Tau misfolds and clumps in about 30 other diseases, including Alzheimer’ s disease, PSP, chronic traumatic encephalopathy, and about half of all cases of frontotemporal dementia, and the initial cause or causes may be different for each. The specific disease depends on the chemical characteristics of the tau clumps and which sets of brain cells are vulnerable to that specific abnormal form of tau. All of these variable features, as well as the ultimate question of why tau disorders occur in some people and not in others, may come down to genetic differences or exposure to certain chemicals or a combination of these. We do know that the physical shape of the mis-folded tau is the same in everyone with CBD and different from that in PSP, Alzheimer’ s and the other tau-based disorders. Knowing the misfolding pattern is helping scientists design drugs for CBD’ s specific form of tau.
For people who are personally impacted by CBD, we recognize that not knowing the cause can be extremely frustrating and confusing. Researchers and doctors are working hard to understand CBD and other related neurodegenerative diagnoses, and we hope this will lead to more answers and treatment options soon.
What are the subtypes of CBD? The microscopic brain abnormalities of CBD can affect different parts of the brain, producing different symptoms in different people. In all forms of CBD, nearly all patients at some point develop a degree of motor parkinsonism, meaning stiffness, slowness, soft speech, reduction in facial expression, balance difficulty and tremor.
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The most common subtype of CBD is called corticobasal syndrome, which affects about half of all people with CBD. About a quarter of people with CBD have symptoms that resemble PSP, which impacts balance, eye movement, speech and swallowing. Another 15 % have symptoms of frontotemporal dementia, with inappropriate, uninhibited behavior and difficulty organizing thoughts. Then there are two rare forms, each accounting for about 5 % of the total number of cases of CBD. One has a dementia similar to that of Alzheimer’ s disease, with particular problems with memory or spatial orientation. The other is a form of aphasia, which means a problem with language— in this case, difficulty finding words and obeying rules of grammar.
What is corticobasal syndrome, and how does it differ from corticobasal degeneration? The classic type of CBD is called corticobasal syndrome( CBS), which starts with difficulty moving one limb, apraxia, dystonia, slowness, stiffness and some degree of sensory problems. The term“ syndrome” means a set of abnormalities that appear in the same person at the same time but may or may not be caused by the same underlying disease in every case. It turns out that only about half of all people with CBS actually have the disease corticobasal degeneration. About 20 % of those with CBS have the same brain abnormalities that underlie Alzheimer’ s