Added value of buccal cell FISH analysis in the diagnosis and management of Turner syndrome

STUDY QUESTION

Is there an added diagnosis value of buccal cell FISH analysis compared with blood lymphocyte chromosomal investigations in patients with Turner syndrome (TS)?

SUMMARY ANSWER

Buccal cell FISH analysis, a non-invasive technique, modified the chromosomal results obtained with the blood karyotype in 17 patients (12%) of our cohort.

WHAT IS KNOWN ALREADY

Few studies have evaluated buccal cell FISH analysis and compared them with blood karyotype in patients with TS.

STUDY DESIGN, SIZE, DURATION

A prospective, monocentric cohort study was conducted in a rare diseases centre (CMERC) between July 2017 and August 2019.

PARTICIPANTS/MATERIALS, SETTING, METHODS

In total, 142 adult patients with TS, and at least 5% 45,X cells in a previous blood karyotype, were recruited. All the patients' files were included in the CEMARA database. This national database has been declared to the French data protection agency (CNIL approval number 1187326). In compliance with French law, consent regarding non-opposition to collect and use the data was obtained from each patient. A FISH analysis on a buccal smear was performed.

MAIN RESULTS AND THE ROLE OF CHANCE

The percentage of 45,X cells was identical between the two tissues in only 32.4% of cases. The discrepancy was higher than 41% for 12% of the cohort. The percentage of 45,X cells was higher in blood in 53 (37.3%) patients, and higher in buccal cells in 43 (30.3%) of cases. In 17 (12%) cases, the blood karyotype had to be reconsidered in regard to the buccal cell analysis.

LIMITATIONS, REASONS FOR CAUTION

It would have been interesting to evaluate karyotypes in cells from other tissues such as cells from skin biopsy or from the urinary tract and even from blood vessels or gonads in case of surgery and to compare them with each patient's phenotype. However, most of the time, these tissues are not available.

WIDER IMPLICATIONS OF THE FINDINGS

Although blood lymphocyte karyotype remains the gold standard for the diagnosis of TS, buccal cell FISH analysis is an efficient tool to evaluate the global chromosomal constitution in these patients, thus allowing them to have better care and follow-up. For instance, identifying a Y chromosome can prevent the occurrence of a gonadoblastoma, as gonadectomy should be discussed. On the other hand, finding normal XX cells in a patient with a previous diagnosis of homogenous 45,X TS, may be psychologically helpful and relevant for gynaecological care.

STUDY FUNDING/COMPETING INTEREST(S)

No specific funding was sought for the study. The authors declare no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Impact on testicular function of a single ablative activity of 3.7 GBq radioactive iodine for differentiated thyroid carcinoma

STUDY QUESTION

What are the consequences of radioactive iodine (RAI) therapy for testicular function?

SUMMARY ANSWER

A single activity of 3.7 GBq RAI for differentiated thyroid carcinoma (DTC) treatment in young men transiently altered Sertoli cell function and induced sperm chromosomal abnormalities.

WHAT IS KNOWN ALREADY

Few studies, mainly retrospective, have reported the potential impacts of RAI on endocrine and exocrine testicular function.

STUDY DESIGN, SIZE, DURATION

A longitudinal prospective multi-center study on testicular function performed in DTC patients before a single 131I ablative activity of 3.7 GBq (V0) and at 3 months (V3) and 13 months (V13) after treatment.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Forty male patients, aged 18-55 years, with DTC participated. Hormonal analysis included FSH, LH, testosterone and inhibin B serum levels at V0, V3 and V13. Furthermore, sperm parameters, DNA fragmentation and sperm chromosomal abnormalities were evaluated at each time points. The differences in all parameters, between V0-V3, V0-V13 and V3-V13, were analyzed, using a Wilcoxon test.

MAIN RESULTS AND THE ROLE OF CHANCE

Prior to RAI administration, all patients had normal gonadal function. At V3, a statistically significant increase in FSH levels and a decrease in inhibin B levels were observed and sperm concentration, as well as the percentage of morphologically normal spermatozoa, were significantly decreased (P < 0.0001). These modifications were transient as both sperm concentration and normal morphology rate returned to baseline values at V13. However, at this later time point, FSH and inhibin B levels were still impacted by RAI administration but remained in the normal range. Although no DNA fragmentation was observed at V3 nor V13, our study revealed a statistically significant increase in the number of sperm chromosomal abnormalities both at V3 (P < 0.001) and V13 (P = 0.01).

LIMITATIONS, REASONS FOR CAUTION

Among the 40 patients included in the study, only 24 had all the parameters available at all visits.

WIDER IMPLICATIONS OF THE FINDINGS

Prospective studies with longer term follow up would be helpful to determine whether the chromosome abnormalities persist. These studies would be required before sperm banking should be suggested for all patients. However, sperm preservation for DTC patients who require cumulative radioiodine activities higher than 3.7 GBq should be proposed.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the Programme Hospitalier de Recherche Clinique, AP-HP (No. P040419). The authors report no conflict of interest in this work.

TRIAL REGISTRATION NUMBER

NCT01150318.

