Mr. P.F. Linehan plinehan at
Wed Mar 13 08:37:46 EST 1996

 In response to a question from Hong-Kong re. VNTRs.

Mostly they are in non transcribed DNA i.e. neither intron nor 
exon but they can be present in introns. They seem to be 
fairly widespread throughout the genome. When they are present in 
transcribed DNA, they can and do (sometimes) lead to various 
genetic conditions - Fragile X is an example where there is 
a microsatellite sequence present in the 5' UTR of the FMR1 gene and 
when this sequence expands beyond a threshold of ~ 200 repeats
of CGG, this causes the Fragile X syndrome. VNTRs can be in the 
exons themselves, i.e. in the case of Huntington's disease and 
also (I think) Myotonic Dystrophy and Machado-Joeseph disease.

As regards minisatellites, they seem to be less common than 
microsatellites and are not generally found in coding DNA. 
Recently, it has been proposed (Nature Genetics 1995) that
variation in a minisatellite adjacent (5') to the insulin 
gene may be the cause or at least a contributory factor 
in diabetes.

There is a vast biological literature about VNTRs, mini- and 
microsatellites and the "Dynamical mutation" diseases.

Happy hunting.


pl1 at

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