Seven Little Piggies Make History

The impregnation resulted in seven identical piglets born in the summer of 2007. Three months later, an autopsy on one piglet showed that the Alzheimer’s gene was indeed active in its brain. The researchers will now watch the remaining pigs age, with the hope that the disease will progress in the same way it does in humans.

What We Know So Far

The heritable form of the disease, also known as early-onset Alzheimer’s, is the result of a genetic mutation passed down in families. It is the cause of between 5 and 10 percent of cases. Late-onset Alzheimer’s, which appears after age 60 in people who usually don’t have a family history of the disease, accounts for the rest. Both forms lead to the destruction of nerve cells and neural connections in the cerebral cortex of the brain. The condition destroys memory and causes confusion, disorientation and, eventually, death. Despite intensive research, Alzheimer’s disease is poorly understood, and doctors still lack medical treatments to prevent the brain damage it causes.

Ovaries: A scientist harvests eggs from pig ovaries and places them in test tubes.

The process of neurodegeneration begins when enzymes snip a component of nerve cells into small pieces. The resulting protein, called beta-amyloid, accumulates in clumps between the cells. Some of these clumps eventually become large plaques. According to Samuel Gandy, a professor of Alzheimer’s-disease research at the Mount Sinai School of Medicine in New York City, amyloid protein outside the nerve cells causes the formation of what are called neurofibrillary tangles inside neurons. Here, a normal component called tau protein accumulates in the twisted fiber proteins. As the disease progresses, brain cells die and the brain itself shrinks, although it’s unknown exactly how the two proteins influence cell death. The disease starts in the hippocampus, a part of the brain involved in learning and memory, and later spreads to the rest of the brain.

Although these major steps have been mapped through brain scans and autopsies, scientists need to study how the disease progresses. That’s where the pigs come into play. If all goes as planned, the pigs should show signs of brain pathology at age two, which in pig years corresponds to the age when people with early-onset Alzheimer’s begin to exhibit symptoms.