Comparative analysis of copy number detection by whole-genome BAC and oligonucleotide array CGH

Small supernumerary marker chromosomes derived from human chromosome 11

Introduction: With only 39 reported cases in the literature, carriers of a small supernumerary marker chromosome (sSMC) derived from chromosome 11 represent an extremely rare cytogenomic condition. Methods: Herein, we present a review of reported sSMC(11), add 18 previously unpublished cases, and closely review eight cases classified as 'centromere-near partial trisomy 11' and a further four suited cases from DECIPHER. Results and discussion: Based on these data, we deduced the borders of the pericentric regions associated with clinical symptoms into a range of 2.63 and 0.96 Mb for chromosome 11 short (p) and long (q) arms, respectively. In addition, the minimal pericentric region of chromosome 11 without triplo-sensitive genes was narrowed to positions 47.68 and 60.52 Mb (GRCh37). Furthermore, there are apparent differences in the presentation of signs and symptoms in carriers of larger sSMCs derived from chromosome 11 when the partial trisomy is derived from different chromosome arms. However, the number of informative sSMC(11) cases remains low, with overlapping presentation between p- and q-arm-imbalances. In addition, uniparental disomy (UPD) of 'normal' chromosome 11 needs to be considered in the evaluation of sSMC(11) carriers, as imprinting may be an influencing factor, although no such cases have been reported. Comprehensively, prenatal sSMC(11) cases remain a diagnostic and prognostic challenge.

Multiplex ligation-dependent probe amplification identifies copy number changes in normal and undetectable karyotype MDS patients

Chromosomal abnormalities play an important role in classification and prognostication of myelodysplastic syndrome (MDS) patients. However, more than 50% of low-risk MDS patients harbor a normal karyotype. Recently, multiplex ligation-dependent probe amplification (MLPA) has emerged as an effective and robust method for the detection of cytogenetic aberrations in MDS patients. To characterize the subset of MDS with normal karyotype or failed chromosome banding analysis, we analyzed 144 patient samples with normal karyotype or undetectable through regular chromosome banding analysis, which were subjected to parallel comparison via fluorescence in situ hybridization (FISH) and MLPA. MLPA identifies copy number changes in 16.7% of 144 MDS patients, and we observed a significant difference in overall survival (OS) (median OS: undefined vs 27 months, p=0.0071) in patients with normal karyotype proved by MLPA versus aberrant karyotype cohort as determined by MLPA. Interestingly, patients with undetectable karyotype via regular chromosome banding indicated inferior outcome. Collectively, MDS patients with normal or undetectable karyotype via chromosome banding analysis can be further clarified by MLPA, providing more prognostic information that benefit for individualized therapy.

Small Supernumerary Ring Chromosome Derived from an Inverted Duplication of 13q11.2q14 in a Fetus with Coarctation of the Aorta

Here, we report a molecular characterization of a small supernumerary marker chromosome (sSMC) derived from the most proximal region of 13q present in a fetus with coarctation of the aorta at ultrasound examination during prenatal diagnosis. Cultured umbilical cord blood cells showed a de novo extra ring-shaped sSMC in 76% of the cells using a standard banding technique. SNP array revealed a tetrasomy of about 28.4 Mb in the long arm of chromosome 13 from band 13q11 to 13q14.11 in the fetus's cells. Metaphase/interphase FISH using specific probes located at 13q11, 13q12.11, and 13q14.11, respectively, demonstrated that the supernumerary ring chromosome was derived from an inverted duplication of the region 13q11q14.11 with a conventional centromere. To the best of our knowledge, this is the first time that an inverted duplication of the most proximal region 13q11q14.11 in a ring chromosome is characterized. The findings we presented here deepen our understanding of the clinical consequences of tetrasomy in this region and may be of help for further studies of critical regions in chromosome 13.

Copy number variants implicate cardiac function and development pathways in earthquake-induced stress cardiomyopathy

The pathophysiology of stress cardiomyopathy (SCM), also known as takotsubo syndrome, is poorly understood. SCM usually occurs sporadically, often in association with a stressful event, but clusters of cases are reported after major natural disasters. There is some evidence that this is a familial condition. We have examined three possible models for an underlying genetic predisposition to SCM. Our primary study cohort consists of 28 women who suffered SCM as a result of two devastating earthquakes that struck the city of Christchurch, New Zealand, in 2010 and 2011. To seek possible underlying genetic factors we carried out exome analysis, genotyping array analysis, and array comparative genomic hybridization on these subjects. The most striking finding was the observation of a markedly elevated rate of rare, heterogeneous copy number variants (CNV) of uncertain clinical significance (in 12/28 subjects). Several of these CNVs impacted on genes of cardiac relevance including RBFOX1, GPC5, KCNRG, CHODL, and GPBP1L1. There is no physical overlap between the CNVs, and the genes they impact do not appear to be functionally related. The recognition that SCM predisposition may be associated with a high rate of rare CNVs offers a novel perspective on this enigmatic condition.

