Trio-based exome sequencing reveals a high rate of the de novo variants in intellectual disability

SNV/Indel and CNV Analysis in Trio-WES for Intellectual and Developmental Disabilities: Diagnostic Yield & Cost-Effectiveness

Intellectual and developmental disabilities (IDD) are clinically and genetically heterogeneous disorders of global concern. While whole exome sequencing (WES) is used to identify single nucleotide variants (SNVs) and small insertions/deletions (Indels) in IDD patients, its detection rate is limited. This study evaluated the value of integrating copy number variation (CNV) analysis into traditional SNV/Indel analysis based on trio-WES. One hundred eighty seven patients with IDD in 140 families from southwest China were incorporated into the study cohort. The overall diagnostic rate was 40.11% (75/187), with 33.16% (62/187) from SNV/Indel analysis and 6.95% (13/187) from CNV analysis. SNV/Indel analysis identified 52 variants in 42 genes, including 30 novel and 22 reported variants; CNV analysis identified 11 CNVs, comprising 1 repeat and 10 deletions, with sizes ranging from 1313 to 55 184 kb. 39.29% (55/140) families benefited from this study for their clinical diagnosis, treatment, and reproduction. Furthermore, our strategy, with an incremental cost-effectiveness ratio (ICER) of $2546.22/diagnosis, had demonstrated significant advantages in terms of cost-effectiveness and detection speed compared to previous methods. In general, by incorporating SNV/Indel and CNV analysis based on trio-WES, a robust, cost-effective, and time-saving approach for diagnosing IDD has been developed.

Diagnostic Utility of Trio-Exome Sequencing for Children With Neurodevelopmental Disorders

Importance

Copy number variants (CNVs) and single-nucleotide variations (SNVs) or insertions and deletions are key genetic contributors to neurodevelopmental disorders (NDDs). Traditionally, chromosome microarray and exome sequencing (ES) have been used to detect CNVs and single gene variants, respectively.

Objective

To identify genetic variants causing NDDs and evaluate the diagnostic yield and clinical utility of ES by simultaneously analyzing CNVs and SNVs in patients with NDDs and their biologic parents (trios).

Design, Setting, and Participants

This retrospective cohort study included pediatric patients with suspected NDDs who visited Shanghai Children's Hospital between January 1, 2018, and December 31, 2023. ES was used to investigate trios (trio-ES) including patients with NDDs who remained undiagnosed after phenotype identification and underwent gene panel testing, multiplex ligation-dependent probe amplification, or karyotyping. Comprehensive clinical and laboratory data were collected. Data were analyzed from July 2022 to December 2023.

Exposure

NDDs, characterized by global developmental delay or intellectual disability.

Main Outcomes and Measures

The study measured the overall diagnostic yield of SNVs and CNVs in the NDD cohort as well as within NDD syndromic subtypes.

Results

Of the 1106 patients with NDDs, 731 (66.1%) were male. The mean (SD) age of patients at diagnosis was 3.80 (2.82) years. The overall diagnostic yield of trio-ES was 46.1% (510 diagnoses among 1106 patients), with 149 CNVs (13.5%), 355 SNVs (32.1%), and 4 cases of uniparental disomy (0.4%). Codiagnosis of SNVs and CNVs occurred in 2 cases (0.2%). Among the trios, 812 candidate germline variants were identified, including 634 SNVs (78.1%), 174 CNVs (21.4%), and 4 cases of uniparental disomy (0.5%). Of these, 423 SNVs (66.7%) and 157 CNVs (90.2%) were diagnostic variants, while 211 SNVs (33.3%) and 17 CNVs (9.8%) were variants of uncertain significance. Sixteen CNVs smaller than 20 kilobase were detected using ES.

Conclusions and Relevance

In this cohort study, trio-ES, by simultaneously detecting SNVs and CNVs, achieved a diagnostic yield of 46.1%. Trio-ES may be particularly applicable for identifying small CNVs and recessive genetic diseases involving both SNVs and CNVs. These findings suggest that in clinical practice, simultaneously analyzing SNVs and CNVs using trio-ES data has a favorable genetic diagnostic yield for children with NDDs.

