ABSTRACT
DNAJC6 encodes auxilin, a co-chaperone protein involved in clathrin-mediated endocytosis (CME) at the presynaptic terminal. Biallelic mutations in DNAJC6 cause a complex, early-onset neurodegenerative disorder characterized by rapidly progressive parkinsonism-dystonia in childhood. The disease is commonly associated with additional neurodevelopmental, neurological and neuropsychiatric features. Currently, there are no disease-modifying treatments for this condition, resulting in significant morbidity and risk of premature mortality. To investigate the underlying disease mechanisms in childhood-onset DNAJC6 parkinsonism, we generated induced pluripotent stem cells (iPSC) from three patients harbouring pathogenic loss-of-function DNAJC6 mutations and subsequently developed a midbrain dopaminergic neuronal model of disease. When compared to age-matched and CRISPR-corrected isogenic controls, the neuronal cell model revealed disease-specific auxilin deficiency as well as disturbance of synaptic vesicle recycling and homeostasis. We also observed neurodevelopmental dysregulation affecting ventral midbrain patterning and neuronal maturation. To explore the feasibility of a viral vector-mediated gene therapy approach, iPSC-derived neuronal cultures were treated with lentiviral DNAJC6 gene transfer, which restored auxilin expression and rescued CME. Our patient-derived neuronal model provides deeper insights into the molecular mechanisms of auxilin deficiency as well as a robust platform for the development of targeted precision therapy approaches.
Subject(s)
Auxilins , Genetic Therapy , HSP40 Heat-Shock Proteins , Induced Pluripotent Stem Cells , Parkinsonian Disorders , Humans , Genetic Therapy/methods , HSP40 Heat-Shock Proteins/genetics , HSP40 Heat-Shock Proteins/metabolism , Induced Pluripotent Stem Cells/metabolism , Parkinsonian Disorders/genetics , Parkinsonian Disorders/therapy , Parkinsonian Disorders/metabolism , Auxilins/genetics , Auxilins/metabolism , Male , Female , Dopaminergic Neurons/metabolism , Mutation , Synapses/genetics , Synapses/metabolism , Endocytosis/physiology , Endocytosis/genetics , ChildABSTRACT
Inosine 5' monophosphate dehydrogenase (IMPDH) is a critical regulatory enzyme in purine nucleotide biosynthesis that is inhibited by the downstream product GTP. Multiple point mutations in the human isoform IMPDH2 have recently been associated with dystonia and other neurodevelopmental disorders, but the effect of the mutations on enzyme function has not been described. Here, we report the identification of two additional missense variants in IMPDH2 from affected individuals and show that all of the disease-associated mutations disrupt GTP regulation. Cryo-EM structures of one IMPDH2 mutant suggest this regulatory defect arises from a shift in the conformational equilibrium toward a more active state. This structural and functional analysis provides insight into IMPDH2-associated disease mechanisms that point to potential therapeutic approaches and raises new questions about fundamental aspects of IMPDH regulation.
Subject(s)
IMP Dehydrogenase , Purines , Humans , Allosteric Regulation , IMP Dehydrogenase/genetics , IMP Dehydrogenase/metabolism , Mutation , Guanosine TriphosphateABSTRACT
PURPOSE: Widespread application of next-generation sequencing, combined with data exchange platforms, has provided molecular diagnoses for countless families. To maximize diagnostic yield, we implemented an unbiased semi-automated genematching algorithm based on genotype and phenotype matching. METHODS: Rare homozygous variants identified in 2 or more affected individuals, but not in healthy individuals, were extracted from our local database of â¼12,000 exomes. Phenotype similarity scores (PSS), based on human phenotype ontology terms, were assigned to each pair of individuals matched at the genotype level using HPOsim. RESULTS: 33,792 genotype-matched pairs were discovered, representing variants in 7567 unique genes. There was an enrichment of PSS ≥0.1 among pathogenic/likely pathogenic variant-level pairs (94.3% in pathogenic/likely pathogenic variant-level matches vs 34.75% in all matches). We highlighted founder or region-specific variants as an internal positive control and proceeded to identify candidate disease genes. Variant-level matches were particularly helpful in cases involving inframe indels and splice region variants beyond the canonical splice sites, which may otherwise have been disregarded, allowing for detection of candidate disease genes, such as KAT2A, RPAIN, and LAMP3. CONCLUSION: Semi-automated genotype matching combined with PSS is a powerful tool to resolve variants of uncertain significance and to identify candidate disease genes.
