As more hospitals have begun using DNA testing to analyze babies with birth defects, doctors have occasionally discovered that a family’s little bundle of joy is also a product of incest. Since this is a new dilemma brought on by the spread of technology, doctors are now debating how to handle these incest surprises.
Geneticist Arthur Beaudet at Baylor College of Medicine addressed the issue yesterday in an article in the medical journal The Lancet. The genetic test, the single nucleotide polymorphism-based array, helps doctors identify missing genes (and can therefore help explain a child’s birth defect or disability)–but it also identifies swaths of identical DNA that a child may have inherited from two closely related parents.
In the few months that Baylor has been performing these detailed genetic tests, there have been fewer than 10 cases of consanguinity — the phenomenon of inheriting the same gene variations from two closely related people, said Dr. Arthur L. Beaudet, chairman of Baylor’s department of molecular and human genetics. However, wider use of such testing in children with disabilities is expected to identify additional cases of incestuous parentage. [ABC News]
Charles Darwin may have been right in worrying that the ill health that plagued his family were a result of inbreeding. Darwin didn’t only marry his first cousin, Emma Wedgwood–in fact, the Darwins and the Wedgwoods made a habit of intermarrying (Darwin’s maternal grandparents were also third cousins). Now a new study, which crunched the numbers on first-cousin marriages over four generations of the two dynasties, suggests that his children had an elevated risk of health problems.
The degree of inbreeding among Darwin’s children, while not excessive, was enough to increase the risk of recessive diseases — ones that occur if a harmful version of a gene is inherited from both parents. Three of his 10 children died before age 10 — 2 of bacterial diseases. Childhood mortality from bacterial infections is associated with inbreeding. So, too, is infertility, and three of Darwin’s children who had long marriages left no children [The New York Times].
Once again, to the bane of myth-makers and fans of historical intrigue, the simplest explanation may be the best: Scientists analyzing the DNA of the world-famous mummy of Tutankhamen say that he wasn’t done in by murder nor any of the exotic diseases put forth as explanations for his death at the age of 19. Rather, they say in the Journal of the American Medical Association, it was likely complications of malaria that killed King Tut, who was already frail thanks to royal inbreeding.
The team led by Egypt’s top archaeologist, Zahi Hawass, spent years taking CT scans and conducting genetic tests on mummies from the royal tombs. They say they confirmed that Tut was the son of Akhenaten, which is what scholars have long believed, but it hints at something else: It also identifies some of his grandparents and great-grandparents for the first time and suggests that his mother was Akhenaten’s sister [The Times]. A brother-sister pair wasn’t unusual during this period in ancient Egypt, medical historian Howard Markel says. Pharaohs were thought of as deities, so it makes sense that the only prospective mates who’d pass muster would be other deities [AP].
In the western world, marriage between first cousins is labeled incest or inbreeding, and in the United States the practice is banned or restricted in 31 states. But a new essay argues that such laws are based on an outdated notion of the genetic risks involved in cousins marrying and reproducing. [T]hose laws “seem ill-advised” and “should be repealed,” a geneticist and medical historian write…. “Neither the scientific nor social assumptions that informed them are any longer defensible” [Scientific American].
First cousins share about an eighth of their genes, and are therefore more likely to receive two copies of some recessive gene that poses health problems. Scientists had assumed that the children of first cousins would therefore be more likely to be born with birth defects. But coauthor Hamish Spencer writes that the risk of congenital defects is about 2 per cent higher than average for babies born to first-cousin marriages – with the infant mortality about 4.4 per cent higher – which is on a par with the risk to babies born to women over 40. “Women over the age of 40 have a similar risk of having children with birth defects and no one is suggesting they should be prevented from reproducing,” said Professor Spencer [The Independent].