Clinical application of oligo array-CGH for detecting balanced translocations in preimplantation genetic diagnosis

Array comparative genomic hybridization (array-CGH), which facilitates to detect unbalanced reciprocal translocation and allows screening aneuploidy for chromosomes, has been repeatedly verified to be valid for diagnosis of translocations in preimplantation human embryos. Currently, the main microarrays used for CGH are bacterial artificial chromosome (BAC)-based arrays. Compared with the BAC-based arrays, oligonucleotide (oligo)-based arrays have a relatively higher resolution and optimal coverage particularly in the subtelomeric regions. Herein, we described the clinical application of a newly designed oligo-based array by Agilent in preimplantation genetic diagnosis (PGD) and aneuploidy screening for balanced translocations. In the study, a total of 144 embryos from 9 couples carrying Robertsonian translocations and 5 carrying reciprocal translocations were biopsied on day 3 for array-CGH analysis. Overall, 135 (93.8%) embryos were successfully diagnosed to be free of either aneuploidies or unbalanced fragments. However, the remained 9 (6.2%) embryos failed to be amplified due to failed cell lysis, DNA damage or the absence of nuclei in the biopsied cells. Collectively, 23 embryos were identified as "euploid and balanced" and suitable to be transferred. Finally, 9 embryos of satisfactory quality were transferred to 6 women, among which 4 recipients exhibited positive hCG level. Fortunately, one recipient with positive hCG level has delivered one baby, and two pregnancies were continuing. Our study served as the first clinical application of oligo-based array CGH technology in PGD for both reciprocal and Robertsonian translocations concomitant with comprehensive aneuploidy screening.

Characterization of a de novo sSMC 17 detected in a girl with developmental delay and dysmorphic features

BACKGROUND

The majority of small supernumerary marker chromosome cases arise de novo and their frequency in newborns is 0.04%. We report on a girl with developmental delay and dysmorphic features with a non-mosaic de novo sSMC that originated from the pericentric region of q arm in chromosome 17.

CASE PRESENTATION

The girl presented with developmental delay, speech delay, myopia, mild muscle hypotonia, hypoplasia of orbicular muscle, poor concentration, and hyperactivity. Main dysmorphic features included: round face, microstomia, small chin, down-slanting palpebral fissures and small lobules of both ears. At present, her developmental abilities are still delayed for her chronological age but she is making evident progress with speech. A postnatal array comparative genomic hybridization showed a 2.31 Mb genomic gain indicating microduplication derived from pericentric regions q11.1 and q11.2 of chromosome 17. Additional conventional cytogenetic analysis from peripheral blood characterized the karyotype as 47,XX,+mar in a non-mosaic form. The location of microduplication was confirmed with fluorescence in situ hybridization.

CONCLUSION

The proband's microduplication encompassed approximately 40 annotated genes, several of which have been associated with phenotypic characteristics of the proband. This is the first report of sSMC 17 including this particular chromosomal region in non-mosaic form.

Custom Array Comparative Genomic Hybridization: the Importance of DNA Quality, an Expert Eye, and Variant Validation

The presence of false positive and false negative results in the Array Comparative Genomic Hybridization (aCGH) design is poorly addressed in literature reports. We took advantage of a custom aCGH recently carried out to analyze its design performance, the use of several Agilent aberrations detection algorithms, and the presence of false results. Our study provides a confirmation that the high density design does not generate more noise than standard designs and, might reach a good resolution. We noticed a not negligible presence of false negative and false positive results in the imbalances call performed by the Agilent software. The Aberration Detection Method 2 (ADM-2) algorithm with a threshold of 6 performed quite well, and the array design proved to be reliable, provided that some additional filters are applied, such as considering only intervals with average absolute log₂ratio above 0.3. We also propose an additional filter that takes into account the proportion of probes with log₂ratio exceeding suggestive values for gain or loss. In addition, the quality of samples was confirmed to be a crucial parameter. Finally, this work raises the importance of evaluating the samples profiles by eye and the necessity of validating the imbalances detected.

Multiplex ligation-dependent probe amplification assay identifies additional copy number changes compared with R-band karyotype and provide more accuracy prognostic information in myelodysplastic syndromes

Cytogenetic analysis provides important diagnostic and prognostic information for patients with Myelodysplastic syndromes (MDS) and plays an essential role in the International Prognostic Scoring System (IPSS) and the revised International Prognostic Scoring System (IPSS-R). Multiplex ligation-dependent probe amplification (MLPA) assay is a recently developed technique to identify targeted cytogenetic aberrations in MDS patients. In the present study, we evaluated the results obtained using an MLPA assay in 437 patients with MDS to determine the efficacy of MLPA analysis. Using R-banding karyotyping, 45% (197/437) of MDS patients had chromosomal abnormalities, whereas MLPA analysis detected that 35% (153/437) of MDS cases contained at least one copy-number variations (CNVs) .2/5 individuals (40%) with R-band karyotype failures had trisomy 8 detected using only MLPA. Clonal cytogenetic abnormalities were detected in 20/235 (8.5%) MDS patients with a normal R-band karyotype, and 12/20 (60%) of those patients were reclassified into a higher-risk IPSS-R prognostic category. When sequencing and cytogenetics were combined, the fraction of patients with MDS-related oncogenic lesions increased to 87.3% (233/267 cases). MLPA analysis determined that the median OS of patients with a normal karyotype (n=218) was 65 months compared with 27 months in cases with an aberrant karyotype (P=0.002) in 240 patients with normal or failed karyotypes by R-banding karyotyping. The high-resolution MPLA assay is an efficient and reliable method that can be used in conjunction with R-band karyotyping to detect chromosomal abnormalities in patients with suspected MDS. MLPA may also provide more accurate prognostic information.

