Prenatal diagnosis of 45,X/46,XY mosaicism with postnatal confirmation in a phenotypically normal male infant

Confirmation of prenatal diagnosis of sex chromosome mosaicism

Prenatal diagnosis of mosaicism causes problems in interpretation and in genetic counselling. Part of the difficulty with any prenatal diagnosis of mosaicism is interpretation of results without knowing the exact origin, embryonic or extraembryonic, of the abnormal cell line. To confuse the issue in cases of prenatal diagnosis of 45,X/46,XY mosaicism is the recent demonstration that a diagnosis of 45,X/46,XY made prenatally is not necessarily associated with the same phenotype as when diagnosed postnatally. We present two cases of prenatal diagnosis of sex chromosome mosaicism (45,X/46,XY and 45,X/47,XYY). Posttermination examination of the phenotypically normal male fetuses and their placentas established that the placenta was the most likely source of the 45,X cell line. An approach to confirming the prenatal diagnosis of sex chromosome mosaicism and establishing its origin utilizing detailed cytogenetic examination of both fetus and placenta is suggested.

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.

Prenatal diagnosis of 45,X/46,XY mosaicism in a fetus with asymmetric gonadal dysgenesis

An 18 week abortus had been prenatally diagnosed as a 45,X/46,XY mosaic. The fetus was a phenotypic male with glandular hypospadias, a horseshoe kidney and asymmetric gonadal dysgenesis. This case represents a rare instance of prenatally diagnosed 45,X/46,XY mosaicism with an abnormal phenotype.

Phenotypic spectrum of 45,X/46,XY individuals

We report on five patients with 45,X/46,XY mosaicism. In these subjects, as well as in 58 individuals from the literature with a similar chromosome constitution, we did not find a preponderance of 46,XY cells among patients showing ambiguous to abnormal male external genitalia when compared to those patients with slight or no virilization. However, the average frequency of 46,XY cells in blood in these mosaic individuals suggests that this sample includes mainly individuals whose mosaicism originated early in embryonic cell division. Those individuals whose mosaicism originated later are not significantly represented in this sample and would have higher frequencies of 46,XY cells. These individuals would be excluded from an intersex sample if they had well-virilized genitalia. This ascertainment bias suggests that the degree of virilization depends on the frequency of 46,XY cells.

Trisomy 20 mosaicism

A further case of trisomy 20 mosaicism found at amniocentesis is presented. Pregnancy was terminated, the fetus showed facial dysmorphia and minor cardial and renal anomalies. 19 published reports of true trisomy 20 mosaicism at amniocentesis are reviewed. Five pregnancies resulted in obviously normal newborns. The significance of mostly minor anomalies found at autopsy of 7 fetuses remains unclear. With regard to genetic counselling the significance of trisomy 20 mosaicism is summarized as follows: (1) true trisomy 20 mosaicism in amniotic fluid cells reflects mosaicism of the fetus; (2) severe malformation is not a major feature of trisomy 20 mosaicism; (3) the risk of mental retardation is still undetermined, due to limited experience. However, there is no definite proof that the condition is harmful at all.

Mosaicism or pseudomosaicism: the problem of hypermodal cells in amniotic fluid cell culture

A series of 2029 consecutive amniotic fluid specimens studied for prenatal genetic diagnosis were reviewed and reassessed so as to evaluate the frequency and clinical significance of hypermodal cells in amniotic fluid cell cultures. Hypermodal cells were defined as those with more than 46 chromosomes, and were characterized by an additional structurally normal or structurally abnormal chromosome. Of 2029 specimens, 47 (2.31 per cent) contained a total of 167 hypermodal cells. True fetal mosaicism was detected in three cases (0.14 per cent). All had hypermodal cells in more than one culture flask or colony which contained the same aberrant chromosome complement. In all but one case the babies were normal when only one cell was hypermodal, or when several cells were hypermodal but present in only one colony or one culture vessel. One case had an extra No. 20 chromosome in one cell. Although the child had multiple anomalies, they were not characteristic of trisomy 20, and subsequent chromosomal study on the baby postnatally revealed a 46,XX karyotype. The in situ coverslip technique is recommended as the preferred method for prenatal diagnosis, and it is useful as an aid in differentiating true mosaicism from pseudomosaicism.

