Confined placental mosaicism is a diagnostic pitfall in dystrophinopathies: a clinical report.

Single-gene copy number variants (CNVs) limited to placenta although rarely identified may have clinical implications. We describe a pregnant woman referred for chorionic villus sampling due to increased fetal nuchal translucency. Incident intragenic deletion of Duchenne muscular dystrophy (DMD) gene, affecting exons 56 and 57, was identified in a male fetus in ~23-30% of placental cells by chromosomal microarray and confirmed using multiplex ligation-dependent probe amplification (MLPA). Rapid aneuploidy testing showed normal results and the deletion was not detected in the mother. Subsequent analyses on amniotic cells yielded a normal DMD gene result, corroborating the confined placental nature of the mosaicism. Hence, this report emphasizes the importance of conducting amniocentesis following detection of mosaicism for single gene CNVs on chorionic villi, in order to preclude confined placental mosaicism (CPM). As far as we know, this report marks only the second documented situation of CPM involving an intragenic DMD deletion.

Mosaic complete tetrasomy 21 in a fetus with complete atrioventricular septal defect and minor morphological variations.

BACKGROUND: Tetrasomy 21 is a very rare aneuploidy which could clinically resemble a Down syndrome. It was most often described in its partial form than complete. We report the prenatal, pathological and genetic characteristics of a fetus with mosaic complete tetrasomy 21. This is the second well-documented description of a complete tetrasomy 21 in the literature. METHODS: Prenatal and fetal pathological examinations, cytogenetic and molecular analyses were performed to characterize fetal features with tetrasomy 21. RESULTS: Prenatal ultrasound examination revealed an isolated complete atrioventricular septal defect with normal karyotype on amniotic fluid. After termination of pregnancy, clinical examination of the fetus evoked trisomy 21 or Down syndrome. Chromosomal microarray analysis and FISH on lung tissue showed a mosaicism with four copies of chromosome 21 (tetrasomy 21). CONCLUSION: Our observation and the review of the literature reported the possibility of very weak mosaicism and disease-causing confined tissue-specific mosaicism in fetus or alive patients with chromosome 21 aneuploidy, mainly Down syndrome. In case of clinical diagnosis suggestive of Down syndrome, attention must be paid to the risk of false-negative test due to chromosomal mosaicism (very weak percentage, different tissue distribution). To overcome this risk, it is necessary to privilege the diagnostic techniques without culture step and to increase the number of cells and tissues analyzed, if possible. This study highlights the limits of microarray as the unique diagnostic approach in case of weak mosaic and French cytogenetics guidelines recommend to check anomalies seen in microarray by another technique on the same tissue.

Disruption of chromatin organisation causes MEF2C gene overexpression in intellectual disability: a case report.

BACKGROUND: Balanced structural variants are mostly described in disease with gene disruption or subtle rearrangement at breakpoints. CASE PRESENTATION: Here we report a patient with mild intellectual deficiency who carries a de novo balanced translocation t(3;5). Breakpoints were fully explored by microarray, Array Painting and Sanger sequencing. No gene disruption was found but the chromosome 5 breakpoint was localized 228-kb upstream of the MEF2C gene. The predicted Topologically Associated Domains analysis shows that it contains only the MEF2C gene and a long non-coding RNA LINC01226. RNA studies looking for MEF2C gene expression revealed an overexpression of MEF2C in the lymphoblastoid cell line of the patient. CONCLUSIONS: Pathogenicity of MEF2C overexpression is still unclear as only four patients with mild intellectual deficiency carrying 5q14.3 microduplications containing MEF2C are described in the literature. The microduplications in these individuals also contain other genes expressed in the brain. The patient presented the same phenotype as 5q14.3 microduplication patients. We report the first case of a balanced translocation leading to an overexpression of MEF2C similar to a functional duplication.

NFIB Haploinsufficiency Is Associated with Intellectual Disability and Macrocephaly.

