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X chromatin in oral mucosal cells in some anomalies of
sex differentiation

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

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
RESEARCH PAPER
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.

 

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.

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Sri Lanka Journal of Medicine 2000; 9(1): 3 - 7