Prenatal diagnosis of 45,X and 45,X mosaicism: the need for thorough cytogenetic and clinical evaluations

OBJECTIVES: Mosaicism involving a 45,X cell line is relatively common in prenatal diagnosis. In prenatally diagnosed cases, the prognosis of non-mosaic 45,X and 45,X/46,XY mosaicism are different. Therefore, accurate identification of a cell line containing Y chromosome is critical for genetic counseling and postnatal management. METHODS: We investigated the ultrasound findings and outcomes of pregnancies with a 45,X cell line identified during mid-trimester cytogenetic analysis. RESULTS: A total of 105 cases were found to have a 45,X cell line by standard cytogenetic analysis. Seventy-four cases were found to have non-mosaic 45,X at initial diagnosis. Of these 74 cases, 68 had abnormal ultrasound findings that were characteristic of Turner syndrome. Of the six cases with normal ultrasound findings, ultrasound examination was normal with male genitalia identified in three cases. Thorough cytogenetic and fluorescent in situ hybridization (FISH) analysis identified Y chromosome material in all three cases, one with a dicentric Y;14 chromosome and the other two cases with a marker chromosome containing Sex-determining Region (SRY) material in a small portion of the cells. In contrast, in 31 cases with a mosaic 45,X karyotype, ultrasound abnormality was identified only in one case. CONCLUSIONS: The present data suggest the need for follow-up ultrasound examination and thorough cytogenetic and molecular analysis for Y chromosome material in 45,X cases with normal ultrasound findings.     

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.     

Detection of mosaicism for 46,X,i(Y) (q10) in the blood lymphocytes in a phenotypically normal male neonate with prenatally detected 45,X/46, XY at amniocentesis and cytogenetic discrepancy in various tissues

ObjectiveWe present detection of mosaicism for 46,X,i(Y) (q10) in the blood lymphocytes in a phenotypically normal male neonate with prenatally detected 45,X/46, XY at amniocentesis and cytogenetic discrepancy in various tissues.Case reportA 35-year-old, gravida 2, para 1, woman underwent amniocentesis at 17 weeks of gestation because of advanced maternal age. Amniocentesis revealed a karyotype of 45,X [8]/46,XY [15]. Simultaneous array comparative genomic hybridization (aCGH) on uncultured amniocytes revealed the result of arr (Y) × 0–1 with 25.493-Mb mosaic deletion of chromosome Yp11.31-q11.23. Prenatal ultrasound findings were unremarkable. The fetus had normal male external genitalia on fetal ultrasound. Following genetic counseling, the pregnancy was carried to 38 weeks of gestation, and a phenotypically normal male baby was delivered without any abnormalities of the male external genitalia. The cord blood had a karyotypes of 46,X,i(Y) (q10)[8]/45,X[3]/46,XY [29], and placenta had a karyotypes of 45,X [25]/46,X,i(Y) (q10)[7]/46,XY [8]. When follow-up at age two months, the neonate was normal in development. The peripheral blood had a karyotypes of 46,X,i(Y) (q10)[8]/45,X[5]/46,XY [27]. Interphase fluorescence in situ hybridization (FISH) analysis on 101 buccal mucosal cells showed normal X and Y signals in 101/101 cells.ConclusionFetuses with 45,X/46, XY at amniocentesis can be associated with mosaicism for 46,X,i(Y) (q10) in the blood lymphocytes, cytogenetic discrepancy in various tissues and a favorable outcome.     