Subject(s)
Genotype , Humans , Phenotype , Mutation , Homozygote , Genetic Association StudiesABSTRACT
Sphingolipids are a diverse family of lipids with critical structural and signalling functions in the mammalian nervous system, where they are abundant in myelin membranes. Serine palmitoyltransferase, the enzyme that catalyses the rate-limiting reaction of sphingolipid synthesis, is composed of multiple subunits including an activating subunit, SPTSSA. Sphingolipids are both essential and cytotoxic and their synthesis must therefore be tightly regulated. Key to the homeostatic regulation are the ORMDL proteins that are bound to serine palmitoyltransferase and mediate feedback inhibition of enzymatic activity when sphingolipid levels become excessive. Exome sequencing identified potential disease-causing variants in SPTSSA in three children presenting with a complex form of hereditary spastic paraplegia. The effect of these variants on the catalytic activity and homeostatic regulation of serine palmitoyltransferase was investigated in human embryonic kidney cells, patient fibroblasts and Drosophila. Our results showed that two different pathogenic variants in SPTSSA caused a hereditary spastic paraplegia resulting in progressive motor disturbance with variable sensorineural hearing loss and language/cognitive dysfunction in three individuals. The variants in SPTSSA impaired the negative regulation of serine palmitoyltransferase by ORMDLs leading to excessive sphingolipid synthesis based on biochemical studies and in vivo studies in Drosophila. These findings support the pathogenicity of the SPTSSA variants and point to excessive sphingolipid synthesis due to impaired homeostatic regulation of serine palmitoyltransferase as responsible for defects in early brain development and function.
Subject(s)
Spastic Paraplegia, Hereditary , Animals , Child , Humans , Spastic Paraplegia, Hereditary/genetics , Serine C-Palmitoyltransferase/genetics , Serine C-Palmitoyltransferase/metabolism , Sphingolipids/metabolism , Cell Membrane/metabolism , Mammals/metabolismABSTRACT
Pathogenic variants in SOD1, encoding superoxide dismutase 1, are responsible for about 20% of all familial amyotrophic lateral sclerosis cases, through a gain-of-function mechanism. Recently, two reports showed that a specific homozygous SOD1 loss-of-function variant is associated with an infantile progressive motor-neurological syndrome. Exome sequencing followed by molecular studies, including cDNA analysis, SOD1 protein levels and enzymatic activity, and plasma neurofilament light chain levels, were undertaken in an infant with severe global developmental delay, axial hypotonia and limb spasticity. We identified a homozygous 3-bp in-frame deletion in SOD1. cDNA analysis predicted the loss of a single valine residue from a tandem pair (p.Val119/Val120) in the wild-type protein, yet expression levels and splicing were preserved. Analysis of SOD1 activity and protein levels in erythrocyte lysates showed essentially no enzymatic activity and undetectable SOD1 protein in the child, whereas the parents had â¼50% protein expression and activity relative to controls. Neurofilament light chain levels in plasma were elevated, implying ongoing axonal injury and neurodegeneration. Thus, we provide confirmatory evidence of a second biallelic variant in an infant with a severe neurological syndrome and suggest that the in-frame deletion causes instability and subsequent degeneration of SOD1. We highlight the importance of the valine residues at positions V119-120, and suggest possible implications for future therapeutics research.
Subject(s)
Amyotrophic Lateral Sclerosis , Amyotrophic Lateral Sclerosis/metabolism , DNA, Complementary , Humans , Infant , Mutation/genetics , Superoxide Dismutase/genetics , Superoxide Dismutase/metabolism , Superoxide Dismutase-1/genetics , Syndrome , Valine/geneticsABSTRACT
Accumulation of unfolded proteins in the endoplasmic reticulum (ER) initiates a stress response mechanism to clear out the unfolded proteins by either facilitating their re-folding or inducing their degradation. When this fails, an apoptotic cascade is initiated so that the affected cell is eliminated. IRE1α is a critical sensor of the unfolded-protein response, essential for initiating the apoptotic signaling. Here, we report an infantile neurodegenerative disorder associated with enhanced activation of IRE1α and increased apoptosis. Three unrelated affected individuals with congenital microcephaly, infantile epileptic encephalopathy, and profound developmental delay were found to carry heterozygous variants (c.932T>C [p.Leu311Ser] or c.935T>C [p.Leu312Pro]) in RNF13, which codes for an IRE1α-interacting protein. Structural modeling predicted that the variants, located on the surface of the protein, would not alter overall protein folding. Accordingly, the abundance of RNF13 and IRE1α was not altered in affected individuals' cells. However, both IRE1α-mediated stress signaling and stress-induced apoptosis were increased in affected individuals' cells. These results indicate that the RNF13 variants confer gain of function to the encoded protein and thereby lead to altered signaling of the ER stress response associated with severe neurodegeneration in infancy.
