Journal of Genetic Disorders & Genetic Reports ISSN: 2327-5790

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Research Article, J Genet Disor Genet Rep Vol: 5 Issue: 1

Severe Expressive-Language Delay and Congenital Malformations in a Boy with Microduplication 7q11.23 Diagnosed by Molecular Cytogenetic Analysis

Inesse Ben Abdallah Bouhjar1*, Amal Al Hashem2, Samia Sobki3, Brahim Tabarki2, Yasser Hassen Babair3 and Hatem Elghezal1
1Cytogenetics and Molecular Cytogenetics Laboratory, Pathology and Laboratory Medicine Department, Prince Sultan Military Medical City, Riyadh, KSA
2Pediatric Department, Prince Sultan Military Medical City, Riyadh, KSA
3Central Military Laboratory and Blood Bank, Pathology and Laboratory Medicine Department, Prince Sultan Military Medical City, Riyadh, KSA
Corresponding author : Inesse Ben Abdallah Bouhjar, PhD
Cytogenetics and Molecular Cytogenetics Laboratory, Prince Sultan Military Medical City, Riyadh, KSA
E-mail: [email protected]
Received: March 27, 2014 Accepted: November 12, 2015 Published: November 18, 2015
Citation: Ben-Abdallah-Bouhjar I, Hashem AA, Sobki S, Tabarki B, Babair YH, et al. (2016) ISevere Expressive-Language Delay and Congenital Malformations in A Boy with Microduplication 7q11.23 Diagnosed by Molecular Cytogenetic Analysis. J Genet Disor Genet Rep 5:1. doi:10.4172/2327-5790.1000127

Abstract

We report a patient with speech delay and hydronephrosis ascertained with array-CGH screening of patients with abnormal neuronal migration and intellectual disability, having a 7q11.23 duplication reciprocal to the Williams-Beuren critical region (WBCR) deletion. Similarly to the reported patients, he showed serious difficulties in expressive language in the absence of severe intellectual disability and marked dysmorphic features. In addition to the abnormal development of the cerebral cortex with simplified gyral pattern and hydronephrosis. Chromosomal analysis showed normal karytoptype, so Micro-array comparative genomic hybridization was used to search for a possible cryptic anomaly. An interstitial duplication of 1.46 Mb was detected in 7q11.23. Fluorescence in situ hybridization confirmed the diagnosis, revealing a tandem duplication of the Williams-Beuren critical region. Our study provides an additional case for better understanding and delineating the duplication 7q11.23. We thus performed a genotype-phenotype correlation analysis to ascertain the contribution of 7q11.23 to the clinical features of our patient.

Keywords: 7q11.23 duplication; Array-CGH; FISH; Hydronephrosis; Speech delay

Keywords

7q11.23 duplication; Array-CGH; FISH; Hydronephrosis; Speech delay.

