RESUMEN
Epigenetic dysregulation has emerged as an important etiological mechanism of neurodevelopmental disorders (NDDs). Pathogenic variation in epigenetic regulators can impair deposition of histone post-translational modifications leading to aberrant spatiotemporal gene expression during neurodevelopment. The male-specific lethal (MSL) complex is a prominent multi-subunit epigenetic regulator of gene expression and is responsible for histone 4 lysine 16 acetylation (H4K16ac). Using exome sequencing, here we identify a cohort of 25 individuals with heterozygous de novo variants in MSL complex member MSL2. MSL2 variants were associated with NDD phenotypes including global developmental delay, intellectual disability, hypotonia, and motor issues such as coordination problems, feeding difficulties, and gait disturbance. Dysmorphisms and behavioral and/or psychiatric conditions, including autism spectrum disorder, and to a lesser extent, seizures, connective tissue disease signs, sleep disturbance, vision problems, and other organ anomalies, were observed in affected individuals. As a molecular biomarker, a sensitive and specific DNA methylation episignature has been established. Induced pluripotent stem cells (iPSCs) derived from three members of our cohort exhibited reduced MSL2 levels. Remarkably, while NDD-associated variants in two other members of the MSL complex (MOF and MSL3) result in reduced H4K16ac, global H4K16ac levels are unchanged in iPSCs with MSL2 variants. Regardless, MSL2 variants altered the expression of MSL2 targets in iPSCs and upon their differentiation to early germ layers. Our study defines an MSL2-related disorder as an NDD with distinguishable clinical features, a specific blood DNA episignature, and a distinct, MSL2-specific molecular etiology compared to other MSL complex-related disorders.
Asunto(s)
Epilepsia , Trastornos del Neurodesarrollo , Ubiquitina-Proteína Ligasas , Adolescente , Niño , Preescolar , Femenino , Humanos , Masculino , Discapacidades del Desarrollo/genética , Metilación de ADN/genética , Epigénesis Genética , Epilepsia/genética , Histonas/metabolismo , Histonas/genética , Células Madre Pluripotentes Inducidas/metabolismo , Discapacidad Intelectual/genética , Trastornos del Neurodesarrollo/genética , Fenotipo , Ubiquitina-Proteína Ligasas/metabolismoRESUMEN
Biallelic pathogenic variants in CDC45 are associated with Meier-Gorlin syndrome with craniosynostosis (MGORS type 7), which also includes short stature and absent/hypoplastic patellae. Identified variants act through a hypomorphic loss of function mechanism, to reduce CDC45 activity and impact DNA replication initiation. In addition to missense and premature termination variants, several pathogenic synonymous variants have been identified, most of which cause increased exon skipping of exon 4, which encodes an essential part of the RecJ-orthologue's DHH domain. Here we have identified a second cohort of families segregating CDC45 variants, where patients have craniosynostosis and a reduction in height, alongside common facial dysmorphisms, including thin eyebrows, consistent with MGORS7. Skipping of exon 15 is a consequence of two different variants, including a shared synonymous variant that is enriched in individuals of East Asian ancestry, while other variants in trans are predicted to alter key intramolecular interactions in α/ß domain II, or cause retention of an intron within the 3'UTR. Our cohort and functional data confirm exon skipping is a relatively common pathogenic mechanism in CDC45, and highlights the need for alternative splicing events, such as exon skipping, to be especially considered for variants initially predicted to be less likely to cause the phenotype, particularly synonymous variants.
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Proteínas de Ciclo Celular , Exones , Humanos , Proteínas de Ciclo Celular/genética , Craneosinostosis/genética , Craneosinostosis/patología , Femenino , Masculino , Empalme Alternativo , Linaje , Trastornos del Crecimiento , Micrognatismo , Rótula/anomalías , Microtia CongénitaRESUMEN
Primary microcephaly (MCPH) is an autosomal recessive disorder characterized by head circumference of at least two standard deviations below the mean. Biallelic variants in the kinetochore gene KNL1 is a known cause of MCPH4. KNL1 is the central component of the KNL1-MIS12-NSL1 (KMN) network, which acts as the signaling hub of the kinetochore and is required for correct chromosomal segregation during mitosis. We identified biallelic KNL1 variants in two siblings from a non-consanguineous family with microcephaly and intellectual disability. The two siblings carry a frameshift variant predicted to prematurely truncate the transcript and undergo nonsense mediated decay, and an intronic single nucleotide variant (SNV) predicted to disrupt splicing. An in vitro splicing assay and qPCR from blood-derived RNA confirmed that the intronic variant skips exon 23, significantly reducing levels of the canonical transcript. Protein modeling confirmed that absence of exon 23, an inframe exon, would disrupt a key interaction within the KMN network and likely destabilize the kinetochore signaling hub, disrupting mitosis. Therefore, this splicing variant is pathogenic and, in trans with a frameshift variant, causes the MCPH phenotype associated with KLN1. This finding furthers the association of splicing variants as a common pathogenic variant class for KNL1.
