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1.
Am J Med Genet A ; 2021 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-34523780

RESUMO

Primary ciliopathies are heterogenous disorders resulting from perturbations in primary cilia form and/or function. Primary cilia are cellular organelles which mediate key signaling pathways during development, such as the sonic hedgehog (SHH) pathway which is required for neuroepithelium and central nervous system development. Joubert syndrome is a primary ciliopathy characterized by cerebellar/brain stem malformation, hypotonia, and developmental delays. At least 35 genes are associated with Joubert syndrome, including the gene KIAA0753, which is part of a complex required for primary ciliogenesis. The phenotypic spectrum associated with biallelic pathogenic variants in KIAA0753 is broad and not well-characterized. We describe four individuals with biallelic pathogenic KIAA0753 variants, including five novel variants. We report in vitro results assessing the function of each variant indicating that mutant proteins are not fully competent to promote primary ciliogenesis. Ablation of KIAA0753 in vitro blocks primary ciliogenesis and SHH pathway activity. Correspondingly, KIAA0753 patient fibroblasts have a deficit in primary ciliation and improper SHH and WNT signaling, with a particularly blunted response to SHH pathway stimulation. Our work expands the phenotypic spectrum of KIAA0753 ciliopathies and demonstrates the utility of patient-focused functional assays for proving causality of genetic variants.

2.
Genes (Basel) ; 12(8)2021 Aug 20.
Artigo em Inglês | MEDLINE | ID: mdl-34440449

RESUMO

ARID1B is one of the most frequently mutated genes in intellectual disability (~1%). Most variants are readily classified, since they are de novo and are predicted to lead to loss of function, and therefore classified as pathogenic according to the American College of Medical Genetics and Genomics (ACMG) guidelines for the interpretation of sequence variants. However, familial loss-of-function variants can also occur and can be challenging to interpret. Such variants may be pathogenic with variable expression, causing only a mild phenotype in a parent. Alternatively, since some regions of the ARID1B gene seem to be lacking pathogenic variants, loss-of-function variants in those regions may not lead to ARID1B haploinsufficiency and may therefore be benign. We describe 12 families with potential loss-of-function variants, which were either familial or with unknown inheritance and were in regions where pathogenic variants have not been described or are otherwise challenging to interpret. We performed detailed clinical and DNA methylation studies, which allowed us to confidently classify most variants. In five families we observed transmission of pathogenic variants, confirming their highly variable expression. Our findings provide further evidence for an alternative translational start site and we suggest updates for the ACMG guidelines for the interpretation of sequence variants to incorporate DNA methylation studies and facial analyses.

3.
Dev Med Child Neurol ; 2021 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-34268734

RESUMO

AIM: To clarify the extent to which medical comorbidities and goals-of-care decisions influence death among individuals with childhood-onset hydrocephalus. METHOD: This was a retrospective cohort study of 1705 individuals (759 males, 946 females, mean age 11y 5mo, SD 6y 6mo, range 0-37y 7mo at last follow-up) with childhood-onset hydrocephalus, of whom 88 (5.2%) were deceased. Existing medical records, death records, and publicly available internet sources were analyzed. We estimated hazard ratios for putative risk factors through Cox regression based upon 10 529 person-years of data and quantitatively and qualitatively analyzed the circumstances surrounding each death. RESULTS: Mortality did not differ statistically by demographic factors, although higher proportions of non-White and Hispanic individuals were deceased. Most deaths were related to medical comorbidities rather than hydrocephalus itself. Of the 14 deaths directly related to hydrocephalus, seven were caused by shunt complications and four occurred after decisions to forgo treatment, apparently in response to poor outcomes predicted by the medical team. Half the deaths were preceded by shifts to comfort-based care; however, these decisions appeared to substantially change the patient's clinical trajectory only half the time. INTERPRETATION: Children are more likely to die with, rather than from, hydrocephalus. Our results emphasize the complexities of medical decision-making and the influence of clinicians in guiding these choices.

4.
Am J Hum Genet ; 108(8): 1436-1449, 2021 08 05.
Artigo em Inglês | MEDLINE | ID: mdl-34216551

RESUMO

Despite widespread clinical genetic testing, many individuals with suspected genetic conditions lack a precise diagnosis, limiting their opportunity to take advantage of state-of-the-art treatments. In some cases, testing reveals difficult-to-evaluate structural differences, candidate variants that do not fully explain the phenotype, single pathogenic variants in recessive disorders, or no variants in genes of interest. Thus, there is a need for better tools to identify a precise genetic diagnosis in individuals when conventional testing approaches have been exhausted. We performed targeted long-read sequencing (T-LRS) using adaptive sampling on the Oxford Nanopore platform on 40 individuals, 10 of whom lacked a complete molecular diagnosis. We computationally targeted up to 151 Mbp of sequence per individual and searched for pathogenic substitutions, structural variants, and methylation differences using a single data source. We detected all genomic aberrations-including single-nucleotide variants, copy number changes, repeat expansions, and methylation differences-identified by prior clinical testing. In 8/8 individuals with complex structural rearrangements, T-LRS enabled more precise resolution of the mutation, leading to changes in clinical management in one case. In ten individuals with suspected Mendelian conditions lacking a precise genetic diagnosis, T-LRS identified pathogenic or likely pathogenic variants in six and variants of uncertain significance in two others. T-LRS accurately identifies pathogenic structural variants, resolves complex rearrangements, and identifies Mendelian variants not detected by other technologies. T-LRS represents an efficient and cost-effective strategy to evaluate high-priority genes and regions or complex clinical testing results.