Chromosomal Microarrays for the Prenatal Detection of Microdeletions and Microduplications

Chromosomal microarray analysis has replaced conventional G-banded karyotype in prenatal diagnosis as the first-tier test for the cytogenetic detection of copy number imbalances in fetuses with/without major structural abnormalities. This article reviews the basic technology of microarray; the value and clinical significance of the detection of microdeletions, microduplications, and other copy number variants; as well as the importance of genetic counseling for prenatal diagnosis. It also discusses the current status of noninvasive screening for some of these microdeletion and microduplication syndromes.

Diagnostic interpretation of array data using public databases and internet sources

The range of commercially available array platforms and analysis software packages is expanding and their utility is improving, making reliable detection of copy-number variants (CNVs) relatively straightforward. Reliable interpretation of CNV data, however, is often difficult and requires expertise. With our knowledge of the human genome growing rapidly, applications for array testing continuously broadening, and the resolution of CNV detection increasing, this leads to great complexity in interpreting what can be daunting data. Correct CNV interpretation and optimal use of the genotype information provided by single-nucleotide polymorphism probes on an array depends largely on knowledge present in various resources. In addition to the availability of host laboratories' own datasets and national registries, there are several public databases and Internet resources with genotype and phenotype information that can be used for array data interpretation. With so many resources now available, it is important to know which are fit-for-purpose in a diagnostic setting. We summarize the characteristics of the most commonly used Internet databases and resources, and propose a general data interpretation strategy that can be used for comparative hybridization, comparative intensity, and genotype-based array data.

Genomic instability of human embryonic stem cell lines using different passaging culture methods

Background

Human embryonic stem cells exhibit genomic instability that can be related to culture duration or to the passaging methods used for cell dissociation. In order to study the impact of cell dissociation techniques on human embryonic stem cells genomic instability, we cultured H1 and H9 human embryonic stem cells lines using mechanical/manual or enzymatic/collagenase-IV dissociation methods. Genomic instability was evaluated at early (<p60) and late (>p60) passages by using oligonucleotide based array-comparative genomic hybridization 105 K with a mean resolution of 50 Kb.

Results

DNA variations were mainly located on subtelomeric and pericentromeric regions with sizes <100 Kb. In this study, 9 recurrent genomic variations were acquired during culture including the well known duplication 20q11.21. When comparing cell dissociation methods, we found no significant differences between DNA variations number and size, DNA gain or DNA loss frequencies, homozygous loss frequencies and no significant difference on the content of genes involved in development, cell cycle tumorigenesis and syndrome disease. In addition, we have never found any malignant tissue in 4 different teratoma representative of the two independent stem cell lines.

Conclusions

These results show that the occurrence of genomic instability in human embryonic stem cells is similar using mechanical or collagenase IV-based enzymatic cell culture dissociation methods. All the observed genomic variations have no impact on the development of malignancy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13039-015-0133-8) contains supplementary material, which is available to authorized users.

Next-generation sequencing of duplication CNVs reveals that most are tandem and some create fusion genes at breakpoints

Interpreting the genomic and phenotypic consequences of copy-number variation (CNV) is essential to understanding the etiology of genetic disorders. Whereas deletion CNVs lead obviously to haploinsufficiency, duplications might cause disease through triplosensitivity, gene disruption, or gene fusion at breakpoints. The mutational spectrum of duplications has been studied at certain loci, and in some cases these copy-number gains are complex chromosome rearrangements involving triplications and/or inversions. However, the organization of clinically relevant duplications throughout the genome has yet to be investigated on a large scale. Here we fine-mapped 184 germline duplications (14.7 kb-25.3 Mb; median 532 kb) ascertained from individuals referred for diagnostic cytogenetics testing. We performed next-generation sequencing (NGS) and whole-genome sequencing (WGS) to sequence 130 breakpoints from 112 subjects with 119 CNVs and found that most (83%) were tandem duplications in direct orientation. The remainder were triplications embedded within duplications (8.4%), adjacent duplications (4.2%), insertional translocations (2.5%), or other complex rearrangements (1.7%). Moreover, we predicted six in-frame fusion genes at sequenced duplication breakpoints; four gene fusions were formed by tandem duplications, one by two interconnected duplications, and one by duplication inserted at another locus. These unique fusion genes could be related to clinical phenotypes and warrant further study. Although most duplications are positioned head-to-tail adjacent to the original locus, those that are inverted, triplicated, or inserted can disrupt or fuse genes in a manner that might not be predicted by conventional copy-number assays. Therefore, interpreting the genetic consequences of duplication CNVs requires breakpoint-level analysis.