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Cinetocoros , Microcefalia , Humanos , Proteínas de Ciclo Celular/genética , Cinetocoros/metabolismo , Cinetocoros/patología , Microcefalia/genética , Microcefalia/patología , Proteínas Asociadas a Microtúbulos/genética , MutaciónRESUMEN
Embryonic development requires tight control of gene expression levels, activity, and localisation. This control is coordinated by multiple levels of regulation on DNA, RNA and protein. RNA-binding proteins (RBPs) are recognised as key regulators of post-transcriptional gene regulation, where their binding controls splicing, polyadenylation, nuclear export, mRNA stability, translation rate and decay. In brain development, the ELAVL family of RNA binding proteins undertake essential functions across spatiotemporal windows to help regulate and specify transcriptomic programmes for cell specialisation. Despite their recognised importance in neural tissues, their molecular roles and connections to pathology are less explored. Here we provide an overview of the neuronal ELAVL family, noting commonalities and differences amongst different species, their molecular characteristics, and roles in the cell. We bring together the available molecular genetics evidence to link different ELAVL proteins to phenotypes and disease, in both the brain and beyond, including ELAVL2, which is the least studied ELAVL family member. We find that ELAVL-related pathology shares a common neurological theme, but different ELAVL proteins are more strongly connected to different phenotypes, reflecting their specialised expression across time and space.
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Proteínas de Unión al ARN , ARN , Humanos , ARN/metabolismo , Proteínas de Unión al ARN/genética , Empalme del ARN , Encéfalo/metabolismo , Biología MolecularRESUMEN
High-throughput sequencing has become a standard first-tier approach for both diagnostics and research-based genetic testing. Consequently, this hypothesis-free testing manner has revealed the true breadth of clinical features for many established genetic disorders, including Meier-Gorlin syndrome (MGORS). Previously known as ear-patella short stature syndrome, MGORS is characterized by growth delay, microtia, and patella hypo/aplasia, as well as genital abnormalities, and breast agenesis in females. Following the initial identification of genetic causes in 2011, a total of 13 genes have been identified to date associated with MGORS. In this review, we summarise the genetic and clinical findings of each gene associated with MGORS and highlight molecular insights that have been made through studying patient variants. We note interesting observations arising across this group of genes as the number of patients has increased, such as the unusually high number of synonymous variants affecting splicing in CDC45 and a subgroup of genes that also cause craniosynostosis. We focus on the complicated molecular genetics for DONSON, where we examine potential genotype-phenotype patterns using the first 3D structural model of DONSON. The canonical role of all proteins associated with MGORS are involved in different stages of DNA replication and in addition to summarising how patient variants impact on this process, we discuss the potential contribution of non-canonical roles of these proteins to the pathophysiology of MGORS.
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Microtia Congénita , Micrognatismo , Femenino , Humanos , Microtia Congénita/genética , Rótula/anomalías , Trastornos del Crecimiento/diagnóstico , Trastornos del Crecimiento/genética , Micrognatismo/genéticaRESUMEN
Histones hold significant interest in development and genetic disorders due to their critical roles in chromatin dynamics, influencing gene expression and genome integrity. These roles are linked to alterations of post-translational marks, which are generally concentrated in the histone tails. The machinery modifying or interpreting these marks, known as chromatin writers, erasers or readers, have been associated with many Mendelian disorders; however, it has been only recently that the histone proteins themselves have been directly implicated in Mendelian conditions. High throughput sequencing has recently identified mutations in genes encoding histone H1, H3 and H4, all causing neurodevelopmental disorders with clinical variability. Notably, many of the mutations lie outside of recognised post-translational modification-associated residues, suggesting disrupting the core functions of histones is a primary molecular mechanism underpinning these neurodevelopmental phenotypes. In this review, we describe the clinical and genetic features of histone-related disorders, focusing on the unique aspects associated with each histone gene family, while noting the commonalities which provide insight into the required roles for histone fidelity in brain development and functioning.
