Overwhelming maternal cell contamination in amniotic fluid samples from patients with oligohydramnios can lead to false prenatal interphase FISH results
✍ Scribed by L. L. Estabrooks; J. Sanford Hanna; A. N. Lamb
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 150 KB
- Volume
- 19
- Category
- Article
- ISSN
- 0197-3851
No coin nor oath required. For personal study only.
✦ Synopsis
reason that a cytogenetic study was performed in the present case.
The finding of an, apparently, non-mosaic 90,XX karyotype was surprising, given its rarity. This chromosomal constitution had to be the product of two errors: one prezygotic originating a 45,X zygote and then an endoreduplication of the chromosomes resulting in a tetraploidy of the autosomes but diploidy of the sex chromosomes.
It can be postulated, moreover, that the fetus had a non-detected mosaicism 45,X/90,XX, when FISH studies were not performed. If that were the case, the percentage of 45,X cells, less than two per cent, could not explain per se the fetal phenotype and it would be difficult to be detected by FISH, given that it is well known that this methodology is useless for detecting very low levels of mosaicism.
To the best of our knowledge only one identical case, phenotypically and karyotypically, has been reported before (Fryns et al., 1987). These authors postulated (quote):
'the phenotypes in 90,XX and in classical 45,X Turner patients do not depend on the X-monosomy itself, but on the altered autosome/X chromosome ratio 44:1 in 45,X and 88:2 in 90,XX and the hemizygote state of some genes in the X chromosome that are under the control of other autosomal genes'.
We agree with the opinion of Fryns et al. (1987) that the fetal phenotype has to be attributed to the 88:2 ratio between autosomes and Xs because cystic hygromata and hydrops are frequent findings in 45,X fetuses. On the other hand, this phenotype has not been consistently described in fetuses with tetraploidy, who more frequently present with microcephaly, complex heart defects, severe central nervous system disruption, and abnormal fingers and toes (Coe et al., 1993;Goyert et al., 1993).