Multiple molecular diagnoses in the field of intellectual disability and congenital anomalies: 3.5% of all positive cases.

PURPOSE: Wide access to clinical exome/genome sequencing (ES/GS) enables the identification of multiple molecular diagnoses (MMDs), being a long-standing but underestimated concept, defined by two or more causal loci implicated in the phenotype of an individual with a rare disease. Only few series report MMDs rates (1.8% to 7.1%). This study highlights the increasing role of MMDs in a large cohort of individuals addressed for congenital anomalies/intellectual disability (CA/ID). METHODS: From 2014 to 2021, our diagnostic laboratory rendered 880/2658 positive ES diagnoses for CA/ID aetiology. Exhaustive search on MMDs from ES data was performed prospectively (January 2019 to December 2021) and retrospectively (March 2014 to December 2018). RESULTS: MMDs were identified in 31/880 individuals (3.5%), responsible for distinct (9/31) or overlapping (22/31) phenotypes, and potential MMDs in 39/880 additional individuals (4.4%). CONCLUSION: MMDs are frequent in CA/ID and remain a strong challenge. Reanalysis of positive ES data appears essential when phenotypes are partially explained by the initial diagnosis or atypically enriched overtime. Up-to-date clinical data, clinical expertise from the referring physician, strong interactions between clinicians and biologists, and increasing gene discoveries and improved ES bioinformatics tools appear all the more fundamental to enhance chances of identifying MMDs. It is essential to provide appropriate patient care and genetic counselling.

Copy number variants calling from WES data through eXome hidden Markov model (XHMM) identifies additional 2.5% pathogenic genomic imbalances smaller than 30 kb undetected by array-CGH.

It has been estimated that Copy Number Variants (CNVs) account for 10%-20% of patients affected by Developmental Disorder (DD)/Intellectual Disability (ID). Although array comparative genomic hybridization (array-CGH) represents the gold-standard for the detection of genomic imbalances, common Agilent array-CGH 4 × 180 kb arrays fail to detect CNVs smaller than 30 kb. Whole Exome sequencing (WES) is becoming the reference application for the detection of gene variants and makes it possible also to infer genomic imbalances at single exon resolution. However, the contribution of small CNVs in DD/ID is still underinvestigated. We made use of the eXome Hidden Markov Model (XHMM) software, a tool utilized by the ExAC consortium, to detect CNVs from whole exome sequencing data, in a cohort of 200 unsolved DD/DI patients after array-CGH and WES-based single nucleotide/indel variant analyses. In five out of 200 patients (2.5%), we identified pathogenic CNV(s) smaller than 30 kb, ranging from one to six exons. They included two heterozygous deletions in TCF4 and STXBP1 and three homozygous deletions in PPT1, CLCN2, and PIGN. After reverse phenotyping, all variants were reported as causative. This study shows the interest in applying sequencing-based CNV detection, from available WES data, to reduce the diagnostic odyssey of additional patients unsolved DD/DI patients and compare the CNV-detection yield of Agilent array-CGH 4 × 180kb versus whole exome sequencing.

GM3 synthase deficiency in non-Amish patients.

PURPOSE: Biallelic loss-of-function variants in ST3GAL5 cause GM3 synthase deficiency (GM3SD) responsible for Amish infantile epilepsy syndrome. All Amish patients carry the homozygous p.(Arg288Ter) variant arising from a founder effect. To date only 10 patients from 4 non-Amish families have been reported. Thus, the phenotypical spectrum of GM3SD due to other variants and other genetic backgrounds is still poorly known. METHODS: We collected clinical and molecular data from 16 non-Amish patients with pathogenic ST3GAL5 variants resulting in GM3SD. RESULTS: We identified 12 families originating from Reunion Island, Ivory Coast, Italy, and Algeria and carrying 6 ST3GAL5 variants, 5 of which were novel. Genealogical investigations and/or haplotype analyses showed that 3 of these variants were founder alleles. Glycosphingolipids quantification in patients' plasma confirmed the pathogenicity of 4 novel variants. All patients (N = 16), aged 2 to 12 years, had severe to profound intellectual disability, 14 of 16 had a hyperkinetic movement disorder, 11 of 16 had epilepsy and 9 of 16 had microcephaly. Other main features were progressive skin pigmentation anomalies, optic atrophy or pale papillae, and hearing loss. CONCLUSION: The phenotype of non-Amish patients with GM3SD is similar to the Amish infantile epilepsy syndrome, which suggests that GM3SD is associated with a narrow and severe clinical spectrum.

