Cytogenetic and molecular characterization of two isodicentric Y chromosomes

Clinical and molecular cytogenetic findings and pregnancy outcomes of fetuses with isochromosome Y

BACKGROUND

The mosaic forms and clinical phenotypes of fetuses with isochromosome Y are difficult to predict. Therefore, we summarized the cases of nine fetuses with isochromosome Y identified in prenatal diagnosis with a combination of molecular cytogenetic techniques, providing clinical evidence for prenatal genetic counseling.

METHODS

The prenatal diagnosis and pregnancy outcomes of nine fetuses with isochromosome Y were obtained by a  retrospective analysis. Isochromosome Y was identified prenatally by different approaches, such as conventional karyotyping, chromosomal microarray analysis (CMA), quantitative fluorescent polymerase chain reaction (QF-PCR) and fluorescence in situ hybridization (FISH).

RESULTS

Seven idic(Y) fetuses and two i(Y) fetuses were identified. One fetus was complete for i(Y)(p10), and the rest with 45,X had mosaic forms. A break and fusion locus was identified in Yp11.3 in one fetus, in Yq11.22 in six fetuses and in Yp10 in two fetuses. The CMA results suggested that different deletions and duplications were found on the Y chromosome. The deletion fragments ranged from 4.7 Mb to the entire Y chromosome, and the duplication fragments ranged from 10.4 to 18.0 Mb. QF-PCR analysis suggested that the AZF region was intact in one fetus, four fetuses had AZFb+c+d deletion, one fetus had AZFa+b+c+d deletion, and one fetus had AZFc+d deletion. Finally, four healthy male neonates were delivered successfully, but the parents of the remaining five fetuses, including three healthy and two unhealthy fetuses, chose to terminate their pregnancies.

CONCLUSION

The fetus and neonate phenotype of prenatally detected isochromosome Y usually is that of a normally developed male, ascertained in the absence of other indicators of a fetal structural anomaly. Our study provides clinical reference materials for risk assessment and permits better prenatally counseling and preparation of parents facing the birth of isochromosome Y fetuses.

Disorders of Sex Development: Classification, Review, and Impact on Fertility

In this review, the elements included in both sex determination and sex differentiation are briefly analyzed, exposing the pathophysiological and clinical classification of disorders or anomalies of sex development. Anomalies in sex determination without sex ambiguity include gonadal dysgenesis, polysomies, male XX, and Klinefelter syndrome (dysgenesis and polysomies with a female phenotype; and sex reversal and Klinefelter with a male phenotype). Other infertility situations could also be included here as minor degrees of dysgenesis. Anomalies in sex determination with sex ambiguity should (usually) include testicular dysgenesis and ovotesticular disorders. Among the anomalies in sex differentiation, we include: (1) males with androgen deficiency (MAD) that correspond to those individuals whose karyotype and gonads are male (XY and testes), but the phenotype can be female due to different hormonal abnormalities. (2) females with androgen excess (FAE); these patients have ovaries and a 46,XX karyotype, but present varying degrees of external genital virilization as a result of an enzyme abnormality that affects adrenal steroid biosynthesis and leads to congenital adrenal hyperplasia; less frequently, this can be caused by iatrogenia or tumors. (3) Kallman syndrome. All of these anomalies are reviewed and analyzed herein, as well as related fertility problems.

Clinical, cytogenetic, and molecular findings of isodicentric Y chromosomes

Background

Isodicentric Y chromosomes [idic(Y)] are one of the most common structural abnormalities of the Y chromosome. The prenatal diagnosis of isodicentric Y chromosomes is of vital importance, and the postnatal phenotypes vary widely. Therefore, we present six patients prenatally diagnosed with isodicentric Y chromosomes and review the literature concerning the genotype-phenotype correlations.

Method

The clinical materials of six patients were obtained. Cytogenetic and molecular approaches were carried out for these six patients.

Results

Isodicentric Y chromosomes were found in all sixpatients. Among them, four patients presented with a mosaic 45,X karyotype, one patient had a 46,XY cell line, and one patient was nonmosaic. Five of these six isodicentric Y chromosomes had a breakpoint in Yq11.2, and the other had a breakpoint in Yp11.3. The molecular analysis demonstrated different duplications and deletions of the Y chromosome. Finally, three patients chose to terminate the pregnancy, two patients gave birth to normal-appearing males, and one patient was lost to follow-up.

Conclusion

The incorporation of multiple cytogenetic and molecular techniques would offer a more comprehensive understanding of this structural chromosomal abnormality for genetic counselling.

Sex chromosomes and sex chromosome abnormalities

This article focuses on constitutional sex chromosome abnormalities detected by conventional cytogenetics and fluorescence in situ hybridization. The author discusses the two general classifications of abnormalities: numerical and structural. Also included are descriptions of unique aspects of X and Y chromosomes, technological advances in detection, and future perspectives.

