45,X/47,XYY mosaicism

Monozygotic Twins with Discordant Sex

A nine-year-old girl with short stature was referred to the department of pediatrics at Kyushu University. The clinical diagnosis was Turner syndrome; karyotypic analysis performed on peripheral blood, using GTG techniques, demonstrated a 45,X/47,XYY (17:83) mosaicism. Her twin brother, a phenotypically normal male, had the same karyotype; 45,X/47,XYY (3:97) on peripheral blood. Their skin fibroblast karyotypes showed the same mosaicism, ie. 45,X/47,XYY (41:59 and 31:69 respectively). On eleven biochemical genetic markers the twin pair were concordant, thus the likelihood of monozygosity was 0.99527034. In addition, the analysis of variable number of tandem repeat (VNTR) markers revealed the likelihood of monozygosity to be 0.99944386. The most plausible explanation of the X/XYY mosaicism was nondisjunction of the Y in the first cleavage division of the 46,XY zygote. A disproportionate rate of cell populations with 45,X and 47.XYY in the twinning process of the X/XYY embryo, especially in the germ lines, would result in discordant sex in twin pairs.

Long term follow-up of a child with ambiguous genitalia, mixed gonadal dysgenesis, and unusual mosaicism

Mixed gonadal dysgenesis (MGD) is a condition of abnormal and asymmetrical gonadal development. This disorder is typically associated with 45,X/46,XY mosaicism; however, other karyotypes have been rarely reported. The phenotype characterizing MGD is highly variable, although in most cases ambiguous genitalia are found. In addition, many individuals with MGD exhibit stigmata of Turner's syndrome. We describe a patient with MGD, found to have a 45,X/47,XYY karyotype, with the majority of the cell lines being 47,XYY. To our knowledge, our report is the first to describe the long-term follow-up of a patient with ambiguous genitalia diagnosed at birth with 45,X/47,XYY mosaicism.

Infant with mos45,x/46,XY/47,XYY/48,XYYY: genetic and clinical findings

We describe an infant with mos45,X/46,XY/47,XYY/48,XYYY who presented with ambiguous genitalia. Her phenotype was also remarkable for minor ear and eye anomalies and coarctation of the aorta with bicuspid aortic valve. Laparoscopy revealed bilateral Fallopian tubes and a left infantile testis with epididymis. Chromosomal analyses of blood, skin, aorta, right Fallopian tube, and left gonadal tissue showed mos45,X/46,XY/47,XYY/48,XYYY. The 46,XY cell line was identified with routine trypsin-Giemsa banding only in cultured cells from an aortic biopsy. Fluorescence in-situ hybridization (FISH) was utilized to identify the presence of 46,XY cells in other tissues. The clinical manifestations of this patient are discussed and compared with those of similar cases of Y chromosome aneuploidy. To our knowledge, this is the first report of a patient with this unusual karyotype.

Phenotype/karyotype correlations of Y chromosome aneuploidy with emphasis on structural aberrations in postnatally diagnosed cases

Over 600 cases with a Y aneuploidy (other than non-mosaic 47,XYY) were reviewed for phenotype/karyotype correlations. Except for 93 prenatally diagnosed cases of mosaicism 45,X/46,XY (79 cases), 45,X/47,XYY (8 cases), and 45,X/46,XY/47,XYY (6 cases), all other cases were ascertained postnatally. Special emphasis was placed on structural abnormalities. This review includes 11 cases of 46,XYp-; 90 cases of 46,XYq- (52 cases non-mosaic; 38 cases 45,X mosaic); 34 cases of 46,X,r(Y) (9 cases non-mosaic and 25 cases 45,X mosaic); 8 cases of 46,X,i(Yp) (4 non-mosaic and 4 mosaic with 45,X); 12 cases of 46,X,i(Yq) (7 non-mosaic and 5 mosaic); 44 cases of 46,X,idic(Yq); 80 cases of 46,X, idic(Yp) (74 cases had breakpoints at Yq11 and 6 cases had breakpoints at Yq12); 130 cases of Y/autosome translocations (50 cases with a Y/A reciprocal translocation, 20 cases of Y/A translocation in 45,X males, 60 cases of Y/DP or Y/Gp translocations); 52 cases of Y/X translocations [47 cases with der(X); 4 cases with der(Y), and 1 case with 45,X with a der(X)], 7 cases of Y/Y translocations; 151 postnatally diagnosed cases of 45,X/46,XY; 14 postnatally diagnosed cases of 45,X/47,XYY; 18 cases of 45,X/46,XY/47,XYY; and 93 aforementioned prenatally diagnosed cases with a 45,X cell line. It is clear that in the absence of a 45,X cell line, the presence of an entire Yp or a region of it including SRY would lead to a male phenotype in an individual with a Y aneuploidy, whereas the lack of Yp invariably leads to a female phenotype with typical or atypical Ullrich-Turner syndrome (UTS). Once there is a 45,X cell line, regardless of whether there is Yp, Yq, or both Yp and Yq, or even a free Y chromosome in other cell line, there is an increased chance for that individual to be a phenotypic female with UTS manifestations or to have ambiguous external genitalia. This review once again shows a major difference in reported phenotypes between postnatally and prenatally diagnosed cases of 45,X/46,XY, 45,X/47,XYY, and 45,X/46,XY/47,XYY mosaicism. It appears that ascertainment bias can explain the fact that all known patients with postnatal diagnosis are phenotypically abnormal, while over 90% of prenatally diagnosed cases are reported to have a normal male phenotype. Further elucidation of major Y genes and their clinical significance can be expected in the rapidly expanding gene mapping projects. More, consequently better, phenotype/karyotype correlations can be anticipated at both the cytogenetic and the molecular level.

45,X/47,XYY mosaicism: clinical discrepancy between prenatally and postnatally diagnosed cases

45,X/47,XYY mosaicism is a rare chromosomal disorder with clinical information limited to 11 postnatal cases in the literature and with uncertainty regarding prenatal prediction of phenotype and prognosis. We report on 7 new cases of 45,X/47,XYY mosaicism, three detected prenatally and 4 diagnosed postnatally. A clinical comparison of the cases of 45,X/47,XYY mosaicism is presented together with a literature review.

A synopsis of the human Y chromosome

Phenotypic features and functions known to depend on the presence of the Y chromosome or the H-Y antigen are discussed in relation to structural anomalies of the Y chromosome and other abnormalities of sexual and somatic development. Recent knowledge about molecular organization of constitutive heterochromatin in relation to the human Y is presented. An attempt is made at assigning different functions, genes and DNA sequences to different regions of the Y chromosome.