She learned sign language for kids with the Signing Time DVDs and sang along with "Shrek 2." She bustled around her toy kitchen, pretending to cook. She could recite every word of her favorite book, "The Little Mouse, the Red Ripe Strawberry and the Big Hungry Bear," as her mom cuddled her and read to her at night.

Eliza loved to dance but was never coordinated. She'd plant her feet in one spot, bend her knees and sway her hips. Her mom noticed she was cautious physically. At age 2, she couldn't run or jump, something that struck Nikki as "weird." But she was assured that kids just develop at their own speed and Eliza was fine. Still, when it came to walking and balancing, the "busy body" moved slowly and with care.

Her eyes gave the first sign of trouble, although her parents couldn't begin to dream what it would portend. When she was 14 months old, they crossed. And over time the color started changing from a bright blue to what is now a grayish-green.

An MRI was normal, so she had eye surgery to correct the muscle pull. It worked for about a week, then one of the eyes turned out, instead of in. She could walk but was "really wobbly." Again, doctors provided reassurance. She's just taking a little longer to use her legs well. Or, it will level off when she heals from the eye surgery.

"I wish now I had been more assertive," says Nikki. "I really felt something was off."

But when you're worried about someone you love and you're being reassured, who wants to argue?

The second sign was not subtle. Eliza started crawling again, something the ophthalmologist said was definitely not normal.

Callahan and Nikki took her to a neurologist, who noted a slight tremor in her right hand, which she was beginning to favor completely over her left. Changes were coming quickly. The little girl locked her knees when she stood and her hips were tight, but her ankles rolled loosely when she walked. The neurologist said something was wrong with her muscles, her spine or her nerves. Finding out what, though, would prove more challenging than they expected.

The doctors first suspected spinal muscular atrophy, a condition that affects motor neurons and is the leading genetic killer of children younger than 2. A nerve conduction test ruled that out. It was likely, they were told, that Eliza had Charcot-Marie-Tooth disease — not good news, but with leg braces and intensive physical therapy, manageable.