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Cromatina , Histonas , Humanos , Histonas/metabolismo , Procesamiento Proteico-Postraduccional , MutaciónRESUMEN
Oculo-auriculo-vertebral syndrome (OAVS) is a clinically heterogeneous disorder, with both genetic and environmental contributors. Multiple genes have been associated with OAVS and common molecular pathways, such as retinoic acid and the PAX-SIX-EYA-DACH (PSED) network, are being implicated in the disease pathophysiology. Biallelic homozygous nonsense or hypomorphic missense mutations in PAX1 cause otofaciocervical syndrome type 2 (OTFCS2), a similar but more severe multi-system disorder that can be accompanied by severe combined immunodeficiency due to thymic aplasia. Here we have identified a multi-generational family with mild features of OAVS segregating a heterozygous frameshift in PAX1. The four base duplication is expected to result in nonsense-mediated decay, and therefore cause a null allele. While there was full penetrance of the variant, expressivity of facial and ear features were variable. Our findings indicate there can be monoallelic and biallelic disorders associated with PAX1, and further implicate the PSED network in OAVS.
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Síndrome de Goldenhar , Factores de Transcripción Paired Box , Inmunodeficiencia Combinada Grave , Síndrome de Goldenhar/genética , Homocigoto , Humanos , Mutación Missense , Factores de Transcripción Paired Box/genética , TretinoinaRESUMEN
The MCM2-7 helicase is a heterohexameric complex with essential roles as part of both the pre-replication and pre-initiation complexes in the early stages of DNA replication. Meier-Gorlin syndrome, a rare primordial dwarfism, is strongly associated with disruption to the pre-replication complex, including a single case described with variants in MCM5. Conversely, a biallelic pathogenic variant in MCM4 underlies immune deficiency with growth retardation, features also seen in individuals with pathogenic variants in other pre-initiation complex encoding genes such as GINS1, MCM10, and POLE. Through exome and chromium genome sequencing, supported by functional studies, we identify biallelic pathogenic variants in MCM7 and a strong candidate biallelic pathogenic variant in MCM3. We confirm variants in MCM7 are deleterious and through interfering with MCM complex formation, impact efficiency of S phase progression. The associated phenotypes are striking; one patient has typical Meier-Gorlin syndrome, whereas the second case has a multi-system disorder with neonatal progeroid appearance, lipodystrophy and adrenal insufficiency. We provide further insight into the developmental complexity of disrupted MCM function, highlighted by two patients with a similar variant profile in MCM7 but disparate clinical features. Our results build on other genetic findings linked to disruption of the pre-replication and pre-initiation complexes, and the replisome, and expand the complex clinical genetics landscape emerging due to disruption of DNA replication.
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Insuficiencia Suprarrenal/diagnóstico , Insuficiencia Suprarrenal/genética , Microtia Congénita/diagnóstico , Microtia Congénita/genética , Trastornos del Crecimiento/diagnóstico , Trastornos del Crecimiento/genética , Lipodistrofia/diagnóstico , Lipodistrofia/genética , Micrognatismo/diagnóstico , Micrognatismo/genética , Componente 3 del Complejo de Mantenimiento de Minicromosoma/genética , Componente 7 del Complejo de Mantenimiento de Minicromosoma/genética , Rótula/anomalías , Adolescente , Alelos , Secuencia de Aminoácidos , Ciclo Celular/genética , Niño , Preescolar , Facies , Femenino , Estudios de Asociación Genética , Predisposición Genética a la Enfermedad , Variación Genética , Genotipo , Humanos , Lactante , Masculino , Componente 3 del Complejo de Mantenimiento de Minicromosoma/química , Componente 7 del Complejo de Mantenimiento de Minicromosoma/química , Modelos Moleculares , Nueva Zelanda , Fenotipo , Conformación ProteicaRESUMEN
Disruption of the initiation of DNA replication is significantly associated with Meier-Gorlin syndrome (MGORS), an autosomal recessive condition of reduced growth, microtia and patellar a/hypoplasia. Biallelic mutations in CDC45, a member of the pre-initiation complex in DNA replication, cause a spectrum of phenotypes ranging from MGORS with craniosynostosis, through to isolated short stature and craniosynostosis. Here we report two affected sibs with MGORS and craniosynostosis, with biallelic variants in CDC45 identified by 10X Chromium whole genome sequencing. One variant is a frameshift mutation, predicted to be pathogenic, and is inherited in trans with a synonymous variant in a non-canonical exon (exon 7) of CDC45. An in vitro splicing assay showed that while the canonical CDC45 exon 6-exon 8 transcript (with skipping of exon 7; numbering as per NM001178010.2) remained as the predominant transcript, the variant allele induced the use of novel splice acceptor sites in intron 6, all of which produced transcripts harbouring premature stop codons. This perturbation of canonical splicing provides evidence that this synonymous variant is indeed a deleterious alteration in this family. This report adds to the initial patient cohort in which several synonymous variants were also described, further highlighting the contribution of this variant type in CDC45. It also reiterates the true potential pathogenicity of synonymous variants, which is a mutation type that is commonly ignored in variant prioritization strategies.
