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.

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.

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.

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.

Diagnosis of exon 12-positive polycythemia vera rescued by NGS.

A JAK2V617F-negative polycythemia associated with low serum epo needs to be tested for an exon 12 JAK2 mutation. When negative, due to potential serious complications in PV, a next generation sequencing is necessary to rule out false negative results.