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Posted at 10:52 AM ET, 01/30/2012

Bella Santorum has Trisomy 18. What is that?

Republican presidential candidate Rick Santorum is reportedly back on the campaign trail Monday after taking time away this weekend as his 3-year-old daughter Isabella was hospitalized with pneumonia.
A supporter of Republican presidential hopeful and former senator Rick Santorum wears a pin with a photo of Bella Santorum. (Andrew Burton - Getty Images)

Isabella, or “Bella,” was born with a genetic disorder known as Trisomy 18, which means that she has three copies of the 18th chromosome instead of two. That causes abnormalities in the development of the brain, heart and other internal organs, says Robert Marion, chief of genetics and developmental medicine at the Children’s Hospital at Montefiore Medical Center in the Bronx, New York. Almost half the children born with the condition die within the first three months of life, Marion notes. “Ninety percent die in the first year,” he says, “And the ten percent who survive have severe developmental problems.”

Trisomy 18 is “similar in etiology” to Down Syndrome, also known as Trisomy 21, Marion explains, though the latter is generally less severe than Trisomy 18. The risk of conceiving a baby with either condition (and another genetic disorder called Trisomy 13) rises with advancing maternal age. Marion says about 1 in 5,000 to 1 in 10,000 live-born children have Trisomy 18.

Marion adds that Trisomy 18 is “almost always diagnosed prenatally, and those pregnancies are almost always terminated.” Even when pregnancy is continued, he says, “Almost all males die in the first and second trimesters, and most females” die during that time, too. Though male and female babies are equally likely to be conceived with Trisomy 18, five times as many female babies as male babies live to full term and are born live.

Marion says it isn’t unusual for a child with Trisomy 18 to contract pneumonia, from which illness Bella Santorum is reportedly recovering. “Almost all children with Trisomy 18 have congenital heart disease,” he says. “That leads to congestive heart failure, in which the heart doesn’t beat well enough to pump blood to the rest of the body. Fluid backs up” and makes the child’s lungs susceptible to infection.

Marion says, “The oldest child I currently follow” who has Trisomy 18 is 13 years old. As such children get older, he explains, they tend to develop cancers typically associated with early childhood.

By  |  10:52 AM ET, 01/30/2012

 
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