Transmission of an unbalanced (Y;1) translocation in Brittany, France

Molecular Cytogenetic and Y Copy Number Analysis of a Reciprocal ECAY-ECA13 Translocation in a Stallion with Complete Meiotic Arrest

We present a detailed molecular cytogenetic analysis of a reciprocal translocation between horse (ECA) chromosomes Y and 13 in a Friesian stallion with complete meiotic arrest and azoospermia. We use dual-color fluorescence in situ hybridization with select ECAY and ECA13 markers and show that the translocation breakpoint in ECAY is in the multicopy region and in ECA13, at the centromere. One resulting derivative chromosome, Y;13p, comprises of ECAY heterochromatin (ETSTY7 array), a small single copy and partial Y multicopy region, and ECA13p. Another derivative chromosome 13q;Y comprises of ECA13q and most of the single copy ECAY, the pseudoautosomal region and a small part of the Y multicopy region. A copy number (CN) analysis of select ECAY multicopy genes shows that the Friesian stallion has significantly (p < 0.05) reduced CNs of TSPY, ETSTY1, and ETSTY5, suggesting that the translocation may not be completely balanced, and genetic material is lost. We discuss likely meiotic behavior of abnormal chromosomes and theorize about the possible effect of the aberration on Y regulation and the progression of meiosis. The study adds a unique case to equine clinical cytogenetics and contributes to understanding the role of the Y chromosome in male meiosis.

Telomeric association between chromosomes Y and 19 in a mosaic Turner with primary ovarian insufficiency

A rare case of telomeric association between Y and 19 chromosomes in a 24-year-old patient with primary ovarian insufficiency is being reported. Clinical evaluation revealed a webbed neck, high-arched palate and short stature with absence of axillary hair. Small uterus and streak gonads were noted on pelvic ultrasonography. Cytogenetic analysis showed a mosaic karyotype 46,X,tas(Y;19)(p11.3;q13.4)/45,X with two centromeres on the derivative chromosome. Fluorescence in situ hybridization (FISH) for X and Y centromere, SRY gene and subtelomeric FISH showed that signals for SRY and heterochromatin of Y chromosome were found at the base of chromosome 19 and the subtelomere regions of 19q and Yp were intact. Multiplex polymerase chain reaction was done to check for common microdeletions in AZF region and showed no microdeletion. Due to the presence of Y chromosome, laparoscopic examination followed by gonadal histopathology was done and confirmed the presence of ovotestes. Gonadectomy was performed to avoid future risk of gonadoblastoma. Artificial reproductive techniques using donor oocytes was suggested to the couple.

Localization of the SRY Gene on Chromosome 3 in a Patient with Azoospermia and a Complex Karyotype 45,X/46,X,i(Y)(q10)/46,XX/ 47,XX,i(Y)(q10)

This study aimed to identify the cause of azoospermia in a 38-year-old infertile man who was referred for genetic testing. Cytogenetic evaluation was performed by G-banding, C-banding, and FISH using centromeric probes for chromosomes X and Y and showed the presence of a monocentric isochromosome Y with a complex, mosaic karyotype 45,X/46,X,i(Y)(q10)/46,XX/47,XX,i(Y)(q10). Multiplex PCR for the commonly deleted genes in the AZFa, AZFb, and AZFc regions of the Y chromosome was performed and indicated the presence of all 3 regions. Further, PCR amplification followed by DNA sequencing of the SRY gene was done, which ruled out mutations in that gene. To identify the position of the SRY gene, FISH using a locus-specific probe was used and showed that the gene had been translocated to chromosome 3. Subtelomere FISH for 3q and Yp evidenced that the subtelomeric region of the Y chromosome was found on the terminal region of 3q. The clinical symptoms of the patient can be attributed to this abnormal genotype. The importance of genetic testing in infertile patients and the need for genetic counselling to prevent the transmission of the defect are emphasized.

Characterisation of supernumerary chromosomal markers: a study of 13 cases

Marker chromosomes are defined as 'structurally abnormal chromosomes in which no part can be identified' (ISCN 1995). Supernumerary marker chromosomes (SMC) are 'additional markers' whose origin and composition cannot be determined by conventional cytogenetics. Molecular cytogenetic methods are necessary to identify these additional chromosomal markers. In one third, the SMCs are clinically well-defined in the literature, the remaining two thirds present a major problem for genetic counselling in prenatal diagnosis. At present, different molecular cytogenetic methods are used to determine the origin of SMCs. In this work, we studied 13 SMCs detected by RHG-banding, completed by C-banding and/or NOR-staining. 24-color FISH was used as the primary technique when the chromosomal origin was unknown. Targeted FISH procedures with specific probes (whole chromosome painting, centromeric probe, locus-specific identifier, BAC, etc.) were then performed to confirm and/or specify the chromosomal material present in the SMC. Seven SMCs were found to be associated with phenotypic abnormalities. Five derived from autosomes and two from gonosomes; these are: der(12)t(4;12), dic(15), i(18p), r(19), der(22)t(11;22), r(X), and der(Y). Two markers, r(8) and idic(15), were identified during investigations of infertile couples. Three cases seemed to be phenotypically normal. Four were discovered prenatally: r(2) and r(19) referred for elevated maternal serum markers, der(13/21) referred for advanced maternal age. The fourth SMC, der(14/22), was found during familial investigation following the identification of the same marker in an infertile son. The precise characterisation of the SMCs is of utmost importance for genetic counselling, especially in prenatal diagnosis.