The impact of clinical heterogeneity in schizophrenia on genomic analyses

Though clinically useful, the diagnostic systems currently employed are not well equipped to capture the substantial clinical heterogeneity observed for most psychiatric disorders, as exemplified by the complex psychotic disorder(s) that Bleuler aptly labeled the "Group of Schizophrenias". The clinical heterogeneity associated with schizophrenia has likely frustrated decades of attempts to illuminate the underlying genetic architecture, although recent genome-wide association studies have begun to provide valuable insight into the role of common genetic risk variants. Here we demonstrate the importance of using diagnostic information to identify a core form of the disorder and to eliminate potential comorbidities in genetic studies. We also demonstrate why applying a diagnostic screening procedure to the control dataset to remove individuals with potentially related disorders is critical. Additionally, subjects may participate in multiple studies at different institutions or may have genotype data released by more than one research group. It is thus good practice to verify that no identical subjects exist within or between samples prior to conducting any type of genetic analysis to avoid potential confounding of results. While the availability of genomic data for large collections of subjects has facilitated many investigations that would otherwise not have been possible, we clearly show why one must use caution when acquiring data from publicly available sources. Although the broad vs. narrow debate in terms of phenotype definition in genetic analyses will remain, it is likely that both approaches will yield different results and that both will have utility in resolving the genetic architecture of schizophrenia.

SNP arrays: comparing diagnostic yields for four platforms in children with developmental delay

Background

Molecular karyotyping is now the first-tier genetic test for patients affected with unexplained intellectual disability (ID) and/or multiple congenital anomalies (MCA), since it identifies a pathogenic copy number variation (CNV) in 10-14% of them. High-resolution microarrays combining molecular karyotyping and single nucleotide polymorphism (SNP) genotyping were recently introduced to the market. In addition to identifying CNVs, these platforms detect loss of heterozygosity (LOH), which can indicate the presence of a homozygous mutation or uniparental disomy. Since these abnormalities can be associated with ID and/or MCA, their detection is of particular interest for patients whose phenotype remains unexplained. However, the diagnostic yield obtained with these platforms is not confirmed, and the real clinical value of LOH detection has not been established.

Methods

We selected 21 children affected with ID, with or without congenital malformations, for whom standard genetic analyses failed to provide a diagnosis. We performed high-resolution SNP array analysis with four platforms (Affymetrix Genome-Wide Human SNP Array 6.0, Affymetrix Cytogenetics Whole-Genome 2.7 M array, Illumina HumanOmni1-Quad BeadChip, and Illumina HumanCytoSNP-12 DNA Analysis BeadChip) on whole-blood samples obtained from children and their parents to detect pathogenic CNVs and LOHs, and compared the results with those obtained on a moderate resolution array-based comparative genomic hybridization platform (NimbleGen CGX-12 Cytogenetics Array), already used in the clinical setting.

Results

We identified a total of four pathogenic CNVs in three patients, and all arrays successfully detected them. With the SNP arrays, we also identified a LOH containing a gene associated with a recessive disorder consistent with the patient’s phenotype (i.e., an informative LOH) in four children (including two siblings). A homozygous mutation within the informative LOH was found in three of these patients. Therefore, we were able to increase the diagnostic yield from 14.3% to 28.6% as a result of the information provided by LOHs.

Conclusions

This study shows the clinical usefulness of SNP arrays in children with ID, since they successfully detect pathogenic CNVs, identify informative LOHs that can lead to the diagnosis of a recessive disorder. It also highlights some challenges associated with the use of SNP arrays in a clinical laboratory.

Electronic supplementary material

The online version of this article (doi:10.1186/s12920-014-0070-0) contains supplementary material, which is available to authorized users.

Mosaikbefunde in der Microarray-Diagnostik bei prä- und postnatalen Untersuchungen

Die molekulare Karyotypisierung mithilfe der „Array“-basierten genomischen Hybridisierung (Microarrays) ermöglicht nicht nur den genomweiten, hochauflösenden Nachweis von Kopienzahlveränderungen, -zugewinnen und -verlusten, sondern auch die Detektion bestimmter Mosaike. Der Beitrag gibt eine Übersicht über Einflussgrößen beim Nachweis von Mosaiken mit Microarrays und über verschiedene Mosaikfälle, die sowohl mit Array-CGH (CGH: „comparative genomic hybridization“) als auch mit SNP-Arrays (SNP: „single nucleotide polymorphism“) erhoben wurden. Dabei wird anhand der Array-CGH eine Möglichkeit aufgezeigt, wie der Prozentsatz eines Mosaiks bestimmt werden kann.

Cryptic and complex chromosomal aberrations in early-onset neuropsychiatric disorders

Structural variation (SV) is a significant component of the genetic etiology of both neurodevelopmental and psychiatric disorders; however, routine guidelines for clinical genetic screening have been established only in the former category. Genome-wide chromosomal microarray (CMA) can detect genomic imbalances such as copy-number variants (CNVs), but balanced chromosomal abnormalities (BCAs) still require karyotyping for clinical detection. Moreover, submicroscopic BCAs and subarray threshold CNVs are intractable, or cryptic, to both CMA and karyotyping. Here, we performed whole-genome sequencing using large-insert jumping libraries to delineate both cytogenetically visible and cryptic SVs in a single test among 30 clinically referred youth representing a range of severe neuropsychiatric conditions. We detected 96 SVs per person on average that passed filtering criteria above our highest-confidence resolution (6,305 bp) and an additional 111 SVs per genome below this resolution. These SVs rearranged 3.8 Mb of genomic sequence and resulted in 42 putative loss-of-function (LoF) or gain-of-function mutations per person. We estimate that 80% of the LoF variants were cryptic to clinical CMA. We found myriad complex and cryptic rearrangements, including a "paired" duplication (360 kb, 169 kb) that flanks a 5.25 Mb inversion that appears in 7 additional cases from clinical CNV data among 47,562 individuals. Following convergent genomic profiling of these independent clinical CNV data, we interpreted three SVs to be of potential clinical significance. These data indicate that sequence-based delineation of the full SV mutational spectrum warrants exploration in youth referred for neuropsychiatric evaluation and clinical diagnostic SV screening more broadly.

