Chromosomal microarray analysis in developmental delay and intellectual disability with comorbid conditions

A cohort study of neurodevelopmental disorders and/or congenital anomalies using high resolution chromosomal microarrays in southern Brazil highlighting the significance of ASD

Chromosomal microarray (CMA) is the reference in evaluation of copy number variations (CNVs) in individuals with neurodevelopmental disorders (NDDs), such as intellectual disability (ID) and/or autism spectrum disorder (ASD), which affect around 3-4% of the world's population. Modern platforms for CMA, also include probes for single nucleotide polymorphisms (SNPs) that detect homozygous regions in the genome, such as long contiguous stretches of homozygosity (LCSH). These regions result from complete or segmental chromosomal homozygosis and may be indicative of uniparental disomy (UPD), inbreeding, population characteristics, as well as replicative DNA repair events. In this retrospective study, we analyzed CMA reading files requested by geneticists and neurologists for diagnostic purposes along with available clinical data. Our objectives were interpreting CNVs and assess the frequencies and implications of LCSH detected by Affymetrix CytoScan HD (41%) or 750K (59%) platforms in 1012 patients from the south of Brazil. The patients were mainly children with NDDs and/or congenital anomalies (CAs). A total of 206 CNVs, comprising 132 deletions and 74 duplications, interpreted as pathogenic, were found in 17% of the patients in the cohort and across all chromosomes. Additionally, 12% presented rare variants of uncertain clinical significance, including LPCNVs, as the only clinically relevant CNV. Within the realm of NDDs, ASD carries a particular importance, owing to its escalating prevalence and its growing repercussions for individuals, families, and communities. ASD was one clinical phenotype, if not the main reason for referral to testing, for about one-third of the cohort, and these patients were further analyzed as a sub-cohort. Considering only the patients with ASD, the diagnostic rate was 10%, within the range reported in the literature (8-21%). It was higher (16%) when associated with dysmorphic features and lower (7%) for "isolated" ASD (without ID and without dysmorphic features). In 953 CMAs of the whole cohort, LCSH (≥ 3 Mbp) were analyzed not only for their potential pathogenic significance but were also explored to identify common LCSH in the South Brazilians population. CMA revealed at least one LCSH in 91% of the patients. For about 11.5% of patients, the LCSH suggested consanguinity from the first to the fifth degree, with a greater probability of clinical impact, and in 2.8%, they revealed a putative UPD. LCSH found at a frequency of 5% or more were considered common LCSH in the general population, allowing us to delineate 10 regions as potentially representing ancestral haplotypes of neglectable clinical significance. The main referrals for CMA were developmental delay (56%), ID (33%), ASD (33%) and syndromic features (56%). Some phenotypes in this population may be predictive of a higher probability of indicating a carrier of a pathogenic CNV. Here, we present the largest report of CMA data in a cohort with NDDs and/or CAs from the South of Brazil. We characterize the rare CNVs found along with the main phenotypes presented by each patient and show the importance and usefulness of LCSH interpretation in CMA results that incorporate SNPs, as well as we illustrate the value of CMA to investigate CNV in ASD.

Combining chromosomal microarray and clinical exome sequencing for genetic diagnosis of intellectual disability

Despite the current widespread use of chromosomal microarray analysis (CMA) and exome/genome sequencing for the genetic diagnosis of unexplained intellectual disability (ID) in children, gaining improved diagnostic yields and defined guidelines remains a significant challenge. This is a cohort study of children with unexplained ID. We analyzed the diagnostic yield and its correlation to clinical phenotypes in children with ID who underwent concurrent CMA and clinical exome sequencing (CES). A total of 154 children were included (110 [71.4%] male; mean [SD] age, 51.9 [23.1] months). The overall diagnosis yield was 26.0-33.8%, with CMA contributing 12.3-14.3% and CES contributing 13.6-19.4%, showing no significant difference. The diagnostic rate was significantly higher when gross motor delay (odds ratio, 6.69; 95% CI, 3.20-14.00; P < 0.001), facial dysmorphism (odds ratio, 9.34; 95% CI 4.29-20.30; P < 0.001), congenital structural anomaly (odds ratio 3.62; 95% CI 1.63-8.04; P = 0.001), and microcephaly or macrocephaly (odds ratio 4.87; 95% CI 2.05-11.60; P < 0.001) were presented. Patients with only ID without any other concomitant phenotype (63/154, 40.9%) exhibited a 6.3-11.1% diagnostic rate.