The nuclear factor I (NFI) family of transcription factors play an important role in normal development of multiple organs. Three NFI family members are highly expressed in the brain, and deletions or sequence variants in two of these, NFIA and NFIX, have been associated with intellectual disability (ID) and brain malformations. NFIB, however, has not previously been implicated in human disease. Here, we present a cohort of 18 individuals with mild ID and behavioral issues who are haploinsufficient for NFIB. Ten individuals harbored overlapping microdeletions of the chromosomal 9p23-p22.2 region, ranging in size from 225 kb to 4.3 Mb. Five additional subjects had point sequence variations creating a premature termination codon, and three subjects harbored single-nucleotide variations resulting in an inactive protein as determined using an in vitro reporter assay. All individuals presented with additional variable neurodevelopmental phenotypes, including muscular hypotonia, motor and speech delay, attention deficit disorder, autism spectrum disorder, and behavioral abnormalities. While structural brain anomalies, including dysgenesis of corpus callosum, were variable, individuals most frequently presented with macrocephaly. To determine whether macrocephaly could be a functional consequence of NFIB disruption, we analyzed a cortex-specific Nfib conditional knockout mouse model, which is postnatally viable. Utilizing magnetic resonance imaging and histology, we demonstrate that Nfib conditional knockout mice have enlargement of the cerebral cortex but preservation of overall brain structure and interhemispheric connectivity. Based on our findings, we propose that haploinsufficiency of NFIB causes ID with macrocephaly.

Looking for Broken TAD Boundaries and Changes on DNA Interactions: Clinical Guide to 3D Chromatin Change Analysis in Complex Chromosomal Rearrangements and Chromothripsis.

Apparition of next-generation sequencing (NGS) was a breakthrough on knowledge of genome structure. Bioinformatic tools are a key point to analyze this huge amount of data from NGS and characterize the three-dimensional organization of chromosomes. This chapter describes usage of different browsers to explore publicly available online data and to search for possible 3D chromatin changes involved during complex chromosomal rearrangements as chromothripsis. Their pathogenic impact on clinical phenotype and gene misexpression can also be evaluated with annotated databases.

Is the resulting phenotype of an embryo with balanced X-autosome translocation, obtained by means of preimplantation genetic diagnosis, linked to the X inactivation pattern?

OBJECTIVE: To examine if a balanced female embryo with X-autosome translocation could, during its subsequent development, express an abnormal phenotype. DESIGN: Preimplantation genetic diagnosis (PGD) analysis on two female carriers with maternal inherited X-autosome translocations. SETTING: Infertility center and genetic laboratory in a public hospital. PATIENT(S): Two female patients carriers undergoing PGD for a balanced X-autosome translocations: patient 1 with 46,X,t(X;2)(q27;p15) and patient 2 with 46,X,t(X;22)(q28;q12.3). INTERVENTION(S): PGD for balanced X-autosome translocations. MAIN OUTCOME MEASURE(S): PGD outcomes, fluorescence in situ hybridization in biopsied embryos and meiotic segregation patterns analysis of embryos providing from X-autosome translocation carriers. RESULT(S): Controlled ovarian stimulation facilitated retrieval of a correct number of oocytes. One balanced embryo per patient was transferred and one developed, but the patient miscarried after 6 weeks of amenorrhea. In X-autosome translocation carriers, balanced Y-bearing embryos are most often phenotypically normal and viable. An ambiguous phenotype exists in balanced X-bearing embryos owing to the X inactivation mechanism. In 46,XX embryos issued from an alternate segregation, der(X) may be inactivated and partially spread transcriptional silencing into a translocated autosomal segment. Thus, the structural unbalanced genotype could be turned into a viable functional balanced one. It is relevant that a discontinuous silencing is observed with a partial and unpredictable inactivation of autosomal regions. Consequently, the resulting phenotype remains a mystery and is considered to be at risk of being an abnormal phenotype in the field of PGD. CONCLUSION(S): It is necessary to be cautious regarding to PGD management for this type of translocation, particularly in transferred female embryos.

Identification of disrupted AUTS2 and EPHA6 genes by array painting in a patient carrying a de novo balanced translocation t(3;7) with intellectual disability and neurodevelopment disorder.