Microarray Technology for the Diagnosis of Fetal Chromosomal Aberrations: Which Platform Should We Use?

The advantage of microarray (array) over conventional karyotype for the diagnosis of fetal pathogenic chromosomal anomalies has prompted the use of microarrays in prenatal diagnostics. In this review we compare the performance of different array platforms (BAC, oligonucleotide CGH, SNP) and designs (targeted, whole genome, whole genome, and targeted, custom) and discuss their advantages and disadvantages in relation to prenatal testing. We also discuss the factors to consider when implementing a microarray testing service for the diagnosis of fetal chromosomal aberrations.

Abnormal brain magnetic resonance imaging in two patients with Smith-Magenis syndrome

Smith-Magenis syndrome (SMS) is a clinically recognizable contiguous gene syndrome ascribed to an interstitial deletion in chromosome 17p11.2. Seventy percent of SMS patients have a common deletion interval spanning 3.5 megabases (Mb). Clinical features of SMS include characteristic mild dysmorphic features, ocular anomalies, short stature, brachydactyly, and hypotonia. SMS patients have a unique neurobehavioral phenotype that includes intellectual disability, self-injurious behavior and severe sleep disturbance. Little has been reported in the medical literature about anatomical brain anomalies in patients with SMS. Here we describe two patients with SMS caused by the common deletion in 17p11.2 diagnosed using chromosomal microarray (CMA). Both patients had a typical clinical presentation and abnormal brain magnetic resonance imaging (MRI) findings. One patient had subependymal periventricular gray matter heterotopia, and the second had a thin corpus callosum, a thin brain stem and hypoplasia of the cerebellar vermis. This report discusses the possible abnormal MRI images in SMS and reviews the literature on brain malformations in SMS. Finally, although structural brain malformations in SMS patients are not a common feature, we suggest baseline routine brain imaging in patients with SMS in particular, and in patients with chromosomal microdeletion/microduplication syndromes in general. Structural brain malformations in these patients may affect the decision-making process regarding their management.

Microarray-based prenatal diagnosis for the identification of fetal chromosome abnormalities

The goal of prenatal cytogenetic testing is to provide reassurance to the couple seeking testing for their pregnancy, identify chromosome abnormalities in the fetus, if present, and provide treatments and medical management for affected babies. Cytogenetic analysis of banded chromosomes has been the standard for identifying chromosome abnormalities in the fetus for over 40 years. With chromosome analysis, whole chromosome aneuploidies and large structural rearrangements can be identified. The sequencing of the human genome has provided the resources to develop molecular tools that allow higher resolution observations of human chromosomes. The future holds the promise of sequencing that may identify chromosomal imbalances and deleterious single nucleotide variants. This review will focus on the use of genomic microarrays for the testing and identification of chromosome anomalies in prenatal diagnosis and will discuss the future directions of fetal testing.

The utility of chromosomal microarray analysis in developmental and behavioral pediatrics

Chromosomal microarray analysis (CMA) has emerged as a powerful new tool to identify genomic abnormalities associated with a wide range of developmental disabilities including congenital malformations, cognitive impairment, and behavioral abnormalities. CMA includes array comparative genomic hybridization (CGH) and single nucleotide polymorphism (SNP) arrays, both of which are useful for detection of genomic copy number variants (CNV) such as microdeletions and microduplications. The frequency of disease-causing CNVs is highest (20%-25%) in children with moderate to severe intellectual disability accompanied by malformations or dysmorphic features. Disease-causing CNVs are found in 5%-10% of cases of autism, being more frequent in severe phenotypes. CMA has replaced Giemsa-banded karyotype as the first-tier test for genetic evaluation of children with developmental and behavioral disabilities.

The use of cytogenetic microarrays in myelodysplastic syndrome characterization

Various microarray platforms, including BAC, oligonucleotide, and SNP arrays, have been shown to -provide clinically useful diagnostic and prognostic information for patients with myelodysplastic syndromes (MDS). Clinically useful arrays are designed with specific purposes in mind and with attention to genomic content and probe density. All array types have been shown to detect genomic copy gains and losses, with SNP arrays having the added advantage of detecting copy neutral loss of heterozygosity (CNLOH). The finding of CNLOH has led to the identification of certain disease genes implicated in the initiation or progression of myeloid diseases. In addition, SNP karyotyping alone, or in conjunction with routine cytogenetics, can affect the outcome prediction and improve prognostic stratification of patients with MDS. Patients who were reclassified after array testing as having adverse-risk chromosomal findings correlated with poor survival. Results of over 25 published studies support the use of arrays in MDS testing. Because few balanced translocations are found in MDS, this disease is particularly amenable to microarray testing, and studies have shown better disease classification, identification of cryptic changes, and prognostication in this heterogeneous group of disorders. Novel genomic alterations identified by array testing may lead to better targeted therapies for treating patients with MDS.