Deletion of CPEB1 Gene: A Rare but Recurrent Cause of Premature Ovarian Insufficiency

CONTEXT

Premature ovarian insufficiency (POI) may be secondary to chemotherapy, radiotherapy, or environmental factors. Genetic causes are identified in 20-25% of cases, but most POI cases remain idiopathic.

OBJECTIVE

This study aimed to identify new genes involved in POI and to characterize the implication of CPEB1 gene in POI.

DESIGN AND SETTING

This was a case report and cohort study replicate conducted in academic medical centers.

PATIENTS AND METHODS

A deletion including CPEB1 gene was first identified in a patient with primary amenorrhea. Secondly, 191 sporadic POI cases and 68 familial POI cases were included. For each patient, karyotype was normal and FMR1 premutation was excluded. Search for CPEB1 deletions was performed by quantitative multiplex PCR of short fluorescent fragments or DNA microarray analysis. Gene sequencing of CPEB1 was performed for 95 patients.

RESULTS

We identified three patients carrying a microdeletion in band 15q25.2. The proximal breakpoint, for the three patients, falls within a low-copy repeat region disrupting the CPEB1 gene, which represents a strong candidate gene for POI as it is known to be implicated in oocyte meiosis. No mutation was identified by sequencing CPEB1 gene. Therefore, heterozygous deletion of CPEB1 gene leading to haploinsufficiency could be responsible for POI in humans.

CONCLUSION

Microdeletions of CPEB1 were identified in 1.3% of patients with POI, whereas no mutation was identified. This microdeletion is rare but recurrent as it is mediated by nonallelic homologous recombination due to the existence of low-copy repeats in the region. This result demonstrates the importance of DNA microarray analysis in etiological evaluation and counseling of patients with POI.

Fourth case of cerebral, ocular, dental, auricular, skeletal syndrome (CODAS), description of new features and molecular analysis

Cerebral, ocular, dental, auricular, skeletal syndrome (CODAS, OMIM 600373) is a very rare congenital malformation syndrome. This clinical entity is highly distinctive and associates mental retardation, cataract, enamel abnormalities, malformations of the helix, epiphyseal and vertebral malformations, and characteristic dysmorphic features. Since 1991, only three affected children have been reported. The etiology and pattern of inheritance of CODAS syndrome still remain unknown. We describe a new sporadic case presenting with all the characteristic features of CODAS syndrome associated with previously unreported malformations of the heart, larynx, and liver. All investigations such as karyotype, metabolic screening and array CGH were normal.

Underlying karyotype abnormalities in IVF/ICSI patients

Cytogenetic investigations are performed in couples asking for IVF or intracytoplasmic sperm injection (ICSI) treatment. These serve a diagnostic purpose because male or female infertility might have a chromosomal origin. Chromosomal aberrations found in these patients include numerical abnormalities, such as Klinefelter syndrome, XYY karyotype or Turner syndrome and its variants; sex reversions, such as XX males or XY females; and also structural abnormalities, such as Robertsonian or reciprocal translocations and inversions. Finding the chromosomal origin of infertility in a patient also has a prognostic value because it aids the management of pregnancies obtained after IVF or ICSI and may lead to a proposal of prenatal or preimplantation genetic diagnosis.

Mutations in the protamine 1 gene associated with male infertility

In elongating spermatids, human sperm chromatin undergoes a complex compaction in which the transition proteins are extensively replaced by the protamine proteins. Several human studies demonstrate that expression of the protamine proteins is altered in some men with male infertility. For this study, we screened the PRM1 (protamine 1) gene for mutations in a large cohort of 281 men seeking infertility treatment. We identified the c.102G>T transversion that results in an p.Arg34Ser amino acid change in two men. One of these patients presented with oligozoospermia associated with increased sperm DNA fragmentation. The second individual was normospermic but together with his partner sought treatment for idiopathic couple infertility. We also identified a novel missense mutation (c.119G>A, p.Cys40Tyr) in a man with oligoasthenozoospermia. These mutations were not observed in control populations. Interestingly, we also detected variants both 5' and 3' to the PRM1 open-reading frame specifically in infertile individuals. Four individuals with unexplained severe oligozoospermia were heterozygote for a c.-107G>C change that is located at -15 bp from the transcription initiation site of the gene. This mutation may influence PRM1 expression. In addition, a c.*51G>C variant was detected in the 3'UTR of PRM1 specifically in a man with severe oligoasthenozoospermia.

