Down Syndrome Ups & Downs

Oct 25, 2004 -- Some things are gradually getting betterwith Down syndrome (once called mongolism).Medical and surgicaladvances are helping remedy certain features such as heart defects. People withthe syndrome now live longer (withan averagelife expectancy into the 50s).And educationandvocational training areimproving for people with Down syndrome. But it is still not possible to prevent themental retardationcharacteristic of Down syndrome.

The Basic Mystery

The basic mystery as to what causesDown syndrome and what to do about it also remains elusive. While most cases are due to an extra chromosome 21, in some cases there istriplication ofonly a small part of chromosome 21This has led to thelogical thought that there is a Down syndrome critical regionon the long (q) arm of chromosome 21that isresponsible for some, if not all, of the features of Down syndrome. A number of genes in this region may be involved in the production of the Down syndrome.

Down Syndrome Critical Region

Things are not simple (or well understood). Triplication of a segment of chromosome 21 containing 33 critical-region genesdoes notresult in the craniofacial abnormalities typical of the syndrome, according to mouse research published this past week in Science.This mouse model would seem to refute the notion that triplication of the 33 critical-region genes is directly responsible for the craniofacial abnormalities of Down syndrome.

Of Mice and Men

However, it is difficult to tell whether a mouse ismentally retarded andalterations in behavior and learned tasks must suffice to flag differences in mental acuity between mutant mice and their normal counterparts. Another challenge is the difference in colinearity of the human and mouse genomes, and the lack of conservation of gene order between mice and men. The more we learn, the more we realize we havemuch moreto learn about Down syndrome.

Sources

  1. Olson LE, Richtsmeier JT, Leszl J, and Reeves RH. A Chromosome 21 Critical Region Does Not Cause Specific Down Syndrome Phenotypes. Science 22 October 2004: 687-690.
  2. Nelson DLand Gibbs RA. The Critical Region in Trisomy 21. Science 22 October 2004: 619-621.

Barbara K. Hecht, Ph.D.
Frederick Hecht, M.D.
Medical Editors, MedicineNet.com

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Last Editorial Review: 10/25/2004




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