Clinical utility of chromosomal microarray analysis

OBJECTIVE

To test the hypothesis that chromosomal microarray analysis frequently diagnoses conditions that require specific medical follow-up and that referring physicians respond appropriately to abnormal test results.

METHODS

A total of 46,298 postnatal patients were tested by chromosomal microarray analysis for a variety of indications, most commonly intellectual disability/developmental delay, congenital anomalies, dysmorphic features, and neurobehavioral problems. The frequency of detection of abnormalities associated with actionable clinical features was tallied, and the rate of physician response to a subset of abnormal tests results was monitored.

RESULTS

A total of 2088 diagnoses were made of more than 100 different disorders that have specific clinical features that warrant follow-up. The detection rate for these conditions using high-resolution whole-genome microarrays was 5.4%, which translates to 35% of all clinically significant abnormal test results identified in our laboratory. In a subset of cases monitored for physician response, appropriate clinical action was taken more than 90% of the time as a direct result of the microarray finding.

CONCLUSIONS

The disorders diagnosed by chromosomal microarray analysis frequently have clinical features that need medical attention, and physicians respond to the diagnoses with specific clinical actions, thus arguing that microarray testing provides clinical utility for a significant number of patients tested.

Germline mosaic transmission of a novel duplication of PXDN and MYT1L to two male half-siblings with autism

Autism is a neurodevelopmental disorder with a strong genetic component to susceptibility. In this study, we report the molecular characterization of an apparent de-novo 281 kb duplication of chromosome 2p25.3 in two male half-siblings with autism. The 2p25.3 duplication was first identified through a low-density microarray, validated with fluorescent in-situ hybridization, and duplication breakpoints were delineated using an Affymetrix 6.0 single-nucleotide polymorphism microarray. The fluorescent in-situ hybridization results validated the novel copy number variant and revealed the mother to be mosaic, with ∼33% of her lymphoblast cells carrying the duplication. Therefore, the duplication was transmitted through the mechanism of germline mosaicism. In addition, duplication breakpoints were refined and showed that PXDN is fully duplicated, whereas seven exons of the terminal portion of the 25 exon gene MYT1L are within the duplicated region. MYT1L, a gene predominately expressed in the brain, has recently been linked with other neuropsychiatric illness such as schizophrenia and depression. Results from this study indicate that the 2p25.3 duplication disrupting PXDN and MYT1L is a potential autism-causing variant in the pedigree reported here and should receive further consideration as a candidate for autism.

Comprehensive DNA copy number profile and BAC library construction of an Indian individual

Bacterial artificial chromosomes (BACs) are used in genomic variation studies due to their capacity to carry a large insert, their high clonal stability, low rate of chimerism and ease of manipulation. In the present study, an attempt was made to create the first genomic BAC library of an anonymous Indian male (IMBL4) consisting of 100,224 clones covering the human genome more than three times. Restriction mapping of 255 BAC clones by pulse field gel electrophoresis confirmed an average insert size of 120 kb. The library was screened by PCR using SHANK3 (SH3 and multiple ankyrin repeat domains 3) and OLFM3 (olfactomedin 3) specific primers. A selection of clones was analyzed by fluorescent in situ hybridization (FISH) and sequencing. Fine mapping of copy number variable regions by array based comparative genomic hybridization identified 467 CNVRs in the IMBL4 genome. The IMBL4 BAC library represents the first cataloged Indian genome resource for applications in basic and clinical research.

Microarray-based comparative genomic hybridization of cancer targets reveals novel, recurrent genetic aberrations in the myelodysplastic syndromes

The myelodysplastic syndromes (MDS) are a heterogeneous group of clonal disorders characterized by ineffective hematopoiesis, cytopenias, and a risk of transformation to acute myeloid leukemia (AML). However, only approximately 50% of primary MDS patients show clonal cytogenetic aberrations. To determine whether high-resolution microarray analysis would reveal new or additional aberrations, we analyzed 35 samples derived from patients with a diagnosis or suspicion of MDS and abnormal karyotypes. We used a whole-genome oligonucleotide microarray with targeted coverage of approximately 1900 genes associated with hematologic and other cancers. Clinically relevant copy number aberrations (CNAs) were identified by microarray-based comparative genomic hybridization (aCGH) in all samples (range 1-31, median 5). In 28 of 35 samples (80%), aCGH revealed new cytogenetic aberrations not seen by karyotype or fluorescence in situ hybridization (FISH). Furthermore, 132 cryptic aberrations (≤5 Mb) were identified in 25 cases (71.4%) including deletions of NF1, RUNX1, RASSF1, CCND1, TET2, DNMT3A, HRAS, PDGFRA and FIP1L1. Additionally, aCGH clarified known complex aberrations in 17 of 35 samples (48.6%). Finally, our results using whole-genome arrays with higher density coverage targeted to cancer features demonstrate the usefulness of arrays to identify rare and cryptic recurring imbalances that may prove to be significant in disease progression or transformation to AML and may improve the suitability or efficacy of molecularly targeted therapy.

Copy number variants of schizophrenia susceptibility loci are associated with a spectrum of speech and developmental delays and behavior problems

PURPOSE

: Recently, molecular cytogenetic techniques have identified novel copy number variants in individuals with schizophrenia. However, no large-scale prospective studies have been performed to characterize the broader spectrum of phenotypes associated with such copy number variants in individuals with unexplained physical and intellectual disabilities encountered in a diagnostic setting.

