Amyloid- 40 and amyloid- 42 – these proteins are the cause fort he most frequent type of senile dementia named Alzheimer’s disease. The beta-amyloids deposit in the brain and clump into large plaques having a neurotoxic effect: They damage the processes of neurons and thus cause their final destruction.
Whatever accumulates in the brains of Alzheimer patients you can also find in the eyes of patients with Down syndrome. Thus the leading of the genetic triggers for intellectual disability and the most frequent brain disorder have a common denominator. This finding – recently presented in Fort Lauderdale during the Annual Meeting of the American Association for Research in Vision and Ophthalmology – means a significant progress for early diagnostics of Alzheimer’s disease.
Triple dose of the APP gene
The amyloid precursor protein APP holds the key role in neurotoxic processes because only these enzymatically split create the beta amyloids with their fatal effects. Now the gene responsible for coding the APP is located exactly on the very chromosome tripled in people with Down syndrome: Chromosome 21. “Chromosomal triplication includes the APP gene located on 21q21”, explains Prof. Dr. Lee E. Goldstein, at the Boston University School of Medicine and the Boston University Alzheimer’s Disease Center. That makes the information for APP characteristics available in a tripled dose which – according to Prof. Goldstein –accelerates APP expression leading to cerebral accumulation of APP-derived amyloid-β peptides (Aβ)”. The results are an early loss of neuro-cognitive abilities and the early onset of Alzheimer neuropathology in Down syndrome patients. “In our study we were able to show that the abnormalities in the patients’ lenses were based on an increased amyloid accumulation” and Prof. Goldstein continues that thus the so far open question of where the supranuclear cataracts typical for the Down syndrome come from has been answered.
»Window to the brain…«
These beta-amyloid accumulations in the lenses are not found in any other demental disease or any healthy people. It also is explicitly different from age-dependent cataracts appearing mainly during the fifth decade of life. According to the Boston scientist, the accumulation of amyloid doubtlessly is an indication of the Alzheimer’s disease. Something that shows in the patients soon: “We have found out that the proteins start accumulating in the lenses very early, sometimes as early as the childhood. “ reports Prof. Goldstein – an indication attributing to the cell metabolism in the lenses. It is comparatively lazy. So the cells have limited capacities catabolizing the deposited proteins,” explains Prof. Goldstein. In other words: Beta-amyloids cannot be “disposed” of thus showing their effects rather early. This pathogenetic link the Boston group of researchers found allows a look into the brain in the word’s meaning. Because the pathological processes in the cell of the lenses occur prior to the cerebral neurotoxic – the cataracts therefore are significant markers allowing the diagnosis of dementia type Alzheimer and in vivo while the patient is still alive. The lenses, says Prof. Goldstein, are so to speak “a window to the brain”.
These findings will now be used for an early detection of brain performance disorders. “We are currently developing an eye scanner measuring the beta-amyloid concentration in the lenses”. This test will open promising doors: as well known, an early diagnosis is the key to success of therapeutic interventions. And according to Prof. Goldstein some effective strategies appear on the horizon. “They could be applied at an early stage thanks to our eye test” an incredibly high motivator for the Boston scientists and their research.