Sperm-FISH analysis in a pericentric chromosome 1 inversion, 46,XY,inv(1)(p22q42), associated with infertility

No phenotypic effect is observed in most inversion heterozygotes. However, reproductive risks may occur in the form of infertility, spontaneous abortions or chromosomally unbalanced children as a consequence of meiotic recombination between inverted and non-inverted chromosomes. An odd number of crossovers within the inverted segment results in gametes bearing recombinant chromosomes with a duplication of the region outside of the inversion segment of one arm and a deletion of the terminal segment of the other arm [dup(p)/del(q) and del(p)/dup(q)]. Using fluorescence in-situ hybridization (FISH), the chromosome segregation of a pericentric inversion of chromosome 1 was studied in spermatozoa of a inv(1)(p22q42) heterozygous carrier. Three-colour FISH was performed on sperm samples using a probe mixture consisting of chromosome 1p telomere-specific probe, chromosome 1q telomere-specific probe and chromosome 18 centromere-specific alpha satellite DNA probe. The frequency of the non-recombinant product was 80.1%. The frequencies of the two types of recombinants carrying a duplication of the short arm and a deletion of the long arm, and vice versa, were respectively 7.6 and 7.2%, and these frequencies were not statistically significant from the expected ratio of 1:1. Sperm-FISH allows the further understanding of segregation patterns and their effect on reproductive failure and allows an accurate genetic counselling.

Haplotypes, mutations and male fertility: the story of the testis-specific ubiquitin protease USP26

Recently, mutations in the X-linked ubiquitin protease 26 (USP26) gene have been proposed to be associated with male infertility. In particular a 371insACA, 494T>C and 1423C>T haplotype, which results in a T123-124ins, L165S and H475Y amino acid change respectively, has been reported to be associated with Sertoli cell-only syndrome (SCOS) and an absence of sperm in the ejaculate. Here, we demonstrate that two of these changes actually correspond to the ancestral sequence of the gene and that the USP26 haplotype is present in significant frequencies in sub-Saharan African and South and East Asian populations, including in individuals with known fertility. This indicates that the allele is not associated with infertility. The pattern of frequency distribution of the derived haplotype (371delACA, 494T), which is present at high frequencies in most non-African populations could be interpreted as either a result of migration followed by simple genetic drift or alternatively as positive selection acting on the derived alleles. The latter hypothesis seems likely, because there is evidence of strong positive selection acting on the USP26 gene.

Identification of transcripts by macroarrays, RT–PCR and in situ hybridization in human ejaculate spermatozoa

Round spermatids contain high levels of extremely varied mRNAs that are synthesized either throughout early spermatogenesis or during spermiogenesis from the haploid genome. Concomitantly, with major changes in the chromatin organization, arrest of transcription occurs at midspermiogenesis. However, previous investigations using RT-PCR have revealed the persistence of numerous and different transcripts in ejaculated spermatozoa. In the present study, a step-by-step analysis by means of macroarray hybridization, RT-PCR and in situ hybridization was performed to identify more accurately the different mRNA species found in the human ejaculated spermatozoa. The data showed an extended pattern of various transcripts encoding a diverse range of proteins involved in signal transduction and cell proliferation. For the first time, they demonstrated that mRNAs coding for the transcription factors NFkappaB, HOX2A, ICSBP, protein kinase JNK2, growth factor HBEGF and receptors RXRbeta and ErbB3 accumulate within the sperm nucleus. The origin and fate of the sperm transcripts remain subject to discussion.

Is the CAG repeat of mitochondrial DNA polymerase gamma (POLG) associated with male infertility? A multi-centre French study

BACKGROUND

Recent data emphasized the implication of polymerase gamma (POLG) CAG repeats in infertility, making it a very attractive gene for study. A comparison of POLG CAG repeats in infertile and fertile men showed a clear association between the absence of the usual 10-CAG allele and male infertility, excluding azoospermia. It has also been suggested that the POLG gene polymorphism should be considered as a possible contributing factor in unexplained couple infertility where semen parameters are normal. In this study, we investigated the POLG CAG repeats, in a well-defined population of patients with severe male factor infertility.

METHODS

We conducted a large study of POLG CAG repeats in 433 infertile and 91 fertile, normozoospermic and healthy males. In all subjects, phenotypic data, including semen parameters, hormonal status and clinical profiles, were available.

RESULTS

Thirteen 'homozygous mutants' (3%) were found among the 433 idiopathic infertile patients. The follow-up of the 13 'homozygous mutant' resulted in pregnancy for more than half of the couples, through assisted reproductive techniques or even spontaneously. In addition, one 'homozygous mutant' was identified in 91 fertile men (1.1%)

CONCLUSION

Under our conditions, our study does not confirm any relationship between the polymorphic CAG repeat in the POLG gene and male infertility.

[The future of cytogenetics after the sequencing of the human genome]

Since the fundamental discovery in 1956 that normal human cell contain 46 chromosomes, human cytogenetics has been transformed by technological advance that have greatly improved resolution and sensibility, first with the introduction of banding and high resolution technologies and, latter, with the fluorescent in situ hybridization (FISH). These latest technique allow to detect extremely subtle alterations in chromosome constitution and had made possible to evaluate the karyotype of non-dividing cells. The latest transformation of cytogenetics came with the technique of comparative genome hybridization which allows genome-wide screens for the loss or gain of chromosomal material in test samples relative to normal controls. Nevertheless, only the conventional cytogenetics techniques are able to detect balanced chromosomals rearrangements particularly in phenotypically abnormal patients in whom candidate genes may be disrupted or functionally altered. Thus, Cytogenetics will still play a central role in our understanding of the molecular basis of human hereditary diseases.