METHODS

: We analyzed 38,779 individuals referred to our diagnostic laboratory for microarray testing for the presence of copy number variants encompassing 20 putative schizophrenia susceptibility loci. We also analyzed the indications for study for individuals with copy number variants overlapping those found in six individuals referred for schizophrenia.

RESULTS

: After excluding larger gains or losses that encompassed additional genes outside the candidate loci (e.g., whole-arm gains/losses), we identified 1113 individuals with copy number variants encompassing schizophrenia susceptibility loci and 37 individuals with copy number variants overlapping those present in the six individuals referred to our laboratory for schizophrenia. Of these, 1035 had a copy number variant of one of six recurrent loci: 1q21.1, 15q11.2, 15q13.3, 16p11.2, 16p13.11, and 22q11.2. The indications for study for these 1150 individuals were diverse and included developmental delay, intellectual disability, autism spectrum, and multiple congenital anomalies.

CONCLUSION

: The results from our study, the largest genotype-first analysis of schizophrenia susceptibility loci to date, suggest that the phenotypic effects of copy number variants associated with schizophrenia are pleiotropic and imply the existence of shared biologic pathways among multiple neurodevelopmental conditions.

Whole exome and whole genome sequencing

PURPOSE OF REVIEW

The purpose of this review is to describe the new DNA sequencing technologies referred to as next-generation sequencing (NGS). These new methods are becoming central to research in human disease and are starting to be used in routine clinical care.

RECENT FINDINGS

Advances in instrumentation have dramatically reduced the cost of DNA sequencing. An individual's entire genome can now be sequenced for $7500. In addition, the software needed to analyze and help interpret this data is rapidly improving. This technology has been used by researchers to discover new genetic disorders and new disease associations. In the clinic, it can define the etiology in patients with undiagnosed genetic disorders and identify mutations in a cancer to help guide chemotherapy.

SUMMARY

Here we discuss how whole-exome sequencing and whole-genome sequencing are used in basic research and clinical care. These new techniques promise to speed research and affect how healthcare is delivered.

Context-based FISH localization of genomic rearrangements within chromosome 15q11.2q13 duplicons

BACKGROUND

Segmental duplicons (SDs) predispose to an increased frequency of chromosomal rearrangements. These rearrangements can cause a diverse range of phenotypes due to haploinsufficiency, in cis positional effects or gene interruption. Genomic microarray analysis has revealed gene dosage changes adjacent to duplicons, but the high degree of similarity between duplicon sequences has confounded unequivocal assignment of chromosome breakpoints within these intervals. In this study, we localize rearrangements within duplicon-enriched regions of Angelman/Prader-Willi (AS/PWS) syndrome chromosomal deletions with fluorescence in situ hybridization (FISH).

RESULTS

Breakage intervals in AS deletions were localized recursively with short, coordinate-defined, single copy (SC) and low copy (LC) genomic FISH probes. These probes were initially coincident with duplicons and regions of previously reported breakage in AS/PWS. Subsequently, probes developed from adjacent genomic intervals more precisely delineated deletion breakage intervals involving genes, pseudogenes and duplicons in 15q11.2q13. The observed variability in the deletion boundaries within previously described Class I and Class II deletion AS samples is related to the local genomic architecture in this chromosomal region.

CONCLUSIONS

Chromosome 15 abnormalities associated with SDs were precisely delineated at a resolution equivalent to genomic Southern analysis. This context-dependent approach can define the boundaries of chromosome rearrangements for other genomic disorders associated with SDs.

Multiplex ligation-dependent probe amplification for detection of chromosomal abnormalities in myelodysplastic syndrome and acute myeloid leukemia

Current strategies for detecting chromosome abnormalities in MDS/AML include FISH or traditional cytogenetics. MLPA detects abnormalities in multiple loci simultaneously, with higher resolution and throughput. Peripheral blood from 50 healthy subjects was used to establish probe-specific reference ranges, increasing MLPA sensitivity and specificity. MLPA was then performed on 110 FISH-tested blood or bone marrow samples from suspected leukemia patients. Our novel MLPA analysis system combined maximum stringency with sensitive detection of low-frequency abnormalities. Accuracy/specificity of MLPA were excellent compared to FISH. Our MLPA analysis/interpretation method provides a clinically robust, high-throughput, high-resolution option for detection of abnormalities associated with MDS/AML.

Evolving applications of microarray analysis in prenatal diagnosis

PURPOSE OF REVIEW

Evaluation of copy number variation by microarray analysis has significant advantages over standard metaphase karyotyping and is quickly becoming the primary means of postnatal genetic evaluation for neonates and infants with dysmorphic features or cognitive difficulties. Before this technology is routinely used for prenatal diagnosis, further evaluation of its value and the clinical dilemmas it may introduce requires further study. This article reviews the recent literature on array technology use in prenatal diagnosis.

RECENT FINDINGS

The use of microarray analysis for routine prenatal diagnosis is still being investigated. Use in certain prenatal situations such as the fetus with structural anomalies or those who are stillborn appears to add important, clinically relevant information. There are a broad range of array designs available and recent research has focused on the appropriate design for prenatal testing. Patient counseling may occasionally be difficult because of the uncertain phenotype associated with some array findings.