Chromosome 4 Duplication Associated with Strabismus Leads to Gene Expression Changes in iPSC-Derived Cortical Neurons

BACKGROUND/OBJECTIVES

Strabismus is the most common ocular disorder of childhood. Three rare, recurrent genetic duplications have been associated with both esotropia and exotropia, but the mechanisms by which they contribute to strabismus are unknown. This work aims to investigate the mechanisms of the smallest of the three, a 23 kb duplication on chromosome 4 (hg38|4:25,554,985-25,578,843).

METHODS

Using CRISPR and bridging oligos, we introduced the duplication into the Kolf2.1J iPSC line. We differentiated the parent line and the line with the duplication into cortical neurons using a three-dimensional differentiation protocol, and performed bulk RNASeq on neural progenitors (day 14) and differentiated neurons (day 63).

RESULTS

We successfully introduced the duplication into Kolf2.1J iPSCs by nucleofecting a bridging oligo for the newly formed junction along with cas9 ribonucleoparticles. We confirmed that the cells had a tandem duplication without inversion or deletion. The parent line and the line with the duplication both differentiated into neurons reliably. There were a total of 37 differentially expressed genes (DEGs) at day 63, 25 downregulated and 12 upregulated. There were 55 DEGs at day 14, 18 of which were also DEGs at day 63. The DEGs included a number of protocadherins, several genes involved in neuronal development, including SLITRK2, CSMD1, and VGF, and several genes of unknown function.

CONCLUSIONS

A copy number variant (CNV) that confers risk for strabismus affects gene expression of several genes involved in neural development, highlighting that strabismus most likely results from abnormal neural development, and identifying several new genes and pathways for further research into the pathophysiology of strabismus.

Trio-whole exome sequencing reveals the importance of de novo variants in children with intellectual disability and developmental delay

Understanding the genetic basis of developmental delay (DD) and intellectual disability (ID) remains a considerable clinical challenge. This study evaluated the clinical application of trio whole exome sequencing (WES) in children diagnosed with DD/ID. The study comprised 173 children with unexplained DD/ID. The participants underwent trio-WES and their demographic, clinical, and genetic characteristics were evaluated. Based on their clinical features, the participants were classified into two groups for further analysis: a syndromic DD/ID group and a non-syndromic DD/ID group. The genetic diagnostic yield of the 173 children diagnosed with DD/ID was 49.7% (86/173). This included 58 pathogenic or likely pathogenic single nucleotide variants (SNVs) in 41 genes identified across 54 individuals (31.2%) through trio-WES. Among these, 22 SNVs had not been previously reported. Additionally, 30 copy number variations (CNVs) were detected in 36 individuals (20.8%). The diagnostic yield in the syndromic DD/ID group was higher than that in the non-syndromic DD/ID group (57.8% vs. 47.2%, P < 0.001). Within the syndromic DD/ID subgroup, the diagnostic yield of the DD/ID with epilepsy subgroup (83.9%) was significantly higher than those of the other subgroups (P < 0.001). Based on the analysis of the individuals' clinical phenotypes, the individuals with facial dysmorphism shown a higher diagnostic yield (68.2%, P < 0.001). The diagnostic yield of SNVs was higher in the individuals with DD/ID accompanied by epilepsy, whereas the diagnostic yield of CNVs was higher in the DD/ID without epilepsy group. Similarly, the diagnostic yield of de novo SNVs was higher in the DD/ID with epilepsy group, while the diagnostic yield of de novo CNVs was higher in the DD/ID without epilepsy group (all P < 0.001). Trio-WES is a crucial tool for the genetic diagnosis of DD/ID, demonstrating a diagnostic yield of up to 49.7%. De novo variants in autosomal dominant genes are significant contributors to DD/ID, particularly in non-consanguineous families.

