20 April 2009

Inbreeding led to decline of royal line

Cosmos Online
Inbreeding contributed to the demise of the Spanish Hapsburg dynasty after almost 200 years of rule, geneticists have concluded.
Hapsburg crest

Bred to death: The royal crest of the Hapsburg dynasty. Credit: Wikimedia

BRISBANE: Inbreeding contributed to the demise of the Spanish Hapsburg dynasty after almost 200 years of rule, researchers have concluded.

The Hapsburgs, who ruled Spain and its empire from 1516 to 1700, married their cousins and other relatives so often that the last king, Charles II, was as inbred as the offspring of a brother-sister coupling, says a report published in the journal PLoS ONE.

“Charles the Hexed”

“In order to keep their heritage in their own hands, the Spanish Hapsburgs began to intermarry more and more frequently among themselves and the result, in a few generations, was a fatal inbreeding,” said lead author Gonzalo Alvarez, a geneticist at the University of Santiago de Compostela in Spain.

The dynasty ended when Charles II died at the age of 39 with no children. He was nicknamed ‘Charles the Hexed’ because of his physical and mental disabilities, which, along with his infertility, were probably a result of inbreeding, Alvarez said.

Alvarez and his team are the first to investigate the genetic evidence that inbreeding was a major cause of the dynasty’s demise, a theory originally proposed by historians.

The team examined the genealogical records for 16 generations of Charles’s family, covering 3,000 of his relatives and ancestors, to calculate an inbreeding coefficient for each of the Spanish Hapsburg kings. See a genealogy of the Hapsburg line here.

Inbreeding coefficient

Everyone carries two copies of most genes, one inherited from the mother and one from the father, and the inbreeding coefficient is the chance that, for any one gene, the copies are identical because of the parents’ common ancestry.

That increases the risk of rare inherited diseases, which are caused by having two copies of a dysfunctional or harmful version of a gene.

The inbreeding coefficient of the dynasty’s founder, Philip I, was 0.025, meaning that he had identical copies for around 2.5% of his genes, while Charles’s coefficient was 0.254, with identical copies in more than 25% of his genes.

Charles’s parents were uncle and niece, but high levels of inbreeding in previous generation gave him an inbreeding coefficient more like the offspring of brother-sister or parent-child couplings, Alvarez said.

Two of the kings in Charles’s ancestry married a niece, two married their first cousins, and four others also married biological relatives. Only Charles and one other Hapsburg king married women they were not related to.

Peter Visscher, a geneticist at the Queensland Institute of Medical Research in Brisbane, Australia, said that although it is impossible to be sure that inbreeding was the cause of the dynasty’s end, Alvarez’s team had shown that there were large inbreeding coefficients in the Hapsburg family.

“It would be nice to know what the inbreeding coefficients of contemporary non-royals were, but pedigree data for ordinary citizens that lived many centuries ago must be hard to come by,” Visscher said.

More information:
The study in PLoS One

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