Chromosomal Aberrations in Pediatric Patients With Moderate/Severe Developmental Delay/Intellectual Disability With Abundant Phenotypic Heterogeneities: A Single-Center Study

BACKGROUND

This study aimed to examine the clinical usefulness of chromosome microarray (CMA) for selective implementation in patients with unexplained moderate or severe developmental delay/intellectual disability (DD/ID) and/or combined with different dysphonic features in the Han Chinese population.

METHODS

We retrospectively analyzed data on 122 pediatric patients with unexplained isolated moderate/severe DD/ID with or without autism spectrum disorders, epilepsy, dystonia, and congenital abnormalities from a single-center neurorehabilitation clinic in southern China.

RESULTS

A total of 46 probands (37.7%) had abnormal CMA results among the 122 study patients. With the exclusion of aneuploidies, uniparental disomies, and multiple homozygotes, 37 patients harbored 39 pathogenic copy number variations (pCNVs) (median [interquartile range] size: 3.57 [1.6 to 7.1] Mb; 33 deletions and 6 duplications), enriched in chromosomes 5, 7, 15, 17, and 22, with a markedly high prevalence of Angelman/Prader-Willi syndrome (24.3% [nine of 37]). Three rare deletions in the regions 5q33.2q34, 17p13.2, and 13q33.2 were reported, with specific delineation of clinical phenotypes. The frequencies of pCNVs were 18%, 33.3%, 38.89%, 41.67%, and 100% for patients with 1, 2, 3, 4, and 5 study phenotypes, respectively; patients with more concomitant abnormalities in the heart, brain, craniofacial region, and/or other organs had a higher CMA diagnostic yield and pCNV prevalence (P < 0.05).

CONCLUSIONS

Clinical application of CMA as a first-tier test among patients with moderate/severe DD/ID combined with congenital structural anomalies improved diagnostic yields and the quality of clinical management in this series of patients.

15q26.3 deletions distal to IGF1R cause growth retardation, congenital heart defect and skeletal anomalies: Case report and review of literature

15q26 deletion is a rare genomic disorder characterized by intrauterine and postnatal growth retardation, microcephaly, intellectual disability, and congenital malformations. Here, we report a 4-month-old female with intrauterine growth retardation, short stature, pulmonary hypertension, atrial septal defect and congenital bowing of long bones of the legs. Chromosomal microarray analysis showed a de novo deletion of approximately 2.1 Mb at 15q26.3 region that does not include IGF1R. Our analysis of patients documented in the literature and the DECIPHER database with 15q26 deletions distal to IGF1R, including 10 patients with de novo pure deletions, allowed us to define the smallest region of overlap to 686 kb. This region includes ALDH1A3, LRRK1, CHSY1, SELENOS, SNRPA1, and PCSK6. We propose haploinsufficiency of one or more genes, besides IGF1R, within this region may contribute to the clinical findings in patients with 15q26.3 deletion.

Genetic Testing in Children with Developmental and Epileptic Encephalopathies: A Review of Advances in Epilepsy Genomics

Advances in disease-related gene discovery have led to tremendous innovations in the field of epilepsy genetics. Identification of genetic mutations that cause epileptic encephalopathies has opened new avenues for the development of targeted therapies. Clinical testing using extensive gene panels, exomes, and genomes is currently accessible and has resulted in higher rates of diagnosis and better comprehension of the disease mechanisms underlying the condition. Children with developmental disabilities have a higher risk of developing epilepsy. As our understanding of the mechanisms underlying encephalopathies and epilepsies improves, there may be greater potential to develop innovative therapies tailored to an individual’s genotype. This article provides an overview of the significant progress in epilepsy genomics in recent years, with a focus on developmental and epileptic encephalopathies in children. The aim of this review is to enhance comprehension of the clinical utilization of genetic testing in this particular patient population. The development of effective and precise therapeutic strategies for epileptic encephalopathies may be facilitated by a comprehensive understanding of their molecular pathogenesis.