Intellectual disability (ID) is a frequent feature but is highly clinically and genetically heterogeneous. The establishment of the precise diagnosis in patients with ID is challenging due to this heterogeneity but crucial for genetic counseling and appropriate care for the patients. Among the etiologies of patients with ID, apparently balanced de novo rearrangements represent 0.6%. Several mechanisms explain the ID in patients with apparently balanced de novo rearrangement. Among them, disruption of a disease gene at the breakpoint, is frequently evoked. In this context, technologies recently developed are used to characterize precisely such chromosomal rearrangements. Here, we report the case of a boy with ID, facial features and autistic behavior who is carrying a de novo balanced reciprocal translocation t(3;7)(q11.2;q11.22)dn. Using microarray analysis, array painting (AP) technology combined with molecular study, we have identified the interruption of the autism susceptibility candidate 2 gene (AUTS2) and EPH receptor A6 gene (EPHA6). We consider that the disruption of AUTS2 explains the phenotype of the patient; the exact role of EPHA6 in human pathology is not well defined. Based on the observation of recurrent germinal and somatic translocations involving AUTS2 and the molecular environment content, we put forward the hypothesis that the likely chromosomal mechanism responsible for the translocation could be due either to replicative stress or to recombination-based mechanisms.

CEP57 mutation in a girl with mosaic variegated aneuploidy syndrome.

Mosaic variegated aneuploidy (MVA) is a rare autosomal recessive disorder characterized by constitutional aneuploidies. Mutations in BUB1B and CEP57 genes, which are involved in mitotic spindle and microtubule stabilization, respectively, are responsible for a subset of patients with MVA. To date, CEP57 mutations have been reported only in four probands. We report on a girl with this disorder due to c.915-925dup11 mutation in CEP57, which predicts p.Leu309ProfsX9 and review the literature in order to facilitate genotype-phenotype correlation. Rhizomelic shortening of the upper limbs, skull anomalies with conserved head circumference, and absence of tumor development could be features suggesting a need for molecular screening of the CEP57 gene in patients with this disorder.

Early-onset obesity and paternal 2pter deletion encompassing the ACP1, TMEM18, and MYT1L genes.

Obesity is a common but highly, clinically, and genetically heterogeneous disease. Deletion of the terminal region of the short arm of chromosome 2 is rare and has been reported in about 13 patients in the literature often associated with a Prader-Willi-like phenotype. We report on five unrelated patients with 2p25 deletion of paternal origin presenting with early-onset obesity, hyperphagia, intellectual deficiency, and behavioural difficulties. Among these patients, three had de novo pure 2pter deletions, one presented with a paternal derivative der(2)t(2;15)(p25.3;q26) with deletion in the 2pter region and the last patient presented with an interstitial 2p25 deletion. The size of the deletions was characterized by SNP array or array-CGH and was confirmed by fluorescence in situ hybridization (FISH) studies. Four patients shared a 2p25.3 deletion with a minimal critical region estimated at 1.97 Mb and encompassing seven genes, namely SH3HYL1, ACP1, TMEMI8, SNTG2, TPO, PXDN, and MYT1L genes. The fifth patient had a smaller interstitial deletion encompassing the TPO, PXDN, and MYT1L genes. Paternal origin of the deletion was determined by genotyping using microsatellite markers. Analysis of the genes encompassed in the deleted region led us to speculate that the ACP1, TMEM18, and/or MYT1L genes might be involved in early-onset obesity. In addition, intellectual deficiency and behavioural troubles can be explained by the heterozygous loss of the SNTG2 and MYT1L genes. Finally, we discuss the parent-of-origin of the deletion.

Somatic mosaicism in trichorhinophalangeal syndrome: a lesson for genetic counseling.