Discordance between prenatal cytogenetic diagnosis and outcome of pregnancy

From 1.3.73 to 30.9.80 5580 women had an amniocentesis performed here or elsewhere; fetal chromosome analyses were carried out in this laboratory. We found 112 abnormal karyotypes (2 per cent) out of 5591 chromosome analyses. In 40 women (0.7 per cent) no cytogenetic diagnosis was obtained. Follow-up was successful in 99.5 per cent. Nine cases are reported in detail: Three cases had discrepancy between the karyotype in amniotic fluid and peripheral blood after delivery, two of these cases turned out to be 46,XX (male) while the third was prenatally determined as trisomy 21, but had a 46,XX karyotype at birth. Six cases had discrepancy between the karyotype in amniotic fluid and the phenotypic outcome at birth/abortion. One case was a prenatally undetected 45,X/46,XY mosaicism; one case was an unexplained 45,X male fetus; two cases were prenatally determined as trisomy 21, but at abortion a normal karyotype was determined and in two cases maternal cells were probably examined. The incidence of cytogenetic errors in this study was very low.     

High-level mosaicism for 45,X in 45,X/46,X,idic(Y)(q11.2) at amniocentesis in a pregnancy with a favorable outcome and postnatal progressive decrease of the 45,X cell line

ObjectiveWe present prenatal diagnosis of high-level mosaicism for 45,X in 45,X/46,X,idic(Y)(q11.2) at amniocentesis in a pregnancy with a favorable outcome and postnatal progressive decrease of the 45,X cell line.Case reportA 36-year-old, gravida 4, para 3, woman underwent amniocentesis at 17 weeks of gestation because of advanced maternal age. Amniocentesis revealed a karyotype of 45,X[22]/46,X,idic(Y)(q11.2)[4]. Prenatal ultrasound was unremarkable, and the fetus had normal male external genitalia. Repeat amniocentesis was performed at 20 weeks of gestation, and the second amniocentesis revealed a karyotype of 45,X[24]/46,X,idic(Y)(q11.2)[3]. Simultaneous interphase fluorescence in situ hybridization (FISH) analysis on uncultured amniocytes revealed that 60% (62/103 cells) were Y-deleted cells. After genetic counseling, the parents decided to continue the pregnancy, and a 3020-g male baby was delivered with a body length of 52 cm, normal male genital organs and no phenotypic abnormalities. The karyotypes of cord blood, umbilical cord and placenta were 45,X[20]/46,X,idic(Y)(q11.2)[20], 45,X[31]/46,X,idic(Y)(q11.2)[9] and 45,X[40], respectively. At age one month, FISH analysis on urinary cells and buccal mucosal cells revealed 11.5% (7/61 cells) and 13.6% (16/118 cells), respectively for mosaicism for the Y-deleted cells. At age five month, the karyotype of peripheral blood was 45,X[9]/46,X,idic(Y)(q11.2)[31]. FISH analysis on buccal mucosal cells showed no abnormal Y-deleted cell (0/101 cells). At age 11 month, the karyotype of peripheral blood was 45,X[5]/46,X,idic(Y)(q11.2)[35]. FISH analysis on 102 buccal mucosal cells showed no abnormal signals. The infant was doing well with normal physical and psychomotor development.ConclusionHigh-level mosaicism for 45,X in 45,X/46,X,idic(Y)(q11.2) at amniocentesis can be associated with a favorable outcome and progressive decrease of the 45,X cell line.     

High-level mosaicism for 45,X in 45,X/46, XY at amniocentesis in a pregnancy with a favorable fetal outcome and cytogenetic discrepancy in various tissues

