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Early Detectable Biological Changes That Precede Alzheimer’s Disease Symptoms Discovered

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Early Detectable Biological Changes That Precede Alzheimer’s Disease Symptoms Discovered

A study published in The New England Journal of Medicine reveals interesting findings on Alzheimer’s disease.
The study, called Dominantly Inherited Alzheimer Network (DIAN) study  included patients at risk to carry mutations for autosomal dominant form of Alzheimer’s disease. All patients included in the study had a family member with Alzheimer’s disease.  All the 128 patients underwent imaging tests, biochemical, clinical and neuropsychological assessments. Of 128 participants, 88 were carriers of mutations for dominant for of Alzheimer’s disease and 40 participants were noncarriers. It was also observed that participants with autosomal dominant inheritance pattern presented mutations in PSEN1, PSEN2, and APP genes. After analyzing the results of paraclinical assessments, researchers found that 50% of the carriers were asymptomatic at the time of the study.

Alzheimer’s disease is a degenerative neurological disorder that affects  most frequently older people. The disease is manifested by memory loss, behavioral disorders and cognitive impairment. In later stages, patients present depression, hallucinations, they become agitated and hardly recognize their family members. Alzheimer’s disease is a slowly, progressive and irreversible neurological disorder.  Current treatment of the disease slows disease progression and  improve symptoms. Alzheimer’s disease has an impact not only on the person affected but, also on the family members who must take care of the patient.

Alzheimer's Disease

Alzheimer’s Disease

Alzheimer’s disease present two forms: a form with early-onset and a form with late-onset.  Early-onset form of Alzheimer’s disease has a poor prognosis and a rapid evolution. Patients with early-onset form of the disease present a positive  family history for Alzheimer’s disease. Late-onset form is the most common form of Alzheimer’s disease, being  also called sporadic form of Alzheimer’s disease. However,  Alzheimer’s disease must be differentiated from mild cognitive impairment, which is considered to be a precondition of Alzheimer’s disease. Mild cognitive impairment is a type of forgetfulness  specific to elderly people. It is known that not every patient with mild cognitive impairment will develop Alzheimer’s disease.

In this study, participants were subjected to paraclinical investigations that are targeting directly the specific changes  for Alzheimer’s disease: atrophy of the hippocampus atrophy, amyloid beta protein present in cerebrospinal fluid. Participants cognitive functions were assessed by neurological examination and by using Clinical Dementia Rating  (CDR) scale. Researchers found significant differences between carriers and noncarriers.  This differences were obvious in neuropsychological tests (Mini-Mental State Examination, MMSE) because carriers presented significant cognitive impairment compared with noncarriers. Brain imaging examination revealed  that carriers presented bilateral hippocampal atrophy. It was also observed that carriers presented elevated levels of beta amyloid protein and elevated levels of tau protein (a structural protein of the brain cells)  in cerebrospinal fluid. Other investigations focused on brain glucose metabolism and amyloid deposition with similar results. All this structural and biochemical modifications occur with 15-20 years before disease onset.

With this study, scientists found that the period of time between brain structural modification and the onset of Alzheimer’s disease is prolonged, for example plaques can be seen on brain scans with 15 years before onset of memory problems and for this reason further therapies should target these early changes in order to prevent symptoms emergence.