Trichorhinophalangeal syndrome type I (TRPSI) is a genetic disorder characterized by sparse hair, a bulbous nasal tip, short stature with severe generalized shortening of all phalanges, metacarpal and metatarsal bones and cone-shaped epiphyses. This syndrome is caused by autosomal dominant mutations in the TRPS1 gene. However, because recurrence has been observed in siblings from healthy parents, an autosomal recessive mode of inheritance has also been suggested. We report on a male patient, born to healthy unrelated parents, with TRPSI. Using Sanger sequencing, we identified a mutation in the TRPS1 gene (c.2735 G>A, P.Cys912Tyr). The same mutation was detected as a 10% mosaic mutation by Pyrosequencing in blood-derived DNA from his healthy mother. To our knowledge, this is the first time that somatic mosaicism has been identified in TRPSI. This data combined with the observations of recurrences in siblings from healthy parents modifies the genetic counseling for TRPSI, which should discuss a 5-10 percent recurrence risk for healthy parents with an affected child because of the possibility of germinal mosaicism.

Expanding the phenotype of IQSEC2 mutations: truncating mutations in severe intellectual disability.

Intellectual disability (ID) is frequent in the general population, with 1 in 50 individuals directly affected worldwide. The multiple etiologies include X-linked ID (XLID). Among syndromic XLID, few syndromes present severe ID associated with postnatal microcephaly and midline stereotypic hand movements. We report on three male patients with ID, midline stereotypic hand movements, hypotonia, hyperkinesia, strabismus, as well as seizures (2/3), and non-inherited and postnatal onset microcephaly (2/3). Using array CGH and exome sequencing we characterised two truncating mutations in IQSEC2, namely two de novo intragenic duplication mapped to the Xp11.22 region and a nonsense mutation in exon 7. We propose that truncating mutations in IQSEC2 are responsible for syndromic severe ID in male patients and should be screened in patients without mutations in MECP2, FOXG1, CDKL5 and MEF2C.

Bipolar affective disorder and early dementia onset in a male patient with SHANK3 deletion.

The SHANK3 protein is a scaffold protein known to stabilize metabotropic glutamate receptor mGluR5 in the post-synaptic membrane of neurons. It is associated with genetic vulnerability in autism and schizophrenia. Here we report the case of an 18 year-old male patient who displayed psychiatric features of bipolar affective disorder associated with early setting of dementia. This mental status is related to sporadic occurrence of SHANK3 gene complex multiple deletions. A low beta amyloid protein rate (479 mg/L) found in cerebrospinal fluid suggests a possible link between SHANK3 deletion syndrome-associated regression and dementia of Alzheimers's type. In addition, we propose an overview of the phenotype related to SHANK3 deletion.

Analysis using fish of sperm and embryos from two carriers of rare rob(13;21) and rob(15;22) robertsonian translocation undergoing PGD.

The majority of fluorescence in situ hybridization (FISH) studies on the meiotic segregation of Robertsonian translocations focus on the most common types, rob(13; 14) and rob(14; 21). Here we report the first study for carriers of rare Robertsonian translocations rob(13; 21) and rob(15; 22) combining analysis of meiotic segregation in sperm and blastomeres following pre-implantation genetic diagnosis (PGD). Dual-colour FISH was applied to nuclei from spermatozoa and blastomeres from PGD embryos using two subterminal contig probes for each translocation, and a second round with probes for chromosomes 16 and 18. Patient 1 had a rob(13; 21) and patient 2 had a rob(15; 22), and 86.3% and 87.5% of gametes respectively were consistent with meiotic segregation resulting in a normal or balanced chromosome complement. Analysis of embryos showed that for patient 1 and 2 respectively, 25% and 46% were balanced, and of the unbalanced embryos, 50% and 31% were mosaic or chaotic. Our patients with a rob(13; 21) and rob(15; 22) were found to have a similar meiotic segregation pattern to that for male carriers of the common Robertsonian translocations. The observed rate in unbalanced embryos being mosaic or chaotic may result in an increased risk of chromosomal abnormalities. Our results may help to improve the genetic counseling for carriers of rare Robertsonian translocations.

Duplication 8q12: confirmation of a novel recognizable phenotype with duane retraction syndrome and developmental delay.

