A 19-year-old has been diagnosed with Alzheimer’s – no one knows why

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Amyloid plaques in Alzheimer's disease

Amyloid plaque buildup, a classic sign of Alzheimer’s disease, is generally only seen in the elderly (Image: Getty/iStockphoto)

A 19-year-old Chinese man who had been experiencing memory problems since the age of 17 was diagnosed with dementia, according to a recent case study published in the Journal of Alzheimer’s Disease.

After conducting a barrage test, researchers at Beijing Medical University diagnosed the teenager with “probable” Alzheimer’s disease. If the diagnosis is correct, he will be the youngest person ever recorded with the mind-robbing disease.

The main risk factor for the disease is aging, which makes this latest case so unusual.

The exact causes of Alzheimer’s disease are still largely unknown, but a classic hallmark of the disease is the accumulation of two proteins in the brain: beta-amyloid and tau. In people with Alzheimer’s, beta-amyloid is usually found in large amounts outside neurons (brain cells), and tau “tangles” are found inside axons, the long, thin projection of neurons.

However, scans failed to show signs of these features in the 19-year-old’s brain. But the researchers found unusually high levels of a protein called p-tau181 in the patient’s cerebrospinal fluid. This usually occurs before tau tangles form in the brain.

Almost all cases of Alzheimer’s disease in people under the age of 30 are due to inherited faulty genes. Indeed, the previous youngest case – a 21-year-old woman – had a genetic cause.

Three genes have been linked to Alzheimer’s disease in young people: amyloid precursor protein (APP), presenilin 1 (PSEN1), and presenilin 2 (PSEN2).

These genes are involved in the production of a protein fragment called beta-amyloid peptide, a precursor to the aforementioned beta-amyloid. If the gene is faulty, it can lead to abnormal accumulation (plaques) of beta-amyloid in the brain – a hallmark of Alzheimer’s disease and a target for treatments such as the recently approved drug lecanemab.

People only need one of APP, PSEN1 or PSEN2 to be defective to develop Alzheimer’s disease, and their children have a 50:50 chance of inheriting the gene from them and also developing the disease.

However, a genetic cause was ruled out in this latter case, as researchers sequenced the patient’s entire genome and failed to find any known genetic mutations. And no one in the teenager’s family has a history of Alzheimer’s disease or dementia.

The young man also had no other illnesses, infections or head trauma that could explain his condition. It is clear that whatever form Alzheimer’s takes, it is extremely rare.

Alzheimer's and dementia research, conceptual image

Alzheimer’s and dementia research, conceptual image. Magnetic resonance imaging (MRI) of a human brain on a screen (Image: Getty/Science Photo Libra)

Severely impaired memory

At the age of 17, the patient began to have problems concentrating in his school studies. This was followed a year later by the loss of his short-term memory. He couldn’t remember if he had eaten or done his homework. His memory loss became so severe that he had to drop out of high school (he was in his senior year).

A possible diagnosis of Alzheimer’s disease was confirmed by standard cognitive tests used to detect memory loss. The results showed that his memory was severely impaired. Brain scans also showed that his hippocampus – a part of the brain involved in memory – had shrunk. This is a typical early sign of dementia.

A brain biopsy would be too risky, so understanding the biological mechanisms of his dementia is difficult – and this case remains a medical mystery at this point.

Cases of early-onset Alzheimer’s disease are increasing in younger patients. Unfortunately, this is unlikely to be the last we hear of such a rare case.

By Osman Shabir, Postdoctoral Research Fellow, University of Sheffield

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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