Mr. P.F. Linehan
plinehan at hgmp.mrc.ac.uk
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
There is a vast biological literature about VNTRs, mini- and
microsatellites and the "Dynamical mutation" diseases.
pl1 at soton.ac.uk
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