Next-Generation Sequencing Technologies and Neurogenetic Diseases

Assessment of whole-exome sequencing results in neurogenetic diseases

Neurogenetic diseases are rare genetic diseases in which neurological findings are prominent. Whole exome sequencing (WES) has led to great advances in the understanding of the causes of neurogenetic diseases. Etiological research ends with the WES method in many patients. This etiological research is called a "diagnostic odyssey" for many families. Here, we present the results of 168 patients who were previously undiagnosed and underwent WES with the suspicion of neurogenetic disease. A total of 168 cases, 94 males and 74 females, with suspected undiagnosed neurogenetic disease were included in the study. We presented the WES results of the patients. The mean age of patients at the time of WES request was 11 years (range 0.25-68 years). Seventy percent (n = 117) of the patients were born from consanguineous marriage. Most of the patients were children (n = 145). Patients were grouped according to age at the time of examination. Patients younger than 18 years of age at the time of examination were classified as children, otherwise adults. Seventy-eight patients had either a pathogenic variant or a likely pathogenic variant so the diagnostic rate for WES in our cohort was %46. Our experience showing the high diagnostic rate of WES, supports its use in undiagnosed neurogenetic diseases. It also affects medical treatment, prognosis and family planning by enabling early diagnosis in patients.

Opportunities and challenges of 5G network technology toward precision medicine

Moving away from traditional "one-size-fits-all" treatment to precision-based medicine has tremendously improved disease prognosis, accuracy of diagnosis, disease progression prediction, and targeted-treatment. The current cutting-edge of 5G network technology is enabling a growing trend in precision medicine to extend its utility and value to the smart healthcare system. The 5G network technology will bring together big data, artificial intelligence, and machine learning to provide essential levels of connectivity to enable a new health ecosystem toward precision medicine. In the 5G-enabled health ecosystem, its applications involve predictive and preventative measurements which enable advances in patient personalization. This review aims to discuss the opportunities, challenges, and prospects posed to 5G network technology in moving forward to deliver personalized treatments and patient-centric care via a precision medicine approach.

Implementation of Exome Sequencing in Clinical Practice for Neurological Disorders

Neurological disorders (ND) are diseases that affect the brain and the central and autonomic nervous systems, such as neurodevelopmental disorders, cerebellar ataxias, Parkinson’s disease, or epilepsies. Nowadays, recommendations of the American College of Medical Genetics and Genomics strongly recommend applying next generation sequencing (NGS) as a first-line test in patients with these disorders. Whole exome sequencing (WES) is widely regarded as the current technology of choice for diagnosing monogenic ND. The introduction of NGS allows for rapid and inexpensive large-scale genomic analysis and has led to enormous progress in deciphering monogenic forms of various genetic diseases. The simultaneous analysis of several potentially mutated genes improves the diagnostic process, making it faster and more efficient. The main aim of this report is to discuss the impact and advantages of the implementation of WES into the clinical diagnosis and management of ND. Therefore, we have performed a retrospective evaluation of WES application in 209 cases referred to the Department of Biochemistry and Molecular Genetics of the Hospital Clinic of Barcelona for WES sequencing derived from neurologists or clinical geneticists. In addition, we have further discussed some important facts regarding classification criteria for pathogenicity of rare variants, variants of unknown significance, deleterious variants, different clinical phenotypes, or frequency of actionable secondary findings. Different studies have shown that WES implementation establish diagnostic rate around 32% in ND and the continuous molecular diagnosis is essential to solve the remaining cases.

Whole exome screening of neurodevelopmental regression disorders in a cohort of Egyptian patients

Developmental regression describes a child who begins to lose his previously acquired milestones skills after he has reached a certain developmental stage and though affects his childhood development. It is associated with neurodegenerative diseases including leukodystrophy and neuronal ceroid lipofuscinosis diseases (NCLs), one of the most frequent childhood-onset neurodegenerative disorders. The current study focused on screening causative genes of developmental regression diseases comprising neurodegenerative disorders in Egyptian patients using next-generation sequencing (NGS)-based analyses as well as developing checklist to support clinicians who are not familiar with these diseases. A total of 763 Egyptian children (1 to 11 years), mainly diagnosed with developmental regression, seizures, or visual impairment, were studied using whole exome sequencing (WES). Among 763 Egyptian children, 726 cases were early clinically and molecularly diagnosed, including 482 cases that had pediatric stroke, congenital infection, and hepatic encephalopathy; meanwhile, 192 had clearly dysmorphic features, 31 showed central nervous system (CNS) malformation, 17 were diagnosed by leukodystrophy, 2 had ataxia telangiectasia, and 2 were diagnosed with tuberous sclerosis. The remained 37 out of 763 candidates were suspected with NCLs symptoms; however, 28 were confirmed to be NCLs patients, 1 was Kaya-Barakat-Masson syndrome, 1 was diagnosed as infantile neuroaxonal dystrophy, and 7 cases required further molecular diagnosis. This study provided an NGS-based approach of the genetic causes of developmental regression and neurodegenerative diseases as it comprised different variants and de novo mutations with complex phenotypes of these diseases which in turn help in early diagnoses and counseling for affected families.