Subject(s)
Blindness/congenital , Blindness/genetics , Failure to Thrive/genetics , Gain of Function Mutation , Heterozygote , Microcephaly/genetics , Spasms, Infantile/genetics , Ubiquitin-Protein Ligases/genetics , Amino Acid Sequence , Apoptosis , Child , Child, Preschool , Developmental Disabilities/genetics , Endoplasmic Reticulum Stress , Humans , Infant , Male , Models, Molecular , Spasms, Infantile/congenital , Ubiquitin-Protein Ligases/chemistry , Unfolded Protein ResponseABSTRACT
We report biallelic missense and frameshift pathogenic variants in the gene encoding human nucleoporin NUP214 causing acute febrile encephalopathy. Clinical symptoms include neurodevelopmental regression, seizures, myoclonic jerks, progressive microcephaly, and cerebellar atrophy. NUP214 and NUP88 protein levels were reduced in primary skin fibroblasts derived from affected individuals, while the total number and density of nuclear pore complexes remained normal. Nuclear transport assays exhibited defects in the classical protein import and mRNA export pathways in affected cells. Direct surface imaging of fibroblast nuclei by scanning electron microscopy revealed a large increase in the presence of central particles (known as "plugs") in the nuclear pore channels of affected cells. This observation suggests that large transport cargoes may be delayed in passage through the nuclear pore channel, affecting its selective barrier function. Exposure of fibroblasts from affected individuals to heat shock resulted in a marked delay in their stress response, followed by a surge in apoptotic cell death. This suggests a mechanistic link between decreased cell survival in cell culture and severe fever-induced brain damage in affected individuals. Our study provides evidence by direct imaging at the single nuclear pore level of functional changes linked to a human disease.
Subject(s)
Acute Febrile Encephalopathy/etiology , Fibroblasts/pathology , Frameshift Mutation , Ion Channels/physiology , Mutation, Missense , Nuclear Pore Complex Proteins/genetics , Nuclear Pore/pathology , Active Transport, Cell Nucleus , Acute Febrile Encephalopathy/metabolism , Acute Febrile Encephalopathy/pathology , Apoptosis , Cell Nucleus/genetics , Cell Nucleus/metabolism , Cell Proliferation , Cells, Cultured , Child , Child, Preschool , Female , Fibroblasts/metabolism , Humans , Infant , Male , Nuclear Pore/genetics , Nuclear Pore/metabolism , Nuclear Pore Complex Proteins/chemistry , Nuclear Pore Complex Proteins/metabolism , Pedigree , Protein ConformationABSTRACT
Ribosomal RNA (rRNA) is transcribed from rDNA by RNA polymerase I (Pol I) to produce the 45S precursor of the 28S, 5.8S, and 18S rRNA components of the ribosome. Two transcription factors have been defined for Pol I in mammals, the selectivity factor SL1, and the upstream binding transcription factor (UBF), which interacts with the upstream control element to facilitate the assembly of the transcription initiation complex including SL1 and Pol I. In seven unrelated affected individuals, all suffering from developmental regression starting at 2.5-7 years, we identified a heterozygous variant, c.628G>A in UBTF, encoding p.Glu210Lys in UBF, which occurred de novo in all cases. While the levels of UBF, Ser388 phosphorylated UBF, and other Pol I-related components (POLR1E, TAF1A, and TAF1C) remained unchanged in cells of an affected individual, the variant conferred gain of function to UBF, manifesting by markedly increased UBF binding to the rDNA promoter and to the 5'- external transcribed spacer. This was associated with significantly increased 18S expression, and enlarged nucleoli which were reduced in number per cell. The data link neurodegeneration in childhood with altered rDNA chromatin status and rRNA metabolism.