Epileptic encephalopathy as a new feature of the sudden infant death with dysgenesis of the testes syndrome caused by TSPYL1 variants.

Sudden infant death with dysgenesis of the testes syndrome (SIDDT) is a rare autosomal recessive disorder associating developmental sex disorder (DSD) in patients with 46,XY karyotype and visceroautonomic dysfunction responsible for sudden infant death. First described in 2004, very few patients have since been reported. We describe here a new patient with SIDDT and epileptic encephalopathy (EE). We provide the phenotypic description and genetic results of a boy carrying biallelic TSPYL1 deleterious variants. We also reviewed the data of the 26 previously described patients with SIDDT. Our patient presented gonadal dysgenesis, cardio-respiratory dysfunction, and repeated seizures, leading in 1 month to severe intractable EE. He died at age 10 months of cardiorespiratory arrest. Four other reported patients from two families presented with progressive epilepsy, including one with severe EE. No similar phenotype was described in the 22 other patients and the recurrent variant p.Val242Glufs*52 appears to be more frequently associated with seizures. To note, our patient is the first case with compound heterozygous TSPYL1 variants. These findings expand the phenotypic spectrum of SIDDT by reporting progressive epilepsy and severe EE as a possible outcome. This information may help in managing patients with SIDDT.

Second-tier trio exome sequencing after negative solo clinical exome sequencing: an efficient strategy to increase diagnostic yield and decipher molecular bases in undiagnosed developmental disorders.

Developmental disorders (DD), characterized by malformations/dysmorphism and/or intellectual disability, affecting around 3% of worldwide population, are mostly linked to genetic anomalies. Despite clinical exome sequencing (cES) centered on genes involved in human genetic disorders, the majority of patients affected by DD remain undiagnosed after solo-cES. Trio-based strategy is expected to facilitate variant selection thanks to rapid parental segregation. We performed a second step trio-ES (not only focusing on genes involved in human disorders) analysis in 70 patients with negative results after solo-cES. All candidate variants were shared with a MatchMaking exchange system to identify additional patients carrying variants in the same genes and with similar phenotype. In 18/70 patients (26%), we confirmed causal implication of nine OMIM-morbid genes and identified nine new strong candidate genes (eight de novo and one compound heterozygous variants). These nine new candidate genes were validated through the identification of patients with similar phenotype and genotype thanks to data sharing. Moreover, 11 genes harbored variants of unknown significance in 10/70 patients (14%). In DD, a second step trio-based ES analysis appears an efficient strategy in diagnostic and translational research to identify highly candidate genes and improve diagnostic yield.

Clinical whole-exome sequencing for the diagnosis of rare disorders with congenital anomalies and/or intellectual disability: substantial interest of prospective annual reanalysis.

PurposeCongenital anomalies and intellectual disability (CA/ID) are a major diagnostic challenge in medical genetics-50% of patients still have no molecular diagnosis after a long and stressful diagnostic "odyssey." Solo clinical whole-exome sequencing (WES) was applied in our genetics center to improve diagnosis in patients with CA/ID.MethodsThis retrospective study examined 416 consecutive tests performed over 3 years to demonstrate the effectiveness of periodically reanalyzing WES data. The raw data from each nonpositive test was reanalyzed at 12 months with the most recent pipeline and in the light of new data in the literature. The results of the reanalysis for patients enrolled in the third year are not yet available.ResultsOf the 416 patients included, data for 156 without a diagnosis were reanalyzed. We obtained 24 (15.4%) additional diagnoses: 12 through the usual diagnostic process (7 new publications, 4 initially misclassified, and 1 copy-number variant), and 12 through translational research by international data sharing. The final yield of positive results was 27.9% through a strict diagnostic approach, and 2.9% through an additional research strategy.ConclusionThis article highlights the effectiveness of periodically combining diagnostic reinterpretation of clinical WES data with translational research involving data sharing for candidate genes.