Whole-exome sequencing of a Saudi epilepsy cohort reveals association signals in known and potentially novel loci

BACKGROUND

Epilepsy, a serious chronic neurological condition effecting up to 100 million people globally, has clear genetic underpinnings including common and rare variants. In Saudi Arabia, the prevalence of epilepsy is high and caused mainly by perinatal and genetic factors. No whole-exome sequencing (WES) studies have been performed to date in Saudi Arabian epilepsy cohorts. This offers a unique opportunity for the discovery of rare genetic variants impacting this disease as there is a high rate of consanguinity among large tribal pedigrees.

RESULTS

We performed WES on 144 individuals diagnosed with epilepsy, to interrogate known epilepsy-related genes for known and functional novel variants. We also used an American College of Medical Genetics (ACMG) guideline-based variant prioritization approach in an attempt to discover putative causative variants. We identified 32 potentially causative pathogenic variants across 30 different genes in 44/144 (30%) of these Saudi epilepsy individuals. We also identified 232 variants of unknown significance (VUS) across 101 different genes in 133/144 (92%) subjects. Strong enrichment of variants of likely pathogenicity was observed in previously described epilepsy-associated loci, and a number of putative pathogenic variants in novel loci are also observed.

CONCLUSION

Several putative pathogenic variants in known epilepsy-related loci were identified for the first time in our population, in addition to several potential new loci which may be prioritized for further investigation.

Pathophysiological Heterogeneity of the BBSOA Neurodevelopmental Syndrome

The formation and maturation of the human brain is regulated by highly coordinated developmental events, such as neural cell proliferation, migration and differentiation. Any impairment of these interconnected multi-factorial processes can affect brain structure and function and lead to distinctive neurodevelopmental disorders. Here, we review the pathophysiology of the Bosch–Boonstra–Schaaf Optic Atrophy Syndrome (BBSOAS; OMIM 615722; ORPHA 401777), a recently described monogenic neurodevelopmental syndrome caused by the haploinsufficiency of NR2F1 gene, a key transcriptional regulator of brain development. Although intellectual disability, developmental delay and visual impairment are arguably the most common symptoms affecting BBSOAS patients, multiple additional features are often reported, including epilepsy, autistic traits and hypotonia. The presence of specific symptoms and their variable level of severity might depend on still poorly characterized genotype–phenotype correlations. We begin with an overview of the several mutations of NR2F1 identified to date, then further focuses on the main pathological features of BBSOAS patients, providing evidence—whenever possible—for the existing genotype–phenotype correlations. On the clinical side, we lay out an up-to-date list of clinical examinations and therapeutic interventions recommended for children with BBSOAS. On the experimental side, we describe state-of-the-art in vivo and in vitro studies aiming at deciphering the role of mouse Nr2f1, in physiological conditions and in pathological contexts, underlying the BBSOAS features. Furthermore, by modeling distinct NR2F1 genetic alterations in terms of dimer formation and nuclear receptor binding efficiencies, we attempt to estimate the total amounts of functional NR2F1 acting in developing brain cells in normal and pathological conditions. Finally, using the NR2F1 gene and BBSOAS as a paradigm of monogenic rare neurodevelopmental disorder, we aim to set the path for future explorations of causative links between impaired brain development and the appearance of symptoms in human neurological syndromes.

Novel variants underlying autosomal recessive neurodevelopmental disorders with intellectual disability in Iranian consanguineous families

Background

Intellectual disability (ID) is a heterogeneous group of neurodevelopmental disorders that is characterized by significant impairment in intellectual and adaptive functioning with onset during the developmental period. Whole‐exome sequencing (WES)‐based studies in the consanguineous families with individuals affected with ID have shown a high burden of relevant variants. So far, over 700 genes have been reported in syndromic and non‐syndromic ID. However, genetic causes in more than 50% of ID patients still remain unclear.

Methods

Whole‐exome sequencing was applied for investigation of various variants of ID, then Sanger sequencing and in silico analysis in ten patients from five Iranian consanguineous families diagnosed with autosomal recessive neurodevelopmental disorders, intellectual disability, performed for confirming the causative mutation within the probands. The most patients presented moderate‐to‐severe intellectual disability, developmental delay, seizure, speech problem, high level of lactate, and onset before 10 years.

Results

Filtering the data identified by WES, two novel homozygous missense variants in FBXO31 and TIMM50 genes and one previously reported mutation in the CEP290 gene in the probands were found. Sanger sequencing confirmed the homozygote variant's presence of TIMM50 and FBXO31 genes in six patients and two affected siblings in their respective families. Our computational results predicted that the variants are located in the conserved regions across different species and have the impacts on the protein stability.

Conclusion

Hence, we provide evidence for the pathogenicity of two novel variants in the patients which will expand our knowledge about potential mutation involved in the heterogeneous disease.