Structural chromosomal mosaicism and prenatal diagnosis

True structural chromosomal mosaicism are rare events in prenatal cytogenetics practice and may lead to diagnostic and prognostic problems. Here is described the case of a fetus carrying an abnormal chromosome 15 made of a whole chromosome 2p translocated on its short arm in 10% of the cells, in association with a normal cell line. The fetal karyotype was 46,XX,add(15)(p10).ish t(2;15)(p10;q10)(WCP2+)[3]/46,XX[27]. Pregnancy was terminated and fetus examination revealed a growth retardation associated with a dysmorphism including dolichocephaly, hypertelorism, high forehead, low-set ears with prominent anthelix and a small nose, which were characteristic of partial trisomy 2p. Possible aetiologies for prenatal mosaicism involving a chromosomal structural abnormality are discussed.

[Genetic origin of spermatogenesis impairments: clinical aspects and relationships with mouse models of infertility]

Human spermatogenesis failures appear frequently as idiopathic and may be due to genetic causes. Mutations of genes involved in the hypothalamic/pituitary control of spermatogenesis have been described and account for several types of hypogonadotropic hypogonadism. Chromosomal abnormalities found in infertile patients are either gonosomal aneuploidies or structural anomalies which interfere with the normal chromosome behaviour at meiosis and lead to germ cell breakdown. Microdeletions of the Y chromosome are often undetectable at karyotype and are responsible for the loss of genes which compose the AZF factor. The increase in the number of mouse models of infertility will allow the description of many human genes involved in the spermatogenesis process provided that a detailed analysis of their genotype-phenotype relationships is performed.

Lack of submicroscopic rearrangements involving telomeres in reproductive failures

BACKGROUND

It has been recognized that chromosomal abnormalities are one of the most important causes of the high mortality rate in human concepti. Among these abnormalities, the unbalanced transmission of a parental chromosomal rearrangement is frequently observed, and couples with a history of pregnancy losses are therefore referred for genetic counselling and to establish their karyotype. Unbalanced chromosomal rearrangements involving telomeres are emerging as an important cause of mental retardation and/or congenital malformations in humans. As suggested by several authors, they could also be responsible for recurrent miscarriages. The aim of this study was to screen cryptic chromosome abnormalities in couples referred to our laboratory for recurrent unexplained miscarriages.

METHODS AND RESULTS

Karyotyping was performed in 57 couples (114 patients). A detectable chromosomal abnormality was diagnosed in seven cases, thus limiting the analysis of telomeres to only 100 patients. Two different protocols were used according to the number of metaphases on slides. No telomeric chromosome abnormality was detected in our study.

CONCLUSION

The use of FISH telomeric probes is not of clinical interest in the systematic screening of couples with multiple miscarriages and should be performed only in those with a familial history of mental retardation and congenital malformations.

French multi-centric study of 2000 amniotic fluid interphase FISH analyses from high-risk pregnancies and review of the literature

This prospective and multi-centric study confirms the accuracy and the limitations of interphase FISH and shows that any cytogenetics laboratory can perform this technique. With regard to the technical approach, we think that slides must be examined by two investigators, because the scoring may be subjective. The main problem with the AneuVysion kit concerns the alpha satellite probes, and especially the chromosome 18 probe, which is sometimes very difficult to interpret because of the high variability of the size of the spots, and this may lead to false negative and uninformative cases. The best solution would be to replace these probes by locus-specific probes. Concerning clinical management, we offer interphase FISH only in very high-risk pregnancies or/and at late gestational age because of the cost of the test. We think that an aberrant FISH result can be used for a clinical decision when it is associated with a corresponding abnormal ultrasound scan. In other cases, most of the time, we prefer to wait for the standard karyotype.

Accumulation of transcripts in the mature human sperm nucleus: implication of the haploid genome in a functional role

The existence of sperm-specific transcripts has been suggested by a number of studies performed both in man and rodents but their origin and role are not yet elucidated. For evaluating the functional significance of these mRNAs, transcripts coding for proteins expressed during spermiogenesis or potentially implicated in the early steps of zygote development, have been searched in human testis and sperm cells by RT-PCR. Furthermore their localization in spermatozoa has been checked by in situ hybridization. Our results confirm the presence of basic nucleoproteins (Transition proteins 1 and 2, Protamines 1 and 2) spermatozoal transcripts which probably represent remnants of previous transcription. They also reveal the existence of sperm specific mRNAs coding for the transcription factor Stat 4, the cyclin B1 and for the testicular isozyme of the angiotensin converting enzyme ACE. On the contrary, mRNAs coding for the heat shock protein Hsp 70 have been found in testis but not in spermatozoa. The possible roles of these transcripts either during the fertilization process or in zygote are discussed.