Genetic and metabolic investigations for neurodevelopmental disorders: position statement of the Canadian College of Medical Geneticists (CCMG)

PURPOSE AND SCOPE

The aim of this position statement is to provide recommendations for clinicians regarding the use of genetic and metabolic investigations for patients with neurodevelopmental disorders (NDDs), specifically, patients with global developmental delay (GDD), intellectual disability (ID) and/or autism spectrum disorder (ASD). This document also provides guidance for primary care and non-genetics specialists caring for these patients while awaiting consultation with a clinical geneticist or metabolic specialist.

METHODS OF STATEMENT DEVELOPMENT

A multidisciplinary group reviewed existing literature and guidelines on the use of genetic and metabolic investigations for the diagnosis of NDDs and synthesised the evidence to make recommendations relevant to the Canadian context. The statement was circulated for comment to the Canadian College of Medical Geneticists (CCMG) membership-at-large and to the Canadian Pediatric Society (Mental Health and Developmental Disabilities Committee); following incorporation of feedback, it was approved by the CCMG Board of Directors on 1 September 2022.

RESULTS AND CONCLUSIONS

Chromosomal microarray is recommended as a first-tier test for patients with GDD, ID or ASD. Fragile X testing should also be done as a first-tier test when there are suggestive clinical features or family history. Metabolic investigations should be done if there are clinical features suggestive of an inherited metabolic disease, while the patient awaits consultation with a metabolic physician. Exome sequencing or a comprehensive gene panel is recommended as a second-tier test for patients with GDD or ID. Genetic testing is not recommended for patients with NDDs in the absence of GDD, ID or ASD, unless accompanied by clinical features suggestive of a syndromic aetiology or inherited metabolic disease.

Evaluation of Individuals with Non-Syndromic Global Developmental Delay and Intellectual Disability

Global Developmental Delay (GDD) and Intellectual Disability (ID) are two of the most common presentations encountered by physicians taking care of children. GDD/ID is classified into non-syndromic GDD/ID, where GDD/ID is the sole evident clinical feature, or syndromic GDD/ID, where there are additional clinical features or co-morbidities present. Careful evaluation of children with GDD and ID, starting with detailed history followed by a thorough examination, remain the cornerstone for etiologic diagnosis. However, when initial history and examination fail to identify a probable underlying etiology, further genetic testing is warranted. In recent years, genetic testing has been shown to be the single most important diagnostic modality for clinicians evaluating children with non-syndromic GDD/ID. In this review, we discuss different genetic testing currently available, review common underlying copy-number variants and molecular pathways, explore the recent evidence and recommendations for genetic evaluation and discuss an approach to the diagnosis and management of children with non-syndromic GDD and ID.

The exploration of genetic aetiology and diagnostic strategy for 321 Chinese individuals with intellectual disability

BACKGROUND

Intellectual disability is a heterogeneous neurodevelopmental disorder with complex genetic architectures. Different sequential methodologies are usually applied to identify the genetic aetiologies of ID patients.

METHODS

We collected 321 consecutive ID patients. All patients underwent karyotyping, while 293 and 164 cases further received copy number variation sequencing (CNV-seq) and whole-exome sequencing (WES). The updated WES technology can detect CNVs simultaneously. The diagnostic data from 137 patients who received WES and CNV-seq were used to define the approach that could be recommended as the first-tier test.

RESULTS

WES obtains the highest diagnostic yield of 50% (82/164), compared with karyotyping (7.79%, 25/321) and CNV-seq (19.80%, 58/293). Among the variants detected by WES, 66.67% (44/66) de novo and 57.58% (38/66) novel pathogenic/likely pathogenic (P/LP) variants were identified in patients with ID. Besides, 24 out of 25P/LP CNVs discovered by CNV-seq can also be accurately identified using WES in 137 patients who received WES and CNV-seq. Thus, genetic abnormalities found through karyotyping, CNV-seq, and WES can be completely detected by combined karyotyping and WES.

CONCLUSIONS

This study illustrates the genetic aberrations of a Chinese ID cohort and expands the mutation spectrum of ID-related genes. Compared with the conventional diagnostic strategy, a combination of karyotype analysis and WES could be recommended as the first-tier diagnostic strategy for ID patients.

