Story highlights Strangers from around the world are sending holiday cards to 6-year-old Addie Fausett

Her family wanted a lifetime of cards for her after a gloomy prognosis

Addie's condition is undiagnosed, but cerebral atrophy is one of the symptoms

By sheer volume, one might assume that letters for Santa Claus were accidentally rerouted to P.O. Box 162 in Fountain Green, Utah. But all the letters, notes and cards coming in are addressed to 6-year-old Addie Fausett.

"Thank you for my cards," Addie told a postal worker on a recent trip to pick up her bounty of seasons greetings. In the small town of just more than 1,000 residents, her letters have outnumbered the population.

Addie made the mailing lists of thousands of strangers around the world after her family asked the public to give her a lifetime of Christmas cards after a gloomy prognosis: A mysterious condition will probably cut her young life short, doctors have told the family.

This year, the Fausetts were told this would probably be Addie's last Christmas. Although her condition remains undiagnosed, she suffers from cerebral atrophy, which has severely affected her speech and motor skills. According to her mother, at age 3, Addie just stopped growing; at 6, she weighs only 23 pounds.

"She likes to laugh and have a good time and hear stories, but lately she has had a lot of days she will just cry all day long," Tami Fausett, Addie's mother, told CNN affiliate KSL

Addie opening letters and celebrating Christmas. As the handwritten letters pour in, Addie's family hopes they will spark a little Christmas cheer during the tough times. They've created the Facebook page for "Little Addie" to update followers with pictures ofAddie opening letters and celebrating Christmas.

"She doesn't get to play with kids, so we thought if everyone sent her a card, we could tell all her they were all her friends, and it would just help make her Christmas a little bit better," Fausett said.

Amber Brosig, managing trustee of the charity Children and the Earth , said Addie's family never fathomed such an amazing response with the letters. The charity has been helping the family with medical costs.

Addie is appreciative of the kind words that have been flooding in, and she had a message for KSL's camera: "Merry Christmas."

"There's no other way to describe her other than she's an absolute sweet soul," Brosig told CNN.