Background

Williams-Beuren syndrome (WBS) (MIM 194050) is an autosomal dominant disorder [1] affecting 1 in 7,500 to 1 in 20,000 births [2] due to sporadic de novo chromosomal microdeletions at 7q11.23 detectable by fluorescence in situ hybridization (FISH). As with many other genomic disorders, the common recurrent 1.55- Mb microdeletion occurs by nonallelic homologous recombination (NAHR) [3] between numerous low copy repeats (LCRs) flanking the commonly deleted region [4]. Inversion of the same segment has been found in 27% of affected individuals with an atypical WBS phenotype and in 33% of transmitting parents, suggesting that the presence of this structural variant in the population may be associated with WBS or may predispose to genomic rearrangements [5].
This genomic disorder is characterized by a distinctive facial phenotype, intellectual disability, developmental and language delay, infantile hypercalcaemia, growth retardation, cardiovascular diseases, connective tissue abnormalities and a unique cognitive and personality profile [6]. The cognitive profile generally consists of mild to moderate mental retardation with severe disturbance of visuo-spatial skills but relative sparing of language. From a behavioral standpoint, a striking feature of individuals with WBS is their high sociability and empathy for others, leading them to engage in social interaction even with strangers. In opposite to the patients with WBSR duplication who is associated with autism spectrum disorders (ASD) [7].
The typical WBS microdeletion is estimated to encompass 25 to 30 genes [8] and haploinsufficiency for several of these genes has been reported to account for parts of the overall phenotype, suggesting that more than one of the genes are sensitive to gene dose or copy number variation. ELN Haploinsufficiency for example, is responsible for Supravalvular aortic stenosis [9]. Haploinsufficiency genes such as LIMK1, CYLN2, RFC2, GTF2I, MAGI2 and GTF2IRD1 have also been linked to the cognitive and craniofacial pathology [10]. However, the contribution of a subset of the genes located within the deleted region still needs to be elucidated, and so far, there have been no specific genes associated with the unusual language pattern and unique personality profile. The recent finding of altered expression levels of genes with normal copy-number adjacent to the deleted region in WBS patients adds further complexity to the interpretation of genotype-phenotype correlations in WBS [11].
Reciprocal duplications have been defining for several deletion disorders mediated by NAHR between LCRs, such as Smith-Magenis syndrome (SMS) involving the 17p11.2 region [12] and DiGeorge/ velocardiofacial syndrome (VCFS) involving the 22q11.2 region [13]. Given the presence of numerous LCRs and the frequency of microdeletions in the WBS region, it was suspected that reciprocal microduplication of the region should also occur. This prediction was recently verified with the publication of a small number case reports describing individuals with microduplication of the WBS critical region [14]. In the children for whom detailed clinical information was reported, speech delay was a significant finding; [15] however, the complete phenotypic spectrum associated with microduplications of this region has yet to be elucidated.
We report the molecular characterization of one patient with dup (7)(q11.23) and the clinical, neurodevelopmental, and behavioral features of the proband, who presented with developmental delay, prominent language delay, abnormal neuronal migration and hydronephrosis. A novel feature observed in our patient is the presence of functionally impairing anxiety, decreased social interactions, and repetitive interests similar to children with autism spectrum disorders (ASDs), indicating that the initial clinical presentation of patients with dup(7) (q11.23) could be an evaluation for autism (Table 1).
Table 1: Comparison of our patient phenotypic features with those of microduplication 7q11.23 syndrome.

