--- Alberto Monteiro <[EMAIL PROTECTED]> wrote: > Deborah Harrell wrote: > > > > A chromosomal mutation like Down's (trisomy 21), > > > It's not a mutation. Trisomy means that the 21 > chromosome > gets a third _copy_. Mutation means that a gene is > alterered.
<nitpick> Well, mutation in biology means "heritable alteration of the genes or chromosomes" (unless they've gone and changed the definition since I last looked - which is actually possible; names of bacteria certainly are changed with distressing frequency!). And while about 94% of Down's Syndrome patients do have 47 chromosomes (the third copy of #21), in some the genetic material of chromosome 21 is 'translocated' (attached) to another chromosome, like #14, so technically the affected person has the correct complement of 46 - even though one of the 14s will be much bigger than it's supposed to be. Still others are "mosaics," having partial trisomy - some cells have 46, others 47 chromosomes; some mosaics will have little outward sign of disease, having average intelligence and height and nearly normal facial features. <nitpick> > >on the other hand, doesn't appear amenable (to me) > to gene therapy, > > > Yes, it is very difficult to "neutralize" the ill > effects of an > extra chromosome in _all_ cells of the body. > > > although it is discoverable if chorionic > > villi sampling or amniocentesis are done; > > > There are other, non-invasive, techniques of > detection, > like the triple test (that checks for three things > in the mother's blood) and ultrasound studies Yes, these non-invasive methods can diagnose fetal Down's, but not until after the 15th week (depending on the test, may be as late as the end of the 2nd trimester). CVS can be done as early as week 10; amnio' is weeks 14-20. (from this 2002 article, not sure if you can access it if you're not registered:) http://www.emedicine.com/oph/topic485.htm Roughly 75% of all embryos/fetus' with full Down's Syndrome spontaneously abort. I have a friend who is a mosaic Turner's Syndrome, who has completed post-doctoral work and is quite successful (full Turner's patients have only 1 X chromosome, with various physical and mental deficits). Debbi __________________________________________________ Do you Yahoo!? Yahoo! Mail Plus - Powerful. Affordable. Sign up now. http://mailplus.yahoo.com _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