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Proteínas de Ciclo Celular/genética , Microtia Congénita/genética , Craneosinostosis/genética , Trastornos del Crecimiento/genética , Micrognatismo/genética , Mutación , Rótula/anomalías , Sitios de Empalme de ARN , Proteínas de Ciclo Celular/metabolismo , Células Cultivadas , Niño , Preescolar , Microtia Congénita/patología , Craneosinostosis/patología , Exones , Trastornos del Crecimiento/patología , Humanos , Masculino , Micrognatismo/patología , Rótula/patología , LinajeRESUMEN
Meier-Gorlin syndrome is an autosomal recessively inherited disorder of growth retardation, accompanied by microtia and patellae a/hypoplasia and characteristic facies. Pathogenic variants in genes associated with the initiation of DNA replication underlie the condition, with biallelic variants in CDT1 the most common cause. Using 10× Chromium genome sequencing, we report CDT1 variants in an adult female, with an inframe amino acid deletion inherited in trans with a deep intronic variant which likely serves as the branchpoint site in Intron 8. Splicing defects arising from this variant were confirmed through in vitro analysis. At 49 years, she represents the oldest patient with a molecular diagnosis described in the literature and is the first reported patient with Meier-Gorlin syndrome to have carried a successful pregnancy to term. Both of her pregnancies were complicated by postpartum hemorrhage and upon subsequent necessary hysterectomy, revealed uterine abnormalities. There is scant knowledge on reproductive ability and success in patients with Meier-Gorlin syndrome. Successful pregnancies among other clinically recognizable forms of primordial dwarfism have also not been described previously. This case is therefore of clinical interest for many forms of inherited growth retardation, and will assist in providing more information and clinical guidance for females of reproductive age.
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Proteínas de Ciclo Celular/genética , Microtia Congénita/genética , Mutación del Sistema de Lectura , Trastornos del Crecimiento/genética , Micrognatismo/genética , Rótula/anomalías , Mutación Puntual , Complicaciones del Embarazo/genética , Alelos , Empalme Alternativo , Secuencia de Bases , Proteínas de Ciclo Celular/deficiencia , Codón sin Sentido/genética , Femenino , Haplotipos/genética , Humanos , Intrones/genética , Persona de Mediana Edad , Paridad , Fenotipo , Hemorragia Posparto/genética , Embarazo , Eliminación de Secuencia , Útero/anomalías , Útero/patología , Secuenciación Completa del GenomaRESUMEN
ABL1 is a proto-oncogene encoding a nonreceptor tyrosine kinase, best known in the somatic BCR-ABL fusion gene associated with chronic myeloid leukaemia. Recently, germline missense variants in ABL1 have been found to cause an autosomal dominant developmental syndrome with congenital heart disease, skeletal malformations and characteristic facies. Here, we describe a series of six new unrelated individuals with heterozygous missense variants in ABL1 (including four novel variants) identified via whole exome sequencing. All the affected individuals in this series recapitulate the phenotype of the ABL1 developmental syndrome and additionally we affirm that hearing impairment is a common feature of the condition. Four of the variants cluster in the myristoyl-binding pocket of ABL1, a region critical for auto-inhibitory regulation of the kinase domain. Bio-informatic analysis of transcript-wide conservation and germline/somatic variation reveals that this pocket region is subject to high missense constraint and evolutionary conservation. Functional work to investigate ABL1 kinase activity in vitro by transient transfection of HEK293T cells with variant ABL1 plasmid constructs revealed increased phosphorylation of ABL1-specific substrates compared to wild-type. The increased tyrosine kinase activity was suppressed by imatinib treatment. This case series of six new patients with germline heterozygous ABL1 missense variants further delineates the phenotypic spectrum of this condition and recognises microcephaly as a common finding. Our analysis supports an ABL1 gain-of-function mechanism due to loss of auto-inhibition, and demonstrates the potential for pharmacological inhibition using imatinib.