Application of multiple mosaic callers improves post-zygotic mutation detection from exome sequencing data

PURPOSE

The gold standard for identification of post-zygotic variants (PZVs) is droplet digital polymerase chain reaction or high-depth sequencing across multiple tissues types. These approaches are yet to be systematically implemented for monogenic disorders. We developed PZV detection pipelines for correct classification of de novo variants.

METHOD

Our pipelines detect PZV in parents (gonosomal mosaicism [pGoM]) and children (somatic mosaicism, "M3"). We applied them to research exome sequencing (ES) data from the Australian Cerebral Palsy Biobank (n = 145 trios) and Simons Simplex Collection (n = 405 families). Candidate mosaic variants were validated using deep amplicon sequencing or droplet digital polymerase chain reaction.

RESULTS

69.2% (M3trio), 63.9% (M3single), and 92.7% (pGoM) of detected variants were validated, with 48.6%, 56.7%, and 26.2% of variants, respectively, meeting strict criteria for mosaicism. In the Australian Cerebral Palsy Biobank, 16.6% of probands and 20.7% of parents had at least 1 true-positive somatic or pGoM variant, respectively. A large proportion of PZVs detected in Simons Simplex Collection parents (79.8%) and child (94.5%) were not previously reported. We reclassified 3.7% to 8.0% of germline de novo variants as mosaic.

CONCLUSION

Many PZVs were incorrectly classified as germline variants or missed by previous approaches. Systematic application of our pipelines could increase genetic diagnostic rate, improve estimates of recurrence risk in families, and benefit novel disease gene identification.

Developmental epileptic encephalopathy in DLG4-related synaptopathy

OBJECTIVE

The postsynaptic density protein of excitatory neurons PSD-95 is encoded by discs large MAGUK scaffold protein 4 (DLG4), de novo pathogenic variants of which lead to DLG4-related synaptopathy. The major clinical features are developmental delay, intellectual disability (ID), hypotonia, sleep disturbances, movement disorders, and epilepsy. Even though epilepsy is present in 50% of the individuals, it has not been investigated in detail. We describe here the phenotypic spectrum of epilepsy and associated comorbidities in patients with DLG4-related synaptopathy.

METHODS

We included 35 individuals with a DLG4 variant and epilepsy as part of a multicenter study. The DLG4 variants were detected by the referring laboratories. The degree of ID, hypotonia, developmental delay, and motor disturbances were evaluated by the referring clinician. Data on awake and sleep electroencephalography (EEG) and/or video-polygraphy and brain magnetic resonance imaging were collected. Antiseizure medication response was retrospectively assessed by the referring clinician.

RESULTS

A large variety of seizure types was reported, although focal seizures were the most common. Encephalopathy related to status epilepticus during slow-wave sleep (ESES)/developmental epileptic encephalopathy with spike-wave activation during sleep (DEE-SWAS) was diagnosed in >25% of the individuals. All but one individual presented with neurodevelopmental delay. Regression in verbal and/or motor domains was observed in all individuals who suffered from ESES/DEE-SWAS, as well as some who did not. We could not identify a clear genotype-phenotype relationship even between individuals with the same DLG4 variants.

SIGNIFICANCE

Our study shows that a subgroup of individuals with DLG4-related synaptopathy have DEE, and approximately one fourth of them have ESES/DEE-SWAS. Our study confirms DEE as part of the DLG4-related phenotypic spectrum. Occurrence of ESES/DEE-SWAS in DLG4-related synaptopathy requires proper investigation with sleep EEG.

Exome sequencing improves the molecular diagnostics of paediatric unexplained neurodevelopmental disorders

BACKGROUND

Neurodevelopmental disorders (NDDs) and/or associated multiple congenital abnormalities (MCAs) represent a genetically heterogeneous group of conditions with an adverse prognosis for the quality of intellectual and social abilities and common daily functioning. The rapid development of exome sequencing (ES) techniques, together with trio-based analysis, nowadays leads to up to 50% diagnostic yield. Therefore, it is considered as the state-of-the-art approach in these diagnoses.