Subject(s)
Brain Diseases/genetics , Cell Nucleolus/pathology , Neurodegenerative Diseases/genetics , Pol1 Transcription Initiation Complex Proteins/genetics , RNA, Ribosomal, 18S/biosynthesis , Adolescent , Adult , Atrophy/genetics , Brain/pathology , Brain Diseases/pathology , Child , Chromatin/metabolism , DNA-Binding Proteins/genetics , Female , Humans , Male , Neurodegenerative Diseases/pathology , Polymorphism, Single Nucleotide/genetics , Promoter Regions, Genetic/genetics , Young AdultABSTRACT
Progressive childhood encephalopathy is an etiologically heterogeneous condition characterized by progressive central nervous system dysfunction in association with a broad range of morbidity and mortality. The causes of encephalopathy can be either non-genetic or genetic. Identifying the genetic causes and dissecting the underlying mechanisms are critical to understanding brain development and improving treatments. Here, we report that variants in TRAPPC12 result in progressive childhood encephalopathy. Three individuals from two unrelated families have either a homozygous deleterious variant (c.145delG [p.Glu49Argfs∗14]) or compound-heterozygous variants (c.360dupC [p.Glu121Argfs∗7] and c.1880C>T [p. Ala627Val]). The clinical phenotypes of the three individuals are strikingly similar: severe disability, microcephaly, hearing loss, spasticity, and characteristic brain imaging findings. Fibroblasts derived from all three individuals showed a fragmented Golgi that could be rescued by expression of wild-type TRAPPC12. Protein transport from the endoplasmic reticulum to and through the Golgi was delayed. TRAPPC12 is a member of the TRAPP protein complex, which functions in membrane trafficking. Variants in several other genes encoding members of the TRAPP complex have been associated with overlapping clinical presentations, indicating shared and distinct functions for each complex member. Detailed understanding of the TRAPP-opathies will illuminate the role of membrane protein transport in human disease.
Subject(s)
Brain Diseases/genetics , Endoplasmic Reticulum/metabolism , Golgi Apparatus/pathology , Membrane Transport Proteins/genetics , Protein Transport/genetics , Transcription Factors/genetics , Atrophy/pathology , Base Sequence , Brain/pathology , Brain Diseases/pathology , Cells, Cultured , Child, Preschool , Exome/genetics , Female , Genetic Predisposition to Disease , Humans , Infant , Magnetic Resonance Imaging , Male , Protein Transport/physiology , Sequence Analysis, DNAABSTRACT
Axon pathfinding and synapse formation are essential processes for nervous system development and function. The assembly of myelinated fibres and nodes of Ranvier is mediated by a number of cell adhesion molecules of the immunoglobulin superfamily including neurofascin, encoded by the NFASC gene, and its alternative isoforms Nfasc186 and Nfasc140 (located in the axonal membrane at the node of Ranvier) and Nfasc155 (a glial component of the paranodal axoglial junction). We identified 10 individuals from six unrelated families, exhibiting a neurodevelopmental disorder characterized with a spectrum of central (intellectual disability, developmental delay, motor impairment, speech difficulties) and peripheral (early onset demyelinating neuropathy) neurological involvement, who were found by exome or genome sequencing to carry one frameshift and four different homozygous non-synonymous variants in NFASC. Expression studies using immunostaining-based techniques identified absent expression of the Nfasc155 isoform as a consequence of the frameshift variant and a significant reduction of expression was also observed in association with two non-synonymous variants affecting the fibronectin type III domain. Cell aggregation studies revealed a severely impaired Nfasc155-CNTN1/CASPR1 complex interaction as a result of the identified variants. Immunofluorescence staining of myelinated fibres from two affected individuals showed a severe loss of myelinated fibres and abnormalities in the paranodal junction morphology. Our results establish that recessive variants affecting the Nfasc155 isoform can affect the formation of paranodal axoglial junctions at the nodes of Ranvier. The genetic disease caused by biallelic NFASC variants includes neurodevelopmental impairment and a spectrum of central and peripheral demyelination as part of its core clinical phenotype. Our findings support possible overlapping molecular mechanisms of paranodal damage at peripheral nerves in both the immune-mediated and the genetic disease, but the observation of prominent central neurological involvement in NFASC biallelic variant carriers highlights the importance of this gene in human brain development and function.
Subject(s)
Cell Adhesion Molecules/genetics , Demyelinating Diseases/genetics , Nerve Growth Factors/genetics , Neurodevelopmental Disorders/genetics , Adolescent , Adult , Alleles , Axons/metabolism , Cell Adhesion Molecules/metabolism , Child , Child, Preschool , Demyelinating Diseases/metabolism , Female , Gene Frequency/genetics , Humans , Infant , Male , Mutation , Myelin Sheath/genetics , Myelin Sheath/metabolism , Nerve Fibers, Myelinated/physiology , Nerve Growth Factors/metabolism , Nervous System Malformations , Neurodevelopmental Disorders/metabolism , Neuroglia/metabolism , Pedigree , Peripheral Nerves , Protein Isoforms/metabolism , Ranvier's Nodes/genetics , Ranvier's Nodes/metabolismABSTRACT
Regulation of neuronal connectivity and synaptic communication are key to proper functioning of the brain. The Netrin-G subfamily and their cognate receptors are vertebrate-specific synaptic cell adhesion molecules with a role in synapse establishment and function, which seem to have co-evolved to contribute to higher brain functions. We identified a homozygous frameshift variant in NTNG2 (NM_032536.3: c.376dup), encoding Netrin-G2, in eight individuals from four families with global developmental delay, hypotonia, secondary microcephaly, and autistic features. Comparison of haplotypes established this as a founder variant. Previous studies showed that Ntng2-knockout mice have impaired visual, auditory, and motor coordination abilities required for demanding tasks, as well as possible spatial learning and memory deficits. Knockout of Ntng2 in a cellular model resulted in short neurites, and knockout of its trans-synaptic partner Ngl2/Lrrc4 in mice revealed autistic-like behavior and reduced NMDAR synaptic plasticity. The Ngl2/Lrrc4-knockout mouse phenotype was rescued by NMDAR activation, suggesting a mechanistic link to autism spectrum disorder. We thus propose NTNG2 as a candidate disease gene and provide further support for the involvement of Netrin-G2 in neuropsychiatric phenotypes.
