What is Trisomy 18? Rick Santorum's Daughter Has Devastating Disorder

"I don't know whether her life is going to be measured, it's always been measured, in days and weeks," Rick Santorum said at the annual "Defenders of Freedom" event in November. "Yet here I am... because I feel like I wouldn't be a good dad if I wasn't out here fighting for a country that would see the dignity in her and every other child."

Many listening to Rick Santorum talk about Bella, however, have another question on their minds, especially since the GOP presidential hopeful has made treating her disorder one of the platforms of his campaign: what, exactly, is Trisomy 18?

Trisomy 18: The Basics

Trisomy 18 affects an estimated one in every 3,000 to 6,000 live births that affects three times as many girls as boys and which has devastating effects on most children.

Instead of having the normal two pairs of chromosome 18, children with Trisomy 18 have three copies, similar to the three copies of chromosome 21 found in people with Down syndrome. The extra material interferes with normal pre-natal development.

Almost all children with Trisomy 18 die before they're born, with many more dying in their first months. Only one in 10, on average, make it to their first birthday, and only 1 percent live to be 10 years old, already making Bella, whom the family calls "Boo," something of an outlier.

Symptoms of Trisomy 18, which is similar to Down syndrome, almost always include mental deficiency and other developmental problems that reduce life expectancy and comfort. According to the U.S. National Library of Medicine, physical manifestations include:

• Low birth weight, a small head and jaw
• Clenched hands, crossed legs (preferred position by baby) and rocker-bottom feet (overly rounded soles)
• Undeveloped physical body (shorter fingernails, undescended testicles, low-set ears)
• Unusual, bowed-out chest shape sometimes called "pigeon chest" (pectus carinatum) causing breathing problems and possibly stunted heart and lung development

Tests of the infant may also reveal congenital heart disease or an array of kidney problems from stunted pre-natal development.

Prevention and Treatment of Trisomy 18