In 2023, neurologists at a memory clinic in China diagnosed a 19-year-old with what they believed to be Alzheimer's disease – making him the youngest person ever to be diagnosed with the condition.
The teen first began experiencing memory decline around age 17, with symptoms worsening over time.
Brain scans revealed shrinkage in the hippocampus, a region involved in memory, while his cerebrospinal fluid showed biomarkers consistent with Alzheimer's – the most common form of dementia.
Although usually associated with older age, early-onset cases of Alzheimer's (those occurring in individuals under age 65) represent up to 10 percent of all diagnoses.
Almost all Alzheimer's patients under the age of 30 can have their disease explained by pathological gene mutations, classifying them as having familial Alzheimer's disease (FAD). The younger a person is when they receive a diagnosis, the more likely it is caused by an inherited faulty gene.
However, researchers at Beijing's Capital Medical University were unable to find any of the usual mutations responsible for the early onset of memory loss, nor any suspect genes, after conducting a genome-wide search.
Before this diagnosis in China, the youngest patient with Alzheimer's was 21 years old. They carried the PSEN1 gene mutation, which causes abnormal proteins to build up in the brain, forming clumps of toxic plaques, a common feature of Alzheimer's.
Cases like this one pose something of a mystery. None of the 19-year-old's family had a history of Alzheimer's or dementia, making it hard to categorize it as FAD, yet the teenager had no other diseases, infections, or head trauma that could explain his sudden cognitive decline either.
Two years before being referred to the memory clinic, the teenage patient began struggling to focus in class. Reading also became difficult and his short-term memory declined. Oftentimes, he couldn't remember events from the day before, and he was always misplacing his belongings.
Ultimately, the cognitive decline became so bad, the young man was unable to finish high school, although he could still live independently.
A year after being referred to the memory clinic, he showed losses in immediate recall, short-delay recall after three minutes, and long-delay recall after 30 minutes.
The patient's full-scale memory score was 82 percent lower than that of peers his own age, while his immediate memory score was 87 percent lower.
Long-term follow-up is needed to support the young man's diagnosis, but his medical team said at the time the patient was "altering our understanding of the typical age of onset of AD."
"The patient had very early-onset AD with no clear pathogenic mutations," neurologist Jianping Jia and colleagues wrote in their study, "which suggests that its pathogenesis still needs to be explored."
The case study, published in February 2023, just goes to show that Alzheimer's doesn't follow a single pathway, and is much more complex than we thought, emerging via numerous avenues with varying effects.
In a statement to the South China Morning Post, the neurologists who described the patient's case argued that future studies should focus on early-onset cases to further improve our understanding of memory loss.
"Exploring the mysteries of young people with Alzheimer's disease may become one of the most challenging scientific questions of the future," they said.
The study was published in the Journal of Alzheimer's Disease.
An earlier version of this article was published in February 2023.