Duane retraction syndrome (DRS) is a rare congenital strabismus condition with genetic heterogeneity. DRS associated with intellectual disability or developmental delay is observed in several genetic diseases: syndromes such as Goldenhar or Wildervanck syndrome and chromosomal anomalies such as 12q12 deletion. We report on the case of a patient with DRS, developmental delay and particular facial features (horizontal and flared eyebrows, long and smooth philtrum, thin upper lip, full lower lip and full cheeks). We identified a duplication of the long arm of chromosome 8 (8q12) with SNP-array. This is the third case of a patient with common clinical features and 8q12 duplication described in the literature. The minimal critical region is 1.2 Mb and encompasses four genes: CA8, RAB2, RLBP1L1 and CHD7. To our knowledge, no information is available in the literature regarding pathological effects caused by to overexpression of these genes. However, loss of function of the CHD7 gene leads to CHARGE syndrome, suggesting a possible role of the overexpression of this gene in the phenotype observed in 8q12 duplication patients. We have observed that patients with 8q12 duplication share a common recognizable phenotype characterized by DRS, developmental delay and facial features. Such data combined to the literature strongly suggest that this entity may define a novel syndrome. We hypothesize that CHD7 duplication is responsible for a part of the features observed in 8q12.2 duplication.

Deletion 2q36.2q36.3 with multiple renal cysts and severe mental retardation.

Interstitial 2q36 deletion is a rare event. We report on a patient with a de novo del(2)(q36.2q36.3) interstitial deletion of the long arm of chromosome 2 diagnosed by classical banding. The phenotype comprised facial dysmorphism, enlarged kidneys with multiple renal cysts, abnormal minora labia, asymmetric lower limbs with dysplastic patella, and severe mental retardation. By physical mapping, using array-comparative genomic hybridisation (CGH) confirmed by Fluorescent In Situ Hybridisation (FISH), the breakpoints of the deletion were mapped and the size of the deletions was measured: 5.61+/-0.19Mb. A skin biopsy was analysed using electronic microscopy showing an alteration of the structure and organisation of the dermal and peri-neuronal basement membrane. The relation between the phenotype and the deletion of both COL4A4 and COL4A3 genes, located in 2q36.3 loci, as well as the disruption of TRIP12 were discussed.

The clinical spectrum associated with a chromosome 17 short arm proximal duplication (dup 17p11.2) in three patients.

The p11.2-p12 region of human chromosome 17 is gene rich and composed of at least two genomically unstable domains: the Smith-Magenis syndrome region (17p11.2) and the Charcot-Marie-Tooth region (17p12), both of which are flanked by several low-copy repeat sequences. Homologous recombination between these flanking repeats results in either deletion- or duplication-associated phenotypes caused by a gene dosage effect. We report on the clinical phenotype of three patients presenting with either a 17p11.2 or 17p11.2p12 duplication, revealed by chromosome analysis and confirmed by fluorescent in situ hybridization analysis, high resolution genomic analysis of the 17p region using oligonucleotide array comparative genomic hybridization, and molecular studies with microsatellite markers. Two patients carry the 17p11.2 duplication, while the third one shows a larger duplication including the 17p12 region. The facial features observed in our patients include triangular face, full cheeks, smooth philtrum, thin upper lip, dental malocclusion, irregular eyebrows, and sparse hair, all of which are consistent with the pure proximal dup 17p phenotype. The patients' other clinical features are compared with previously published cases.

Molecular cytogenetic characterization of terminal 14q32 deletions in two children with an abnormal phenotype and corpus callosum hypoplasia.