Subject(s)
Autistic Disorder/genetics , Developmental Disabilities/genetics , Frameshift Mutation , GPI-Linked Proteins/genetics , Homozygote , Muscle Hypotonia/genetics , Netrins/genetics , Autistic Disorder/complications , Cell Adhesion , Cell Adhesion Molecules/genetics , Child , Developmental Disabilities/complications , Exome , Female , Haplotypes , Humans , Male , Muscle Hypotonia/complications , Neuronal Plasticity , Pedigree , Phenotype , Synapses/metabolismABSTRACT
The primary cilium is a key organelle in numerous physiological and developmental processes. Genetic defects in the formation of this non-motile structure, in its maintenance and function, underlie a wide array of ciliopathies in human, including craniofacial, brain and heart malformations, and retinal and hearing defects. We used exome sequencing to study the molecular basis of disease in an 11-year-old female patient who suffered from growth retardation, global developmental delay with absent speech acquisition, agenesis of corpus callosum and paucity of white matter, sensorineural deafness, retinitis pigmentosa, vertebral anomalies, patent ductus arteriosus, and facial dysmorphism reminiscent of STAR syndrome, a suspected ciliopathy. A homozygous variant, c.870_871del, was identified in the CDK10 gene, predicted to cause a frameshift, p.Trp291Alafs*18, in the cyclin-dependent kinase 10 protein. CDK10 mRNAs were detected in patient cells and do not seem to undergo non-sense mediated decay. CDK10 is the binding partner of Cyclin M (CycM) and CDK10/CycM protein kinase regulates ciliogenesis and primary cilium elongation. Notably, CycM gene is mutated in patients with STAR syndrome. Following incubation, the patient cells appeared less elongated and more densely populated than the control cells suggesting that the CDK10 mutation affects the cytoskeleton. Upon starvation and staining with acetylated-tubulin, γ-tubulin, and Arl13b, the patient cells exhibited fewer and shorter cilia than control cells. These findings underscore the importance of CDK10 for the regulation of ciliogenesis. CDK10 defect is likely associated with a new form of ciliopathy phenotype; additional patients may further validate this association.
Subject(s)
Agenesis of Corpus Callosum/genetics , Cyclin-Dependent Kinases , Deafness/genetics , Genetic Association Studies , Homozygote , Mutation , Retinal Dysplasia/genetics , Agenesis of Corpus Callosum/diagnosis , Alleles , Brain/abnormalities , Brain/diagnostic imaging , Child , DNA Mutational Analysis , Deafness/diagnosis , Exome , Facies , Female , Gene Expression , Humans , Pedigree , Phenotype , RNA, Messenger/genetics , Retinal Dysplasia/diagnosisABSTRACT
De novo mutations of the TRIM8 gene, which codes for a tripartite motif protein, have been identified using whole exome sequencing (WES) in two patients with epileptic encephalopathy (EE), but these reports were not sufficient to conclude that TRIM8 was a novel gene responsible for EE. Here we report four additional patients presenting with EE and de novo truncating mutations of TRIM8 detected by WES, and give further details of the patient previously reported by the Epi4K consortium. Epilepsy of variable severity was diagnosed in children aged 2 months to 3.5 years of age. All patients had developmental delay of variable severity with no or very limited language, often associated with behavioral anomalies and unspecific facial features or MRI brain abnormalities. The phenotypic variability observed in these patients appeared related to the severity of the epilepsy. One patient presented pharmacoresistant EE with regression, recurrent infections and nephrotic syndrome, compatible with the brain and kidney expression of TRIM8. Interestingly, all mutations were located at the highly conserved C-terminus section of TRIM8. This collaborative study confirms that TRIM8 is a novel gene responsible for EE, possibly associated with nephrotic syndrome. This report brings new evidence on the pathogenicity of TRIM8 mutations and highlights the value of data-sharing to delineate the phenotypic characteristics and biological basis of extremely rare disorders.