RESULTS

In our study, we present the results of ES in a cohort of 85 families with 90 children with severe NDDs and MCAs. The interconnection of the in-house bioinformatic pipeline and a unique algorithm for variant prioritization resulted in a diagnostic yield of up to 48.9% (44/90), including rare and novel causative variants (41/90) and intragenic copy-number variations (CNVs) (3/90). Of the total number of 47 causative variants, 53.2% (25/47) were novel, highlighting the clinical benefit of ES for unexplained NDDs. Moreover, trio-based ES was verified as a reliable tool for the detection of rare CNVs, ranging from intragenic exon deletions (GRIN2A, ZC4H2 genes) to a 6-Mb duplication. The functional analysis using PANTHER Gene Ontology confirmed the involvement of genes with causative variants in a wide spectrum of developmental processes and molecular pathways, which form essential structural and functional components of the central nervous system.

CONCLUSION

Taken together, we present one of the first ES studies of this scale from the central European region. Based on the high diagnostic yield for paediatric NDDs in this study, 48.9%, we confirm trio-based ES as an effective and reliable first-tier diagnostic test in the genetic evaluation of children with NDDs.

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.

Trio-based exome sequencing broaden the genetic spectrum in keratoconus

Keratoconus (KC) is a complex corneal disorder with genetic factors involving in its pathogenesis. The genetic etiology of KC has not been fully elucidated. In this study, we aimed to expand the genetic spectrum in KC by trio-based exome sequencing. Trio-based exome sequencing was conducted in 20 patients with KC and their unaffected parents to broaden the genetic spectrum of the disease. With a series of filtering criteria, de novo, recessive homozygous, and compound heterozygous variants in candidate genes were identified, and the candidate genes were classified for further analysis. Finally, we identified 60 variants in 32 candidate genes through trio-based exome sequencing. Among the candidate genes, 10 genes (ARHGEF10, ARHGEF17, ASPM, FLNA, NDRG1, NEB, PLS3, STARD8, SYNE1, TTN) were classified as cytoskeleton-related genes, 4 genes (COL28A1, SDK1, STAB1, TENM2) were classified as cell adhesion-related genes, and 18 genes (APLP2, BCORL1, CCNB3, FOXN1, FUT8, GALNT10, HEPH, HHIP, HMGB3, HS6ST2, JADE3, KIAA0040, MCF2L, MYOF, QRICH2, RPS6KA6, SMARCA1, TNRC6A) were classified into other genes group. Additionally, the candidate rare deleterious variants in TTN were highly repeated in 25% trios. In conclusion, the study provided new insights into the genetic spectrum of KC which might underlie the genetic etiology for the disease. The findings would improve our understanding of pathogenesis in KC and provide critical clues to future functional validation.

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.

Analysis of trio test in neurodevelopmental disorders

BACKGROUND

Trio test has been widely used for diagnosis of various hereditary disorders. We aimed to investigate the contribution of trio test in genetically diagnosing neurodevelopmental disorders (NDD).

METHODS

We retrospectively reviewed 2,059 NDD cases with genetic test results. The trio test was conducted in 563 cases. Clinical usefulness, optimal timing, and methods for the trio test were reviewed.

RESULTS

Pathogenic or likely pathogenic variants were detected in 112 of 563 (19.9%) patients who underwent the trio test. With trio test results, the overall diagnostic yield increased by 5.4% (112/2,059). Of 165 de novo variants detected, 149 were pathogenic and we detected 85 novel pathogenic variants. Pathogenic, de novo variants were frequently detected in CDKL5, ATP1A3, and STXBP1.

CONCLUSION

The trio test is an efficient method for genetically diagnosing NDD. We identified specific situations where a certain trio test is more appropriate, thereby providing a guide for clinicians when confronted with variants of unknown significance of specific genes.