Risk estimation of uniparental disomy of chromosome 14 or 15 in a fetus with a parent carrying a non-homologous Robertsonian translocation. Should we still perform prenatal diagnosis?

OBJECTIVE: Uniparental disomy (UPD) testing is currently recommended during pregnancy in fetuses carrying a balanced Robertsonian translocation (ROB) involving chromosome 14 or 15, both chromosomes containing imprinted genes. The overall risk that such a fetus presents a UPD has been previously estimated to be around ~0.6-0.8%. However, because UPD are rare events and this estimate has been calculated from a number of studies of limited size, we have reevaluated the risk of UPD in fetuses for whom one of the parents was known to carry a nonhomologous ROB (NHROB). METHOD: We focused our multicentric study on NHROB involving chromosome 14 and/or 15. A total of 1747 UPD testing were performed in fetuses during pregnancy for the presence of UPD(14) and/or UPD(15). RESULT: All fetuses were negative except one with a UPD(14) associated with a maternally inherited rob(13;14). CONCLUSION: Considering these data, the risk of UPD following prenatal diagnosis of an inherited ROB involving chromosome 14 and/or 15 could be estimated to be around 0.06%, far less than the previous estimation. Importantly, the risk of miscarriage following an invasive prenatal sampling is higher than the risk of UPD. Therefore, we do not recommend prenatal testing for UPD for these pregnancies and parents should be reassured.

Application of a new molecular technique for the genetic evaluation of products of conception.

OBJECTIVES: Karyotyping is a well-established method of investigating the genetic content of product of conceptions (POCs). Because of the high rate of culture failure and maternal cell contamination, failed results or 46,XX findings are often obtained. Different molecular approaches that are not culture dependent have been proposed to circumvent these limits. On the basis of the robust experience previously obtained with bacterial artificial chromosomes (BACs)-on-Beads™ (BoBs™), we evaluated the same technology that we had used for the analysis of prenatal samples on POCs. METHOD: KaryoLite™ BoBs™ includes 91 beads, each of which is conjugated with a composite of multiple neighboring BACs according to the hg19 assembly. It quantifies proximal and terminal regions of each chromosome arm. The study included 376 samples. RESULTS: The failure rate was 2%, and reproducibility >99%; false-positive and false-negative rates were <1% for non-mosaic aneuploidies and imbalances effecting all three BACs in a contig. Detection rate for partial terminal imbalances was 65.5%. The mosaic detection threshold was 50%, and the success rate in macerated samples was 87.8%. The aneuploidy detection rate in samples with cell growth failure was 27.8%, and maternal cell contamination was suspected in 23.1% of 46,XX cultured cells. CONCLUSION: KaryoLite™ BoBs™ as a 'first-tier' test in combination with other approaches showed beneficial, cost-effective and clearly enhanced POC testing.

Prenatal BACs-on-Beads™: the prospective experience of five prenatal diagnosis laboratories.

OBJECTIVE: We previously reported on the validation of Prenatal BACs-on-Beads™ on retrospectively selected and prospective prenatal samples. This bead-based multiplex assay detects chromosome 13, 18, 21 and X/Y aneuploidies and the nine most frequent microdeletion syndromes. We demonstrated that Prenatal BACs-on-Beads(TM) is a new-generation, prenatal screening tool. Here, we describe the experience of five European prenatal diagnosis laboratories concerning the ongoing use of Prenatal BACs-on-Beads™ . METHODS: Some 1653 samples were analyzed. All results were confirmed by conventional karyotyping or another appropriate technique. All indications for invasive prenatal diagnosis were included. Amniotic fluid and chorionic villus samples were analyzed in equivalent proportions. RESULTS: The failure rate was 3.3% and the overall abnormality detection rate was ~1/10. Eighty-five percent of the detected abnormalities were common aneuploidies. Eleven microdeletions and duplications were identified, thus giving an overall yield for microdeletion and microduplication detection of 1/145. Compared with QF-PCR, Prenatal BACs-on-Beads™ provides an additional detection rate of ~1/250 for low-risk pregnancies. The false positive and negative rates were both <1%. CONCLUSION: When associated with conventional karyotyping, the Prenatal BACs-on-Beads™ assay combines a short turnaround time (typical of rapid aneuploidy detection tests) with valuable detection of the most frequent microdeletion syndromes that cannot be detected in cytogenetic analyses.

