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SPOILER ALERT: Incest is not a healthy behavior

From the beginning, incest and Game of Thrones have been as entwined as kissing cousins: the very first episode saw Jaime Lannister push little Bran Stark out of a tower window for spying on his tryst with twin sister Cersei.

Sunday night’s Season 7 finale ended with the coupling of Jon Snow and Daenerys Targaryen, the Mother of Dragons, yes; but unbeknownst-to-them, Auntie Dany to nephew Jon.

Besides it being illegal and the total "ick" factor, what’s the downside of forming a family "wreath" versus "tree?"

Plenty.

Incest and the overlapping of genetic material elevates the chances of health and development problems.

And incest is not just relegated to Westeros - or Hollywood. Throughout the centuries, ruling families around the globe have suffered by trying to keep their bloodlines "pure." King Tut’s many health issues — necrosis, a partially cleft palate and stillborn children with his own sister-wife—are thought to be connected to generations of incestuous coupling. Perhaps the most famous example of the perils of inbreeding is King Charles II, the last of Spain’s Hapsburg rulers. The result of 200 years of intermarriage, Charles’s tongue was so large he could barely speak, and his infamous Hapsburg jaw was so pronounced that he was unable to chew.

"The behavior that royal families practiced to keep the crown ended up causing lots of health issues," explained W. Andrew Faucett, MS, Geisinger genetic counselor, director of Genomic Policy and Education, and professor.

The biological issue is that people who are related and become pregnant have a much greater chance of passing along problematic recessive genes. One well-known study of Czechoslovakian children showed that fewer than half of babies that were the product of incest were born healthy, and 42 percent were born with severe birth defects or suffered early death.

When the same mothers had children fathered by a non-relative, only seven percent of their children were born with a birth defect.

"In a traditional relationship between two people who are not related, those recessive genes potentially are still passed on to the offspring, but the chance of getting two copies are less likely," Faucett added. "We call these conditions caused by recessive genes ‘autosomal recessive disorders,’ and you need to inherit a non-working copy from both parents. They can include conditions such as cystic fibrosis and sickle cell anemia."

Other side effects of an incestuous relationship include an increased risk of infertility, miscarriage, cleft palates, heart conditions, facial asymmetry, low birth weight, slow growth rate and neonatal mortality.

"Even if there's not always a mutation, inbreeding brings up a lot of problems involving recessive traits. Because the two of you have similar genes, any recessive abnormalities you have can be passed on more easily and expressed more visibly in your offspring. This also means that usually the parents do not show any signs of the condition because they have only one copy of the gene that doesn’t work correctly," Faucett said.

Too bad the Mad King was unaware.

A national leader in the field of genomics, Geisinger’s MyCode Community Health Initiative is the largest whole exome-sequencing project in the U.S. linked to the electronic health record of a single, integrated healthcare delivery system. MyCode is committed to returning medically actionable, sometimes life-saving, results to patients, their children and grandchildren. For more information on participating in the study, email JoinMyCode@geisinger.edu or call 844-798-1687.

Game of Thrones Jon Dany