Complex Diagnostics of Non-Specific Intellectual Developmental Disorder

Intellectual development disorder (IDD) is characterized by a general deficit in intellectual and adaptive functioning. In recent years, there has been a growing interest in studying the genetic structure of IDD. Of particular difficulty are patients with non-specific IDD, for whom it is impossible to establish a clinical diagnosis without complex genetic diagnostics. We examined 198 patients with non-specific IDD from 171 families using whole-exome sequencing and chromosome microarray analysis. Hereditary forms of IDD account for at least 35.7% of non-specific IDD, of which 26.9% are monogenic forms. Variants in the genes associated with the BAF (SWI/SNF) complex were the most frequently identified. We were unable to identify phenotypic features that would allow differential diagnosis of monogenic and microstructural chromosomal rearrangements in non-specific IDD at the stage of clinical examination, but due to its higher efficiency, exome sequencing should be the diagnostic method of the highest priority study after the standard examination of patients with NIDD in Russia.

Utility of Chromosomal Microarray in Children with Unexplained Developmental Delay/Intellectual Disability

ObjectiveTo evaluate the chromosomal microarray (CMA) yield among children who presented with global developmental delay/intellectual disability (GDD/ID) with/without co-occurring conditions. Methods: The pathogenic copy number variation (pCNVs) findings on CMA of all children who presented with unexplained GDD/ID were categorized based on the clinical features. The karyotype results were compared with CMA. Results: The overall pCNV yield in children presenting with GDD/ID with or without comorbid conditions constituted 20.9%. Among the 17 pCNVs, 13 were losses and four were gains. Cardiac defect was the only co-morbidity in our study that demonstrated statistically significant prediction for pCNV (odds ratio 6.13, p value- 0.031). Six children who were karyotyped prior to CMA testing showed a structural abnormality. Conclusions: In our study, 20.9% of children with GDD/ID showed pCNVs on CMA. Cardiac defect alongside GDD/ID, emerged as the single strongest phenotype associated with pCNVs. CMA also provided vital information in previously karyotyped patients.

Genome sequencing demonstrates high diagnostic yield in children with undiagnosed global developmental delay/intellectual disability: a prospective study

Genome sequencing(GS) has been used in the diagnosis of global developmental delay(GDD)/intellectual disability(ID). However, the performance of GS in patients with inconclusive results from chromosomal microarray analysis(CMA) and exome sequencing(ES) is unknown. We recruited 100 pediatric GDD/ID patients from multiple sites in China from February 2018 to August 2020 for GS. Patients have received at least one genomic diagnostic test prior to enrollment. Reanalysis of their CMA/ES data was performed. The yield of GS was calculated and explanations for missed diagnoses by CMA/ES were investigated. Clinical utility was assessed by interviewing the parents by phone. The overall diagnostic yield of GS was 21%. Seven cases could have been solved with reanalysis of ES data. Thirteen families were missed by previous CMA/ES due to improper methodology. Two remained unsolved after ES reanalysis due to complex variants missed by ES, and a CNV in untranslated regions. Follow-up of the diagnosed families revealed that nine families experienced changes in clinical management, including identification of targeted treatments, cessation of unnecessary treatment, and considerations for family planning. GS demonstrated high diagnostic yield and clinical utility in this undiagnosed GDD/ID cohort, detecting a wide range of variant types of different sizes in a single workflow. This article is protected by copyright. All rights reserved.

Chromosomal microarray analysis of 410 Han Chinese patients with autism spectrum disorder or unexplained intellectual disability and developmental delay

Copy number variants (CNVs) are recognized as a crucial genetic cause of neurodevelopmental disorders (NDDs). Chromosomal microarray analysis (CMA), the first-tier diagnostic test for individuals with NDDs, has been utilized to detect CNVs in clinical practice, but most reports are still from populations of European ancestry. To contribute more worldwide clinical genomics data, we investigated the genetic etiology of 410 Han Chinese patients with NDDs (151 with autism and 259 with unexplained intellectual disability (ID) and developmental delay (DD)) using CMA (Affymetrix) after G-banding karyotyping. Among all the NDD patients, 109 (26.6%) carried clinically relevant CNVs or uniparental disomies (UPDs), and 8 (2.0%) had aneuploidies (6 with trisomy 21 syndrome, 1 with 47,XXY, 1 with 47,XYY). In total, we found 129 clinically relevant CNVs and UPDs, including 32 CNVs in 30 ASD patients, and 92 CNVs and 5 UPDs in 79 ID/DD cases. When excluding the eight patients with aneuploidies, the diagnostic yield of pathogenic and likely pathogenic CNVs and UPDs was 20.9% for all NDDs (84/402), 3.3% in ASD (5/151), and 31.5% in ID/DD (79/251). When aneuploidies were included, the diagnostic yield increased to 22.4% for all NDDs (92/410), and 33.6% for ID/DD (87/259). We identified a de novo CNV in 14.9% (60/402) of subjects with NDDs. Interestingly, a higher diagnostic yield was observed in females (31.3%, 40/128) compared to males (16.1%, 44/274) for all NDDs (P = 4.8 × 10^-4), suggesting that a female protective mechanism exists for deleterious CNVs and UPDs.