Subject(s)
Carrier Proteins/genetics , Mutation/genetics , Nerve Tissue Proteins/genetics , Adolescent , Amino Acid Sequence , Carrier Proteins/chemistry , Child , Child, Preschool , Female , Humans , Infant , Infant, Newborn , Male , Nerve Tissue Proteins/chemistryABSTRACT
BACKGROUND: Of our 1400 exome-studied patients, 67% originate from consanguineous families. â¼80% suffer from variable degree of intellectual disability (ID). The search for disease causing genes using homozygosity mapping was progressing slowly until 2010, then markedly accelerated by the introduction of exome analysis. OBJECTIVES: To identify the disease causing mutation(s) in three patients from two unrelated families who suffered from global developmental delay, severe ID and drug-responsive seizure disorder. METHODS: Exome analysis was performed in DNA of the three patients. The identified PIGC variants were generated and transfected into PIGC-defective mouse cells and the restoration of the surface expression of mouse CD90, CD48 and FLAER was assessed using flow cytometry. The expression of these proteins was also studied on the surface of patients' leucocytes. RESULTS: Three PIGC mutations were identified; homozygous p.L189W in one family and compound heterozygosity for p.L212P/p.R21X variants in another. PIGC participates in the biosynthesis of the glycosylphosphatidylinositol (GPI) anchor which tethers proteins to plasma membrane. In cells lacking PIGC protein, which were transfected with each of the PIGC variants, we detected a clear reduction of surface expression of GPI-anchored proteins. Furthermore, analyses of patients' leucocytes showed significant and constant decrease of CD16 surface expression in granulocytes, and moderate decrease of CD14, CD55, CD59 and FLAER levels. CONCLUSIONS: PIGC joins the list of genes in which mutations result in defective biosynthesis of GPI anchoring, manifesting by global developmental delay and seizure disorder. The lack of specific biomarker dictates exome sequencing as the diagnostic procedure of choice in similar patients.
Subject(s)
Epilepsy/genetics , Hexosyltransferases/genetics , Intellectual Disability/genetics , Membrane Proteins/genetics , Abnormalities, Multiple , Amino Acid Sequence/genetics , Animals , Developmental Disabilities , Epilepsy/physiopathology , Exome/genetics , Female , Genetic Association Studies , Homozygote , Humans , Intellectual Disability/physiopathology , Male , Mice , Mutation , PedigreeABSTRACT
INTRODUCTION: Thirteen years after the completion of the human genome project, the determination of the genomic sequence of the coding parts of the DNA (the exones, hence the exome), has turned into a primary diagnostic tool in daily use in clinical practice. The Department of Genetics at Hadassah was the first in Israel to introduce exome analysis as a robust diagnostic tool into the pediatric departments. Till now 2600 exomes were analyzed at Hadassah, 850 of them in 2016 alone. Exome analysis is cheap and fast, enabling precise and non-invasive diagnosis for a vast array of genetic disorders and congenital malformations. The unique composition of the population which the hospital serves (marked by a high rate of consanguinity) enabled reaching diagnosis in 65% of the cases, twice the rate in medical centers worldwide. The results of this analysis enable genetic counseling to patients' families and prevention of serious disorders. Moreover, the results contribute to the understanding of the biological basis of newly identified disorders and in certain cases assist in the management of the patients. The major limitation of exome analysis is the multitude of identified variants which exist in any individual and which challenge our ability to pick the disease-causing variant. In the case of a disease-causing variant in a new gene, experimental proof is required to validate the causality of the variant; occasionally, an incidental finding with possible clinical significance is identified, raising serious ethical concerns. In this article, we will review the use of this technology through the experience of three pediatric departments at Hadassah.
Subject(s)
Exome , Human Genome Project , Sequence Analysis, DNA , Child , Genetic Counseling , Genomics , Humans , Israel , PediatricsABSTRACT
Hypomyelinating leukodystrophies are a group of neurodevelopmental disorders that affect proper formation of the myelin sheath in the central nervous system. They are characterized by developmental delay, hypotonia, spasticity, and variable intellectual disability. We used whole exome analysis to study the molecular basis of hypomyelinating leukodystrophy in two sibs from a consanguineous family. A homozygous mutation, c.3068+5G>A, was identified in the ATRN gene, with the consequent insertion of an intronic sequence into the patients' cDNA and a predicted premature termination of the ATRN polypeptide. ATRN encodes Attractin, which was previously shown to play a critical role in central myelination. Several spontaneous ATRN rodent mutants exhibited impaired myelination which was attributed to oxidative stress and accelerated apoptosis. ATRN can now be added to the growing list of genes associated with hypomyelinating leukodystrophy. The disease seems to be confined to the CNS; however, given the young age of our patients, longer follow-up may be required.
