A study published Wednesday in the journal Environmental Research found symptoms of Alzheimer’s disease in babies less than a year old in Mexico City—suggesting not only that the disease takes shape earlier on than previously suspected but that environmental factors may be to blame.

The researchers, led by Lilian Calderón-Garcidueñas at the University of Montana, investigated the autopsies of 203 Mexico City residents between the ages of 11 months and 40 years old.

The team specifically looked at levels of two proteins strongly connected to Alzheimer’s: hyperphosphorylated tau and beta amyloid. Beta amyloid buildup in the brain, in particular, has been associated in patients with Alzheimer’s over the age of 65, around the time when the disease normally onsets. They compared the buildup to those of healthy people, along with other factors: gender, socioeconomic status, IQ, nutritional statistics, and education.

The researchers found that levels of both proteins were at above-normal levels in 99.5 percent of the autopsies—including that of the 11-month-old baby.

Furthermore, the study found that these elevated levels of hyperphosphorylated tau and beta amyloid are directly related to exposure to what’s referred to as fine-particulate-matter pollution, or the type of hazy, thick, hard-to-breathe smog that is found in Mexico City and other similar urban areas around the world. The particulate matter, PM2.5, is about 30 times smaller than the diameter of a human hair.

Of course, it’s worth noting here that there was only one 11-month-old baby in the sample, and a variety of factors ranging from the environmental one being discussed in the paper and genetics could have made created the elevated levels of proteins seen in the baby.

But Calderon-Garciduenas’ research over the years has shown a clear correlation between Mexico City’s air pollution and Alzheimer’s symptom development. It’s also important because research has shown that those carrying a gene associated with Alzheimer’s, APOE4, are almost five times more likely to commit suicide. According to an interview that Calderon-Garciduenas gave to Newsweek, up to 20 percent of Americans carry the APOE4 allele.

The study comes to similar conclusions as Calderon-Garciduenas’ previous research: that air pollution has a big role to play in spiked, abnormal protein levels in these younger brains. In contrast, kids exposed to cleaner air showed better health and were less likely to have these symptomatic protein buildups.

And it’s also important to note that while the the study doesn’t prove that air pollution is directly connected to Alzeheimer’s, it yet again shows correlation between breathing in poor quality air and brain health.

Which means that while having a genetic predisposition to Alzheimer’s is not something that can be avoided, air pollution can be—and drives at the fact that human induced climate change has far reaching effects beyond simply making the weather more extreme. As Calderon-Garciduenas told Newsweek: “Air pollution has to be prioritized. Pollution is serious [and] chronic, people are exposed from conception to death.”