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Deformidades del Pie/genética , Deformidades de la Mano/genética , Pérdida Auditiva/genética , Cardiopatías Congénitas/genética , Proteínas Proto-Oncogénicas c-abl/genética , Adolescente , Adulto , Sitios de Unión , Niño , Preescolar , Femenino , Deformidades del Pie/patología , Células HEK293 , Deformidades de la Mano/patología , Pérdida Auditiva/patología , Cardiopatías Congénitas/patología , Humanos , Masculino , Mutación Missense , Ácido Mirístico/metabolismo , Fenotipo , Unión Proteica , Proteínas Proto-Oncogénicas c-abl/química , Proteínas Proto-Oncogénicas c-abl/metabolismo , SíndromeRESUMEN
Variants in SLC35C1 underlie leucocyte adhesion deficiency (LADII) or congenital disorder of glycosylation type 2c (CDGIIc), an autosomal recessive disorder of fucosylation. This immunodeficiency syndrome is generally characterized by severe recurrent infections, Bombay blood group, reduced growth and intellectual disability (ID). Features are all caused by an inability to generate key fucosylated molecules due to a defective transport of GDP-fucose into the Golgi. Here we report the use of exome sequencing to identify biallelic variants in SLC35C1 (c.501_503delCTT, p.(Phe168del) and c.891T > G, p.(Asn297Lys)) in an individual with short stature and ID. Retrospective clinical examination based on the genetic findings revealed increased otitis media as the only immunological feature present in this child. Biochemical analysis of patient serum identified a clear but mild decrease in protein fucosylation. Modelling all described missense mutations on a SLC35C1 protein model showed pathogenic substitutions localise to close to the dimer interface, providing insight into the possible pathophysiology of non-synonymous causative variants identified in patients. Our evidence confirms this is the second family presenting with only a subset of features and broadens the clinical presentation of this syndrome. Of note, both families segregated a common allele (p.Phe168del), suggesting there could be an associated genotype-phenotype relationship for specific variants. Based on two out of 14 reported families not presenting with the characteristic features of SLC35C1-CDG, we suggest there is clinical utility in considering this gene in patients with short stature and ID.
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Trastornos Congénitos de Glicosilación/genética , Enanismo/genética , Discapacidad Intelectual/genética , Proteínas de Transporte de Monosacáridos/genética , Alelos , Preescolar , Cromatografía Liquida , Trastornos Congénitos de Glicosilación/sangre , Trastornos Congénitos de Glicosilación/complicaciones , Enanismo/sangre , Enanismo/complicaciones , Enanismo/fisiopatología , Femenino , Estudios de Asociación Genética , Glicómica , Humanos , Discapacidad Intelectual/sangre , Discapacidad Intelectual/complicaciones , Discapacidad Intelectual/fisiopatología , Proteínas de Transporte de Monosacáridos/química , Mutación Missense , Plasma/química , Plasma/inmunología , Plasma/metabolismo , Estudios Retrospectivos , Alineación de Secuencia , Espectrometría de Masas en Tándem , Secuenciación del ExomaRESUMEN
MATERIAL: Linked-read whole genome sequencing (WGS) presents a new opportunity for cost-efficient singleton sequencing in place of traditional trio-based designs while generating informative-phased variants, effective for recessive disorders when parental DNA is unavailable. METHODS: We have applied linked-read WGS to identify novel causes of Meier-Gorlin syndrome (MGORS), a condition recognised by short stature, microtia and patella hypo/aplasia. There are eight genes associated with MGORS to date, all encoding essential components involved in establishing and initiating DNA replication. RESULTS: Our successful phasing of linked-read data led to the identification of biallelic rare variants in four individuals (24% of our cohort) in DONSON, a recently established DNA replication fork surveillance factor. The variants include five novel missense and one deep intronic variant. All were demonstrated to be deleterious to function; the missense variants all disrupted the nuclear localisation of DONSON, while the intronic variant created a novel splice site that generated an out-of-frame transcript with no residual canonical transcript produced. CONCLUSION: Variants in DONSON have previously been associated with extreme microcephaly, short stature and limb anomalies and perinatal lethal microcephaly-micromelia syndrome. Our novel genetic findings extend the complicated spectrum of phenotypes associated with DONSON variants and promote novel hypotheses for the role of DONSON in DNA replication. While our findings reiterate that MGORS is a disorder of DNA replication, the pathophysiology is obviously complex. This successful identification of a novel disease gene for MGORS highlights the utility of linked-read WGS as a successful technology to be considered in the genetic studies of recessive conditions.
