Pericentric inversion of the Y chromosome and prenatal diagnosis

Chromosomal abnormalities of 19,000 couples with recurrent spontaneous abortions: a multicenter study

OBJECTIVE

To investigate the demographic data and karyotypes of 19,000 couples who experienced recurrent spontaneous abortion (RSA).

DESIGN

A cross-sectional study of 19,000 couples.

SETTING

Five hospitals.

PATIENT(S)

A total of 19,000 couples experiencing RSA.

INTERVENTION(S)

Not applicable.

MAIN OUTCOME MEASURE(S)

Cytogenetic analysis of blood lymphocytes.

RESULT(S)

A total of 844 couples (4.44%) showed chromosomal aberrations in either partner. Females were more likely to have chromosomal aberrations. The mean age of females and males with chromosomal aberrations was younger than that of females and males without chromosomal aberrations. Interestingly, sex and age distribution varied significantly depending on the subtypes of chromosomal aberrations. We detected 324 balanced translocations, including 223 novel ones. They were distributed across all chromosomes; the frequency of balanced translocations decreased according to the numerical order of autosomes (strong negative correlation; r = -0.84). Individuals with balanced translocations were younger than other groups. All 58 inversions, including 25 novel ones, were detected in autosomes; the negative correlation also existed. Thirteen Robertsonian translocations, 5 deletions, and 3 duplications were detected. Six types of Turner variants, triple X mosaicism, and mosaic Down syndrome were detected in females; Klinefelter variants and mosaic XYY syndrome were detected in males. Marker chromosomes at various mosaic levels and 7 different complex chromosomal rearrangements were also observed.

CONCLUSION(S)

Patients who experienced RSA induced by chromosomal aberrations experienced miscarriages at a younger age. Significant correlations existed between the patients' age or sex and the subtypes of chromosomal aberrations. This study detected several chromosomal abnormalities associated with RSA, including various novel aberrations.

Molecular Cytogenetic Characterization of an inv(Y)(p11.2q11.221∼q11.222) in a Syrian Family

Constitutional chromosomal abnormalities are an important cause of miscarriage, infertility, congenital anomalies and mental retardation in humans. Pericentric inversions of the human Y-chromosome [inv(Y)] are rather common and show an estimated incidence of 0.6–1:1,000 in males in the general population. Most of the reported cases with inv(Y) are familial. For carriers of pericentric inversions the risk of mental retardation or multiple abortions is not apparently increased and there is no relation with abnormal phenotypic features. Polymerase chain reaction (PCR) analysis to detect microdeletions along the Y-chromosome as well as cytogenetic and fluorescence in situ hybridization (FISH) analysis were done to delineate the characteristics of an inv(Y) in a Syrian family. Thus, we present a detailed molecular-cytogenetic characterization of a father and his two sons having an inv(Y)(p11. 2q11.221∼q11.222) with varying mental retardation features but otherwise normal phenotype.

Intrachromosomal homologous recombination between inverted amplicons on opposing Y-chromosome arms

Amplicons--large, nearly identical repeats in direct or inverted orientation--are abundant in the male-specific region of the human Y chromosome (MSY) and provide targets for intrachromosomal non-allelic homologous recombination (NAHR). Thus far, NAHR events resulting in deletions, duplications, inversions, or isodicentric chromosomes have been reported only for amplicon pairs located exclusively on the short arm (Yp) or the long arm (Yq). Here we report our finding of four men with Y chromosomes that evidently formed by intrachromosomal NAHR between inverted repeat pairs comprising one amplicon on Yp and one amplicon on Yq. In two men with spermatogenic failure, sister-chromatid crossing-over resulted in pseudoisoYp chromosome formation and loss of distal Yq. In two men with normal spermatogenesis, intrachromatid crossing-over generated pericentric inversions. These findings highlight the recombinogenic nature of the MSY, as intrachromosomal NAHR occurs for nearly all Y-chromosome amplicon pairs, even those located on opposing chromosome arms.

Heterogeneity of pericentric inversions of the human y chromosome

Pericentric inversions of the human Y chromosome (inv(Y)) are the result of breakpoints in Yp and Yq. Whether these breakpoints occur recurrently on specific hotspots or appear at different locations along the repeat structure of the human Y chromosome is an open question. Employing FISH for a better definition and refinement of the inversion breakpoints in 9 cases of inv(Y) chromosomes, with seemingly unvarying metacentric appearance after banding analysis, unequivocally resulted in heterogeneity of the pericentric inversions of the human Y chromosome. While in all 9 inv(Y) cases the inversion breakpoints in the short arm fall in a gene-poor region of X-transposed sequences proximal to PAR1 and SRY in Yp11.2, there are clearly 3 different inversion breakpoints in the long arm. Inv(Y)-types I and II are familial cases showing inversion breakpoints that map in Yq11.23 or in Yq11.223, outside the ampliconic fertility gene cluster of DAZ and CDY in AZFc. Inv(Y)-type III shows an inversion breakpoint in Yq11.223 that splits the DAZ and CDY fertility gene-cluster in AZFc. This inversion type is representative of both familial cases and cases with spermatogenetic impairment. In a further familial case of inv(Y), with almost acrocentric morphology, the breakpoints are within the TSPY and RBMY repeat in Yp and within the heterochromatin in Yq. Therefore, the presence of specific inversion breakpoints leading to impaired fertility in certain inv(Y) cases remains an open question.