Material and Methods

Patient
The proband was the first child of healthy and unrelated parents. The boy was born prematuly by normal delivery after rupture of membrane at 30 weeks of gestation. At birth, Apgar scores were 9/10, his weight was 2400 g (<3rd percentile), length 45 cm (10th percentile) and a cranial circumference (OFC) 34 cm (30th percentile). The neonatal period was complicated by hypotonia, congenital heart diseases and hydronephrosis. At the age of 12 months, the boy had a significant psychomotor delay with major axial hypotonia, developmental and speech delay and growth retardation. He had hypotonia, macrocephaly and dysmorphic features with low set ears, cleft lip, high and broad nose, short philtrum, small mouth, and he had a short neck (Figure 1A). There were anomalies of hands and feet with polydactyly. Renal ultrasound showed hydronephrosis and MAG was done which showed reducedperfusion in the left kidney. No obstruction in either kidney. He was referred to Cardiology because of systolic murmur and found to have transposition of great arteries with intact ventricular septum, patent ductus arteriosus, usual coronary arteries, balloon atrial septostomy was done for him followed by pulmonary artery banding. He is on regular follow-up with Cardiology. His cleft lip was repaired by the ENT. Genital exam showed a normal penis and testes. Cerebral magnetic resonance imaging revealed a simplified gyral patern.
Figure 1: A-Frontal view of our patient’s face showing low set ears, cleft lip, high and broad nose, short philtrum, small mouth, and short neck. B- Results of microarray analysis of patient DNA showing duplication in 7q11.23. Dotted lines represent log 2 ratios. C-D: Metaphases and Interphases FISH analysis using Williams and Beuren critical region probes confirm the diagnosis showing the hybridisation of the ELN (Single red) with three signals in the nucleus and a big red signal in the duplicated chromosome on metaphase, confirming a tandem duplication of WBSR.
Cytogenetic analysis
Chromosomal analysis was performed according to standard procedures. Peripheral blood lymphocytes were cultured in Roswell Park Memorial Institute medium 1640 (RPMI, Gibco®, Grand Island, NY, USA) enriched with 20% fetal calf serum, L-glutamine, antibiotics (penicillin and streptomycin) and antibodies (Phytohemmaglutinine). The cells were cultured for 72 hours in a humidified environment with 5% CO2 in 37°C incubator until harvest. For the 72 hours culture, the sample was incubated with Colcemid solution (final concentration 0.05μg/ml) for 45 minutes. After harvesting, the cells were exposed to hypotonic solution (0.075mol/L KCl) and fixed with methanol/acetic acid (3:1).
The slides were prepared and stained using the G banding technique on peripheral blood lymphocyte cultures. A minimum of 50 metaphases were analyzed from each sample and karyograms were prepared using the Applied imaging CytoVision Automated Karyotyping System®. Chromosomal abnormalities have been reported in accordance with the current international standard nomenclature [16].
Fluorescence in situ hybridization
FISH using commercial probes was performed according to the manufacturer instructions. (Williams and Beuren critical region probes, Abott-Vysis®) 10 μl of probe mixture was applied to metaphase slides and codenaturized 5 minutes at 72°C. After an overnight hybridization at 37°C, the slides were washed for 5 min in 2X SSC/NP40 (Vysis®) at 72°C. Finally, the slides were mounted with 15 μl of DAPI (4,6-diamidino-2-phenyllindole, Vysis®) and analysed using a cytovision FISH station (Cytovision, APPLIED IMAGING®).
Comparative genomic hybridization
A 180000 Agilent Technologies® oligonucleotides array was used according to the manufacturer’s instructions « Human Genome 180K OligoMicroarray ». The patient’s DNA and the reference DNA were digested with RsaI and AluI. Digested DNA produced was labelled by random priming with Al5-dUTP or Al3-dUTP. After Columnspurification, the probes were denaturized and pre-annealed with 50 μg of human Cot-1 DNA (Invitrogen®, Calif., USA). The hybridization was performed at 65°C for 24h. After washing, the microarray was then scanned by the Agilent Microarray Scanner. Data analysis was performed by Agilent Feature Extraction® 9.1 software. Interpretations of results were carried out with CGH analytics® 4.5 Software with the following parameters: z-score threshold: 2.0, window: 0.5 Mb. A copy number variation was noted if at least 3 contiguous oligonucleotides presented an abnormal log2 ratio (> +0.5 or < - 0.5). The results were compared to the data recorded in the database of genomic variants. Web resources included the Database of Genomic Variants : (http:// projects.tcag.ca/variation/), University of California Santa Cruz Genome Bioinformatics:(http://genome.ucsc.edu/),Ensembl:(http://www. ensembl.org/index.html), OMIM :(http://www.ncbi.nlm.nih.gov/sites/ entrez) and DECIPHERv5.0 database: (http://decipher.sanger.ac.uk/)

Results

Chromosomal analysis of the proband showed a normal karyotype in all metaphases.
Array-CGH analysis of the patient DNA showed a microduplication of the long arm of the chromosome 7 involving the 7q11.23. This duplication was not associated with other anomalies. The size of the duplication in chromosome 7q was estimated about 1.46 Mb (Figure 1B) (base position chromosome 7: 72,677,301- 74,143,240. (hg18)).
Interphase FISH analysis using Williams and Beuren critical region probes confirm the diagnosis showing the hybridisation of the ELN (Single red) with three signals (Figure 1C and 1D).
FISH analysis on parental chromosomes using the same probes shows a normal result with two copies of ELN gene in both parents.