ObjectiveWe present prenatal diagnosis of high-level mosaicism for 45,X by amniocentesis in a pregnancy with a favorable fetal outcome.Case reportA 35-year-old, gravida 2, para 1, woman underwent amniocentesis at 17 weeks of gestation because of advanced maternal age. Amniocentesis revealed a karyotype of 45,X[13]/46,XY[11]. Simultaneous array comparative genomic hybridization (aCGH) on uncultured amniocytes revealed the result of Yp11.3q11.21 × 0–1 [0.1], Yq11.21q11.23 × 0–1 [0.6]. At 19 weeks of gestation, she underwent the second amniocentesis which revealed a karyotype of 45,X[13]/46,XY[12], and aCGH and multiplex ligation-dependent probe amplification (MLPA) on uncultured amniocytes showed 37% mosaicism for Y-deleted cells. At 28 weeks of gestation, she underwent the third amniocentesis which revealed a karyotype of 45,X[25]/46,XY[25], and aCGH on uncultured amniocytes revealed the result of Yq11.21q11.23 × 0.5, Yq11.23q12 × 0.7. Interphase fluorescence in situ hybridization (FISH) analysis on uncultured amniocytes revealed that 16.67% (20/120 cells) were Y-deleted cells. The parental karyortypes and prenatal ultrasound were normal. At 37 weeks of gestation, a 2707-g phenotypically normal male baby was delivered with normal male external genitalia. The karyotypes of cord blood, umbilical cord and placenta were 45,X[25]/46,XY[15], 45,X[18]/46,XY[22] and 45,X[25]/46,XY[15], respectively. When follow-up at age five months, the neonate was normal in external genitalia and physical development. The peripheral blood had a karyotype of 45,X[29]/46,XY[11], and FISH analysis on 100 buccal mucosal cells showed no abnormal signals. When follow-up at age 11 months, the neonate was physically normal, and the peripheral blood had a karyotype of 45,X[17]/46,XY[23].ConclusionHigh-level mosaicism for 45,X in 45,X/46, XY at amniocentesis can be associated with a favorable fetal outcome despite the presence of cytogenetic discrepancy in various tissues.     

Mucinous cystadenoma in a female patient with 45,X/46,XY karyotype

The mosaic karyotype of 45,X/46,XY has a wide phenotypic spectrum and there are substantial differences between prenatally and postnatally diagnosed cases. The phenotype varies between normal male to classical Turner syndrome. There is a high risk of gonadal tumor development in the dysgenetic gonads of patients with sex chromosome mosaicism. We report a case of a 24-year-old patient with a pelvic mass and amenorrhea referred to our laboratory for karyotyping. Peripheral blood chromosome analysis showed a mosaic karyotype of 45,X[17]/46,XY[83]. The tumor originated from the left ovary and the right ovary was found to be a streak gonad. The uterus was intact. Pathologic examination of the tumor revealed mucinous cystadenoma. Physical examination of the patient showed signs of Turner syndrome, as short stature (145 cm), short neck and asymmetric shoulders. Her mental state was normal. Y chromosome microdeletion screening involving SRY and ZFY genes was performed and no deletion was found. The patient was informed about the condition during the genetic counseling session.     

45,X/46,X,del(Yq) sex chromosome mosaicism--analysis of the phenotypic expression

Three female patients with Turner-syndrome (sexual infantilism, short stature and somatic Turner-stigmata) have been analysed cytogenetically by means of different banding techniques. A deletion of the distal heterochromatic band Yq12 of the Y chromosome was observed in a mosaic with a 45,X-cell line, i.e. the karyotype is 45,X/46,X,del(Y)(q12). In order to get information about the phenotypic expression of the 45,X/46,X,del(Yq) mosaicism all previously published cases have been reviewed. Comparing the phenotypes of all 45,X/46,X,del(Yq) mosaic cases three different phenotype categories of sexual development can be distinguished: female individuals with sexual infantilism and Turner-stigmata, individuals with ambiguous genitals, ranging from clitoris hypertrophy of female genitals to hypospadia of males, male individuals, who are infertile (azoospermic). A comparison of the appearance of external genitals with the status of gonads of all patients revealed an unequivocal relationship between the gonad status and the resulting phenotype category. Furthermore, the role of Y-chromosomal loci determining testicular differentiation (biological function of H-Y antigen) for male development has been emphasized. The effect of the 45,X-cell line on the expression of short stature and somatic Turner-stigmata is independent of sexual development. Considering the great phenotypic variability of the 45,X/46,X,del(Yq) mosaicism it seems impossible to deduce a definitive phenotype. This problem is acute in prenatal diagnosis especially.     

Prenatal application of fluorescent in situ hybridization (FISH) for identification of a mosaic Y-chromosome marker, idic(Yp).