Chromosomal Microarray Analysis Has a Poor Diagnostic Yield in Children with Developmental Delay/Intellectual Disability When Concurrent Cerebellar Anomalies Are Present

Chromosomal microarray analysis is commonly used as screening test for children with neurodevelopmental issues, also in case of complex neurological phenotypes. Developmental delay/intellectual disability is a common presentation sign in pediatric ataxias, diseases with high clinical and genetic heterogeneity. In order to determine the diagnostic yield of Array-CGH in such conditions, all the tests performed in the last 10-year activity of a single referral center in children who present, besides the neurodevelopmental impairment, cerebellar abnormalities have been systematically gathered. The study demonstrates that, except for Dandy-Walker malformation or poly-malformative phenotypes, chromosomal microarray analysis should be discouraged as first-line diagnostic test in pediatric ataxias with neurodevelopmental disability.

Genetic Testing in Neurodevelopmental Disorders

Neurodevelopmental disorders are the most prevalent chronic medical conditions encountered in pediatric primary care. In addition to identifying appropriate descriptive diagnoses and guiding families to evidence-based treatments and supports, comprehensive care for individuals with neurodevelopmental disorders includes a search for an underlying etiologic diagnosis, primarily through a genetic evaluation. Identification of an underlying genetic etiology can inform prognosis, clarify recurrence risk, shape clinical management, and direct patients and families to condition-specific resources and supports. Here we review the utility of genetic testing in patients with neurodevelopmental disorders and describe the three major testing modalities and their yields - chromosomal microarray, exome sequencing (with/without copy number variant calling), and FMR1 CGG repeat analysis for fragile X syndrome. Given the diagnostic yield of genetic testing and the potential for clinical and personal utility, there is consensus that genetic testing should be offered to all patients with global developmental delay, intellectual disability, and/or autism spectrum disorder. Despite this recommendation, data suggest that a minority of children with autism spectrum disorder and intellectual disability have undergone genetic testing. To address this gap in care, we describe a structured but flexible approach to facilitate integration of genetic testing into clinical practice across pediatric specialties and discuss future considerations for genetic testing in neurodevelopmental disorders to prepare pediatric providers to care for patients with such diagnoses today and tomorrow.

Genetic diagnoses in pediatric patients with epilepsy and comorbid intellectual disability

PURPOSE

The aim of this retrospective study is to investigate the genetic etiology and propose a diagnostic strategy for pediatric patients with epilepsy and comorbid intellectual disability (ID).

METHODS

From September 2014 to May 2020, a total of 102 pediatric patients diagnosed with epilepsy with co-morbid ID with unknown causes were included in this study. All patients underwent tests of single nucleotide polymorphism (SNP) array for chromosomal abnormalities. Whole exome sequencing (WES) was consecutively performed in patients without diagnostic copy number variants (CNVs) (n = 85) for single nucleotide variants (SNVs). Subgroup analyses based on the age of seizure onset and ID severity were done.

RESULTS

The overall diagnostic yield of genetic aberrations was 33.3 % (34/102), which comprised 50.0 % with diagnostic CNVs and 50.0 % with diagnostic SNVs. The yield nominally increased with ID severity and decreased with age of seizure onset, though this result was not statistically significant. The diagnostic yield of SNVs in patients with seizure onset in the first year of life (25.0 % (11/44)) was significantly higher than those with childhood-onset epilepsy (10.3 % (6/58)) (p = 0.049), however, the diagnostic yield of CNVs in patients with childhood-onset epilepsy (17.2 % (10/58) was higher than the diagnostic yield of SNVs (10.3 % (6/58)). The most frequently syndromic epilepsy detected by SNP array was Angelman syndrome (n=4), including one confirmed with paternal uniparental disomy. Meanwhile, the most frequent SNVs were mutations of MECP2 (n=2) and IQSEC2 (n = 2) in sporadic cases.