Electron microscopic in situ hybridization study of simultaneous expression of TNP1 and PRM1 genes in human spermatids

Nuclear changes in the basic nucleoprotein complement occur during human spermiogenesis. Somatic type histones are displaced by transition proteins which are replaced themselves by protamines, the major nuclear proteins found in late spermatids and spermatozoa nuclei. Digoxigenin or Biotin labeled probes, coding respectively for human transition protein 1 (TP1) and protamine 1 (HP1), were used for double EM in situ hybridization. Immunodetection of hybrids with specific antibodies coupled to colloidal gold particles of different size (10 nm and 15 nm) was performed on the same preparations. Quantitative analysis of the nuclear and cytoplasmic labeling densities for the mRNAs coding for TP1 and HP1 showed the presence of transcripts in both the nucleus and cytoplasm of round spermatids until the elongation phase. Transcripts accumulated in the spermatid cytoplasm without any particular cellular compartmentalization. At the end of the spermatid elongation phase, the disappearing of TP1 and HP1 transcripts may be related to the arrest of transcriptional activity while the deposition of transition proteins and protamines successively occurs within spermatid nuclei.

Expression of the TAR RNA binding protein in human testis

In testis, several RNA binding proteins have been shown to play a role in the translational regulation of specific transcripts. The human protein TRBP (TAR RNA binding protein) is the homologue of the mouse Prbp (Prm-1 RNA binding protein) involved in the protamine mRNA translational delay. TRBP is known to activate the HIV-1 long terminal repeat but this protein has never been investigated during spermatogenesis. The aim of this work was to analyse the TRBP expression in human testis. By Northern blot analysis, we demonstrated a major 1.5 kb transcript present at a high level in human testis and, to a lesser extent, in some other tissues. In-situ hybridization revealed that this transcript was present only in elongating spermatids. Antibodies raised against a 27 amino acid TRBP-specific peptide revealed a single protein of 43 kDa expressed in the cytoplasm of elongated spermatids. At the ultrastructural level, quantitative analysis of both TRBP mRNA and protein, using electron microscopy in-situ hybridization and immunocytochemistry, showed that TRBP is expressed mainly in spermatids at steps 3-4 of spermiogenesis. These results are in agreement with the probable role of TRBP in the control of human protamine mRNA translation.

Acrocentric chromosome polymorphisms: beware of cryptic translocations

Cryptic translocations may escape diagnosis, especially when they implicate chromosomal regions that are known to be polymorphic in the human karyotype. We describe a case of postnatal diagnosis of Beckwith-Wiedemann syndrome (BWS) due to an unbalanced translocation that had not been diagnosed in the fetal karyotype. This first cytogenetic analysis revealed that one chromosome 14 presented as a common acrocentric short arm polymorphism. Further analyses after birth, using C-banding, NOR staining and fluorescence in situ hybridization (FISH) with telomeric probes, revealed that it was the result of an unbalanced de novo t(11;14)(p15;p13) translocation leading to partial 11p trisomy and to BWS. Prenatal cytogenetic management of such apparently inoffensive chromosome markers is discussed.

Chromosomal factors of infertility in candidate couples for ICSI: an equal risk of constitutional aberrations in women and men

To assess the frequency of chromosomal aberrations in French candidates for intracytoplasmic sperm injection (ICSI), and to explore the existence of a female chromosomal factor in some cases of couple infertility, a collaborative retrospective clinical and cytogenetic study was performed, launched by the Association des Cytogénéticiens de Langue Franciaise (ACLF). The karyotypes of 3208 patients [2196 men (68.4%), 1012 (31.6%) women] included in ICSI programmes over a 3-year period in France were collected. A total of 183 aberrant karyotypes was diagnosed, corresponding to an abnormality frequency of 6.1% (134/2196) for men and 4.84% (49/1012) for women. The following frequencies of abnormalities were observed respectively for men and women: 1.23% (n = 27) and 0.69% (n = 7) for reciprocal translocations, 0.82% (n = 18) and 0.69% (n = 7) for Robertsonian translocations, 0.13% (n = 3) and 0.69% (n = 7) for inversions, 3.32% (n = 73) and 2.77% (n = 28) for numerical sex chromosome aberrations, and 0.59% (n = 13) and 0% for other structural aberrations. Among the male patients of this latter group, 0.40% (n = 9) had a Y chromosome abnormality. Among the male patients with numerical sex chromosome abnormalities, 2.23% (n = 49) were 47,XXY, 0.32% (n = 7) were 47,XYY, and 0.77% (n = 17) had a mosaicism for numerical sex chromosome anomalies. All the female patients with sex chromosome abnormalities (2.77%, n = 28) had mosaicism for numerical sex chromosome anomalies. Even if these cases-the significance of which was sometimes questioned-were disregarded in the analysis, 2.08% (21/1012) of abnormal karyotypes remained in women. An overall increased frequency of chromosomal aberrations was found, and this confirmed that in some cases of poor reproductive outcome there may be a contribution of maternal chromosome aberrations. Indeed, the existence of a chromosome abnormality in the female partner was associated with the group of infertile men in which there was no apparent cause of infertility.

