Turner phenotype in a girl with a 45,X/46,XX/47,XX,+18 mosaicism

Abstract

We report a girl with Turner syndrome phenotype, whose karyotype on amniocyte culture was 45,X, while cytogenetic analysis on peripheral blood lymphocytes showed the presence of a mosaic chromosome constitution with three different cell lines: 45,X[5]/46,XX[3]/47,XX,+18 [35]. No signs of trisomy 18 were observed and a follow up during childhood revealed normal psychomotor development. Parental origin and mechanism of formation were studied using high polymorphic microsatellites and Quantitative Fluorescent PCR. The 18-trisomic cells showed one paternal allele and two maternal homozygous alleles at different loci of chromosome 18, suggesting a maternal M-II meiotic or a postzygotic error. A biparental origin of the X-alleles in the trisomic cells were determined, being the paternal allele retained in the 45,X cells. The possible mechanism of formation implying meiotic and/or mitotic errors is discussed.

Unexpected diagnosis of 45,X/47,XX,+18 mosaicism in a girl with mild phenotype

“…Most of cases consist of monosomy X and trisomy 21 [Harada et al, 1998]. Only six cases involving monosomy X and trisomy 18 have been reported so far [Schinzel et al, 1974; Serville et al, 1977; Franceschini et al, 1996; Genuardi et al, 1999; Schubert et al, 2002; Lorda‐Sanchez et al, 2003]. Little is known about patient phenotype, evolution, and mechanisms leading to this double aneuploidy.…”

“…We showed that this rearrangement was due to the loss of a maternal chromosome X and the gain of a maternal chromosome 18. Association of monosomy X and trisomy 18 is a rare condition and, to our knowledge, only six cases have been reported since 1974 [Schinzel et al, 1974; Serville et al, 1977; Franceschini et al, 1996; Genuardi et al, 1999; Schubert et al, 2002; Lorda‐Sanchez et al, 2003] (Table II). Phenotype is extremely variable.…”

“…Phenotype is extremely variable. Most cases were referred for Turner stigmata including short stature and ovarian dysgenesis and/or dysfunction [Schinzel et al, 1974; Serville et al, 1977; Franceschini et al, 1996; Genuardi et al, 1999; Lorda‐Sanchez et al, 2003]. Two patients had a 47,XY,+18 constitution and appeared to have a typical female Turner phenotype despite the presence of the Y chromosome [Schinzel et al, 1974; Serville et al, 1977].…”

Mild clinical presentation in a child with prenatally diagnosed 45,X/47,XX,+18 mosaicism

“…We report on a case of a prenatally diagnosed constitutional mosaicim for trisomy 18 and monsomy X, associated with a very mild phenotype. Review of the literature cites seven previous cases, [Schinzel et al, 1974; Serville et al, 1977; Franceschini et al, 1996; Genuardi et al, 1999; Schubert et al, 2002; Lorda‐Sanchez et al, 2003; Picone et al, 2006] however, only two were diagnosed prenatally [Schubert et al, 2002; Picone et al, 2006]. Both prenatally diagnosed cases were terminated due to severe congenital anomalies.…”

“…The difficulty lay in not being able to predict outcome with the amniocentesis results. The limited literature available indicates that children with this type of mosaicism usually have a combination of features found in Trisomy 18 and Turner syndrome [Schinzel et al, 1974; Serville et al, 1977; Franceschini et al, 1996; Genuardi et al, 1999; Schubert et al, 2002; Lorda‐Sanchez et al, 2003; Picone et al, 2006]. The cases with mild or no mental retardation usually have more of a Turner syndrome phenotype.…”