Further clinical and molecular characterization of an XLID syndrome associated with BRWD3 variants, a gene implicated in the leukemia-related JAK-STAT pathway.

BACKGROUND: Since the first description of a BRWD3-associated nonsydromic intellectual disability (ID) disorder in 2007, 21 additional families have been reported in the literature. METHODS: Using exome sequencing (ES) and international data sharing, we identified 14 additional unrelated individuals with pathogenic BRWD3 variants (12 males and 2 females, including one with skewed X-inactivation). We reviewed the 31 previously published cases in the literature with clinical data available, and describe the collective phenotypes of 43 males and 2 females, with 33 different BRWD3 variants. RESULTS: The most common features in males (excluding one patient with a mosaic variant) included ID (39/39 males), speech delay (24/25 males), postnatal macrocephaly (28/35 males) with prominent forehead (18/25 males) and large ears (14/26 males), and obesity (12/27 males). Both females presented with macrocephaly, speech delay, and epilepsy, while epilepsy was only observed in 4/41 males. Among the 28 variants with available segregation reported, 19 were inherited from unaffected mothers and 9 were de novo. CONCLUSION: This study demonstrates that the BRWD3-related phenotypes are largely non-specific, leading to difficulty in clinical recognition of this disorder. A genotype-first approach, however, allows for the more efficient diagnosis of the BRWD3-related nonsyndromic ID. The refined clinical features presented here may provide additional diagnostic assistance for reverse phenotyping efforts.

Same performance of exome sequencing before and after fetal autopsy for congenital abnormalities: toward a paradigm shift in prenatal diagnosis?

Prenatal exome sequencing could be complex because of limited phenotypical data compared to postnatal/portmortem phenotype in fetuses affected by multiple congenital abnormalities (MCA). Here, we investigated limits of prenatal phenotype for ES interpretation thanks to a blindly reanalysis of postmortem ES data using prenatal data only in fetuses affected by MCA and harboring a (likely)pathogenic variant or a variant of unknown significance (VUS). Prenatal ES identified all causative variant previously reported by postmortem ES (22/24 (92%) and 2/24 (8%) using solo-ES and trio-ES respectively). Prenatal ES identified 5 VUS (in four fetuses). Two of them have been previously reported by postmortem ES. Prenatal ES were negative for four fetuses for which a VUS were diagnosed after autopsy. Our study suggests that prenatal phenotype is not a limitation for implementing pES in the prenatal assessment of unsolved MCA to personalize fetal medicine and could influence indication of postmortem examination.

OMIXCARE: OMICS technologies solved about 33% of the patients with heterogeneous rare neuro-developmental disorders and negative exome sequencing results and identified 13% additional candidate variants.

