Ask Dr. H: Retardation that is inherited
Question: What can you tell me about "Fragile X syndrome"? I have a relative who might have it.
Answer: Fragile X syndrome may be the most common cause of genetically inherited mental retardation you've never heard of (Note: Down syndrome is the most common cause of mental retardation overall, but it's not inherited). One in every 2,000 males and 1 in every 4,000 females are born with Fragile X syndrome. Surprisingly, 1 in 259 women in the general population carry the Fragile X gene.
It's tricky, because some people have the genetic defect and are normal by all appearances and IQ tests - and those at the other end of the spectrum have severe mental retardation and 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. Remember, 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 a DNA sequence. Normally, there's supposed to be some repeating of this DNA sequence - approximately 6 to 45 copies. But in Fragile X, there are 200 or more copies. This stuttering gene defect results in shutting off a certain protein called "FMR-1" and causes 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 just be a 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 short attention, hyperactivity, aggression and depression. Future treatments may involve gene therapy to repair the sequential repetition of DNA that seems to shut down FMR-1 production and trigger Fragile X syndrome.
For more information, go to the National Fragile X Foundation at www.fragilex.org.
Is that 'useless' appendix really so?
Q: Why do we have an appendix if we're able to live all right without one? Do you know what causes appendicitis, so that we may avoid getting it?
A: The appendix may be seen as a useless organ of our evolutionary past, whose removal in appendicitis is a source of great relief. But is it really useless? 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 long believed that it's vestigial, meaning that it's a nonessential 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 supporting 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 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.
Mitchell Hecht is a physician specializing in internal medicine. Send questions to him at: "Ask Dr. H.," Box 767787, Atlanta, Ga. 30076.