Sex chromosome mosaicism in males carrying Y chromosome long arm deletions

Microdeletions of the long arm of the Y chromosome (Yq) are a common cause of male infertility. Since large structural rearrangements of the Y chromosome are commonly associated with a 45,XO/46,XY chromosomal mosaicism, we studied whether submicroscopic Yq deletions could also be associated with the development of 45,XO cell lines. We studied blood samples from 14 infertile men carrying a Yq microdeletion as revealed by polymerase chain reaction (PCR). Patients were divided into two groups: group 1 (n = 6), in which karyotype analysis demonstrated a 45,X/46,XY mosaicism, and group 2 (n = 8) with apparently a normal 46,XY karyotype. 45,XO cells were identified by fluorescence in-situ hybridization (FISH) using X and Y centromeric probes. Lymphocytes from 11 fertile men were studied as controls. In addition, sperm cells were studied in three oligozoospermic patients in group 2. Our results showed that large and submicroscopic Yq deletions were associated with significantly increased percentages of 45,XO cells in lymphocytes and of sperm cells nullisomic for gonosomes, especially for the Y chromosome. Moreover, two isodicentric Y chromosomes, classified as normal by cytogenetic methods, were detected. Therefore, Yq microdeletions may be associated with Y chromosomal instability leading to the formation of 45,XO cell lines.

[Fetal cells in the maternal blood and prenatal diagnosis]

Fetal loss after amniocentesis or chorionic villus sampling is a limit to prenatal diagnosis practice and to its generalization. The existence of fetal cells in the blood of pregnant women is now well established. Recognizing these cells with specific antibodies and isolating them with fluorescent or magnetic systems are the subject of numerous studies. However, to date, neither the sensitivity nor the specificity of these methods are sufficient to allow a non invasive prenatal diagnosis.

Y chromosome microdeletions and germinal mosaicism in infertile males

Molecular deletions of the Y chromosome long arm are a frequent cause of male infertility. Because these deletions are thought to be inherited from fathers without Y chromosome deletions, the question arises as to whether their relatively high incidence in the male population could be due to the existence of a mosaicism in somatic and/or germinal paternal cells. This study included a total of 181 infertile men, among whom 18 were found to have an abnormal karyotype. In the other 163, polymerase chain reaction (PCR) analysis detected nine (5.5%) Y chromosome microdeletions. Blood, spermatozoa or testicular cells from 47 men (27 oligozoospermia, 20 azoospermia), including six Y-deleted patients, were screened for mosaicism using double target fluorescence in-situ hybridization (FISH) with Y centromeric and deleted in azoospermia (DAZ) gene-specific probes. Results indicated that: (i) percentages of double (intact Y chromosome) or single (deleted Y chromosome) fluorescent signals by FISH were in agreement with PCR data, thus demonstrating the reliability of the method; and (ii) a weak germ cell mosaicism was found in only two oligozoospermic patients, carrying 1.97 and 4.13% respectively of spermatozoa with a deleted Y chromosome. Further studies on larger populations are needed to evaluate precisely the incidence of Y deletion mosaicisms in infertile men.

Usefulness of fluorescence in situ hybridization for the diagnosis of Turner mosaic fetuses with small ring X chromosomes

OBJECTIVE

To emphasize the usefulness of fluorescence in situ hybridization (FISH) techniques on uncultured amniocytes for the diagnosis of abnormal mosaic karyotypes.

METHODS

In the course of three prenatal diagnoses, specific fluorescent probes, coding, respectively, for chromosomes X, Y, 18, 13, and 21, were applied on amniocyte preparations directly after amniocentesis. At least 50 nuclei were counted in each case. Parallel to the FISH procedure, cell cultures were set up in order to obtain karyotypes. FISH and cytogenetic results were then compared.

RESULTS

In each case, FISH showed an abnormal mosaic chromosomal constitution, 45,X/46,XX, which was related to the existence of tiny ring X chromosomes in karyotypes.

CONCLUSION

Because very small ring X chromosomes can escape identification when standard cytogenetic techniques are used alone, we show that misdiagnosis can be avoided when FISH is performed beforehand.

Connexin43 gene expression and regulation in the rodent seminiferous epithelium

Connexin43 (Cx43) is one of the most predominant gap junction proteins found in the testis. We used in situ hybridization and indirect immunofluorescence to study the distribution of Cx43 mRNA and protein in the rodent seminiferous epithelium. During mouse testis maturation, Cx43 mRNA and its corresponding protein were first detected in the adluminal compartment of the growing seminiferous tubules (early postnatal age: Day 12) to become progressively located in the basal compartment at later ages (Days 16, 19, 27). In seminiferous tubules of sexually mature animals, the intensity of the hybridization signal was stage-dependent, with a maximum at Stage VII compared with Stages V and IX of the spermatogenic cycle (p<0.05). The highest expression of Cx43 mRNA was observed in the supporting Sertoli cells and, to a lesser extent, in the most basally located and less mature germ cells (spermatogonia and spermatocytes). Consistent with these observations, in situ dye coupling was observed between Sertoli cells and basal germ cells. In a mutant mouse deficient for the retinoid X receptor beta, which exhibited abnormal spermatogenesis due to altered Sertoli cell function, Cx43 transcripts were markedly decreased in the seminiferous epithelium (p<0.01). The immunoreactive signal for Cx43 was significantly reduced in seminiferous tubules of the 3-month-old mutant mice (p<0.05) and undetectable in older animals. These data provide new information about the precise localization of Cx43 mRNA and protein in seminiferous tubules of immature and mature rodent testes. Moreover, they suggest that retinoids, through the RXRbeta receptors, could be involved in the control of Cx43 gene expression in Sertoli cells.