Characterization of cells of amniotic fluids by immunological identification of intermediate-sized filaments: presence of cells of different tissue origin

Antibodies against intermediate-sized filaments, of the prekeratin or vimentin type, were used to investigate the presence of these filaments by indirect immunofluorescence microscopy in cultured and non-cultured amniotic fluid cells, in frozen sections of the placenta and in isolated cells of the amniotic epithelium. Two major classes of cells can be cultured from amniotic fluids, namely cells of epithelial origin containing filaments of the prekeratin type and cells of different origin which contain filaments of the vimentin type but are negative when tested with antibodies to epidermal prekeratin. The presence of prekeratin type filaments correlates with the morphology of colonies of amniotic fluid cell cultures in vitro as classified by Hoehn et al. (1974). Cells of E-type colonies are shown to be of epithelial origin. In contrast our data indicate a different origin of almost all cells of F-type colonies and of the large majority of cells of AF-type colonies. Cells of epithelial origin and positively stained with antibodies to epidermal prekeratin are occasionally scattered in F-type colonies and in variable percentages (up to 30%) in AF-type colonies. Surprisingly, cryostat sections of the amniotic epithelium and isolated groups of amniotic cells showed positive reactions with both antibodies to vimentin and prekeratin. The possibility that amniotic cells may be different from other epithelial cells in that they contain both types of filaments simultaneously already in situ is presently under investigation.

Two dicentric Y isochromosomes, one without and the Yqh heterochromatic segment: review of the Y isochromosomes

Two women with primary amenorrhoea and few other stigmata of Turner's syndrome were found to be chromosome mosaics: 45,X/46,X,idic(Y). In Case 1, the dicentric isochromosome Y was found to have a long-arm breakpoint of formation. This structure was interpreted as containing two Y short arms and centromeres separated by a region derived from the proximal Y long arm. One of the centromeres in the Case 1--idic(Y) was suppressed in 80% of cells in blood, and in these cells it appeared as a regular Y-shaped chromosome. In Case 2 the idic(Y) was derived by a short-arm breakpoint of formation. In all the dicentrics of this case with one primary constriction (functional monocentrics) there was a single Cd band. In the 10% of dicentrics with two primary constrictions, there were two Cd bands. It is argued that the instability of sex isochromosomes is due to this functional dicentricity in some cells. These cases are compared with 42 other Y isochromosomes with various short- and long-arm breakpoints of formation. It is suggested that some of the nonheterochromatic, nonfluorescent Y chromosomes previously reported may be explained as dicentric i(Y) with proximal long-arm breakpoints of formation and one suppressed centromere.

46,XY/45,X mosaicism in an amniotic fluid cell culture: suppression of abnormal cell line after subcultivation

An abnormal cell population, 45,X, appeared in 3 of 4 cell lines established from an amniotic fluid specimen obtained from a normal mid-trimester pregnancy. Two of the cell lines were subjected to repeated chromosome analyses until VII passage. The abnormal cells were suppressed after repeated trypsinisations; simultaneously, fibroblast-like cells outgrew the cultures, which were previously predominated by epithelial-like cells. Polyploidy was found in 0 to 12% of the cells, the highest level existing in the early passages. The question of whether chromosomally abnormal cells present in primary cultures and the early subcultures reflect the karyotype of the fetus is discussed.

Prenatal diagnosis of trisomy 20 mosaicism

Three cases of trisomy 20 mosaicism in amniotic fluid cell cultures are described. Two of the pregnancies resulted in normal full-term infants. The third pregnancy was terminated and revealed a phenotypically normal fetus. A review of five previously reported cases is presented. Explanations of these findings include in vitro nondisjunction, culture of extraembryonic tissue, and true fetal mosaicism. The diagnostic dilemma this presents is discussed.

Three cases of sex chromosome mosaicism with a nonfluorescent Y

Clinical and cytogenetic findings in three patients mosaic for sex chromosomes (45,X0/46,XY; 45,X0/46,XY/46,XYq-, and 45,X0/46,XY/46,XYY), each with a nonfluorescent Y, are presented. Hypotheses for the origin and effect of these chromosome constitutions are discussed.

XO/XY mosaicism and non-fluorescing Y chromosome in a male

An adult male of short stature and with underdeveloped external genitalia is described, who carried out a number of sexual assaults on young women. He proved to have XO/XY mosaicism and a non-fluorescing Y chromosome. It was considered to be a terminal deletion on morphological grounds. It is suggested, on the evidence of the small number of XO/XY mosaics examined by appropriate staining methods, that an abnormal Y chromosome, whether terminally deleted or non-fluorescing owing to an altered chemical state, predisposes to anaphase lagging and non-disjunction. Of eleven reported cases of XO/XY mosaicism with a non-fluorescing Y chromosome, this is the fifth of male phenotype. The severe behaviour disturbance of early onset is considered to be probably causally associated with the chromosome anomaly.

