Unstable dicentric iso(Yq) chromosome in a pseudohermaphrodite

An infant with a mosaic 45,X/46,X,psu dic(Y) (pter-->q11.2::q11.2-->pter) karyotype and mixed gonadal dysgenesis studied for extent of mosaicism in the gonads

AN infant with mixed gonadal dysgenesis was found to have a 45,X/46,Xpsu dic(Y) karyotype. A low level (8%) of mosaicism for the dic(Y) cell line was observed in peripheral blood lymphocytes and skin fibroblasts. The dicentric nature of the Y chromosome became apparent in fluorescence in situ hybridization studies. The presence of Y centromeric sequences was demonstrated in the paraffin-embedded testis and streak ovary sections. The ration of Y-positive cells was higher in the testis than in the streak ovary.

Isodicentric Y chromosome: cytogenetic, molecular and clinical studies and review of the literature

Dicentrics are among the most common structural abnormalities of the human Y chromosome. Predicting the phenotypic consequences of different duplications and deletions of dicentric Y chromosomes is usually complicated by varying degrees of mosaicism (45,X cell lines), which may, in some cases, remain undetected. Molecular studies in patients with dicentric Y chromosomes have been few, and only two studies have attempted to determine the presence of SRY (the putative testis-determining factor gene). We report an 18-year-old female with short stature, amenorrhea, hirsutism, hypoplastic labia minora, and clitoromegaly who has a 45,X/46,X,idic(Y)(p11.32)/47,X,idic(Y)(p11.32),idic(Y) (p11.32) karyotype. Southern analysis using Y-specific probes (Y97, 2D6, 1F5, pY3.4) and polymerase chain reaction (PCR) analysis using primers for ZFY and SRY were positive for all loci tested, indicating that almost all of the Y chromosome was present. Our findings and an extensive review of the literature emphasize the importance of molecular analyses of abnormal Y chromosomes before any general conclusions can be reached concerning the relative effects of the Y-chromosome abnormality and mosaicism on sexual differentiation.

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.

Dicentric Y chromosome in a patient with gonadal dysgenesis and seminoma

A male patient with ambiguous external genitalia developed a seminoma in the left inguinal region; his internal genitalia included a streak gonad on the right and a small uterus. Cytogenetic studies demonstrated a dicentric Y chromosome with unstable behavior during cell division, which resulted in 45,X/46,X,dic(Y)/47,X,dic(Y),dic(Y) mosaicism. Immunogenetic studies allowed the identification of the male-determining H-Y antigen on both leukocytes and red cells of the patient. The significance of these results is discussed with respect to recent data on the genetic control of H-Y antigen.

Localisation of male determining factors in man: a thorough review of structural anomalies of the Y chromosome

It is widely accepted that male determination in man depends on the presence of a factor or factors on the Y chromosome. These factors may be localised within the Y chromosome through the study of structural anomalies of the Y. A thorough review of seven different structural anomalies of the Y is presented: dicentric Y chromosomes, Y isochromosomes, ring Y chromosomes, Y; autosome, Y;X, and Y;Y translocations, and Y deletions. The evidence from these studies indicates that a gene or genes on the short arm or the Y near the centromere play a crucial role in the development of the testes. A few studies indicate that one or more factors on the long arm of the Y may also influence testicular development. If such a factor is present on the long arm, then it too must be very near the centromere. The theory that separate genes independently control the initial development and maturation of the tests (on the long and short arms of the Y, respectively) may be premature. Recently proposed arguments in its favour are examined. Some evidence also indicates the presence of a fertility factor on the non-fluorescent segment of the long arm. Relevant information on the H-Y antigen is discussed.

Dicentric Y chromosome arising via tandem translocation

We describe a 22-year-old woman with primary amenorrhea, bilateral gonadoblastomas, and short stature (148.0 cm), but no other signs of the Ullrich-Turner syndrome. There were three cell lines identified in peripheral blood lymphocytes - 45,X (30%), 46,XY (60%), and 46,X,tan dic(Y) (10%). Cells cultured from gonadal biopsies showed only the 45,X karyotype. However, frozen sections of the biopsies showed frequent single and rare double-Y-chromatin bodies. Lymphocytes were H-Y antigen-negative. This previously undescribed structurally abnormal chromosome probably consists of two Y chromosomes attached end-to-end in a tandem translocation. One of the centromeres forms the primary (functional) constriction, the other being detectable only as C-positive material on each chromatid, so presumably inactive. The discrepancy between the presence of Y-chromatin in frozen sections of the gonads and its absence from karyotype in gonadal cultures is indicative of cell selection in tissue culture. Finally, the case confirms the high risk of gonadoblastoma in women with a Y chromosome, even in the absence of H-Y antigen.