Characterization of a de novo balanced 1;Y translocation in a phenotypically normal twin male infant

OBJECTIVE

To report a translocation between an autosome and the Y chromosome.

DESIGN

Amniocentesis of a fetus because of mother's advanced age followed by karyotype and PCR analysis.

SETTING

Tertiary health center.

PATIENT(S)

A phenotypically normal twin male infant.

INTERVENTION(S)

Karyotype with G and Q banding and amplification of testis-specific protein 1-Y and of azoospermia factor (AZF) a, AZFb, AZFc, and distal AZFc regions of Y chromosome.

MAIN OUTCOME MEASURE(S)

Karyotype, PCR.

RESULT(S)

We report a phenotypically normal twin male infant with de novo 46,ChiY,t(1;Y)(p22;p11) that was found in amniocentesis. In genetic counseling, it was recommended that the fetus be monitored through a detailed prenatal ultrasonographic examination, which did not indicate any pathological findings. A phenotypically normal male baby was born who is now a 12-month-old healthy infant. The karyotype was confirmed in the peripheral blood with G and Q banding. Amplification of testis-specific protein 1-Y, AZFa, AZFb, AZFc, and distal AZFc regions of the Y chromosome did not reveal any deletions.

CONCLUSION(S)

We cannot predict whether this male infant will have oligospermia or azoospermia as an adult and, furthermore, whether in case of fertility there is a risk for unbalanced autosome;Y translocations in the offspring, with congenital malformations and dysmorphic features. This case illustrates the complexities in counseling for prenatally diagnosed de novo autosome;Y translocations and the need for additional cases to be reported.

Prenatal detection of a de novo Yqh-acrocentric translocation

OBJECTIVES

To identify the extra chromosomal material on 46,XX,21p+ for prenatal diagnosis.

DESIGN AND METHODS

Conventional cytogenetic studies using GTG (G bands by trypsin using Giemsa) and CBG (C bands by barium hydroxide using Giemsa) techniques were performed on chromosomes at metaphase obtained from cultured amniocytes and parental blood lymphocytes. Molecular cytogenetic techniques, QF-PCR (quantitative fluorescent polymerase chain reaction), FISH (fluorescent in-situ hybridization), and DA-DAPI (Distamycin A and 4,6-diamino-2-phenylindole) staining, were then used to clarify the extra material present on fetal chromosome 21 p.

RESULTS

The extra material on fetal chromosome 21 p has originated from Yqh, most likely at PAR2 (the secondary pseudoautosomal region). The karyotype should be 46,XX,der(21)t(Y;21)(q12;p13)de novo.ish der(21)t(Y;21)(q12;p13) (EST Cdy16c07+).

CONCLUSION

This case demonstrates the usefulness of molecular techniques in the investigation of rare chromosomal rearrangements.

Unique t(Y;1)(q12;q12) reciprocal translocation with loss of the heterochromatic region of chromosome 1 in a male with azoospermia due to meiotic arrest: a case report

A de novo reciprocal translocation 46,X,t(Y;1)(q12;q12) was found in an azoospermic male with meiotic arrest. Cytogenetics and fluorescent in situ hybridization (FISH) were used to define the karyotype, translocation breakpoints and homologue pairing. SRY (Yp), Yq11.2-AZF regions, DAZ gene copies and the distal Yq12 heterochromatin were studied by PCR and restriction analysis using sequence-tagged sites and single nucleotide variants. High resolution GTL, CBL and DA-DAPI staining revealed a (Y;1) translocation in all metaphases and a normal karyotype in the patient's father. FISH showed the presence of the distal Yq12 heterochromatic region in der(1) and loss of the heterochromatic region of chromosome 1. PCR demonstrated the intactness of the Y chromosome, including the SRY locus, AZF regions, DAZ genes and distal heterochromatin. A significant decrease (P = 0.005) of Xp/Yp pairing (18.6%), as compared with controls (65.7%), was found in arrested primary spermatocytes, and cell culture and mRNA expression studies confirmed an irreversible arrest at meiosis I, with induction of apoptosis and removal of germ cells by Sertoli cells. We characterized a de novo t(Y;1)(q12;q12) balanced reciprocal translocation with loss of the heterochromatic region of chromosome 1, that caused unpairing of sex chromosomes followed by meiosis I arrest, apoptotic degeneration of germ cells and azoospermia.