47,X,idic(Y),inv dup(Y): a non-mosaic case of a phenotypically normal boy with two different Y isochromosomes and neocentromere formation

A de novo aberrant karyotype with 47 chromosomes including 2 different-sized markers was identified during prenatal diagnosis. Fluorescence in situ hybridization (FISH) with a Y painting probe tagged both marker chromosomes which were supposed to be isochromosomes of the short and the long arm, respectively. A normal boy was born in time who shows normal physical and mental development. To characterize both Y markers in detail, we postnatally FISH-mapped a panel of Y chromosomal probes including SHOX (PAR1), TSPY, DYZ3 (Y centromere), UTY, XKRY, CDY, RBMY, DAZ, DYZ1 (Yq12 heterochromatin), SYBL1 (PAR2), and the human telomeric sequence (TTAGGG)(n). The smaller Y marker turned out to be an isochromosome containing an inverted duplication of the entire short arm, the original Y centromere, and parts of the proximal long arm, including AZFa. The bigger Y marker was an isochromosome of the rest of the Y long arm. Despite a clearly visible primary constriction within one of the DAPI- and DYZ1-positive heterochromatic regions, hybridization of DYZ3 detected no Y-specific alphoid sequences in that constriction. Because of its stable mitotic distribution, a de novo formation of a neocentromere has to be assumed.

A case of mosaic Klinefelter syndrome associated with isodicentric Yp

We describe a case of mosaic Klinefelter syndrome demonstrating an isodicentric Y chromosome. A 70-year-old man visited our outpatient clinic complaining of dysuria resulting from atrophy of the penis. His height was 170 cm and his weight was 60 kg. A serum hormonal analysis revealed hypergonadotropic hypogonadism. A chromosomal analysis with fluorescence in situ hybridization revealed four cell lines in which the karyotypes were 47,XXY, 46,XY, 46,XX and 47,XX,idic(Y) (q11.2). To the best of our knowledge this is the first case of mosaic Klinefelter syndrome bearing an isodicentric Y chromosome. The origin of the isodicentric Y is discussed. (Reprod Med Biol 2008; 7: 177-180).

Molecular and clinical description of a girl with a 46,X,t(Y;4)(q11.2;p16)/45,X,der(4)t(Y;4)(q11.2;p16) karyotype and a small cryptic 4p subtelomeric deletion

We report on a 13-year-old female with short stature, minimal axillary and pubic hair, no breast development, absence of uterus and ovaries, with the following karyotype on lymphocyte cultures: 46,X,t(Y;4)(q11.2;p16)[40]/45,X,der(4)t(Y;4)(q11.2;p16)[10]. Loss of the small derivative Y chromosome in 20% of the cells was also confirmed in skin fibroblast cultures. FISH analyses using Y centromere, SRY, subtelomere XpYp/XqYq, Y and 4 painting probes, confirmed the cytogenetic findings. High-resolution STS analyses using 40 markers covering the Y chromosome did not identify any deletion on the Y. However, de novo absence of the 4p subtelomeric region was noted by FISH, although this deletion was not revealed by Array-CGH at 1 Mb resolution, the last array clone being 0.35 or 1 Mb distal to the 4p FISH probe. The female phenotype of this patient must be due to the loss of the derivative Y chromosomes in some of her cells, especially the gonads, while the 4p subtelomeric deletion does not seem to contribute to her phenotype.

Mixed gonadal dysgenesis associated with an isodicentric Y chromosome

A szerzők egy izodicentrikus Y-kromoszómát tartalmazó kariotípusú kevert gonáddiszgenezises esetükről számolnak be, melyet fiatal csecsemőkorban diagnosztizáltak. Szükségesnek tartják a perineoscrotalis hypospadiasissal és az egy- vagy kétoldali hereleszállás zavarával született újszülöttek speciális kivizsgálását közvetlenül a szülés után. A részletes kivizsgálás eredménye biztosítja a korrekt nemi besorolást és a diszgenetikus gonád malignus elfajulásának megelőzését.

Natural history of prenatally diagnosed 46,X,isodicentric Y

OBJECTIVES

The karyotype 46,X,isodicentric Y has rarely been reported in the context of prenatal diagnosis. The literature is replete with descriptions of individuals with 46,X,isodicentric Y/45,X mosaicism, presenting with a spectrum of phenotypes. The postnatal phenotype is believed to depend on the extent of mosaicism in the gonads or other affected tissues. The purpose of this article is to delineate the natural history of this chromosomal abnormality when identified in the context of prenatal diagnosis.

METHODS

We identified a 45,X/46,X,idicY karyotype in the structurally normal male fetus of a woman presenting with an abnormal triple screen. Four other prenatally ascertained cases were found in our files as well as ten in the medical literature.

RESULTS

Of the 15 cases presented here, 11 (73%) were reported as phenotypically normal males, 1 was found to have an epididymal cyst, and 1 had normal male genitalia, but was also found to have a cardiovascular defect. One out of 15 (7%) was found to have female genitalia and was therefore confirmed to have Turner syndrome. In one case, the outcome was not reported.

CONCLUSION

An individual diagnosed prenatally with idic(Y) may in many cases be a normal male, similar to the outcome for prenatally diagnosed 45,X/46,XY.

