IP is one of a group of diseases known as neurocutaneous disorders. In most cases, it is caused by mutations in an X-linked gene called NEMO (NF-kappaB essential modulator). Emmerich said that her foundation's international research arm helped identify the gene so that women who carry IP and who may not have symptoms can be tested.
Women with IP have a 50 percent chance of having a child with the disorder.
The mutation is carried on the X chromosome and is nearly always fatal in males, who have only one X. Females, with two X chromosomes, can compensate for the devastating symptoms of the disorder when one chromosome is normal.
In milder cases, skin abnormalities -- blue or brown wavy lines -- usually fade by adolescence and can disappear with age, according to the National Institutes of Health.
But there may be residual neurological effects, such a seizures, muscle spasms and mild paralysis that can be controlled with medication.
Dental malformations are common, such as missing or pegged shaped teeth -- in both baby and second teeth.
No one knows how prevalent the disorder is, according to Dr. Judith Willner, a retired geneticist from New York's Mt. Sinai Medical Center, who is head of the IP scientific advisory council.
"We used to think it was extremely rare until Suzanne Emmerich started her website and people have been contacting her from all over the world," Willner said. "It's much more frequent than previously thought. Sometimes it's so mild that people don't identify that they actually have it, and the symptoms can change over time."
The disorder's manifestations are "variable" in females.
"After the first couple of days (after birth), there is a blistering rash distributed on the trunk and limbs, but it spares the face," Willner said. "Gradually in most girls the rash flattens out and becomes more wart-like -- a raised brownish rash."
Eventually, the rash leaves only brown streaks behind.
"A woman may not even know she has the disorder," she said. More commonly, as in Lyons' case, IP involves the teeth and the hair. "They have patches of scalp with bald spots.
IP is "certainly compatible with a normal life," Willner said. "They can fix their hair and the rash is usually not disfiguring."
But the psychological effects, especially on looks-conscious girls, can be difficult.
"It's pretty terrible if a teen has bad teeth and the hair is not good -- it can be stigmatizing for girls," she said. "You can't put dental implants in a young child and have to wait until the second teeth come in."
Where the damaged X chromosomes are located -- in the brain, eyes or skin -- determine who will develop the severest symptoms like retardation or blindness, and who, like Jenna Lyons, will escape its devastation.
"It's a matter of luck and chance," said Willner. "It's totally random. You can be lucky or unlucky."