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Proteínas de Ciclo Celular/genética , Microtia Congénita/genética , Predisposición Genética a la Enfermedad , Trastornos del Crecimiento/genética , Micrognatismo/genética , Proteínas Nucleares/genética , Rótula/anomalías , Adulto , Alelos , Secuencia de Bases/genética , Niño , Microtia Congénita/fisiopatología , Replicación del ADN/genética , Femenino , Genoma Humano/genética , Trastornos del Crecimiento/fisiopatología , Humanos , Masculino , Micrognatismo/fisiopatología , Rótula/metabolismo , Rótula/fisiopatología , EmbarazoRESUMEN
Coffin-Siris syndrome (CSS) is a clinically and genetically heterogeneous developmental disorder, linked to disruption of the BAF chromatin-remodeling complex. Recently, de novo missense and truncating variants have been reported in DPF2 in patients sharing some of the common features of CSS. Here we report a further individual harboring a novel de novo missense DPF2 variant, c.1066T>G, p.Cys356Gly. Structural modeling indicated that the predicted amino acid substitution affects a core residue required for zinc ion coordination and would likely alter the PHD2 domain structure of DPF2. The clinical presentation of Pierre Robin sequence and diaphragmatic hernia did not immediately suggest CSS, with the more common CSS features of hypoplastic toenails and characteristic facial features very subtle. This individual further broadens the phenotypic features of DPF2-related CSS, as well as CSS more generally.
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Proteínas de Unión al ADN/genética , Estudios de Asociación Genética , Predisposición Genética a la Enfermedad , Mutación , Fenotipo , Factores de Transcripción/genética , Anomalías Múltiples/diagnóstico , Anomalías Múltiples/genética , Alelos , Sustitución de Aminoácidos , Proteínas de Unión al ADN/química , Cara/anomalías , Facies , Estudios de Asociación Genética/métodos , Genoma , Deformidades Congénitas de la Mano/diagnóstico , Deformidades Congénitas de la Mano/genética , Humanos , Discapacidad Intelectual/diagnóstico , Discapacidad Intelectual/genética , Micrognatismo/diagnóstico , Micrognatismo/genética , Modelos Moleculares , Cuello/anomalías , Conformación Proteica , Relación Estructura-Actividad , Factores de Transcripción/químicaRESUMEN
Microcephalic primordial dwarfism (MPD) is a group of rare single-gene disorders characterized by the extreme reduction in brain and body size from early development onwards. Proteins encoded by MPD-associated genes play important roles in fundamental cellular processes, notably genome replication and repair. Here we report the identification of four MPD individuals with biallelic variants in DNA2, which encodes an adenosine triphosphate (ATP)-dependent helicase/nuclease involved in DNA replication and repair. We demonstrate that the two intronic variants (c.1764-38_1764-37ins(53) and c.74+4A>C) found in these individuals substantially impair DNA2 transcript splicing. Additionally, we identify a missense variant (c.1963A>G), affecting a residue of the ATP-dependent helicase domain that is highly conserved between humans and yeast, with the resulting substitution (p.Thr655Ala) predicted to directly impact ATP/ADP (adenosine diphosphate) binding by DNA2. Our findings support the pathogenicity of these variants as biallelic hypomorphic mutations, establishing DNA2 as an MPD disease gene.
