Sisters Elana, left, and Jolie Cohen visit their great-grandmother, Barbara Rukovina, who is losing her memory because of Alzheimer's disease, at Asbury Methodist Village in Gaithersburg, Md. The fatal illness kills brain cells that help people remember, think and behave.

Cutaways of a healthy brain, left, and a brain affected by Alzheimer's. The severe form of the disease might last one to five years. Because of cell damage, the brain shrinks, patients can't communicate and they fail to recognize family and close friends.

Jolie Cohen helps her great-grandmother, nicknamed Mucker, find the correct room at Asbury Methodist Village in Gaithersburg, Md. The girls say that watching Mucker, who has Alzheimer's disease, get worse is sad and sometimes scary.

Washington ? When Elana and Jolie Cohen visited their great-grandmother in Gaithersburg, Md., recently, she greeted them with a gleeful “Oh, my girls! My girls!”

But what followed wasn’t a typical chat. Their great-grandmother, Barbara Rukovina (whom the girls call Mucker), usually makes no sense. She doesn’t remember their names. Often, she doesn’t seem to know where she is.

Rukovina is quickly losing her memory – and not because she’s 92. She has Alzheimer’s disease.

The fatal illness, which is named after a German doctor and pronounced ALTS-high-merz, kills brain cells that help people remember, think and behave.

Everyone forgets sometimes, like when you leave your backpack at school. But people with Alzheimer’s lose so much of their memory that they can’t remember basic things such as how to make a sandwich.

About 5 million Americans have the disease, which usually affects those older than 65. Researchers are trying to find a cause and a cure.

Rukovina’s illness started three years ago. Jolie remembers when Mucker suddenly announced that she had to leave an ice cream parlor because she needed to get back to the nursing home for her wedding. (Her husband died in 2000.)

Watching their great-grandmother get worse is sad and sometimes scary for the girls. Mucker lives on a locked floor at Asbury Methodist Village – visitors must punch in a code to get in or out – because Alzheimer’s patients often try to wander outside, where they could get lost or hurt.

On a recent visit, Elana, who is 8, gave Mucker a colorful placemat she had made in her second-grade class. About 10 minutes later, Mucker acted as if she had never seen it. “Oh, what’s this?” she said with a pleasant smile.

Sometimes she’s funny. The girls shared a giggle when Mucker turned to Elana and asked, for no reason, “Do you want me to be a dumbbell?”

Once in a while, she surprises them by making perfect sense. “Those are cute,” she said, eyeing Jolie’s pink Crocs.

But most of the time she’s difficult to understand. Elana and Jolie smile and nod anyway. They say they don’t want to hurt her feelings.

“You just sort of go along with it,” said Jolie, who is 10 and in fourth grade.

Experts say such visits are key to staying close. Kids should remember that people with Alzheimer’s “still love them, even if the disease is affecting them,” said Peter Reed, of the Alzheimer’s Association, which is based in Chicago. “They’re still the person they’ve always known and loved, and they can still do things with them.”

Jolie and Elana agreed. “I still love her,” Elana said of Mucker. “She’s part of our family.”