A 19-year-old Chinese man is the youngest person with Alzheimer's, and the cause is a mystery

A 19-year-old Chinese man, with memory problems since he was 17, has been diagnosed with dementia, according to a recent study published in the Journal of Alzheimer's Disease.

After carrying out a barrage of tests, researchers at the Capital Medical University (Beijing) concluded that the teenager suffered from “probable” Alzheimer's disease. If they are correct, this makes him the youngest known person to suffer from this disease. Something quite unusual and surprising if we take into account that the main risk factor for the disease is, precisely, aging.

Although the exact causes of Alzheimer's are still unknown, a classic characteristic of the disease is the accumulation of two proteins in the brain: beta-amyloid and tau. In Alzheimer's patients, beta-amyloid is usually found in large quantities outside neurons (brain cells), while tau "tangles" are found inside axons, the long, thin projection of neurons.

However, scans showed no signs of these characteristics in the brain of the affected 19-year-old. What the researchers did find was abnormally high levels of a protein called p-tau181 in the patient's cerebrospinal fluid. This usually occurs before tau tangles form in the brain.

Genetic origin ruled out
Almost all cases of Alzheimer's disease in people under 30 years of age are due to inherited defective genes. In fact, the previous similar case – a 21-year-old young man – had a genetic cause.

Three genes have so far 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 defective it can lead to an abnormal buildup (plaques) of beta-amyloid in the brain, a hallmark of Alzheimer's that has become a target of treatments such as the recently approved drug lecanemab.

It is enough for one of the APP, PSEN1 or PSEN2 genes to be defective for a person to develop the neurodegenerative disease. Additionally, their children would have a 50:50 chance of inheriting the gene and also developing the disease.

The surprising thing is that, in the case of the newly diagnosed young Chinese man, genetic origin was ruled out. Although the researchers sequenced the patient's entire genome, they did not find any known mutations. And no one in the teen's family has a history of Alzheimer's or dementia.

To make matters worse, the young man did not suffer from any other diseases, infections or head injuries that could explain his condition. It is clear that whatever form of Alzheimer's he suffers from is extremely rare.

Severe memory impairment
At 17 years old, the young man already began to have problems concentrating in his school studies. A year later he lost his short-term memory. He couldn't remember if he had eaten or done his homework. His memory loss became so severe that he even had to drop out of high school (he was a senior).

Standard cognitive tests used to detect memory loss confirmed a probable diagnosis of Alzheimer's disease. The results indicated that his memory was severely damaged. Additionally, brain scans showed that the size of her hippocampus – a part of the brain linked to memory – had shrunk, a typical early sign of dementia.

Since performing a brain biopsy would be too risky, it is not possible to decipher the biological mechanisms of his dementia. For now, this case remains an absolute medical mystery.

Unfortunately, this is unlikely to be the last such rare case we hear about, as early cases of Alzheimer's in younger patients are on the rise.

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Source: The Conversation. Authorship:

Osman Shabir
Postdoctoral Research Associate, University of Sheffield