Purpose: Patients with rare or ultra-rare genetic diseases, which affect 350 million people worldwide, may experience a diagnostic odyssey. High-throughput sequencing leads to an etiological diagnosis in up to 50% of individuals with heterogeneous neurodevelopmental or malformation disorders. There is a growing interest in additional omics technologies in translational research settings to examine the remaining unsolved cases. Methods: We gathered 30 individuals with malformation syndromes and/or severe neurodevelopmental disorders with negative trio exome sequencing and array comparative genomic hybridization results through a multicenter project. We applied short-read genome sequencing, total RNA sequencing, and DNA methylation analysis, in that order, as complementary translational research tools for a molecular diagnosis. Results: The cohort was mainly composed of pediatric individuals with a median age of 13.7 years (4 years and 6 months to 35 years and 1 month). Genome sequencing alone identified at least one variant with a high level of evidence of pathogenicity in 8/30 individuals (26.7%) and at least a candidate disease-causing variant in 7/30 other individuals (23.3%). RNA-seq data in 23 individuals allowed two additional individuals (8.7%) to be diagnosed, confirming the implication of two pathogenic variants (8.7%), and excluding one candidate variant (4.3%). Finally, DNA methylation analysis confirmed one diagnosis identified by genome sequencing (Kabuki syndrome) and identified an episignature compatible with a BAFopathy in a patient with a clinical diagnosis of Coffin-Siris with negative genome and RNA-seq results in blood. Conclusion: Overall, our integrated genome, transcriptome, and DNA methylation analysis solved 10/30 (33.3%) cases and identified a strong candidate gene in 4/30 (13.3%) of the patients with rare neurodevelopmental disorders and negative exome sequencing results.

Accelerated genome sequencing with controlled costs for infants in intensive care units: a feasibility study in a French hospital network.

Obtaining a rapid etiological diagnosis for infants with early-onset rare diseases remains a major challenge. These diseases often have a severe presentation and unknown prognosis, and the genetic causes are very heterogeneous. In a French hospital network, we assessed the feasibility of performing accelerated trio-genome sequencing (GS) with limited additional costs by integrating urgent requests into the routine workflow. In addition to evaluating our capacity for such an approach, this prospective multicentre pilot study was designed to identify pitfalls encountered during its implementation. Over 14 months, we included newborns and infants hospitalized in neonatal or paediatric intensive care units with probable genetic disease and in urgent need for etiological diagnosis to guide medical care. The duration of each step and the pitfalls were recorded. We analysed any deviation from the planned schedule and identified obstacles. Trio-GS was performed for 37 individuals, leading to a molecular diagnosis in 18/37 (49%), and 21/37 (57%) after reanalysis. Corrective measures and protocol adaptations resulted in a median duration of 42 days from blood sampling to report. Accelerated trio-GS is undeniably valuable for individuals in an urgent care context. Such a circuit should coexist with a rapid or ultra-rapid circuit, which, although more expensive, can be used in particularly urgent cases. The drop in GS costs should result in its generalized use for diagnostic purposes and lead to a reduction of the costs of rapid GS.

Interest of exome sequencing trio-like strategy based on pooled parental DNA for diagnosis and translational research in rare diseases.

BACKGROUND: Exome sequencing (ES) has become the most powerful and cost-effective molecular tool for deciphering rare diseases with a diagnostic yield approaching 30%-40% in solo-ES and 50% in trio-ES. We applied an innovative parental DNA pooling method to reduce the parental sequencing cost while maintaining the diagnostic yield of trio-ES. METHODS: We pooled six (Agilent-CRE-v2-100X) or five parental DNA (TWIST-HCE-70X) aiming to detect allelic balance around 8-10% for heterozygous status. The strategies were applied as second-tier (74 individuals after negative solo-ES) and first-tier approaches (324 individuals without previous ES). RESULTS: The allelic balance of parental-pool variants was around 8.97%. Sanger sequencing uncovered false positives in 1.5% of sporadic variants. In the second-tier approach, we evaluated than two thirds of the Sanger validations performed after solo-ES (41/59-69%) would have been saved if the parental-pool segregations had been available from the start. The parental-pool strategy identified a causative diagnosis in 18/74 individuals (24%) in the second-tier and in 116/324 individuals (36%) in the first-tier approaches, including 19 genes newly associated with human disorders. CONCLUSIONS: Parental-pooling is an efficient alternative to trio-ES. It provides rapid segregation and extension to translational research while reducing the cost of parental and Sanger sequencing.

Increased diagnostic and new genes identification outcome using research reanalysis of singleton exome sequencing.

