Sadie will never grow up. And her parents will never give up.

When school starts Tuesday, Sadie Lane will be in preschool again while her peers move on to kindergarten.

To her mother, it's a sign that Sadie's path is irrevocably diverging from the rest of the kids her age.

Sadie, a bright-eyed child with a huge grin, has a rare chromosome disorder. Although she's been seen by rounds of doctors since she was born, the only name for the condition is a jumble of genetic code. There's no predicted path, no treatment, no cure. Just Sadie being herself.

"I'm in the day-to-day moment of life with Sadie," said her mother, Lisa Lane, an elementary school teacher who stopped working to stay home when Sadie was born.

At age 5, Sadie looks just like her peers. But developmentally, she is more like a 2-year-old. She loves to push around a stroller and babbles on a toy phone. She says a few words, such as 'ba-ba' for bubbles, and wears "Dora the Explorer" pull-up diapers.

"When you get out of the moment, it's heartbreaking to think that she's not going to do the things you want your kids to do," Lisa said. "Knowing your 5-year-old will always live with you and will never marry - there's no pretending."

Sadie will always need supervision. She might walk right off a set of stairs without looking. A few moments with an art project, and she has glitter around her mouth.

She likes going to Birdneck Elementary School, where they have a special class that mixes children with disabilities with other preschoolers. In class, Sadie sits politely during circle time and stands up when she's called on. She's learned to hold hands in the hallway.

But her teachers don't think she's ready for kindergarten, where there's more academics and less free play.

Sadie still needs practice playing. Last spring, she'd head toward the crayons or the dress-up corner in her class, then stop. She'd make a sound or smile and look up with big blue eyes, as if unsure what to do next.

At Grommet Island Park at 2nd Street on the Oceanfront this summer, Sadie ran with a side-to-side gait along the raised platform that connects the play equipment. She stopped to shake a row of musical metal bars, making a jingling noise. Then she ran the other way.

"It's arbitrary. You don't know what's next," said her father, Bill Lane, a mortgage banker, watching as Sadie shifted directions yet again. Sadie's sister, Shelbi, now 3, shimmied down a silver pole and played in the sand.

A few minutes later, Bill had to leave the park for a meeting.

"Sadie girl, can I have a kiss?" Bill asked. Sadie scooted forward toward her father, who stood below the railing of the play area. "C'mere sweetheart. Gimme a kiss," he said. She scooted backward. Bill looked deflated.

Minutes before, he had wondered aloud: "How does a Dad go by without hearing 'da-da?' "

Shelbi came over for a kiss on her head. Then Bill went up to where Sadie was sitting and gave her a kiss on the head, too.

The first signs that something was different about Sadie came before she was born.

Her parents conceived Sadie on their honeymoon. Doctors told them that the 20-week ultrasound showed the fetus had club feet. They also recommended a closer look at her heart.

"We were madly in love. We could only think about that the child inside was half him and half me," Lisa said. Club feet run in Lisa's family. Elated by the pregnancy, they declined further tests. "We decided to take it as it may," Lisa said.

Sadie was a healthy 8 pounds, 1 ounce and 21 inches when she was born April 7, 2005, but in less than a day a doctor detected a heart murmur. A cardiologist diagnosed Sadie with several heart defects.

"This is truly the beginning of our journey," Lisa Lane wrote about those early days in a blog that she began at the end of 2007. She told her readers her blog was a way to "vent, share and inform people about life with a disabled child." From the very first scary moments, she has shared both the high and low points.

As a baby, Sadie never seemed hungry, so Lisa fed her on a schedule. Surgeries and treatments on her feet, and later her heart, began quickly.

"She was always an extremely happy baby," Lisa wrote in her blog. "She always babbled, cooed, smiled and giggled. She was a snuggle bug and we would always nap together."

Sadie wore shoes attached by a bar until she was nearly a year old, and she began crawling and pulling up to stand shortly after they were removed. But her parents' elation at her mobility was short-lived. She smiled and laughed, but she didn't walk or talk.

When she was 18 months old, Sadie was referred first to a physical therapist, and then to a neurologist. Lisa had a feeling the news wasn't going to be good.

When Sadie was 22 months old, a doctor called and said there was a problem with her eighth chromosome.

Lisa came to learn that parts of one of Sadie's chromosomes were rearranged.

"We asked for a support group," Lisa said. But the doctors said there was nothing here for something this rare.

On one copy of Sadie's chromosome No. 8, the short end had broken off. In addition, a third copy of part of her X chromosome is attached to the end. Because of this, genes are missing or added in every cell in her body.

There is no other case exactly like Sadie's, according to a British group called Unique that tracks rare chromosome disorders. About 60 people have a similar break and a different piece of another chromosome attached.

"It's not that she's rare," Lisa Lane said. "She's unique."

Dr. Virginia Proud, director of the division of medical genetics and metabolism at Children's Hospital of The King's Daughters, has worked with Sadie since she was 22 months old.

Doctors don't know why pieces of chromosomes break off. The joining of egg and sperm results in abnormal chromosomes in about 1 in 200 births. It's particularly mysterious in spontaneous cases such as Sadie's, which was not inherited from either parent.

"Everyone and their cousin is trying to figure it out," Proud said. What Proud tries to do is identify abnormal genes that cause developmental or medical effects to build a road map for doctors and parents.

Sadie's case has been "frustrating and difficult," Proud said. It's taken three tests of increasing precision - each traumatic for Sadie - "to get even a bit of an answer," she said.

Youngsters with similar chromosomal changes have had heart troubles, just like Sadie. Many have learning difficulties and mental disabilities of varying severity. Sadie may also be at heightened risk for seizures, and she's anemic.

Keeping Sadie safe, happy and healthy can be all-consuming, and it's put a strain on the family.

Their sunshine-filled Shadowlawn home has two playrooms, one with a toy kitchen and art corner. The house also has baby-proof locks on the refrigerator and plastic gates by the doors. Voice buttons with pictures of ice, a car and bubbles are on the wall, a gate and the floor, waiting for Sadie to try them.

Her sister, Shelbi, will start preschool this week. Quiet, with white-blond hair, she has been dressing herself for more than a year and potty-trained for two years. When she knows Sadie needs something, she'll tell their mother.

Lisa has taken charge of her frustrations by becoming a resource for other parents.

When she discovered there was no Hampton Roads chapter of the ARC, a national group for people with intellectual disabilities, she joined with a few other parents and started one.

She also advocates for community-based care for people with disabilities, looking forward to a future in which an adult Sadie might be able to live semi-independently, instead of in an institution.

And she keeps blogging.

A few weeks ago, she posted an anonymous quote:

"I thought I would have to teach my child about the world, but instead I have to teach the world about my child."

Lisa said of her daughter: "We love her to death. If I could fix her, I would. But I'd never trade her in or wish I hadn't done this."

Then she called, tearfully, to her "Sadie girl" and gave her a hug.

Lauren Roth, (757) 222-5133, lauren.roth@pilotonline.com