Absence of mutations involving the INSL3 gene in human idiopathic cryptorchidism

The aetiology of cryptorchidism is for the most part unknown and appears to be multifactorial. Recently, a product of Leydig cells termed Leydig insulin-like hormone (INSL3) has been proposed as a putative trophic hormone of the first part of descent. Absence of Insl3 in male mice results in bilateral cryptorchidism and mutations involving this gene may be a cause of cryptorchidism in man. We sequenced both exons of the human INSL3 gene in 31 men who presented with idiopathic unilateral or bilateral cryptorchidism. The only sequence variant was an amino acid substitution in the C-peptide of the molecule. This change was also found in a control group of normal fertile men indicating that it is a polymorphism unrelated to the phenotype. These results suggest that mutations involving the human INSL3 gene are not a common cause of cryptorchidism in man.

A high frequency of Y chromosome deletions in males with nonidiopathic infertility

Microdeletions of the long arm of the human Y chromosome are associated with spermatogenic failure and have been used to define three regions of Yq (AZFa, AZFb, and AZFc) that are recurrently deleted in infertile males. In a blind study we screened 131 infertile males (46 idiopathic and 85 nonidiopathic) for Y chromosome microdeletions. Nineteen percent of idiopathic males, with an apparently normal 46,XY chromosome complement had microdeletions of either the AZFa, AZFb, or AZFc region. There was no strict correlation between the extent or location of the deletion and the phenotype. The AZFb deletions did not include the active RBM gene. Significantly, a high frequency of microdeletions (7%) was found in patients with known causes of infertility and a 46,XY chromosome complement. These included deletions of the AZFb and AZFc regions, with no significant difference in the location or extent of the deletion compared with the former group. It is recommended that all males with reduced or absence sperm counts seeking assisted reproductive technologies be screened for deletions of the Y chromosome.

Co-localization of HP1 and TP1 transcripts in human spermatids by double electron microscopy in situ hybridization

Nuclear changes in the basic nucleoprotein complement occur during spermiogenesis in man. Somatic type histones are displaced by transition proteins which are replaced themselves by protamines, the major nuclear proteins present in late spermatids and sperm nuclei. Sense and antisense 35S-labelled riboprobes, coding respectively for human transition protein 1 (TP1) and protamine 1 (HP1), were synthesized with modified specific oligonucleotides and were used for light microscopy in situ hybridization. A double EM in situ hybridization was performed using a digoxigenin-labelled probe for TP1 and a biotin-labelled probe for HP1, and hybrids were revealed, respectively, with specific antibodies coupled to colloidal gold particles of different sizes (10 nm and 15 nm). For both types of transcripts, histological study revealed a specific distribution of the silver grains in the adluminal region of the seminiferous tubules where spermatids are localized. Quantitative ultrastructural analysis of the nuclear and cytoplasmic labelling densities for the mRNAs coding for TP1 and HP1 showed that the transcripts were found in both the nucleus and cytoplasm of round spermatids and persisted until the elongation phase. Transcripts accumulated in the spermatid cytoplasm without any particular cellular compartmentalization. At the end of the spermatid elongation phase, the disappearance of TP1 and HP1 transcripts may be related to the arrest of transcriptional activity, while the deposition of transition proteins and protamines occurs successively within spermatid nuclei.

Identification and characterization of a de novo partial trisomy 10p by comparative genomic hybridization (CGH)

We report the characterization of a de novo unbalanced chromosome rearrangement by comparative genomic hybridization (CGH) in a 15-day-old child with hypotonia and dysmorphia. We describe the combined use of CGH and fluorescence in situ hybridization (FISH) to identify the origin of the additional chromosomal material on the short arm of chromosome 6. Investigation with FISH revealed that the excess material was not derived from chromosome 6. Identification of unknown unbalanced aberrations that could not be identified by traditional cytogenetics procedures is possible by CGH analysis. Visual analysis of digital images from CGH-metaphase spreads revealed a predominantly green signal on the telomeric region of chromosome 10p. After quantitative digital ratio imaging of 10 CGH-metaphase spreads, a region of gain was found in the chromosome band 10p14-pter. The CGH finding was confirmed by FISH analysis, using a whole chromosome 10 paint probe. These results show the usefulness of CGH for a rapid characterization of de novo unbalanced translocation, unidentifiable by karyotype alone.

Unexpected inherited chromosomal translocation during prenatal diagnosis for maternal age: risk for a nondetectable karyotype imbalance in offspring

An unexpected t(1;19) translocation is described in a fetus. Inherited from the mother, this translocation was found during the course of a normal prenatal diagnosis made for maternal age. The very short length of chromosomal translocated segments and their labelling pattern made high-resolution cytogenetic methods and fluorescence in situ hybridization techniques necessary for the correct identification of this karyotype rearrangement, both in mother and fetus. Different modes of meiotic segregation, leading to potential erroneous prenatal diagnoses, are discussed.

