Étude cytogénétique moléculaire d'une translocation t(X;Y) générant un second remaniement du chromosome X (à propos d'une famille)

Nous avons rapporté une famille au sein de laquelle une anomalie du chromosome X à type de translocation entre les chromosomes X et Y ségrége. Cette anomalie a été transmise à la descendance sous deux formes : certains des descendants sont porteurs de la même anomalie tandis qu'un emaniement à type de délétion du chromosome X est retrouvé dans une autre partie de la descendance. Dans ce travail nous avons effectué des analyses cytogénétiques conventionnelles et moléculaires chez deux patientes porteuses chacune d'un des remaniement du chromosome X afin de définir précisément les points de cassure et de mettre en évidence une région minimale critique de remaniements et un lien entre les deux. Ce travail nous a permis de réaliser que la physiopathologie des remaniements chromosomiques est un mécanisme complexe qui fait intervenir des séquences répétées dans le génome. Les techniques innovantes et l'étude plus approfondie des familles permettent de mieux appréhender les remaniements afin d'en prévenir les conséquences. Pour les familles, le conseil génétique surtout en cas de grossesse est ainsi plus envisageable.We described a family in which an abnormality from the X chromosome which is a translocation between the X and Y chromosomes is segregating. This abnormality has been transmitted in two ways: some of the descendants share the same abnormality, whereas other members of the family share another abnormality which is a deletion on the same chromosome. In this study is we died conventionnal and molecular cytogenetic analysis in two patients who share either the deletion or the translocation in order to refine the breakpoints and to bring forward evidence of possible critical minimal region and a link between both. This study allows us to realise that physiopathology of chromosomal modifications is a complex mechanism in which repetitive sequences are getting involved. New technologies such CGH and SNP array are some better tools to study more accurately the breakpoints in order to prevent consequences. In this way genetic counseling is more easily to envisage, specially for pregnancies.AMIENS-BU Santé (800212102) / SudocSudocFranceF

ANOMALIES CHROMOSOMIQUES DU BRAS COURT DU CHROMOSOME 12 DANS LES HEMOPATHIES MALIGNES (APPORT DES DIFFERENTES METHODES DANS LEUR DIAGNOSTIC)

PARIS6-Bibl.Pitié-Salpêtrie (751132101) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Severe Psychomotor Delay in a Severe Presentation of Cat-Eye Syndrome

Cat-eye syndrome is a rare genetic syndrome of chromosomal origin. Individuals with cat-eye syndrome are characterized by the presence of preauricular pits and/or tags, anal atresia, and iris coloboma. Many reported cases also presented with variable congenital anomalies and intellectual disability. Most patients diagnosed with CES carry a small supernumerary bisatellited marker chromosome, resulting in partial tetrasomy of 22p-22q11.21. There are two types of small supernumerary marker chromosome, depending on the breakpoint site. In a very small proportion of cases, other cytogenetic anomalies are reportedly associated with the cat-eye syndrome phenotype. Here, we report a patient with cat-eye syndrome caused by a type 1 small supernumerary marker chromosome. The phenotype was atypical and included a severe developmental delay. The use of array comparative genomic hybridization ruled out the involvement of another chromosomal imbalance in the neurological phenotype. In the literature, only a few patients with cat-eye syndrome present with a severe developmental delay, and all of the latter carried an atypical partial trisomy 22 or an uncharacterized small supernumerary marker chromosome. Hence, this is the first report of a severe neurological phenotype in cat-eye syndrome with a typical type 1 small supernumerary marker chromosome. Our observation clearly complicates prognostic assessment, particularly when cat-eye syndrome is diagnosed prenatally

Prenatal diagnosis of isochromosome 20q in a fetus with vertebral anomaly and rocker-bottom feet

Objective: Isochromosome of the long arm of chromosome 20 (i(20q)) is a rare structural abnormality in prenatal diagnosis. Thirty prenatal cases of mosaic i(20q) have been reported, among which only four are associated with fetal malformations. We describe a new prenatal case of i(20q) with fetal malformations. Materials and methods: We also observed a discrepancy between uncultured and cultured amniotic fluid cells by using conventional cytogenetic, fluorescence in situ hybridization and array-SNP analysis. Results: The short arm deletion of chromosome 20 arising from the isochromosome encompassed two candidate genes PAX1 and JAG1 involved in cranio-facial and vertebral development. Conclusion: The data would allow establishing a phenotype–genotype correlation. Thus, we proposed to define a recognizable syndrome combining cranio-facial dysmorphism, vertebral bodies' anomalies, feet and cerebral malformations

15q24.1 BP4-BP1 microdeletion unmasking paternally inherited functional polymorphisms combined with distal 15q24.2q24.3 duplication in a patient with epilepsy, psychomotor delay, overweight, ventricular arrhythmia

IF 2.004 (2018)International audience15q24 microdeletion and microduplication syndromes are genetic disorders caused by non-allelic homologous recombination between low-copy repeats (LCRs) in the 15q24 chromosome region. Individuals with 15q24 microdeletion and microduplication syndromes share a common 1.2 Mb critical interval, spanning from LCR15q24B to LCR15q24C. Patients with 15q24 microdeletion syndrome exhibit distinct dysmorphic features, microcephaly, variable developmental delay, multiples congenital anomalies while individuals with reciprocal 15q24 microduplication syndrome show mild developmental delay, facial dysmorphism associated with skeletal and genital abnormalities. We report the first case of a 10 year-old girl presenting mild developmental delay, psychomotor retardation, epilepsy, ventricular arrhythmia, overweight and idiopathic central precocious puberty. 180K array-CGH analysis identified a 1.38 Mb heterozygous interstitial 15q24.1 BP4-BP1 microdeletion including HCN4 combined with a concomitant 2.6 Mb heterozygous distal 15q24.2q24.3 microduplication. FISH analysis showed that both deletion and duplication occurred de novo in the proband. Of note, both copy number imbalances did not involve the 1.2 Mb minimal deletion/duplication critical interval of the 15q24.1q24.2 chromosome region (74.3-75.5 Mb). Sequencing of candidate genes for epilepsy and obesity showed that the proband was hemizygous for paternal A-at risk allele of BBS4 rs7178130 and NPTN rs7171755 predisposing to obesity, epilepsy and intellectual deficits. Our study highlights the complex interaction of functional polymorphisms and/or genetic variants leading to variable clinical manifestations in patients with submicroscopic chromosomal aberrations