CONCLUSION

Both CMA and WES are advantageous as unbiased approaches for a genetically heterogeneous condition. We proposed an effective diagnostic strategy for pediatric patients with epilepsy. For patients with seizure onset in the first year of life, WES is recommended as the first-tier test. However, for patients with childhood-onset epilepsy, SNP array should be considered for the first-tier test.

Detection of Copy Number Variants by Short Multiply Aggregated Sequence Homologies

Chromosomal microarray testing is indicated for patients with diagnoses including unexplained developmental delay or intellectual disability, autism spectrum disorders, and multiple congenital anomalies. The short multiply aggregated sequence homologies (SMASH) genomic assay is a novel next-generation sequencing technology that performs copy number analysis at resolution similar to high-coverage whole genome sequencing but requires far less capacity. We benchmarked the performance of SMASH on a panel of genomic DNAs containing known copy number variants (CNVs). SMASH was able to detect pathogenic copy number variants of ≥10 kb in 77 of 77 samples. No pathogenic events were seen in 32 of 32 controls, indicating 100% sensitivity and specificity for detecting pathogenic CNVs >10 kb. Repeatability (interassay precision) and reproducibility (intra-assay precision) were assessed with 13 samples and showed perfect concordance. We also established that SMASH had a limit of detection of 20% for detection of large mosaic CNVs. Finally, we analyzed seven blinded specimens by SMASH analysis and successfully identified all pathogenic events. These results establish the efficacy of the SMASH genomic assay as a clinical test for the detection of pathogenic copy number variants at a resolution comparable to chromosomal microarray analysis.

The diagnostic yield of intellectual disability: combined whole genome low-coverage sequencing and medical exome sequencing

Background

Intellectual disability (ID) is a heterogeneous neurodevelopmental disorder with a complex genetic underpinning in its etiology. Chromosome microarray (CMA) is recommended as the first-tier diagnostic test for ID due to high detection rate of copy number variation (CNV).

Methods

To identify an appropriate clinical detection scheme for ID in Han Chinese patients, whole genome low-coverage sequencing was performed as the first-tier diagnostic test, and medical exome sequencing (MES) as the second-tier diagnostic test for patients with negative results of CNVs.

Results

A total of 19 pathogenic CNVs in 16/95(16.84%) ID patients and 10 pathogenic single-nucleotide variations (SNVs), including 6 novel mutations in 8/95(8.42%) ID patients were identified on whom no pathogenic CNVs were discovered. The detection rate of CNVs in ID with multiple congenital anomalies (MCA) subgroup was significantly higher than ID with autism spectrum disorders and other IDs subgroups. And the single-nucleotide variations showed a higher occurrence rate in the other IDs subgroup.

Conclusions

There were differences in the diagnostic yields of different variation types among the three ID subgroups. Our findings provided a new perspective on appropriate clinical detection scheme in different ID subgroups based on statistically significant differences among the three ID subgroups. The application of whole genome low-coverage sequencing as the first-tier diagnostic test for ID with MCA subgroup and MES as the first-tier diagnostic test for other ID subgroup was considered as an efficient clinical detection scheme.

Genome-Wide Sequencing for Unexplained Developmental Disabilities or Multiple Congenital Anomalies: A Health Technology Assessment

BACKGROUND

People with unexplained developmental disabilities or multiple congenital anomalies might have had many biochemical, metabolic, and genetic tests for a period of years without receiving a diagnosis. A genetic diagnosis can help these people and their families better understand their condition and may help them to connect with others who have the same condition. Ontario Health (Quality), in collaboration with the Canadian Agency for Drugs and Technologies in Health (CADTH) conducted a health technology assessment about the use of genome-wide sequencing for patients with unexplained developmental disabilities or multiple congenital anomalies. Ontario Health (Quality) evaluated the effectiveness, cost-effectiveness, and budget impact of publicly funding genome-wide sequencing. We also conducted interviews with patients and examined the quantitative evidence of preferences and values literature to better understand the patient preferences and values for these tests.

