By Dr. Brian McDonough

PHILADELPHIA (CBS) – Republican presidential candidate Rick Santorum was spending Sunday in the hospital rather than the campaign trail, after his daughter was fell ill Saturday night.

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Bella Santorum is 3-and-a-half-years-old and suffers from Trisomy-18, a genetic condition caused by the presence of all or part of an extra 18th chromosome.

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As KYW Newsradio‘s Dr. Brian McDonough explains, An infant with Trisomy-18 rarely makes it through the first week. And even after that, complications from something as simple as a common cold can be deadly.

In Trisomy-18, early on there are so many problems, they can actually affect a child’s survival at that point, and problems like a common cold or other issues can become so much more problematic because the immune system is affected and it’s a tough — with so many problems, you’re talking kidney, heart and other issues it’s very difficult to fight through a lot of things, so there’s always that concern.

When a child is born in this situation, they very rarely make it past the first week, because one or two problems can be overwhelming and it just kind of piles up. And, even with the great institutions we have, it’s tough to get children through that first week. Those who do get through it tend to do a little better, but again, we’re talking about a short lifespan, and that’s one the tragedies associated with it.

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The fact this child’s 3-and-a-half, means there’s obviously been a great deal of care, but also the child has done well with treatments as well. So, going to the hospital certainly is not something that would be unexpected, but every time a child goes to the hospital with Trisomy-18, you worry a great deal.