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ADN Helicasas/genética , Enanismo/genética , Variación Genética , Microcefalia/genética , Adolescente , Alelos , ADN Helicasas/química , Femenino , Predisposición Genética a la Enfermedad , Humanos , Intrones , Masculino , Persona de Mediana Edad , Modelos Moleculares , Mutagénesis Insercional , Mutación Missense , Polimorfismo de Nucleótido SimpleRESUMEN
During genome replication, polymerase epsilon (Pol ε) acts as the major leading-strand DNA polymerase. Here we report the identification of biallelic mutations in POLE, encoding the Pol ε catalytic subunit POLE1, in 15 individuals from 12 families. Phenotypically, these individuals had clinical features closely resembling IMAGe syndrome (intrauterine growth restriction [IUGR], metaphyseal dysplasia, adrenal hypoplasia congenita, and genitourinary anomalies in males), a disorder previously associated with gain-of-function mutations in CDKN1C. POLE1-deficient individuals also exhibited distinctive facial features and variable immune dysfunction with evidence of lymphocyte deficiency. All subjects shared the same intronic variant (c.1686+32C>G) as part of a common haplotype, in combination with different loss-of-function variants in trans. The intronic variant alters splicing, and together the biallelic mutations lead to cellular deficiency of Pol ε and delayed S-phase progression. In summary, we establish POLE as a second gene in which mutations cause IMAGe syndrome. These findings add to a growing list of disorders due to mutations in DNA replication genes that manifest growth restriction alongside adrenal dysfunction and/or immunodeficiency, consolidating these as replisome phenotypes and highlighting a need for future studies to understand the tissue-specific development roles of the encoded proteins.
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Insuficiencia Suprarrenal/genética , ADN Polimerasa II/genética , Retardo del Crecimiento Fetal/genética , Mutación/genética , Osteocondrodisplasias/genética , Proteínas de Unión a Poli-ADP-Ribosa/genética , Anomalías Urogenitales/genética , Adolescente , Adulto , Alelos , Niño , Preescolar , Inhibidor p57 de las Quinasas Dependientes de la Ciclina/genética , Replicación del ADN/genética , Femenino , Humanos , Lactante , Masculino , Persona de Mediana Edad , Fenotipo , Adulto JovenRESUMEN
Ataxia Telangiectasia and Rad3 related (ATR) is one of the main regulators of the DNA damage response. It coordinates cell cycle checkpoint activation, replication fork stability, restart and origin firing to maintain genome integrity. Mutations of the ATR gene have been reported in Seckel patients, who suffer from a rare genetic disease characterized by severe microcephaly and growth retardation. Here, we report the case of a Seckel patient with compound heterozygous mutations in ATR. One allele has an intronic mutation affecting splicing of neighboring exons, the other an exonic missense mutation, producing the variant p.Lys1665Asn, of unknown pathogenicity. We have modeled this novel missense mutation, as well as a previously described missense mutation p.Met1159Ile, and assessed their effect on ATR function. Interestingly, our data indicate that both missense mutations have no direct effect on protein function, but rather result in defective ATR splicing. These results emphasize the importance of splicing mutations in Seckel Syndrome.
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Proteínas de la Ataxia Telangiectasia Mutada/genética , Enanismo/genética , Microcefalia/genética , Mutación Missense , Empalme del ARN , Animales , Proteínas de la Ataxia Telangiectasia Mutada/metabolismo , Línea Celular , Pollos , Enanismo/metabolismo , Exones , Humanos , Intrones , Microcefalia/metabolismo , Secuenciación del ExomaRESUMEN
To ensure efficient genome duplication, cells have evolved numerous factors that promote unperturbed DNA replication and protect, repair and restart damaged forks. Here we identify downstream neighbor of SON (DONSON) as a novel fork protection factor and report biallelic DONSON mutations in 29 individuals with microcephalic dwarfism. We demonstrate that DONSON is a replisome component that stabilizes forks during genome replication. Loss of DONSON leads to severe replication-associated DNA damage arising from nucleolytic cleavage of stalled replication forks. Furthermore, ATM- and Rad3-related (ATR)-dependent signaling in response to replication stress is impaired in DONSON-deficient cells, resulting in decreased checkpoint activity and the potentiation of chromosomal instability. Hypomorphic mutations in DONSON substantially reduce DONSON protein levels and impair fork stability in cells from patients, consistent with defective DNA replication underlying the disease phenotype. In summary, we have identified mutations in DONSON as a common cause of microcephalic dwarfism and established DONSON as a critical replication fork protein required for mammalian DNA replication and genome stability.