Ask A Scientist© Molecular Biology Archive

name         Corinne C.
status       other
age          30s

Question -   I have a triple X chromosone. I do not have Downs and the
only real effects I seem to have is infertility.  I have no eggs.  I have
tried to do IVF twice(with a donor) and have had no success.  Do you know
if someone with my condition can concieve with IFV and carry to term, or
does this condition make it impossible.  I've been told I am the only
case in my state who has lived past 30.  How common is my condition and
what is the usual outcome of it?
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Triple X syndrome was initially found in individuals suffering from certain
mental disabilities and has been discovered in about 1:1000 apparently
normal females in routine examinations of newborns.  Sterility is sometimes
present and sometimes not with several Triple X women giving birth to
chromosomally and physically normal children .  It seems that there is, as
is common in the world of genetics, a large clinical variation in the level
of problems that the Triple X causes from nothing to quite a bit.  I would
check with a specialist in the field (which might be difficult to find)
including any endocrinologists that specialize in this and also read
whatever you can find.  As in most of biology, these things are incompletely
or poorly understood.


I also got this from the Merk Manual (on-line)

SEX CHROMOSOME ABNORMALITIES
Sex determination in humans is controlled by the X and the Y chromosomes.
The female has two X chromosomes, and the male has one X plus one Y. The Y
chromosome is among the smallest of the 46 chromosomes, and its major
function seems to be related to male sex determination. In contrast, the X
is one of the largest chromosomes and contains hundreds of genes, most of
which have nothing to do with sex determination.
Lyon hypothesis (X-inactivation): The normal female has two loci for every
X-linked gene, as compared with the male's single locus. This would seem to
produce a genetic "dosage" problem. However, according to the Lyon
hypothesis, one of the two X chromosomes in each somatic cell of the female
is genetically inactivated early in the life of the embryo. The Barr body,
or sex chromatin mass within the nuclei of female somatic cells, represents
the second inactivated X chromosome. The gene responsible for inactivating
the genes of the X chromosome has been identified (XIST). Molecular genetic
studies have demonstrated that not all genes on the second X chromosome are
inactivated, but most are. In fact, no matter how many X chromosomes are
present in the genome, all but one has most of the genes inactivated.
X-inactivation has interesting clinical implications. For example, X
chromosome abnormalities are relatively benign, compared with analogous
autosomal abnormalities. Females with three X chromosomes are often normal
physically and mentally and are fertile. In contrast, all the known
autosomal trisomies have devastating effects. Similarly, the absence of one
X chromosome, although it leads to a specific syndrome (Turner syndrome), is
relatively benign; the absence of an autosome is invariably lethal.


  Good luck.

Peter Faletra Ph.D.
Office of Science
Department of Energy
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