Discussion

Only 30 cases of micro-duplication of 7q11.23 region have been reported [17]. These children frequently present speech and language delay, varying from moderate to severe, moderate intellectual disability, behavioural disorders (ADHD) with higer level of separation anxiety, craniofacial anomalies, serious congenital heart disease, urinary tract anomalies and renal anomalies [17-20].
The use of comparative genomic hybridization (CGH) array has increased the identification of 7q11.23 duplication segment explaining intellectual disorders and/or congenital malformations. In fact, this technology becomes an essential tool for the detection of micro-imbalances in 10-15% of cases involving intellectual disorders and congenital malformations [21]. Microarray-based technology demonstrated that the 7q11.23 duplication breakpoints are the same as the common deletion with the proximal breakpoint (71.846 Mb) and the distal breakpoint (73.926 Mb) [22].
The WBSR disorder is mediated by non-allelic homologous recombination (NAHR), this recurrent rearrangement is often flanked by low-copy repeats (LCRs). Due to their high degree of sequence homology, these segmental duplications provides substrates for NAHR, in which crossing over occurs between two similar sequences at non-allelic positions that erroneously align in mitosis or meiosis. Depending on their location and orientation, they give rise to various types of rearrangements like deletion, duplications or inversions. Given the presense of numerous LCRs in the WBSR, occurs of microdeletions and reciprocal microduplications are frequent in this region [23,24].
For our patient, like the patients described previously, indicates that the main clinical feature associated with dup (7) (q1.23) is speech and language delay, varying from moderate to severe, but no hearing or anatomic defect of the phonoarticultory district were published in the reported patients [18-22]. We suppose that the duplicated region contains one or more genes, where the dosage gene can affect the language skills. Also recently with the MRI investigations the duplication 7q11.23 is associated with the left temporal dysplasia [18-22] might indeed underline the poor language development.
It is surprising that microduplication of the WBS region was reported only recently. This is likely due to a convergence of factors. First, the phenotype seen in patients with microduplications of chromosome 7q11.23 are quite unlike those seen with the common WBS microdeletion, also FISH technique of metaphases cells is unsuitable to detect the microduplication. Second, it would have been difficult to predict the phenotype associated with microduplication based on what was known about the contribution of genes in this region to the WBS phenotype. However, a screen of patients with a relatively non specific phenotype using comparative genomic hybridization technologies have identified the microduplication of chromosome 7q11.23.
Based on the previous case reports and our current finding [14,17-19], patients with microduplication of chromosome 7q11.23 showed a variety of dysmorphic features, including a prominent forehead, high nasal bridge and/or deep-set eyes, thick helices of the ears, thin lip , and short philtrum. Usually, each of the children reported is described in having minor dysmorphic features, the overall appearance was not particularly striking or specific [14,17-19]. Nevertheless, it is clear that the overall facial dysmorphology in patients with dup(7) (q11.23) syndrome is not a distinctive as well-characterized faces associated with WBS. The expressive language delay with sparing of visuospatial cognition in patients with duplication of the WBS region is in direct contrast to the well-characterized cognitive profile seen in typical WBS patients [18]. We might assume that, in addition to gene dosage other mechanisms such as genetic and/or environmental interactions may be significant in determining the phenotype of patients with microduplication 7q11.23. However, overexpression of genes such as GTF2I and LIMK2 seems to play an important role in controlling of visuospatial and speaking skills, and could participate in the clinical features caused by the duplication 7q11.23.
Interestingly, in WBS, the WBSR deletion is associated with features opposite to impaired social skills such as poor social relationships, abnormal use of non-verbal behaviours including eye-to eye gaze, facial expression and gestures to regulate social interactions. These observations strongly suggest that the WBSR contain one or more genes sensitive to dosage and associated with impairment in social interactions. Many finding support the existence of several genes in 7q11.23 region that are sensitive to alterations in dosage and involved in the development of human language skills. Tassabehji et al and Hirota et al performed a Genotype-Phenotype correlations in patients with 7q11.23 region rearrangement and studies of mice models have suggested that the gene located in the telomeric part of the 7q11.23 region, are the main candidates sensitive to dosage and are involved in language impairment and mental disabilities [25,26].

Conclusion

In conclusion, the Array-CGH diagnostic provide high resolution genomic analysis and reveal specific etiological molecular abnormalities. This approach allows analysis of copy number variation in a large number of genomic regions known to be involved in recurrent deletions or duplications and copy number variations where the phenotype may not be clinically recognizable or remains to be fully delineated. Although FISH can reliably detect genomic deletions the difficulty of obtaining accurate interphase FISH interpretation for duplications and the discrepancy between chromosomic interphases and interphase FISH in one case, so it renders interphase FISH highly problematic in making the diagnosis of dup(7) (q11.23).

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