An amniocentesis was performed at 13.3 weeks' gestation for advanced maternal age. A mosaic sex chromosome pattern was found: of 50 cells examined, 34 had a 45,X karyotype. In 14 cells with a modal number of 46, a recognizable Y was substituted by a small non-fluorescent marker. C-banding identified the marker as an isodicentric in 12 cells. In two cells, the non-fluorescent marker appeared to be monocentric and looked like a non-fluorescent del (Yq), but could have been an isodicentric Y with inactivation of one of the centromeres. Two cells with a modal number of 47 showed two copies of the monocentric marker. Fluorescent in situ hybridization with an alpha satellite Y-specific centromeric probe confirmed the Y-chromosome origin of the markers and allowed for more accurate prenatal diagnostic information.     

Delineation of an isodicentric Y chromosome in a mosaic 45,X/46,X,idic(Y)(qter-p11.3::p11.3-qter) fetus by SRY sequencing, G-banding, FISH, SKY and study of distribution in different tissues.

Many factors such as genetic, developmental and hormonal are involved in mammalian sex determination. The relative importance and the mutual interactions among those factors are obscure. Study of cytogenetic mosaicism involving sex chromosomes may help to further unravel the mysterious process. We report a fetus with a mosaic karyotype, 45,X/46,X,idic(Y)(qter-p11.3::p11.3-qter), with unambiguous male external genitalia and a defect in the interventricular septum of the heart. Genotype of this fetus was extensively studied by technologies including sequencing of SRY (sex-determining region on the Y chromosome) gene, G-banding, FISH (fluorescence in situ hybridization) and SKY (spectral karyotyping). A markedly higher percentage of Y-containing cells was observed in the gonads (55%) than in the amniotic fluid (17%) and placental villi (11%), which was considered to be the major reason why the fetus did not have ambiguous genitalia.     

Prenatal diagnosis of 45,X/46,XY mosaicism--a review and update

A total of 54 cases with prenatal diagnosis of 45,X/46,XY mosaicism was reviewed. Of 47 cases with information on phenotypic outcome, 42 cases (89.4 per cent) were reported to be associated with a grossly normal male phenotype. Three cases (6.4 per cent) were diagnosed as having mixed gonadal dysgenesis with internal asymmetrical gonads. Two other cases were questionably abnormal. In 40 cases with successful cytogenetic confirmatory studies, the overall rate of cytogenetic confirmation of 45,X/46,XY from tissues derived from fetus/liveborn/placenta was 70.0 per cent. This review shows a major difference in the phenotypic outcome between postnatal diagnosis and prenatal diagnosis. Due to the ascertainment bias, almost all known patients with postnatal diagnosis of 45,X/46,XY mosaicism are phenotypically abnormal. Therefore, caution must be used in translating information derived from postnatal diagnosis to prenatal diagnosis. This review calls for collection of more data on 45,X/46,XY mosaicism diagnosed prenatally, more long-term follow-up of liveborn infants, and pathological studies of all abortuses. Emphasis is placed also on the importance of genetic counselling, ultrasound examination, and cytogenetic confirmation.     

Sonographic genital ambiguity in a fetus due to a mosaic 45,X/46,X,idic(Y)(qter-p11.32::p11.32-qter) karyotype

Nowadays, improved ultrasound techniques enable the detection of more subtle congenital abnormalities at an earlier stage of fetal development. Current cytogenetic techniques can characterize a chromosomal abnormality in greater detail. These advancements in both diagnostic possibilities have helped to answer many questions but have also created new issues and dilemmas in counselling. This is illustrated by this case report of a 35-year-old woman, who presented at the end of the second trimester of her first pregnancy. Sonographic examination indicated an abnormal external genital in a male fetus. A differential diagnosis of hypospadia was made. During follow-up, an amniocentesis was performed, and this showed a 45,X/46,X,idic(Y)(qter-p11.32::p11.32-qter) karyotype as the cause of the sonographic findings. Cytogenetic characterization of the isodicentric Y chromosome and pre- and post-natal findings in the child are reported. Cases with a similar karyotype reported in the literature are reviewed.     