Detecting single DNA copy number variations in complex genomes using one nanogram of starting DNA and BAC-array CGH

Comparative genomic hybridization to bacterial artificial chromosome (BAC)-arrays (array-CGH) is a highly efficient technique, allowing the simultaneous measurement of genomic DNA copy number at hundreds or thousands of loci, and the reliable detection of local one-copy-level variations. We report a genome-wide amplification method allowing the same measurement sensitivity, using 1 ng of starting genomic DNA, instead of the classical 1 μg usually necessary. Using a discrete series of DNA fragments, we defined the parameters adapted to the most faithful ligation-mediated PCR amplification and the limits of the technique. The optimized protocol allows a 3000-fold DNA amplification, retaining the quantitative characteristics of the initial genome. Validation of the amplification procedure, using DNA from 10 tumour cell lines hybridized to BAC-arrays of 1500 spots, showed almost perfectly superimposed ratios for the non-amplified and amplified DNAs. Correlation coefficients of 0.96 and 0.99 were observed for regions of low-copy-level variations and all regions, respectively (including in vivo amplified oncogenes). Finally, labelling DNA using two nucleotides bearing the same fluorophore led to a significant increase in reproducibility and to the correct detection of one-copy gain or loss in >90% of the analysed data, even for pseudotriploid tumour genomes

Duplication 16p13.3 and the CREBBP gene: confirmation of the phenotype

The introduction of molecular karyotyping technologies into the diagnostic work-up of patients with congenital disorders permitted the identification and delineation of novel microdeletion and microduplication syndromes. Interstitial 16p13.3 duplication, encompassing the CREBBP gene, which is mutated or deleted in the Rubinstein-Taybi syndrome, have been proposed to cause a recognisable syndrome with variable intellectual disability, normal growth, mild facial dysmophism, mild anomalies of the extremities, and occasional findings such as developmental defects of the heart, genitalia, palate or the eyes. We here report the phenotypic and genotypic delineation of 9 patients carrying a submicroscopic 16p13.3 duplication, including the smallest 16p13.3 duplication reported so far. Careful clinical assessment confirms the distinctive clinical phenotype and also defines frequent associated features : marked speech problems, frequent ocular region involvement with upslanting of the eyes, narrow palpebral fissures, ptosis and strabismus, frequent proximal implantation of thumbs, cleft palate/bifid uvula and inguinal hernia. It also confirms that CREBBP is the critical gene involved in the duplication 16p13.3 syndrome.status: publishe

Should prenatal chromosomal microarray analysis be offered for isolated fetal growth restriction? A French multicenter study

International audienceBackground: Compared with standard karyotype, chromosomal microarray analysis improves the detection of genetic anomalies and is thus recommended in many prenatal indications. However, evidence is still lacking on the clinical utility of chromosomal microarray analysis in cases of isolated fetal growth restriction.Objective: This study aimed to estimate the proportion of copy number variants detected by chromosomal microarray analysis and the incremental yield of chromosomal microarray analysis compared with karyotype in the detection of genetic abnormalities in fetuses with isolated fetal growth restriction.Study design: This retrospective study included all singleton fetuses diagnosed with fetal growth restriction and no structural ultrasound anomalies and referred to 13 French fetal medicine centers over 1 year in 2016. Fetal growth restriction was defined as an estimated fetal weight of <tenth percentile for gestational age identified in ultrasound reports. For this analysis, we selected fetuses who underwent invasive genetic testing with karyotype and chromosomal microarray analysis results. Data were obtained from medical records and ultrasound databases and postmortem and placental examination reports in case of spontaneous stillbirths and terminations of pregnancy. Following the American College of Medical Genetics and Genomics guidelines, copy number variants were classified into 5 groups as following: pathogenic, likely pathogenic, variant of unknown significance, likely benign, and benign.Results: Of 682 referred fetuses diagnosed with isolated fetal growth restriction, both karyotype and chromosomal microarray analysis were performed in 146 fetuses. Overall, the detection rate of genetic anomalies found by chromosomal microarray analysis was estimated to be 7.5% (11 of 146 [95% confidence interval, 3.3-11.8]), including 10 copy number variants classified as pathogenic and 1 copy number variant classified as likely pathogenic. Among the 139 fetuses with normal karyotype, 5 were detected with pathogenic and likely pathogenic copy number variants, resulting in an incremental yield of 3.6% (95% confidence interval, 0.5-6.6) in chromosomal microarray analysis compared with karyotype. All fetuses detected with pathogenic or likely pathogenic copy number variants resulted in terminations of pregnancy. In addition, 3 fetuses with normal karyotype were detected with a variant of unknown significance (2.1%). Among the 7 fetuses with abnormal karyotype, chromosomal microarray analysis did not detect trisomy 18 mosaicism in all fetuses.Conclusion: Our study found that compared with karyotype, chromosomal microarray analysis improves the detection of genetic anomalies in fetuses diagnosed with isolated fetal growth restriction. These results support the use of chromosomal microarray analysis in addition to karyotype for isolated fetal growth restriction