Dementia is a progressive decay of intellectual functions. The most common cause of dementia is Alzheimer's disease. This illness can occur at any age, but primarily affects elders. People who are diagnosed with dementia early in life (prior to 45 years of life) - are diagnosed as neurodegenerative diseases with rare occurrence of Alzheimer's disease. Early Alzheimer's disease affects a working-age population and is therefore a major public health, medical and socioeconomic problem. Alzheimer's disease is a multifactorial disease in which degeneration of neuronal pathways and blood vessels occurs with the formation of abnormally aggregated proteins such as β-amyloid and tau. There are two hypotheses that describe the pathophysiological changes in Alzheimer's early disease, which are: "amyloid hypothesis" and "tau hypothesis".This disease is a very complex disease caused by the action of several genes and the risk of the environment. The inherited form of Alzheimer's disease is also called early-onset Alzheimer's disease. 1% of the total affected by this disease belongs to the group of hereditary Alzheimer's disease. The genes that are important for early start are: APP, presenilin 1 (PSEN1) and (PSEN2). The development of new diagnostic methods that will enable earlier and more accurate detection of AD is extremely important. It is believed that early diagnostic methods are going to be able to diagnose early stage illnesses that will not yet have any significant brain changes. Today's treatment of AD is symptomatic. Mechanisms of the onset of this disease are still unknown and therefore no suitable therapy to treat or even cure this disease has been found.