Subject(s)
Brain/pathology , Membrane Proteins/genetics , Mutation , Nerve Fibers, Myelinated/pathology , Pelizaeus-Merzbacher Disease/genetics , Female , Homozygote , Humans , Introns , Male , Muscle Hypotonia/genetics , Mutation/genetics , PhenotypeABSTRACT
OBJECTIVE: The objective of this work was to report on the outcome of eculizumab treatment in pediatric patients with recurrent acute predominantly motor, demyelinating neuropathy with conduction block, and chronic hemolysis attributed to p.Cys89Tyr mutation in the CD59 gene. METHODS: Four patients were recruited from our new registry of patients with homozygosity for the p.Cys89Tyr mutation on CD59. Participants received repeated intravenous eculizumab. In this 24-month open-label phase IIa study, we aimed to determine whether eculizumab reduces chronic hemolysis, and cumulative doses of steroids and intravenous immunoglobulin (IVIG), and ameliorates neurological deficits, compared to pretreatment status. Treatment response was evaluated every 2 to 4 weeks over 104 weeks and included examination with gross motor scoring by American Spinal Injury Association Impairment Scale and Inflammatory Neuropathy Cause and Treatment disability score, laboratory examination, well-being [12-item Short Form Health Survey; SF-12]). Neurological relapses and cumulative dose of IVIGs and/or corticosteroids before and after treatment were documented. Red blood cells (RBCs) and neutrophils were stained to evaluate C5b-9 deposition. ClinicalTrials.gov: NCT01579838. RESULTS: Dramatic and significant neurological amelioration in the upper limbs and trunk with more-modest amelioration in the lower limbs was observed in all patients. Corticosteroid and IVIG treatment was completely stopped. No patient relapsed during treatment despite infections, and there were no hospital admissions. Decreased C3bi and C5b-9 deposition on RBCs and neutrophils was documented (p < 0.0001). The SF-12 health questionnaires indicated significant improvement (p < 0.003). INTERPRETATION: Eculizumab was safely administered to these patients. Marked clinical improvement suggests that eculizumab may be a life-saving treatment for patients with acute predominantly motor, demyelinating neuropathy with conduction block, and secondary axonal damage attributed to primary p.Cys89Tyr mutation in the CD59 gene. Ann Neurol 2016;80:708-717.
Subject(s)
Anemia, Hemolytic/complications , Antibodies, Monoclonal, Humanized/pharmacology , CD59 Antigens/genetics , Hemoglobinuria/complications , Hemolysis/drug effects , Polyradiculoneuropathy , Registries , Antibodies, Monoclonal, Humanized/administration & dosage , Child, Preschool , Female , Humans , Infant , Male , Mutation , Polyradiculoneuropathy/drug therapy , Polyradiculoneuropathy/etiology , Polyradiculoneuropathy/physiopathology , Treatment OutcomeABSTRACT
OBJECTIVE: Succinate dehydrogenase-deficient leukoencephalopathy is a complex II-related mitochondrial disorder for which the clinical phenotype, neuroimaging pattern, and genetic findings have not been comprehensively reviewed. METHODS: Nineteen individuals with succinate dehydrogenase deficiency-related leukoencephalopathy were reviewed for neuroradiological, clinical, and genetic findings as part of institutional review board-approved studies at Children's National Health System (Washington, DC) and VU University Medical Center (Amsterdam, the Netherlands). RESULTS: All individuals had signal abnormalities in the central corticospinal tracts and spinal cord where imaging was available. Other typical findings were involvement of the cerebral hemispheric white matter with sparing of the U fibers, the corpus callosum with sparing of the outer blades, the basis pontis, middle cerebellar peduncles, and cerebellar white matter, and elevated succinate on magnetic resonance spectroscopy (MRS). The thalamus was involved in most studies, with a predilection for the anterior nucleus, pulvinar, and geniculate bodies. Clinically, infantile onset neurological regression with partial recovery and subsequent stabilization was typical. All individuals had mutations in SDHA, SDHB, or SDHAF1, or proven biochemical defect. INTERPRETATION: Succinate dehydrogenase deficiency is a rare leukoencephalopathy, for which improved recognition by magnetic resonance imaging (MRI) in combination with advanced sequencing technologies allows noninvasive diagnostic confirmation. The MRI pattern is characterized by cerebral hemispheric white matter abnormalities with sparing of the U fibers, corpus callosum involvement with sparing of the outer blades, and involvement of corticospinal tracts, thalami, and spinal cord. In individuals with infantile regression and this pattern of MRI abnormalities, the differential diagnosis should include succinate dehydrogenase deficiency, in particular if MRS shows elevated succinate.