Advanced paternal age and de-novo complex chromosomal rearrangement in offspring

We report one case of a de-novo complex chromosomal rearrangement (CCR), t(1;5;13)ins(14;13), in an abnormal 19-month-old boy. Clinical features associated were a mild facial dysmorphy and a psychomotor retardation. Parental ages were, respectively, 29 years for the mother and 60 years for the father. We point out the usefulness of fluorescence in-situ hybridization in elucidating CCRs, and discuss the possible correlation between the existence of a chromosomal aberration and advanced paternal age.

Different proximal and distal rearrangements of chromosome 7q associated with holoprosencephaly

Four new cases of holoprosencephaly are described in fetuses exhibiting abnormal karyotypes with different distal and proximal rearrangements of the long arm of chromosome 7. Three of them showed terminal deletions of chromosome 7q, confirming the importance of the 7q36 region in holoprosencephaly. The karyotype of the fourth fetus showed an apparently balanced de novo translocation, t(7;13) (q21.2;q33), without any visible loss of the distal part of chromosome 7q. The involvement of new genes, different from the human Sonic Hedgehog gene (hShh) responsible for holoprosencephaly, or a positional effect are discussed.

Assisted reproductive technology and complex chromosomal rearrangements: the limits of ICSI

Complex chromosomal rearrangements are very rare events in the human population. According to our knowledge on the consequences of simple reciprocal translocations for male fertility, translocations involving three or more chromosomes are thought to lead to severe reproductive impairments in terms of meiotic disturbance or chromosomal imbalance of gametes. We report the case of a 48 year old man whose sperm count revealed either oligozoospermia (<10(3) spermatozoa/ml) or azoospermia. He was referred to the laboratory for in-vitro fertilization after intracytoplasmic sperm injection. Cytogenetic investigations showed a complex chromosomal rearrangement involving firstly a translocation between the short arm of chromosome 7 and the long arm of chromosome 13 and secondly a translocation between the short arm of the same chromosome 13 and the short arm of chromosome 9. Diagnosis was ascertained by fluorescence in-situ hybridization and staining of the nucleolar organizer regions. Theoretical study of the translocated chromosomes predicted a 'chain' configuration of the hexavalent at the pachytene stage of meiosis. In all, 32 modes of segregation were considered and only one resulted either in a normal or a balanced gamete karyotype. Genetic counselling and choice of appropriate artificial reproduction technique are discussed.

Parental origin and mechanisms of formation of three cases of 12p tetrasomy

Pallister-Killian syndrome is a clinically recognizable syndrome characterized by tissue-limited mosaicism for an extra 12p isochromosome. Very little is known about the underlying mechanism of this rare rearrangement. Microsatellite markers were studied from three fetuses with Pallister-Killian syndrome and their parents to determine the parent of origin and the cell division yielding the additional isochromosome. In two cases the isochromosome contained the same allele(s) as a normal transmitted chromosome 12, one paternal and one maternal in origin. A third case showed inheritance of two different maternal alleles, indicating that at least one meiotic error was involved in the ultimate formation of the extra isochromosome.

The fetal phenotype of partial 2q trisomy

A 22-week-old fetus with partial trisomy 2q (q24.1-->qter) and 7q35 monosomy is described. To our knowledge, this represents the greatest unbalanced 2q chromosomal segment published in the literature. The clinical phenotype is in agreement with previous descriptions in children and allows us to propose a fetal phenotype for this chromosomal abnormality.

Ultrastructural localization of rDNA and rRNA by in situ hybridization in the nucleolus of human spermatids

The ultrastructural localization of rDNA and rRNA within the nucleolus of human spermatids was investigated by in situ hybridization at steps 1 and 2. Two different digoxigenin-labeled human probes from the rRNA transcription unit were used. Identification of hybrids was performed with immunogold techniques. Comparative observations in the Sertoli cell nucleolus as controls revealed that rDNA was predominantly visualized in the threads of the dense fibrillar component, while rRNA was detected over both the fibrillar component and the granular component. Within the nucleolus of round spermatids in the same sections of seminiferous tubules, rDNA labeling was localized over the spherical or stranded dense fibrillar components. rRNA labeling was found not only over these components but also in the adjacent nucleoplasm rich in ribonucleoprotein particles. These results are consistent with the view that the round spermatid nucleolus is transcriptionally active.

Unstable translocation t(14;21) in a man, inherited as a t(13;14) in one of his daughters

The transmission of a Robertsonian translocation was studied in a family after diagnosis of a t rob. (13;14) in a foetus, in the course of a prenatal diagnosis for maternal age. The father was found to be a carrier of a balanced t rob. (14;21) in mosaicism with a normal karyotype. The t rob(14;21) was inherited from the paternal grandfather. A second prenatal diagnosis, 1 year later, revealed a girl with the paternal t rob(14;21). Mitotic and germinal instability of the paternal t rob.(14;21) is discussed, with relation to the long period of drug addiction.