A 19-year-old Chinese man is the youngest person to have Alzheimer’s, and the reason is a mystery.

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

After conducting a flurry of tests, researchers at the Capital Medical University (Beijing) came to the conclusion that the teenager suffered from “probable” Alzheimer’s disease. If they are correct, this makes him the youngest known person to have suffered from the disease. Something rather unusual and surprising, given that aging is the main risk factor for the disease.

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

However, scans showed no evidence of these characteristics in the brain of the affected 19-year-old. What the researchers did find were 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 younger than 30 years of age are associated with inherited defective genes. In fact, a previous similar case – in a 21-year-old young man – had a genetic cause.

To date, 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 that has been targeted for 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 a neurodegenerative disease. In addition, their children will have a 50:50 chance of inheriting the gene as well as getting the disease.

What is surprising is that in the case of a newly diagnosed Chinese young man, a genetic origin was ruled out. Although the researchers sequenced the patient’s entire genome, they found no 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 other diseases, infections, or head injuries that could explain his condition. It is clear that whatever form of Alzheimer’s you have, it is extremely rare.

severe memory impairment

At the age of 17, the young man had already begun to have problems concentrating at school. A year later, he lost his short-term memory. She couldn’t remember if she ate or did her homework. The memory loss became so severe that he even had to drop out of school (he was in his senior year).

Standard cognitive tests used to detect memory loss have confirmed a likely diagnosis of Alzheimer’s disease. The results showed that his memory was severely impaired. In addition, brain scans showed that the size of her hippocampus, the part of the brain associated with memory, has shrunk, a typical early sign of dementia.

Since performing a brain biopsy would be too risky, it is impossible to decipher the biological mechanisms of his dementia. So far, this case remains an absolute medical mystery.

Unfortunately, this is unlikely to be the last such rare event we hear about as the number of early cases of Alzheimer’s disease in young patients is on the rise.

Osman Shabir, Postdoctoral Research Fellow, University of Sheffield

This article was originally published on The Conversation. Read the original.