Influence of Nuclear Selection Criteria on Sex Chromatin Frequency in Oral Mucosa Cells of Newborn Females

Abstract

The frequency of sex chromatin positive nuclei was determined in oral mucosa smears of 47 newborn females during their first three days of life. In contrast to some previous reports, the lowest sex chromatin frequency found was 21 %, and the means for days 1, 2 and 3 were 33.5 %, 34.1 %and 37.0% respectively. The mean value for day 3 was nearly identical with that obtained for six normal adult women. The slight increase over the three days was statistically significant, although the magnitude of this increase was much less than that reported by other workers. By determining the ratio of nuclei with morphologic characteristics suitable for sex chromatin determinations to those which do not meet minimal morphologic criteria, it was possible to show that there are more unsuitable, probably degenerating nuclei present shortly after birth than later on. This factor may explain the low initial frequencies other workers have reported. It may be difficult to differentiate some degenerated nuclei from viable nuclei. The former may be ‘false negatives’, and their inadvertent inclusion in a count would decrease the frequency of sex chromatin positive nuclei. This argument is supported by our findings on sex chromatin counts performed in the absence of selection criteria. Smears with many unsuitable nuclei had a much lower frequency than those with few unsuitable nuclei. This bias can be reduced, if not eliminated, when stringent selection criteria are applied. With standard criteria, reproducible and reliable sex chromatin frequency determinations can be made on oral smears of newborn infants.