METHODS

Ontario Health (Quality) performed a systematic literature search of the clinical evidence. We assessed the risk of bias of each included study using the Risk of Bias Assessment tool for Non-randomized Studies (RoBANS) and the quality of the body of evidence according to the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) Working Group criteria. We also performed a search of the quantitative evidence and undertook direct patient engagement to ascertain patient preferences for genetic testing for unexplained developmental disabilities or multiple congenital anomalies. CADTH performed a review of qualitative literature about patient perspectives and experiences, and a review of ethical issues.Ontario Health (Quality) performed an economic literature review of genome-wide sequencing in people with unexplained developmental disabilities or multiple congenital anomalies. Although we found eight published cost-effectiveness studies, none completely addressed our research question. Therefore, we conducted a primary economic evaluation using a discrete event simulation model. Owing to its high cost and early stage of clinical implementation, whole exome sequencing is primarily used for people who do not have a diagnosis from standard testing (referred to here as whole exome sequencing after standard testing; standard testing includes chromosomal microarray and targeted single-gene tests or gene panels). Therefore, in our first analysis, we evaluated the cost-effectiveness of whole exome sequencing after standard testing versus standard testing alone. In our second analysis, we explored the cost-effectiveness of whole exome and whole genome sequencing used at various times in the diagnostic pathway (e.g., first tier, second tier, after standard testing) versus standard testing. We also estimated the budget impact of publicly funding genome-wide sequencing in Ontario for the next 5 years.

RESULTS

Forty-four studies were included in the clinical evidence review. The overall diagnostic yield of genome-wide sequencing for people with unexplained development disability and multiple congenital anomalies was 37%, but we are very uncertain about this estimate (GRADE: Very Low). Compared with standard genetic testing of chromosomal microarray and targeted single-gene tests or gene panels, genome-wide sequencing could have a higher diagnostic yield (GRADE: Low). As well, for some who are tested, genome-wide sequencing prompts some changes to medications, treatments, and referrals to specialists (GRADE: Very Low).Whole exome sequencing after standard testing cost an additional $3,261 per patient but was more effective than standard testing alone. For every 1,000 persons tested, using whole exome sequencing after standard testing would lead to an additional 240 persons with a molecular diagnosis, 272 persons with any positive finding, and 46 persons with active treatment change (modifications to medications, procedures, or treatment). The resulting incremental cost-effectiveness ratios (ICERs) were $13,591 per additional molecular diagnosis. The use of genome-wide sequencing early in the diagnostic pathway (e.g., as a first- or second-tier test) can save on costs and improve diagnostic yields over those of standard testing. Results remained robust when parameters and assumptions were varied.Our budget impact analysis showed that, if whole exome sequencing after standard testing continues to be funded through Ontario's Out-of-Country Prior Approval Program, its budget impact would range from $4 to $5 million in years 1 to 5. If whole exome sequencing becomes publicly funded in Ontario (not through the Out-of-Country Prior Approval Program), the budget impact would be about $9 million yearly. We also found that using whole exome sequencing as a second-tier test would lead to cost savings ($3.4 million per 1,000 persons tested yearly).Participants demonstrated consistent motivations for and expectations of obtaining a diagnosis for unexplained developmental delay or congenital anomalies through genome-wide sequencing. Patients and families greatly value the support and information they receive through genetic counselling when considering genome-wide sequencing and learning of a diagnosis.

CONCLUSIONS

Genome-wide sequencing could have a higher diagnostic yield than standard testing for people with unexplained developmental disabilities or multiple congenital anomalies. Genome-wide sequencing can also prompt some changes to medications, treatments, and referrals to specialists for some people tested; however, we are very uncertain about this. Genome-wide sequencing could be a cost-effective strategy when used after standard testing to diagnose people with unexplained developmental disabilities or multiple congenital anomalies. It could also lead to cost savings when used earlier in the diagnostic pathway. Patients and families consistently noted a benefit from seeking a diagnosis through genetic testing.

Proband-Only Clinical Exome Sequencing for Neurodevelopmental Disabilities

BACKGROUND

Whole exome sequencing on family trios gives the highest diagnostic yield, but high cost limits its application. Here, we performed proband-only clinical exome sequencing in a population of patients with neurodevelopmental disabilities and tested the diagnostic yield.

METHODS

This observational, retrospective study included 108 unrelated patients with neurodevelopmental disabilities who underwent clinical exome sequencing at the outpatient clinics of the Severance Children's Hospital, Seoul, South Korea, between March 2017 and May 2018. Clinical exome sequencing targeted 4503 disease-causing genes.