Isodicentric Yp: prenatal diagnosis and outcome in 12 cases

OBJECTIVES

1. To present the prenatal cytogenetic findings and postnatal outcome of 12 cases with an isodicentric chromosome composed of the short arm of the Y chromosome.2. To review the literature and provide recommendations for cytogenetic analysis and counseling.

METHODS

Prenatal and postnatal cytogenetic data and clinical findings of isodicentric Yp ascertained in six institutions were gathered and reviewed.

RESULTS

Nine of the twelve cases were referred for advanced maternal age (AMA), one of which was a twin pregnancy with one twin having an increased nuchal translucency measurement. The remaining cases were referred owing to a family history of hemophilia and an abnormal maternal serum screen, respectively. Nine of these pregnancies resulted in the birth of a normal-appearing male infant with subsequent normal growth and psychomotor development. Follow-up ranged from birth to 7 years. In two cases, the pregnancy was terminated and the fetuses showed male external genitalia. In the case ascertained because of an increased nuchal translucency measurement, the prenatal diagnosis of 45,X was made. At birth, there were ambiguous genitalia, and postnatal cytogenetic studies found an isodicentric Yp. In 11 of the 12 cases, mosaicism was present.

CONCLUSION

Our cases show that the prenatal finding of an isodicentric Yp, with or without 45,X mosaicism, is compatible with normal male phenotype in most cases, particularly in the absence of other anomalies. To ensure accuracy in cytogenetic reporting and prenatal counseling, the identification of a structurally abnormal or small Y chromosome, either alone or in the presence of 45,X colonies, should be followed immediately by confirmatory molecular cytogenetic investigations as well as by ultrasound determination of the phenotypic sex of the fetus.

Phenotypic variability in isodicentric Y patients: study of nine cases

Isodicentric chromosomes are the most commonly reported aberrations of the human Y chromosome. As they are unstable during cell division and can generate various types of cell lines, most reported patients are chromosomal mosaics, generally including a 45,X cell line. Phenotypes depend on the location of the breakpoints as well as on the proportion of each cell line and vary from male to abnormal female or individual with ambiguous genitalia. Although phenotypic variability is known to also depend on the degree of mosaicism in the various tissues, gonads are rarely studied. We report nine cases of isodicentric Y chromosomes studied by conventional and molecular cytogenetic: three males, five females, and one individual with sexual ambiguity. Two males had a non-mosaic karyotype, while the third male was a mosaic with a predominant 46,XY cell line. Three of the females had a major 45,X cell line, while the last two females and the patient with ambiguous genitalia had a major 46,X,idic(Y) cell line. Analyses of gonadal tissues from the individual with sexual ambiguity and of three of the five female patients gave results concordant with their phenotype, allowing us to better understand the sexual differentiation of these patients.

Molecular and cytogenetic characterization of a non-mosaic isodicentric Y chromosome in a patient with Klinefelter syndrome

We report on an adult male with Klinefelter phenotype and an isodicentric Y chromosome (47,XX,+idic(Y)(q12)), a combination which has to the best of our knowledge not been reported before. The patient was hospitalized in forensic psychiatry because of repeated delinquency, aggressive, aberrant and inappropriate behavior, and borderline intelligence. Molecular cytogenetic studies (FISH) showed that the SRY gene was present on both ends of the idicY, while there was only one signal for the Yq subtelomere probe. Molecular investigations by multiplex PCR, using STS markers covering the short and long arm of the Y chromosome did not indicate a deletion of Y chromosomal material. Molecular investigations of STR markers located on Xp22.3 and Xq28 indicated paternal origin of the additional X chromosome and an error in paternal meiosis I. Results of FISH analysis and molecular investigations are compatible with a phenotype as described for individuals with a 48,XXYY karyotype and support the findings that isodicentric Y chromosomes are frequently accompanied by other sex chromosomal abnormalities.

Fine mapping of an isodicentric Y chromosomal breakpoint from a schizophrenic patient

We report on a male schizophrenic patient who carried an isodicentric Y chromosome [idic(Y)] with a mosaic karyotype [mos 45,X/46,X,idic(Y)(q11)]. Although a potential association between sex chromosome abnormalities and a susceptibility to psychoses has been documented, there has only been one previous report of idic(Y) coincident with schizophrenia. The [45,X] karyotype is known to be associated with Turner syndrome (TS), but our patient lacked most of the phenotypic features of TS, except for short stature. To define the precise position of the breakpoint on the patient's abnormal Y chromosome, we carried out polymerase chain reaction (PCR) analysis, using primers for 15 marker loci along the chromosome. The breakpoint was localized to between the marker loci sY118 and sY119 on Yq in the 5M interval of the deletion map. This position represents the most centromeric breakpoint recorded for idic(Y). We cannot exclude the possibility that the development of schizophrenia is unrelated to the Y chromosome abnormality in this patient but we hope that this study will stimulate further cytogenetic and molecular genetic analyses of Y chromosome regions that may influence psychiatric traits.