Chromosome Six

Jean C. Zenklusen sa83165 at ODIN.MDA.UTH.TMC.EDU
Mon Oct 2 14:15:17 EST 1995


On Sept. 29 Jeff Taylor wrote:

>nsuyeda at aol.com on 29-Sept-95 writes:
>
>>A friend's amniocentesis shows an abnormal wide band on six. The lab's
>>first response is to .......
>-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
>
>This is regarding your question about your friend's amniocentesis.  There is a
>question I would have for you (or her).  If they are normal, healthy parents
>with a normal sonogram why have they had an amnio?  I am going to assume the
>answer to this is because of the mother's age.
>
>You say there is a band that is wider than normal.  (It would help immensely
>to know which band).  This basically means there is extra DNA present.  There
>are 2 possibilities:
>
>1) The extra DNA does not contain any genes (nor affect any genes normally
>present in this region).  There would most likely be no repercussions to the
>baby.  The only way of knowing this for sure is if one of the parents has the
>same anomaly.  That is why the first thing the lab is doing is to test the
>parents.
>
This is a very unlikely situation since the band amplification has been
determined by cytogenetics. Such an amplif ication has to be at least 20Mb
long in order to be detected. It is very unlikely that no genes would be
found here.



>2) The extra DNA contains genes.  If this is the case then the baby has one
>too many copies of the extra gene(s).  Because a chromosome analysis is
>looking for gross chromosomal abnormalities, the fact that they have found
>something means that there is a lot of extra DNA.  This is not good news.
>
>To do any kind of research you would have to know the specific band on
>chromosome 6 that is affected and then go to a medical library (most
>universities have one).  You would then have to check the literature to see if
>there are any reported cases of people having extra DNA (trisomy) in this
>band.
>>To date 23 patients with partial trisomy of the long arm of chromosome 6 have
>been reported.  These all involve duplication of more than a single band so
>are more severe than what you say is a single abnormal wide band. Therefore it
>is impossible to speculate on your case.
>

The case reported here is not a trisomy but a gross a band amplification.
Trisomy only aplies to duplication of an entire chromosome or chromosomal
band. This amplifications tend to be highly significative as in the case of
several proto-oncogenes that get deregulated by a dose imbalance.
Amplifications in chr 6 are very well known for the long arm, but to be
certain of which could be the consequences of this trait, one has to know
which band is amplified. If nsuyeda at aol.com could provide this information,
maybe we could help some more.


>The best news would be for one of the parents to have the same phenomenon.
>Otherwise, I feel there may very well be physical and/or neurological
>problems.
>
>
>Hilary Taylor
>(MSc Human & Medical Genetics)

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sa83165 at odin.mda.uth.tmc.edu
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