RESULTS

The overall diagnostic rate was 38.0% (41 of 108) when proband-only clinical exome sequencing was performed without additional parental testing. Four sequence variants were reclassified as likely pathogenic after parental testing, representing an additional 3.7% of the diagnostic yield. The final diagnostic rate was 41.7% (45 of 108). Of 45 patients with genetic abnormalities, a total of 38 sequence variations were detected in 33 (30.6%) patients with five homozygous cases, and 13 chromosomal copy number variants were detected in 12 (11.1%) patients. Novel variants of known causal genes for neurodevelopmental disabilities were detected in 18 (16.7%) patients. These were variants that could be reclassified as likely pathogenic if the de novo nature of the mutation was confirmed after testing of parental samples.

CONCLUSIONS

Proband-only clinical exome sequencing is a practical diagnostic tool that may be implemented in the clinical setting for patients with neurodevelopmental disabilities. A cost-effective approach to neurodevelopmental disabilities would be a proband-only clinical exome sequencing followed by parental testing of selective candidate variants.

Rare Copy Number Variations in a Chinese Cohort of Autism Spectrum Disorder

Autism spectrum disorder (ASD) is heterogeneous in symptom and etiology. Rare copy number variations (CNVs) are important genetic factors contributing to ASD. Currently chromosomal microarray (CMA) detecting CNVs is recommended as a first-tier diagnostic assay, largely based on research in North America and Europe. The feature of rare CNVs has not been well characterized in ASD cohorts from non-European ancestry. In this study, high resolution CMA was utilized to investigate rare CNVs in a Chinese cohort of ASD (n = 401, including 177 mildly/moderately and 224 severely affected individuals), together with an ancestry-matched control cohort (n = 197). Diagnostic yield was about 4.2%, with 17 clinically significant CNVs identified in ASD individuals, of which 12 CNVs overlapped with recurrent autism risk loci or genes. Autosomal rare CNV burden analysis showed an overrepresentation of rare loss events in ASD cohort, whereas the rate of rare gain events correlated with the phenotypic severity. Further analysis showed rare losses disrupting genes highly intolerant of loss-of-function variants were enriched in the ASD cohort. Among these highly constrained genes disrupted by rare losses, RIMS2 is a promising candidate contributing to ASD risk. This pilot study evaluated clinical utility of CMA and the feature of rare CNVs in Chinese ASD, with candidate genes identified as potential risk factors.

Prenatal Diagnosis of BACs-on-Beads Assay in 3647 Cases of Amniotic Fluid Cells

OBJECTIVE

To evaluate the diagnostic accuracy of the BACs-on-Beads (BoBs) assay for the rapid diagnosis of common aneuploidies and microdeletion syndromes.

METHODS

BACs-on-Beads and chromosomal karyotyping were used for detecting 3647 cases of amniotic fluid samples with indications for prenatal diagnosis, which were collected from January 2015 to June 2017 in Xijing Hospital. Fluorescence in situ hybridization (FISH) or chromosomal microarray analysis (CMA) provided further validation.

RESULTS

The overall abnormality detection rate (BoBs combined with karyotyping) was 7.73% (282/3647). A total of 209 chromosomal aneuploidies, 10 mosaic cases, 11 microdeletion/microduplication syndromes, and 52 structural abnormalities were observed. Both assays were concordant for trisomy 21 (4.22%, 154/3647), trisomy 18 (0.69%, 25/3647), trisomy 13 (0.05%, 2/3647), and sex chromosome aneuploidies (0.77%, 28/3647). Meanwhile, DiGeorge syndrome (0.05%, 2/3647), 22q11.2 microduplication (0.08%, 3/3647), Smith-Magenis syndrome (0.03%, 1/3647), 17p11.2 microduplication (0.03%, 1/3647), Wolf-Hirschhorn syndrome (0.03%, 1/3647), Williams-Beuren syndrome (0.03%, 1/3647), Cri du Chat syndrome (0.03%, 1/3647), and Miller-Dieker syndrome (0.03%, 1/3647) were identified by BoBs assay, thus giving the incidence of the detection of these syndromes of 0.30% (11/3647).

CONCLUSION

BACs-on-Beads assay is a reliable test for rapid detection of common aneuploidies and microdeletion syndromes, combining with karyotyping, FISH, and CMA, to improve the efficiency and accuracy of prenatal diagnosis to alleviate maternal emotional anxiety.