Sperm meiotic segregation and aneuploidy in a 46,X,inv(Y),t(10;15) carrier: case report

OBJECTIVE

To analyze the meiotic segregation and an interchromosomal effect in sperm of an inv(Y) (p11.1;q11.2),t(10;15) (q25.2;q12) carrier.

DESIGN

Case report.

SETTING

Research institute.

PATIENT(S)

Man with a karyotype 46,X,inv(Y),t(10;15), normal sperm parameters, and secondary infertility.

INTERVENTION(S)

Multicolor fluorescence in situ hybridization using probes for chromosomes 10, 15, 8, 18, 21, X, and Y.

MAIN OUTCOME MEASURE(S)

Frequencies of meiotic segregation products and aneuploidy of chromosomes 8, 18, 21, X, and Y.

RESULT(S)

The most frequent type of meiotic segregation was the alternate (40.82%), followed by the adjacent 1 (28.09%), adjacent 2 (16.33%), and 3:1 (9.91%) segregations. Neither deviation from the expected 1:1 ratio of the X- and Y-bearing spermatozoa nor any evidence of an interchromosomal effect on aneuploidy of chromosomes X, Y, 8, 18, and 21 and diploidy was observed in the carrier compared with control donors. The disomies of chromosomes 8 and 21 were equally frequent in X- and Y-bearing spermatozoa of the carrier.

CONCLUSION(S)

The fluorescence in situ hybridization analysis of meiotic segregation and aneuploidy helps to personalize the reproductive risk in carriers of balanced structural chromosomal aberrations. Complete information concerning the quality of spermatogenesis is necessary in all donors (both translocation carriers and controls) implicated in interchromosomal effect studies.

Prenatal diagnosis of a familial interchromosomal insertion of Y chromosome heterochromatin

An apparently unbalanced karyotype containing an abnormal chromosome 11 was identified in a 16-week female fetus by analysis of cultured amniocytes. Fluorescence in situ hybridization (FISH) with a chromosome 11 paint identified the presence of an insertion in band 11q24. Parental karyotyping documented an unbalanced karyotype with the same der(11) chromosome in the phenotypically normal father. CBG-banding and FISH identified the insertion to be Yq12 heterochromatin: 46,XY, der(11)ins(11;Y)(q24;q12q12).ish der(11) (wcp11+,DYZ1+). The same der(11) chromosome was also found in the phenotypically normal paternal grandmother, demonstrating this additional Y chromosomal material did not affect normal female sexual development or fertility. The parents elected to continue the pregnancy and a normal girl was born at term, further confirming that this rare familial variant has no clinical significance. This case illustrates the importance of family studies, appropriate banding, and FISH analyses to accurately characterize apparent chromosomal abnormalities.

Molecular cytogenetics: applications in clinical genetics

To illustrate the advantage of fluorescence in situ hybridization (FISH) in clinical genetics, we have chosen six clinical cases from our routine laboratory where we have used molecular cytogenic techniques to optimise the cytogenetic analysis. Using centromere-specific DNA probes and whole chromosome DNA libraries either obtained from somatic cell hybrids or generated from flow-sorted chromosomes, we have been able to identify small marker chromosomes, chromosomal duplications and inversions, to determine the ploidy in interphase nuclei, and to characterize subtle chromosomal translocations. We conclude that molecular cytogenetics is a valuable technique that should be used as a supplement to conventional cytogenetics to reduce the number of unresolved karyotypes in clinical genetics.

Chromosomal polymorphisms of 1, 9, 16, and Y in 4 major ethnic groups: a large prenatal study

Using trypsin Giemsa banding (GTG), major polymorphisms of the constitutive heterochromatin regions of chromosome 1, 9, 16, and Y were recorded in a New York City population. Polymorphisms were recorded from amniotic fluid specimens received from 6,250 patients from 4 major population groups, ie, White (European)-2,334 cases, American Black-1,795 cases, Hispanic descent-1,737 cases, and Asian (Oriental and Indian)-384 cases. The major chromosomal polymorphisms were classified as follows: obvious pericentric inversion of the constitutive heterochromatin of the long arm of the chromosome (inv qh); significantly enlarged heterochromatic region of the long arm (qh + is greater than, or equal to, twice the size of the short arm of chromosome 16 [16p]); very small or deficient heterochromatic region in the long arm (qh-); large Y (Yq + greater than size of chromosome 18), small Y (Yq- less than size of a G-group chromosome), and pericentric inversion of Y. Our prenatal study confirmed that the incidence of specific chromosomal variants is different in each population group. The most striking examples of this are the pericentric inversion of chromosome 9 and the different polymorphisms of the Y chromosome. The incidence of inv (9) is highest in the Black population (3.57%); slightly above average in Hispanics (2.42%); and relatively low in Whites (0.73%) and Asians (0.26%). The Y appears to be more variable in Asian (3.37%) and Hispanic (1.82%) than in White or Black groups. The 9qh+ is seen more frequently than 1qh+, or 16qh+. Inv (1), 9qh-, and 16qh- are rare. There were no cases of either 1qh- or inv (16).(ABSTRACT TRUNCATED AT 250 WORDS)