A gene called apolipoprotein E, or APOE, is linked to risk for developing Alzheimer's disease, a neurological disorder which occurs when the brain cells die, causing memory loss and cognitive decline that get worse over time.

Now, a new study has revealed that the effects of this Alzheimer's gene on the mental ability and brain structure of a person may start to show as early as preschool, confirming what earlier studies have found.

In the new study, researchers looked at the MRI brain scans of nearly 1,200 healthy children and young adults between 3 and 20 years old.

They found that the size of the hippocampus, the region of the brain involved in memory formation, tend to be significantly smaller in those with at least one of the APOE gene's e4 variant.

APOE has three forms: e2, e3 and e4, and each carries two copies of the gene. Only 14 percent of people carry the e4 variant, which is linked to increased odds for Alzheimer's. Having two copies of this variant is known to further boost risks for the neurological condition.

Brain scans also revealed that young children with at least one copy of the e4 variant showed slower development in regions of the brain that atrophy in people with Alzheimer's. Those with e4 also performed worse in memory and thinking skills tests, although the gap disappeared between ages 8 and 10.

Study author Linda Chang, from the University of Hawaii in Manoa, said that these kinds of brain structure changes are often attributed to Alzheimer's disease, which often occurs in individuals who are aged 60 years and older, but they may already be present in childhood.

Chang and colleagues said that studying APOE in young children may help provide the earliest indicators for those who may benefit from early interventions that may help prevent future brain injuries and dementia.

Studies have shown the certain behaviors such as engaging in physical activities, a healthy diet and participating in mentally stimulating activities can reduce the risk of developing Alzheimer's.

"Our findings validated and extended prior smaller studies that showed altered brain development in APOE e4-carrier children," the researchers wrote in their study, which was published in the journal Neurology on July 13.

"The ε4ε4 and ε2ε4 genotypes may negatively influence brain development and brain aging at the extremes of age."

More than 5.3 million people in the United States currently have Alzheimer's disease. The number is expected to explode to more than double by 2050 due to the country's aging population.

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