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Ask Dr. H

December 1, 2009

‘Fragile X’ carriers may not necessarily pass it along Ask Dr. H Mitchell Hecht

Q: What can you tell me about “Fragile X syndrome”?

I have a relative who I’m told might have it.

A: Fragile X syndrome may be the most common cause of genetically inherited mental retardation you’ve never heard of (note: Down’s syndrome is the most common cause of mental retardation overall, but it’s not inherited). One in every 2,000 males and one in every 4,000 females are born with Fragile X syndrome. Surprisingly, one in 259 women in the general population carry the Fragile X gene.

It’s a bit tricky, because there are some who have the genetic defect and are normal by all appearances and IQ tests — and then there are those at the other end of the spectrum with severe mental retardation; specific physical appearances (long face, large ears, mitral valve prolapse, double-jointed fingers and men with large testicles); and behavioral problems like autism or attention-deficit hyperactivity disorder (ADHD). Those with Fragile X syndrome may have signs and symptoms that fall anywhere in this spectrum. Keep in mind that this is a genetically inherited disorder, and not everyone with large ears or hyperactivity or slow learning has Fragile X syndrome.

What goes wrong in Fragile X syndrome? Every gene is made up of many units of DNA sequences. In Fragile X, there seems to be a stuttering-like repeat of the same DNA sequence. Normally, there’s supposed to be some repeating of this DNA sequence — approximately six-45 copies. But in Fragile X, there are 200 or more copies of this DNA sequence. This stuttering gene defect results in shutting off a certain protein called “FMR-1,” and the signs and symptoms of Fragile X syndrome.

Fragile X is carried on the X chromosome. Since a woman is genetically “XX,” and only one of her chromosomes carries the Fragile X gene, she has a 50-50 chance of passing on the gene. If she passes on the gene to her son (genetically, males are “XY”), he’ll likely be affected significantly. On the other hand, if she passes on the gene to her daughter, she still has one normal X chromosome, and she’ll either be mildly affected or she’ll be a mere carrier of the gene. Unfortunately, there’s no cure for Fragile X syndrome.

Treatment includes special educational instruction; speech therapy; physical and occupational therapy; and medication to deal with attention-deficit disorder, hyperactivity, aggression and depression. Future treatments may involve gene therapy where the sequential repetition of DNA that seems to shut down FMR-1 production and bring about Fragile X syndrome is repaired. For more information, check out the National Fragile X Foundation at www.fragilex.org.

Q: Why do we have an appendix if we’re able to live alright without one? Do you know what causes appendicitis, so that we may avoid getting it?

A: We may regard the appendix as a useless organ of our evolutionary past, whose removal in cases of appendicitis is a source of great relief. But is it really a useless organ? After all, we certainly do just fine without the “vermiform appendix,” a long, narrow, worm-shaped tube that projects off the cecum (first part of the colon) in the lower right quadrant of the abdomen.

We’ve always believed that it’s a vestigial organ, meaning that it’s a non-essential holdover from our evolutionary past. However, there’s evidence that it may have some purpose, even if we’re not sure what it is. One feature of the vermiform appendix that supports this view is that it has its own blood supply. This means that it’s an organ unto itself and is attached to, but not a part of, the small intestine. Researchers have suggested that its role is to help combat the overgrowth of bacteria in the colon. There are a lot of white blood cell-containing lymph channels within the appendix. These channels may help to ward off serious colon infection in that part of our digestive tract. Without the appendix, we seem to do quite well, but perhaps it provides additional defense against infection, similar to the way that our tonsils do.

By the way, appendicitis rarely occurs before the age of 5 or after the age of 50. No one knows why.

Dr. Mitchell Hecht is a physician specializing in internal medicine. Send questions to him at: “Ask Dr. H,” P.O. Box 767787, Atlanta, GA 30076. Due to the large volume of mail received, personal replies are not possible. — Anonymous, Dublin, Ga. —D.Y., Augusta, Wis.

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