Mosaicism in 45,X Turner syndrome: does survival in early pregnancy depend on the presence of two sex chromosomes?

Abstract

Cytogenetic and molecular genetic findings in 91 patients with Turner syndrome are reported. In 87 patients, chromosome studies were carried out both in lymphocyte and fibroblast cultures. Mosaicism was demonstrated in 58 of these patients (66.7%), whereas only 18 (20.7%) were apparent non-mosaic 45,X, and 11 patients (12.6%) showed non-mosaic structural aberrations of the X chromosome. Among the mosaic cases 16 (18.4% of all patients) displayed a second cell line containing small marker chromosomes. The association of Y-specific chromosomal material with the presence of marker chromosomes was demonstrated in 6 out of 7 mixoploid fibroblast cell lines by polymerase chain reaction amplification and by Southern-blot analysis. The observation of ring formation and morphological variability in vivo and in vitro, and the continuous reduction in the percentage of cells containing marker chromosomes in longterm cultivation experiments indicated an increased instability of marker chromosomes. The findings suggest that in vivo selection of structurally altered sex chromosomes exists. Thus, the observation of apparent non-mosaic 45,X chromosomal complements in liveborn individuals with Turner syndrome does not contradict the hypothesis that some degree of mosaicism is necessary for survival in early pregnancy.

Cytogenetic findings in Serbian patients with Turner’s syndrome stigmata

“…They hypothesized that these patients had a second cell line in some organs or tissues in which a double dose of the same locus or loci of the long arm of the X-chromosome is necessary for fetal survival. Because of differences in ascertainment, the prevalence rate of 45,X Turner's syndrome varies between 40 and 60% in different studies (Held et al, 1992). The detection of chromosomal mosaicism depends on several factors, including the number of cells examined, the number and type of tissues studied, the culture techniques employed, and whether in vivo or in vitro selection against one of the cell line occurs (Held et al, 1992).…”

Frequency of 677C -> T and 1298A -> C polymorphisms in the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene in Turner syndrome individuals

“…Turner syndrome individuals frequently show mosaicism (Hook and Warbuton, 1983;Robinson, 1990) and the presence of a normal cell lineage along with the 45,X lineage is considered to increase the probability of survival of those with 45,X Turner syndrome (Held et al, 1992, Kelly et al, 1992.…”

Current status of non-invasive prenatal testing (NIPT): genetic counseling, dominant methods and overall performance

“…Second, feto-placental and maternal mosaicism is more frequent for SCAs: it has been demonstrated, that with advanced maternal age, the mosaic loss of a single maternal X-chromosome is more likely [44,45]. Additionally, placental mosaicism is observed in around 60% of Turner syndrome neonates [46,47]. Third, prenatally obtained fetal sex information can favor unethical sex selection, if not prohibited by legal obligations.…”