Among previously reported cases of 14q terminal deletions, only 11 have dealt with pure terminal deletion of 14q (14q3-14qter) and the break points were mapped by fluorescent in situ hybridisation (FISH) or genotyping in only four of them. Thanks to a collaborative study on behalf of the 'Association des Cytogeneticiens de langue Française'(ACLF), we report two patients with terminal deletion of the long arm of chromosome 14, del(14)(q32.2) and del(14)(q32.32), diagnosed by subtelomere screening. In the two cases, a thick nuchal skinfold was detected by early ultrasound with normal prenatal karyotype. Their postnatal phenotype included large forehead, narrow palpebral fissures, epicanthic folds, upturned tip of the nose, narrow mouth and thin upper lip, microretrognathia, prominent earlobes, hypotonia, delayed psychomotor development and hypoplastic corpus callosum. By physical mapping using FISH, the size of the deletions was measured for patients 1 and 2: 6.55+/-1.05 and 4.67+/-0.10 Mb, respectively. The paternal origin of the deleted chromosome 14 was established by genotyping of microsatellites for patient 1 and the phenotype of terminal del(14)(q32) was compared to maternal uniparental disomy 14.

Pure direct duplication (12)(q24.1-->q24.2) in a child with Marcus Gunn phenomenon and multiple congenital anomalies.

Partial trisomy of the region 12q24.1-->q24.2 is rare and usually associated with other rearrangements. We report on the clinical and cytogenetic findings in a girl with a pure de novo direct duplication dup(12)(q24.1-->q24.2). She had developmental and growth retardation, facial dysmorphism with upslanting palpebral fissures, wide downturned mouth, short neck, and Marcus Gunn phenomenon. She also had single transverse creases, hypoplasia of the corpus callosum, and cardiac malformations consisting of a bicuspid aortic valve, multiple ventricular septal defects, and kinking of the aorta. The size of the duplication was characterized by molecular cytogenetics and comparative genomic hybridization (CGH) to be 11.5 Mb in size and extended from the BAC probe RP11-256L11 loci (108.2 Mb) +/- 1 Mb to the BAC probe RP11-665J20 loci (119.7 Mb) +/- 1 Mb. No such pure 12q24 duplication was detected out of the 23 patients reported in the literature with duplications in 12q region. Comparison with these reported 12q trisomies suggests the duplication dup(12)(q24.1-->q24.2) is associated with a recognizable phenotype consisting of characteristic facial dysmorphism, growth retardation, and cardiac malformation.

Characteristic pattern of chromosomal imbalances in posttransplantation lymphoproliferative disorders: correlation with histopathological subcategories and EBV status.

BACKGROUND: Posttransplantation lymphoproliferative disorders (PTLDs) are a spectrum of lymphoid proliferations, occurring in immunosuppressed organ transplant recipients. They comprise early lesions, polymorphic (P-PTLD), monomorphic (M-PTLD), and Hodgkin/Hodgkin-like lymphoma PTLD (HL-PTLD) lesions. Most of them are associated with Epstein-Barr virus (EBV). Little is known about their genetic changes. MATERIALS AND METHODS: We have studied 35 PTLDs[7 P-PTLDs (3/7 polyclonal IgH), 26 M-PTLDs (22 B-cell PTLD, 4 T-cell PTLD), 2 HL-PTLDs], using comparative genomic hybridization (CGH), a DNA-based technique allowing a screening of chromosomal imbalances without needing cultured cells. RESULTS.: Overall incidence of chromosomal imbalances: 51.5 %. The most frequent gains involved 8q24, 3q27 [4 cases each]; 2p24p25, 5p, 9q22q34, 11, 12q22q24, 14q32, 17q, 18q21 [2 cases each]. Nonrandom losses were 17p13 [4 cases]; 1p36, 4q [3 cases each]; 17q23q25, Xp [2 cases each]. Three high-level amplifications were detected: 4p16, 9p22p24, 18q21q23. In this latter imbalance, involvement of Bcl2 has been confirmed by FISH. The nonrandom CGH imbalances occurring in M-PTLD are usually described in lymphomas of immunocompetent patients and contain genes known to be involved in lymphomagenesis, while genomic abnormalities detected in half cases of EBV positive P-PTLD are mostly unknown. CONCLUSION: This study reported nonrandom chromosomal imbalances in PTLD and also identified early genomic alterations in EBV positive P-PTLD. These results raise two questions: the role of such lesions in the development and progression of those EBV induced-lymphoproliferations and their clinical significance especially in P-PTLD.