Meiotic segregation of X-autosome translocation in two carriers and implications for assisted reproduction.

The aim of this study was to analyse and compare the meiotic segregation of X-autosome translocation in two male carriers and to discuss couple-specific treatment modality before intracytoplasmic sperm injection (ICSI). Meiotic segregation was analysed by fluorescence in-situ hybridization (FISH) in spermatozoa of two men who were carriers of a X-autosome translocation: 46,Y,t(X;2)(p21;p25.3) (patient 1) and 46,Y,t(X;18)(qll;pl1.1) (patient 2). The results indicated a majority of unbalanced spermatozoa (62.05%) for patient 1, but normal or balanced spermatozoa (54.36%) for patient 2. Moreover, the unbalanced gametes resulted from adjacent I, adjacent II and 3:1 segregation, in decreasing frequencies, for patient 1 but from 3:1, adjacent I, adjacent II segregation for patient 2. The results of the meiotic segregation analysis had different treatment implications for assisted reproduction. Couple 1 were advised against ICSI, due to the results of the meiotic segregation in spermatozoa from patient 1 and the age of his wife. For couple 2, the clinic viewed favourably an attempt with ICSI followed by conventional prenatal diagnosis. A 46,XY child was born without malformations.

The high frequency of sperm aneuploidy in klinefelter patients and in nonobstructive azoospermia is due to meiotic errors in euploid spermatocytes.

For nonobstructive azoospermic (NOA) patients with a normal karyotype or for Klinefelter syndrome (47,XXY) patients, intracytoplasmic sperm injection is associated with an increased aneuploidy risk in offspring. We examined testicular cells from patients with different azoospermia etiologies to determine the origin of the aneuploid spermatozoa. The incidence of chromosome abnormalities was investigated in all types of azoospermia. Four study subgroups were constituted: Klinefelter patients (group 1), NOA patients with spermatogenesis failure but a normal karyotype (group 2), obstructive azoospermic patients with normal spermatogenesis (group 3), and control patients with normal sperm (group 4). The pachytene stage (in the three azoospermic groups) and postmeiotic cells (in all groups) were analyzed with fluorescence in situ hybridization. No aneuploid pachytene spermatocytes were observed. Postmeiotic aneuploidy rates were higher in the two groups with spermatogenesis failure (5.3% and 4.0% for groups 1 and 2, respectively) than in patients with normal spermatogenesis (0.6% for group 3 and group 4). Whatever the etiology of the azoospermia, the spermatozoa originated from euploid pachytene spermatocytes. These results strengthen the hypothesis whereby sperm aneuploidy in both Klinefelter patients and NOA patients with a normal karyotype results from meiotic abnormalities and not from aneuploid spermatocytes. The fact that sperm aneuploidy was more frequent when spermatogenesis was altered suggests a deleterious testicular environment. The study results also provide arguments for offering preimplantation genetic diagnosis or prenatal diagnosis when a pregnancy occurs for fathers with NOA (whatever the karyotype).

The chromosomal risk in sperm from heterozygous Robertsonian translocation carriers is related to the sperm count and the translocation type.