In clinical exome sequencing (cES), the American College of Medical Genetics and Genomics recommends limiting variant interpretation to established human-disease genes. The diagnostic yield of cES in intellectual disability and/or multiple congenital anomalies (ID/MCA) is currently about 30%. Though the results may seem acceptable for rare diseases, they mean that 70% of affected individuals remain genetically undiagnosed. Further analysis extended to all mutated genes in a research environment is a valuable strategy for improving diagnostic yields. This study presents the results of systematic research reanalysis of negative cES in a cohort of 313 individuals with ID/MCA. We identified 17 new genes not related to human disease, implicated 22 non-OMIM disease-causing genes recently or previously rarely related to disease, and described 1 new phenotype associated with a known gene. Twenty-six candidate genes were identified and are waiting for future recurrence. Overall, we diagnose 15% of the individuals with initial negative cES, increasing the diagnostic yield from 30% to more than 40% (or 46% if strong candidate genes are considered). This study demonstrates the power of such extended research reanalysis to increase scientific knowledge of rare diseases. These novel findings can then be applied in the field of diagnostics.

Secondary actionable findings identified by exome sequencing: expected impact on the organisation of care from the study of 700 consecutive tests.

With exome/genome sequencing (ES/GS) integrated into the practice of medicine, there is some potential for reporting incidental/secondary findings (IFs/SFs). The issue of IFs/SFs has been studied extensively over the last 4 years. In order to evaluate their implications in care organisation, we retrospectively evaluated, in a cohort of 700 consecutive probands, the frequency and burden of introducing the search for variants in a maximum list of 244 medically actionable genes (genes that predispose carriers to a preventable or treatable disease in childhood/adulthood and genes for genetic counselling issues). We also focused on the 59 PharmGKB class IA/IB pharmacogenetic variants. We also compared the results in different gene lists. We identified variants (likely) affecting protein function in genes for care in 26 cases (3.7%) and heterozygous variants in genes for genetic counselling in 29 cases (3.8%). Mean time for the 700 patients was about 6.3 min/patient for medically actionable genes and 1.3 min/patient for genes for genetic counselling, and a mean time of 37 min/patients for the reinterpreted variants. These results would lead to all 700 pre-test counselling sessions being longer, to 55 post-test genetic consultations and to 27 secondary specialised medical evaluations. ES also detected 42/59 pharmacogenetic variants or combinations of variants in the majority of cases. An extremely low metabolizer status in genes relevant for neurodevelopmental disorders (CYP2C9 and CYP2C19) was found in 57/700 cases. This study provides information regarding the need to anticipate the implementation of genomic medicine, notably the work overload at various steps of the process.

Reducing diagnostic turnaround times of exome sequencing for families requiring timely diagnoses.

BACKGROUND AND OBJECTIVE: Whole-exome sequencing (WES) has now entered medical practice with powerful applications in the diagnosis of rare Mendelian disorders. Although the usefulness and cost-effectiveness of WES have been widely demonstrated, it is essential to reduce the diagnostic turnaround time to make WES a first-line procedure. Since 2011, the automation of laboratory procedures and advances in sequencing chemistry have made it possible to carry out diagnostic whole genome sequencing from the blood sample to molecular diagnosis of suspected genetic disorders within 50 h. Taking advantage of these advances, the main objective of the study was to improve turnaround times for sequencing results. METHODS: WES was proposed to 29 patients with severe undiagnosed disorders with developmental abnormalities and faced with medical situations requiring rapid diagnosis. Each family gave consent. The extracted DNA was sequenced on a NextSeq500 (Illumina) instrument. Data were analyzed following standard procedures. Variants were interpreted using in-house software. Each rare variant affecting protein sequences with clinical relevance was tested for familial segregation. RESULTS: The diagnostic rate was 45% (13/29), with a mean turnaround time of 40 days from reception of the specimen to delivery of results to the referring physician. Besides permitting genetic counseling, the rapid diagnosis for positive families led to two pre-natal diagnoses and two inclusions in clinical trials. CONCLUSIONS: This pilot study demonstrated the feasibility of rapid diagnostic WES in our primary genetics center. It reduced the diagnostic odyssey and helped provide support to families.