Subject(s)
Leukoencephalopathies/enzymology , Leukoencephalopathies/pathology , Magnetic Resonance Imaging/methods , Spinal Cord/pathology , Succinate Dehydrogenase/deficiency , Thalamus/pathology , Female , Humans , Infant , Infant, Newborn , Male , Pyramidal Tracts/enzymology , Pyramidal Tracts/pathology , Spinal Cord/enzymology , Thalamus/enzymologyABSTRACT
OBJECTIVE: Thin filament myopathies are among the most common nondystrophic congenital muscular disorders, and are caused by mutations in genes encoding proteins that are associated with the skeletal muscle thin filament. Mechanisms underlying muscle weakness are poorly understood, but might involve the length of the thin filament, an important determinant of force generation. METHODS: We investigated the sarcomere length-dependence of force, a functional assay that provides insights into the contractile strength of muscle fibers as well as the length of the thin filaments, in muscle fibers from 51 patients with thin filament myopathy caused by mutations in NEB, ACTA1, TPM2, TPM3, TNNT1, KBTBD13, KLHL40, and KLHL41. RESULTS: Lower force generation was observed in muscle fibers from patients of all genotypes. In a subset of patients who harbor mutations in NEB and ACTA1, the lower force was associated with downward shifted force-sarcomere length relations, indicative of shorter thin filaments. Confocal microscopy confirmed shorter thin filaments in muscle fibers of these patients. A conditional Neb knockout mouse model, which recapitulates thin filament myopathy, revealed a compensatory mechanism; the lower force generation that was associated with shorter thin filaments was compensated for by increasing the number of sarcomeres in series. This allowed muscle fibers to operate at a shorter sarcomere length and maintain optimal thin-thick filament overlap. INTERPRETATION: These findings might provide a novel direction for the development of therapeutic strategies for thin filament myopathy patients with shortened thin filament lengths. Ann Neurol 2016;79:959-969.
Subject(s)
Cytoskeleton/genetics , Muscle Proteins/genetics , Muscular Diseases/genetics , Muscular Diseases/physiopathology , Sarcomeres/genetics , Actins/genetics , Animals , Case-Control Studies , Cytoskeleton/physiology , Humans , Mice, Knockout , Muscle Contraction/genetics , Muscle Contraction/physiology , Muscle Proteins/metabolism , Muscle Proteins/physiology , Muscle, Skeletal/metabolism , Mutation , Sarcomeres/physiologyABSTRACT
BACKGROUND: Cell survival critically depends on the integrity of mitochondria, which play a pivotal role during apoptosis. Extensive mitochondrial damage promotes release of pro-apoptotic factors from the intermembrane space of mitochondria. Released mitochondrial proteins include Smac/DIABLO and HTRA2/Omi, which inhibit the cytosolic E3 ubiquitin ligase XIAP and other inhibitors of apoptosis proteins. AIMS: Here we investigated the cause of extreme hypertonia at birth, alternating with hypotonia, with the subsequent appearance of extrapyramidal symptoms, lack of psychomotor development, microcephaly, intractable seizures and early death in four patients from two unrelated families. The patients showed lactic acidemia, 3-methylglutaconic aciduria, intermittent neutropenia, evolving brain atrophy and disturbed cristae structure in muscle mitochondria. METHODS AND RESULTS: Using whole-exome sequencing, we identified missplicing mutation and a 5â bp deletion in HTRA2, encoding HTRA2/Omi. This protein was completely absent from the patients' fibroblasts, whose growth was impaired and which were hypersensitive to apoptosis. Expression of HtrA2/Omi or of the proteolytically inactive HTRA2/Omi protein restored the cells' apoptotic resistance. However, cell growth was only restored by the proteolytically active protein. CONCLUSIONS: This is the first report of recessive deleterious mutations in HTRA2 in human. The clinical phenotype, the increased apoptotic susceptibility and the impaired cell growth recapitulate those observed in the Htra2 knockout mice and in mutant mice with proteolytically inactive HTRA2/Omi. Together, they underscore the importance of both chaperone and proteolytic activities of HTRA2/Omi for balanced apoptosis sensitivity and for brain development. Absence of HTRA2/Omi is associated with severe neurodegenerative disorder of infancy, abnormal mitochondria, 3-methylglutaconic aciduria and increased sensitivity to apoptosis.