SUMMARY

We present a brief overview of microarray technology including benefits and limitations. Previous research regarding use of microarray in prenatal diagnosis including specific scenarios of anomalous fetuses and abnormal karyotype is reviewed. Current guidelines and the authors' recommendations are presented.

Evaluating chromosomal mosaicism by array comparative genomic hybridization in hematological malignancies: the proposal of a formula

Array-based comparative genomic hybridization (aCGH) has proven indispensable to the study of unbalanced constitutional and acquired chromosomal anomalies, but its sensitivity for detecting mosaicism is still not well established. On the basis of the ADM2 algorithm used for microarray image analysis with one of the most widely used oligomer-based aCGH platforms [the whole genome 244K system by Agilent Technologies (Santa Clara, CA)] we suggest a formula to infer the percentage of cells bearing a chromosome imbalance in cases with constitutional or acquired mosaicism. Three examples of acquired mosaicism in which this formula was applied are reported together with parallel fluorescence in situ hybridization (FISH) to interphase nuclei with informative probes. Although some approximation affects both the results inferred from aCGH and FISH data, the proposed formula was successful in the three patients studied.

Utilization of targeted array comparative genomic hybridization, MitoMet, in prenatal diagnosis of metabolic disorders

Metabolic disorders are inborn errors that often present in the neonatal period with a devastating clinical course. If not treated promptly, these diseases can result in severe, irreversible disease or death. Determining the molecular defects in metabolic diseases is important in providing a definitive diagnosis for patient management. Therefore, prenatal diagnosis for families with known mutations causing metabolic disorders is crucial for timely intervention. Here we present three families in which standard Sanger sequencing failed to provide a definitive diagnosis, but the detection of genomic deletions by array comparative genomic hybridization (CGH) specifically targeted to mitochondrial and metabolic disease genes, MitoMet®, was fundamental in providing accurate prenatal diagnosis. In addition, to our knowledge, two deletions are the smallest detected by oligonucleotide array CGH reported for their respective genes, OTC and ARG1. These data highlight the importance of targeted array CGH in patients with suspected metabolic disorders and incomplete or negative sequencing results, as well as its emerging role in prenatal diagnosis.

Whole-genome array CGH identifies pathogenic copy number variations in fetuses with major malformations and a normal karyotype

Despite a wide range of clinical tools, the etiology of mental retardation and multiple congenital malformations remains unknown for many patients. Array-based comparative genomic hybridization (aCGH) has proven to be a valuable tool in these cases, as its pangenomic coverage allows the identification of chromosomal aberrations that are undetectable by other genetic methods targeting specific genomic regions. Therefore, aCGH is increasingly used in clinical genetics, both in the postnatal and the prenatal settings. While the diagnostic yield in the postnatal population has been established at 10-12%, studies investigating fetuses have reported variable results. We used whole-genome aCGH to investigate fetuses presenting at least one major malformation detected on ultrasound, but for whom standard genetic analyses (including karyotype) failed to provide a diagnosis. We identified a clinically significant chromosomal aberration in 8.2% of tested fetuses (4/49), and a result of unclear clinical significance in 12.2% of tested fetuses (6/49). Our results document the value of whole-genome aCGH as a prenatal diagnostic tool and highlight the interpretation difficulties associated with copy number variations of unclear significance.

Comparative genomic hybridization on microarray (a-CGH) in constitutional and acquired mosaicism may detect as low as 8% abnormal cells

Background

The results of cytogenetic investigations on unbalanced chromosome anomalies, both constitutional and acquired, were largely improved by comparative genomic hybridization on microarray (a-CGH), but in mosaicism the ability of a-CGH to reliably detect imbalances is not yet well established. This problem of sensitivity is even more relevant in acquired mosaicism in neoplastic diseases, where cells carrying acquired imbalances coexist with normal cells, in particular when the proportion of abnormal cells may be low.

We constructed a synthetic mosaicism by mixing the DNA of three patients carrying altogether seven chromosome imbalances with normal sex-matched DNA. Dilutions were prepared mimicking 5%, 6%, 7%, 8%, 10% and 15% levels of mosaicism. Oligomer-based a-CGH (244 K whole-genome system) was applied on the patients' DNA and customized slides designed around the regions of imbalance were used for the synthetic mosaics.

Results and conclusions

The a-CGH on the synthetic mosaics proved to be able to detect as low as 8% abnormal cells in the tissue examined. Although in our experiment some regions of imbalances escaped to be revealed at this level, and were detected only at 10-15% level, it should be remarked that these ones were the smallest analyzed, and that the imbalances recurrent as clonal anomalies in cancer and leukaemia are similar in size to those revealed at 8% level.

Development of new postnatal diagnostic methods for chromosome disorders

Chromosome imbalances are the leading cause of intellectual and developmental disabilities in the population. This paper reviews the current methods used to diagnose chromosome abnormalities in children including karyotyping, fluorescence in situ hybridization and microarray technologies. Advances in molecular cytogenetics, especially with the use of microarrays, have substantially increased the detection of chromosome abnormalities in children with disabilities and congenital anomalies above that achievable with conventional cytogenetic banding and light microscopy.