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Introduction The observation of X chromatin bodies (inactive X chromosomes) in oral mucosal cells in buccal smears is a simple, inexpensive and reliable method of confirming the number of X chromosomes in an individual 1 Combining the results of this test with the phenotypic sex of an individual it is possible to deduce his or her chromosomal sex. Sex is determined at fertilisation by the sex chromosome complement XY (male) or XX (female). Sex differentiation following on the determined sex results in a phenotypic male or phenotypic female. The Y chromosome in the male induces the development of a testis and the androgens secreted by this foetal testis masculinises the indifferent external genitalia in to the male phenotype seen at birth. With the appearance of the secondary sexual characteristics of the male after puberty differentiation is completed. In the absence of a Y chromosome and therefore a testis and in the presence of two X chromosomes the external genitalia assume the |
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female phenotype and sex differentiation
is completed after puberty with the appearance of female secondary sexual
characteristics. Although females have two X chromosomes at the 1,000
cell stage of development one of the X chromosomes of each cell is inactivated
and remains stuck to the nuclear membrane of somatic cells as an X chromatin
body. One functional X chromosome found in the chromatin network of
the nucleus is essential for life. By observing the X chromatin in the
oral mucosal cells of an individual the number of X chromosomes can
therefore be deduced, X chromatin positive XX (two X ’s) , X chromatin
negative X (one X). Normal females are expected to be X chromatin positive
and normal males X chromatin negative. Anomalies in sex differentiation
leading to errors in differentiation will result in X chromatin positive
males: XXY Klinefelter syndrome and X chromatin negative females: XO
Turner syndrome. Anomalies in sex differentiation may also result from
insensitivity of target organs in a male XY testicular feminisation
syndrome or by the action
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RESEARCH PAPER
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Summary: The X chromatin status in the oral mucosal
cells has been studied in 226 referrals (25 phenotypic males and 201
phenotypic females) suspected of having the Klinefelter, Turner, Testicular
Feminisation or Congenital Adrenal Hypoplasia syndromes. Seven Klinefelters
6 Turners and 9 cases of congenital adrenal hypoplasia were detected.
Twenty one phenotypic females could have been either Turner or testicular
feminisation. The importance of gynaecomastia in a screening for Klenefelter,
short stature in Turner and primary amenorrhoea in both Turner and testicular
feminisation syndromes is highlighted.
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E. R. Wikramanayake, MBBS (Cey), Ph.D (Glasgow), Department of Anatomy, Faculty of Medicine, Peradeniya.
Correspondence & reprints: Prof. E. R. Wikramanayake, Dept. of Anatomy, Faculty of Medicine, Peradeniya.