Trisomy 18: What is it?

The genetic disorder known as Trisomy 18, also known as Edwards Syndrome, has been brought into the spotlight by presidential candidate Rick Santorum’s young daughter Isabella, who suffers from it. She was recently hospitalized for pneumonia, and is making a recovery.

More on GlobalPost: Rick Santorum's daughter recovering from pneumonia; Candidate rejoins campaign

According to the National Institutes of Health’s MedlinePlus:

Trisomy 18 is a genetic disorder in which a person has a third copy of material from chromosome 18, instead of the usual two copies.

Trisomy 18 occurs in approximately 1 in 5,000 births, and around 80 percent of the newborns affected are female, according to Genetics Home Reference.

The more common chromosomal abnormality, Trisomy 21, is more well known as Down Syndrome and affects 1 in 800 newborns.

The Trisomy 18 Foundation states that unlike the less severe Down Syndrome, Edwards Syndrome is more likely to be life-threatening in the early months of life. Around 50 percent of babies who are carried to term are stillborn, with baby boys experiencing a higher mortality rate.

“Most children with Trisomy 18 die in the first three months of life, and only 10 to 20 percent survive past the first year,” Dr. Robert Marion, Chief of Genetics and Developmental Medicine at Children’s Hospital at Montefiore and Albert Einstein College of Medicine, told ABC News.

The symptoms of Trisomy 18 include a low birth weight, mental deficiencies, clenched hands, crossed legs, a small head and jaw, and low-set ears, according to Medline Plus. There might also be signs of congenital heart disease and problems with the kidneys.

The risk of Trisomy 18 increases with maternal age, and prenatal testing can detect the disorder, reported TIME.

Marion told The Washington Post that the oldest patient he follows who suffers from Trisomy 18 is 13 years old. He said the disorder predisposes them to other complications such as pneumonia and cancer.