June 17, 2005

They Saved Einstein's Brain (and cut it up into little pieces)

There's an interesting article on Yahoo, coming originally from the Los Angeles Times.

Deep, Dark Secrets of His and Her Brains

It is a discussion of the work of Sandra Witelson, who has the world's largest collection of brains. The article touches on her analysis of Einstein's brain, but is mainly focused on her work analyzing the difference between the brains of men and women. She's found many, but fortunately Witelson's managed to avoid hysterical picketing by Harvard faculty.

The one problem I had with the article is that the author, Robert Lee Hotz, seems to not understand the whole of the situation in the anecdote that serves as his epilogue:

Brain Conquers All

Last year, a worried farming couple brought their youngest child to McMaster University Medical Center.

They were no longer certain whether their child was a girl or a boy. The youngster had traits of both, as occurs in about one in 5,000 births. In this child, nature had devised a living test of gender and the brain.

The medical experts determined that the child's body was a composite of normal and abnormal cells. Some had a girl's usual complement of two female sex chromosomes. Many, perhaps due to a mutation, had only one female chromosome and consequently were almost male.

"Which cells got to the brain?" wondered Witelson, who was called in as a consultant. "You have to consider the sex of the brain."

The doctors all suspected the child's brain was masculine. There was no way to know for sure. They could not safely take a sample of neural tissue to biopsy.

Until recently, reconstructive surgery based on a doctor's best guess was the rule in such cases. But in Hamilton, they counseled patience, Witelson recalled.

"We said, 'Let the child's behavior tell us what sex the child is.' "

Given time, she believed, the brain would reveal itself.

The problem is here: Some had a girl's usual complement of two female sex chromosomes. Many, perhaps due to a mutation, had only one female chromosome and consequently were almost male.

A little background in human genetics:

Normal females have two X chromosomes, XX.
Normal males have one X and one Y chromosome, XY.

People with Turner's syndrome have only one copy of the X chromosome, XO.

But people with Turner's syndrome are pretty clearly female! A person made up of XX and XO cells isn't going to be exhibiting any specially masculine traits due to that combination.

What strikes me as what is most probably the case is that the kid is an XX/XY chimaera. This isn't a result of a mutation. What has happened is that the child's mother released two eggs. Both were fertilized, one by a sperm carrying the Y chromosome (generating a male embryo), the other by sperm carrying the X chromosome (generating a female embryo).

The usual outcome of this is that the nine months later, the mother gives birth to a pair of fraternal twins, one female, one male. But that didn't happen; instead the embryos fused, creating what is called a chimaera -- a child composed of cells with two distinct origins.

Posted by jeffreyb at June 17, 2005 12:44 AM
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