46,XY pure gonadal dysgenesis with non-fluorescent Y chromosome

A 46,XY karyotype with a non-fluorescent Y chromosome was found in an infantile girl aged 16 with primary amenorrhea. Identification of the Y chromosome was made by different staining techniques and a photometric scanning method. The histology of the streak gonad also indicated the Y character of the chromosome. The authors' interpretation is a 46,XY pure gonadal dysgenesis with a non-fluorescent Y chromosome.

Amniotic fluid cell mosaicism for presumptive trisomy 20

Trisomy for an F-like chromosome with banding characteristics of chromosome 20 was observed, respectively, in 25 and 8% of amniotic fluid cell clones in two cases of prenatal diagnosis for advanced maternal age. No such aneuploidy was found upon examination of fetal or postnatal tissues. In both instances there were no detectable malformation. It is suggested that propensity to nondisjunction for an F-like chromosome, not unlike tetraploidy, might be another characteristic of amniotic fluid cells in culture.

Small marker chromosome mosaicism confirmed in two cases ascertained prenatally

Two cases of chromosomal mosaicism were prenatally diagnosed and confirmed in tissues cultured from subsequently aborted fetuses. In both cases a small marker chromosome was observed which proved de novo in origin, since parental chromosomes were normal. The implications and interpretation of such findings in counselling families undergoing amniocenteses is discussed. Mosaicism for small marker chromosomes may be more frequent than hitherto suggested.

Mosaicism in amniotic fluid cell cultures: classification and significance

The last decade has witnessed increasing application of human cytogenetic technology to prenatal chromosome analysis. However, unlike the rather uniform peripheral blood T-lymphocyte system which has provided most of our experience in human cytogenetics, long-term amniotic-fluid cell cultures display extreme cellular heterogeneity and disproportionate growth of certain cell types as a consequence of clonal amplification. When they enter cell culture, many of these cells are approaching the terminal stages of their respective, life spans and may have accumulated chromosomal aberrations. Concern about the possibility of true fetal mosaicism seems warranted chiefly in situations were multiple colonies display potentially viable aberrations. Clonal analysis, preferably of multiple clonal types, and attention to details of clonal morphology are likely to minimize diagnostic errors and undue apprehension resulting from mosaicism in amniotic-fluid cell cultures.

Prenatal cytogenetic diagnosis: first 1,000 successful cases

From February 1969 to August 1976, we studied 1,048 amniotic fluids. Of these, 958 (91.4%) were primarily for prenatal cytogenetic diagnosis. Cytogenetic studies were attempted in 1,021 cases; the diagnosis was successful in 1,000 of these. The failure rate of obtaining a diagnosis from the amniotic fluid cell culture of the first amniocentesis was 5% (50 cases); 29 cases had a repeat tap and successful diagnosis was achieved in all. In 21 cases, a repeat tap was refused. Thus, the overall failure rate of obtaining a final cytogenetic diagnosis was 2.06% (21/1,021). There were 32 fetal losses after amniocentesis including 16 spontaneous second trimester abortions, 7 fetal deaths in utero and 9 stillbirths. In two additional cases, fetal death had occurred before amniocentesis. This number of fetal losses does not exceed the number that would be expected in the same maternal age group without amniocentesis. In our series, the frequencies of trisomy in maternal age groups 40 years and over, 37-39 years, 35-36 years, and under 35 years were 4.5, 3.14, 0 and 0% respectively. These frequencies are comparable to those reported from other prospective prenatal studies and higher than those of retrospective live born studies. Various problems and pitfalls in prenatal cytogenetic diagnosis are discussed.

A survey of amniocentesis in 925 patients at high risk of fetal genetic disorder

Over a nine-year period, 925 pregnancies at an Israeli medical centre were selected for investigation by amniocentesis for genetic reasons. In only 30 pregnancies did failure of laboratory methods or difficulty with amniocentesis lead to a lack of results with which to assess the normality of the fetus. The information obtained by examination of the amniotic fluid in the other 895 pregnancies is presented and discussed.