Prenatal detection of 45,X/46,XX/47,XXX mosaicism through amniocentesis: mosaicism confirmed in cord blood, amnion, and chorion.

Sex chromosome mosaicism in amniotic fluid cells poses a serious dilemma in prenatal diagnosis. Chromosome analysis of 56 primary clones of amniocytes revealed three distinct cell lines. Nine cells (16.1 per cent) demonstrated a 45,X karyotype, 11 cells (19.6 per cent) a 47,XXX karyotype, and the remaining 36 cells (64.3 per cent) had a modal number of 46 chromosomes (46,XX). Cytogenetic evaluation of 100 cells from cord blood, amnion, and chorion following delivery confirmed this triple mosaicism. However, the distribution of the three karyotypes in the pre- and postnatal samples was not found in the same proportions. The cord blood had the most similar frequency to that of the amniotic fluid sample, while the chorion had a significantly increased frequency of 47,XXX cells (41 per cent) and a decreased frequency of 45,X cells (2 per cent). Physical examination of the infant at birth revealed no discernible phenotypic abnormalities. Parental karyotypes were normal. This case highlights the difficulty in determining whether a prenatally detected abnormality will be associated with postnatal phenotypic deviation.     

Complete karyotype discrepancy between placental and fetal cells in a case of ring chromosome 18.

A case of complete karyotype discrepancy between cultured chorionic villi and amniotic in addition to fetal cells is reported. Ring chromosome 18 and monosomy 18 mosaicism was detected after amniocentesis. The pregnancy was terminated in the 23rd gestational week. Cytogenetic analysis of cultured umbilical cord tissue after termination confirmed the finding of ring chromosome 18/monosomy 18 mosaicism. In cultured umbilical blood lymphocytes monosomic cells 45,-18 were not detected and the karyotype was 46,XY,r(18). In contrast, short-term and long-term cultured chorionic villi showed a normal male karyotype of 46,XY. Ultrasonographic examination revealed amniotic band syndrome and scoliosis in the caudal region of the spine.     

High-level mosaicism for 45,X in 45,X/46,XX at amniocentesis in a pregnancy with a favorable outcome and postnatal progressive decrease of the 45,X cell line

ObjectiveWe present prenatal diagnosis of high-level mosaicism for 45,X in 45,X/46,XX at amniocentesis in a pregnancy with a favorable outcome and postnatal progressive decrease of the 45,X cell line.Case reportA 32-year-old, gravida 2, para 1, woman underwent amniocentesis at 17 weeks of gestation because of the abnormal first-trimester maternal serum screening result indicating a 1/34 risk for Down syndrome. Amniocentesis revealed a karyotype of 45,X[27]/46,XX[15]. Simultaneous array comparative genomic hybridization (aCGH) on uncultured amniocytes revealed 12% mosaicism for monosomy X. Prenatal ultrasound was normal. The pregnancy was carried to term, and a 2780-g phenotypically normal female baby was delivered. The cord blood had a karyotype of 45,X[12]/46,XX[28]. At age one month, the peripheral blood had a karyotype of 45,X[13]/46,XX[27]. Interphase fluorescence in situ hybridization (FISH) analysis on the buccal mucosal cells revealed 2% (2/102 cells) mosaicism for monosomy X, compared with 1% (1/100 cells) in the normal control. When follow-up at age one year, she was doing well with normal physical and psychomotor development. Her body weight was 9.9 Kg (50th – 85th centile), and her body height was 75 cm (50th – 85th centile). The peripheral blood had a karyotype of 45,X[4]/46,XY[36].ConclusionHigh-level mosaicism for 45,X in 45,X/46,XX at amniocentesis can be associated with a favorable outcome and postnatal progressive decrease of the 45,X cell line.     

