| MadSci Network: Genetics |
X-inactivation works just the same for the X chromosomes in Klinefelter's syndrome as it does for XX females. As a general rule of thumb, the number of Barr bodies in a cell is always equal to the number of X chromosomes minus one. So, for people with Klinefelter's syndrome, who have a genotype of XXY, there will be one Barr body per cell. As you mentioned, this would leave one activated X and the normally active Y chromosome in these individuals, which you would predict would be a normal male genotype. The reason this isn't the case is because not all of the genes on the inactivated X chromosome are totally silenced. Some of the genes on the inactivated X are still expressed, and it is this over- abundance of gene products that causes the disease known as Klinefelter's. This disease seems to appear to slightly "feminize" an otherwise male appearance. People with Klinefelter's have male genitalia, but many other physical apperances seem to be things normally found in females. Some of these effects include breast development, osteoporosis, poor beard growth, and other effects.
Hope this has helped.
References:
Shamsuddin AK. Tang CK. Barr bodies in testis with Klinefelter syndrome.
Urology. 15(1):74-6, 1980
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Admin note:
James Cotton provided another answer:
Good Question! The short answer is I don't know, but I've dived into the medical
literature on the subject and tried to find out. Klinefelter patients certainly do have Barr bodies, as reported in
several papers: As for how many they have, that's a much more difficult question. I
could only find one paper on this, and that's in a journal that I can't
get access to very easily, so I've only been able to read the abstract
which mentions this explicitly. Clinical, endocrinological,
histological and chromosomal investigations on Klinefelter's
syndrome, Andrologia 1979 May-Jun;11(3):182-96, Grabski J Pusch H
Schirren C Passarge E Held K Bartsch W Wernicke I. It says "The number of Barr-bodies ranged from 1-45 (200 cells
evaluated) x mean was 9,6." Which I take to mean there were on average
only 9.6 Barr bodies per 200 cells in these patients, or only 4.8% of
cells contained Barr bodies at all. This means that the vast majority of
cells have two active X chromosomes and an active Y. This presumably
leads to the clinical effects of Klinefelter's syndrome. Presumably the
presence of Y chromosome genes interferes with Barr body
condensation. For more information on Klinefelter's, check out
I hope this is OK, but if you want any more details, I suggest you could
try either re-asking the question here, pointing out to the moderators
that somebody who's really an expert in chromosome abnormalities, or at
least a specialist in medical genetics will be needed, or you could try
looking for an "ask-a-doctor" service and seeing if they can help. You
could even try getting in touch with the authors of the above paper for
clarification: most scientists are very happy to help with short
queries about their work, and even flattered that somebody is taking
some notice of it!
Jim McCarter has written a splendid, more general,answer on Barr bodies in MadSci already.
Hope this is of some use, and good luck in discovering more!
Yours,
James
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