Doctors in China have identified the world’s youngest case of Alzheimer’s disease in a 19-year-old, yet scientists are baffled as to how he developed the memory-robbing condition at such a young age.

The unnamed teen boy first began experiencing memory decline at 17. He often forgot what he did the day before and was always misplacing his belongings. He was eventually unable to graduate from high school, though he could still live on his own.

Before he was formally diagnosed with early-onset Alzheimer's, the teen was sent to a memory care clinic for about a year, where experts found that his overall memory score was 82 percent lower than that of his peers of the same age and his immediate memory score was 87 percent lower.

In 2022, brain scans showed shrinkage in the hippocampus, a crucial memory formation region in the brain and one of the first areas affected by Alzheimer's, the most common form of dementia that affects roughly 6.7 million Americans.

Doctors at that clinic analyzed his cerebrospinal fluid and detected telltale markers of the disease, including abnormal levels of amyloid and tau proteins.

When they conducted a thorough search of his DNA for mutations that made him more susceptible to the disease, they found nothing.

Almost all patients diagnosed under the age of 30 have specific genetic mutations, typically in genes like PSEN1, leading to a classification of familial Alzheimer's disease. This unidentified man, however, had no such mutations nor any family history of dementia, ruling out known disease pathways. 

Researchers from Capital Medical University, who described the patient, noted that the disease's ‘pathogenesis still needs to be explored,’ implying that undiscovered genetic factors, unique environmental interaction or never-before-documented disease pathways could be at play.

The unnamed teen's memory decline began at age 17, with symptoms like forgetting the previous day and constantly misplacing items. This progressed to the point where he could not finish high school (stock)

To date, the youngest person known to have been diagnosed with Alzheimer’s disease was 21 years old and carried the PSEN1 gene mutation. This young man’s case, though, appears to be ‘sporadic,’ according to the researchers, with causes unknown. 

This 19-year-old patient is the youngest known case of Alzheimer's disease with no known genetic contribution, according to the researchers. 

Their case report, published in the Journal of Alzheimer’s Disease, said: ‘Although the patient’s age of onset is very early, he met the diagnostic criteria for probable AD dementia, according to the diagnostic criteria of the National Institute on Aging-Alzheimer’s Association.’