OBJECTIVE: To study the chromosomal risk in sperm from Robertsonian translocation (RobT) carriers as a function of the sperm count and translocation type. DESIGN: Prospective study. SETTING: Departments of reproductive biology, cytogenetics, gynecology, and obstetrics. PATIENT(S): A total of 29 RobT patients (8 normozoospermic and 21 oligozoospermic) and 20 46,XY patients (10 normozoospermic and 10 oligozoospermic). INTERVENTION(S): Sperm fluorescence in situ hybridization with probes for translocation malsegregation and chromosome 13, 18, 21, X, and Y probes for studying the interchromosomal effect (ICE). MAIN OUTCOME MEASURE(S): Translocation malsegregation and ICE aneuploidy rates. RESULT(S): In RobT carriers, the sperm translocation malsegregation rate was significantly lower in normozoospermic patients (9.7%) than in oligozoospermic patients (18.0%). Considering only oligozoospermic patients, sperm malsegregation rates were significantly lower for rob(14;21) than for rob(13;14) (11.4% vs. 18.9%). In turn, the rates were significantly lower for rob(13;14) than for rare RobTs (18.9% vs. 25.3%). In sperm from normozoospermic RobT, an ICE was suggested by higher chromosome 13 and 21 aneuploidy rates than in control sperm. Conversely, chromosome 13 and 21 sperm aneuploidy rates were lower in oligozoospermic RobT patients than in oligozoospermic 46,XY patients, but higher than in control subjects. CONCLUSION(S): Both translocation type and sperm count influence the RobT malsegregation risk. Of the chromosomes analyzed (13, 18, 21, X, and Y), only chromosomes 13 and 21 were found to be associated with an ICE. Relative to the RobT effect, idiopathic alterations in spermatogenesis in 46,XY patients appear to be more harmful for meiosis.

Sperm chromosome analysis of an infertile patient with a 95% mosaic r(21) karyotype and normal phenotype.

OBJECTIVE: To examine sperm meiotic segregation in a man with mosaic ring chromosome 21. DESIGN: Case report. SETTING: Hospital departments of reproductive biology, cytogenetics, gynecology, and obstetrics. PATIENT(S): One patient referred for cryptozoospermia, heterozygous for a ring chromosome. INTERVENTION(S): Fluorescence in situ hybridization with chromosome 21-specific probes after sperm selection. RESULT(S): A total of 169 spermatozoa were selected; 92.3% carried a normal 21 chromosome, 6.5% the ring chromosome, and 1.2% both. CONCLUSION(S): Ring chromosome frequency in mature sperm cells was low and may be due to preferential meiosis of normal spermatogonia,which could explain the cryptozoospermia and unexpected ratio in this case.

Is classic pericentric inversion of chromosome 2 inv(2)(p11q13) associated with an increased risk of unbalanced chromosomes?

OBJECTIVE: To study pericentric inversion segregation and interchromosomal effect on sperm for men heterozygous for inv(2)(p11q13), to assess the risk of miscarriage. DESIGN: Case report. SETTING: Department of reproductive biology, cytogenetics, gynecology, and obstetrics. PATIENT(S): Seven patients heterozygous for inv(2)(p11q13) and five patients with normal karyotype with experience of recurrent spontaneous miscarriage. INTERVENTION(S): Fluorescence in situ hybridization on sperm with 2 p and 2q subtelomeric probes to screen for inversion segregation, and X, Y, and 18 centromeric probes to study interchromosomal effects. One thousand sperm were analyzed per experiment and per patient. MAIN OUTCOME MEASURE(S): Rate of unbalanced chromosomes and aneuploid sperm. RESULT(S): The inv(2)(p11q13) patients showed a 0.3% rate of sperm with unbalanced chromosomes. For interchromosomal effects, a 0.6% aneuploid sperm rate was observed for patients heterozygous for inv(2)(p11q13). This is similar to the 0.5% rate observed for control patients. CONCLUSION(S): Inv(2)(p11q13) seems not to increase miscarriage for couples with men heterozygous for this inversion.

Prenatal diagnosis of de novo (7;19)(q11.2;q13.3) translocation associated with a thick corpus callosum and Wilms tumor of the kidneys.

We present a case of prenatal diagnosis of a de novo (7;19)(q11.2;q13.3) translocation associated with ultrasound features, including enlarged cisterna magna, normal vermis, thick corpus callosum, micrognathia, small and low-set ears and right hyperechogenic kidney. Karyotyping was performed at 24 weeks of gestation. Termination of pregnancy was accepted at the parents' request. Postmortem examination confirmed the prenatal findings, but revealed bilateral Wilms tumors of the kidneys. Parental karyotype was normal.