accessed June 18, 2019.
Onyike, C.U., Diehl-Schmid, J. “The epidemiology of frontotemporal dementia.” International Review of Psychiatry, April 2013. Accessed June 18, 2019.
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