Anomalies de structure du chromosome Y et syndrome de Turner

Although specifically male, the human Y chromosome may be observed in female karyotypes, mostly in women with Turner syndrome stigmata. In women with isolated gonadal dysgenesis but otherwise normal stature, the testis determining factor or SRY gene may have been removed from the Y chromosome or may be mutated. In other women with Turner syndrome, the karyotype is usually abnormal and shows a frequent 45,X/46,XY mosaicism. In these cases, the phenotype depends on the ratio between Y positive and 45,X cell lines in the body. When in mosaicism, Y chromosomes are likely to carry structural abnormalities which explain mitotic instability, such as the existence of two centromeres. Dicentric Y isochromosomes for the short arm (idic[Yp]) or ring Y chromosomes (r[Y]) are the most frequent abnormal Y chromosomes found in infertile patients and in Turner syndrome in mosaic with 45,X cells. Although monocentric, deleted Y chromosomes for the long arm and those carrying microdeletions in the AZF region are also instable and are frequently associated with a 45,X cell line. Management of infertile patients carrying such abnormal Y chromosomes must take into account the risk and the consequences of a mosaicism in the offspring.     

Laparoscopic gonadectomy in a case of a dicentric fluorescent Y-chromosome mosaicism with Turner-like phenotype and virilized external genitalia

In few cases of Turner syndrome the karyotype reveals the presence of an additional Y-bearing cell line, which is referred to as a borderline case of mixed gonadal dysgenesis. We report a 20-year-old woman with primary amenorrhea, virilization and a few Turner stigmata, who revealed rare mosaicism of 45,X/46,X dic (Y; 5)(q12; q11), +5/46,X, der (Y), which was detected by conventional G-banding and multicolor spectral karyotyping. She underwent laparoscopic gonadectomy in which mixed gonadal dysgenesis was found and both gonads were removed. No evidence of gonadoblastoma was noted on the gonads. Virilization improved postoperatively. We recommend gonadectomy via laparoscope in women presenting with Turner-like phenotype, virilization and the presence of a Y chromosome. This report describes the role of cytogenetic and molecular genetic investigations in the definition of mosaicism in Turner syndrome.     

Management of prenatally detected trisomy 8 mosaicism.

We report on ten pregnancies with trisomy 8 mosaicism. Nine cases were prenatally detected in chorionic villi (n=6), amniotic fluid (AF) cells (n=2) or fetal blood (FB) lymphocytes (n=1). Follow-up laboratory investigations showed confined placental mosaicism (CPM) or pseudomosaicism in eight cases. In one case with ultrasound abnormalities, trisomy 8 mosaicism was detected in FB cells although cultured AF cells showed normal cells only. Another case of mosaic trisomy 8 was prenatally missed; cytogenetic analysis of short-term cultured villi revealed a normal male karyotype, while postnatally, trisomy 8 mosaicism was detected in peripheral blood lymphocytes and skin fibroblasts of the affected child. These findings indicate the difficulties in the prenatal diagnosis of trisomy 8 mosaicism. When found in chorionic villi, it mostly represented CPM, while in a case of true fetal trisomy 8 mosaicism, the cytotrophoblast cells showed a normal karyotype. So, the cytotrophoblast compartment of chorionic villi is a poor indicator of the presence or absence of fetal trisomy 8 mosaicism. Follow-up investigations including amniocentesis and especially fetal blood sampling are required to come to a definite prenatal diagnosis of trisomy 8 mosaicism.     

Normal karyotype in cultured chorionic villus cells, but mosaicism in amniotic and fetal cells.

A case with a normal male karyotype in cultured chorionic villus cells, but 46,XY/45,X/46,X,i(Yq) mosaicism in amniotic and fetal tissue is reported. The fetus was a phenotypic male. Pathological examination revealed discrete features, which might indicate a syndrome, and histological examination showed large, bright cells in the tubules of the testes. Possible explanations for discordance between the karyotype of embryonic and extraembryonic tissue are discussed.