Assuntos
Aberrações Cromossômicas , Análise Citogenética/métodos , Doenças Genéticas Inatas/diagnóstico , Doenças Genéticas Inatas/genética , Predisposição Genética para Doença , Genoma Humano , Mutação , Variações do Número de Cópias de DNA , Feminino , Testes Genéticos , Sequenciamento de Nucleotídeos em Larga Escala , Humanos , Cariotipagem , Masculino , Análise de Sequência de DNA
5.
Nat Neurosci ; 24(8): 1163-1175, 2021 08.
Artigo em Inglês | MEDLINE | ID: mdl-34140698

RESUMO

The human neonatal cerebellum is one-fourth of its adult size yet contains the blueprint required to integrate environmental cues with developing motor, cognitive and emotional skills into adulthood. Although mature cerebellar neuroanatomy is well studied, understanding of its developmental origins is limited. In this study, we systematically mapped the molecular, cellular and spatial composition of human fetal cerebellum by combining laser capture microscopy and SPLiT-seq single-nucleus transcriptomics. We profiled functionally distinct regions and gene expression dynamics within cell types and across development. The resulting cell atlas demonstrates that the molecular organization of the cerebellar anlage recapitulates cytoarchitecturally distinct regions and developmentally transient cell types that are distinct from the mouse cerebellum. By mapping genes dominant for pediatric and adult neurological disorders onto our dataset, we identify relevant cell types underlying disease mechanisms. These data provide a resource for probing the cellular basis of human cerebellar development and disease.


Assuntos
Cerebelo/embriologia , Neurogênese , Feto , Humanos , Microdissecção e Captura a Laser , Análise de Célula Única , Transcriptoma
7.
Hum Mutat ; 41(12): 2179-2194, 2020 12.
Artigo em Inglês | MEDLINE | ID: mdl-33131181

RESUMO

Ciliopathies are clinically and genetically heterogeneous diseases. We studied three patients from two independent families presenting with features of Joubert syndrome: abnormal breathing pattern during infancy, developmental delay/intellectual disability, cerebellar ataxia, molar tooth sign on magnetic resonance imaging scans, and polydactyly. We identified biallelic loss-of-function (LOF) variants in CBY1, segregating with the clinical features of Joubert syndrome in the families. CBY1 localizes to the distal end of the mother centriole, contributing to the formation and function of cilia. In accordance with the clinical and mutational findings in the affected individuals, we demonstrated that depletion of Cby1 in zebrafish causes ciliopathy-related phenotypes. Levels of CBY1 transcript were found reduced in the patients compared with controls, suggesting degradation of the mutated transcript through nonsense-mediated messenger RNA decay. Accordingly, we could detect CBY1 protein in fibroblasts from controls, but not from patients by immunofluorescence. Furthermore, we observed reduced ability to ciliate, increased ciliary length, and reduced levels of the ciliary proteins AHI1 and ARL13B in patient fibroblasts. Our data show that CBY1 LOF-variants cause a ciliopathy with features of Joubert syndrome.

8.
Science ; 370(6518)2020 11 13.
Artigo em Inglês | MEDLINE | ID: mdl-33184180

RESUMO

The chromatin landscape underlying the specification of human cell types is of fundamental interest. We generated human cell atlases of chromatin accessibility and gene expression in fetal tissues. For chromatin accessibility, we devised a three-level combinatorial indexing assay and applied it to 53 samples representing 15 organs, profiling ~800,000 single cells. We leveraged cell types defined by gene expression to annotate these data and cataloged hundreds of thousands of candidate regulatory elements that exhibit cell type-specific chromatin accessibility. We investigated the properties of lineage-specific transcription factors (such as POU2F1 in neurons), organ-specific specializations of broadly distributed cell types (such as blood and endothelial), and cell type-specific enrichments of complex trait heritability. These data represent a rich resource for the exploration of in vivo human gene regulation in diverse tissues and cell types.


Assuntos
Cromatina/metabolismo , Feto/citologia , Feto/metabolismo , Perfilação da Expressão Gênica , Regulação da Expressão Gênica no Desenvolvimento , Análise de Célula Única , Atlas como Assunto , Humanos , Neurônios/metabolismo , Fatores de Transcrição/metabolismo
9.
Science ; 370(6518)2020 11 13.
Artigo em Inglês | MEDLINE | ID: mdl-33184181

RESUMO

The gene expression program underlying the specification of human cell types is of fundamental interest. We generated human cell atlases of gene expression and chromatin accessibility in fetal tissues. For gene expression, we applied three-level combinatorial indexing to >110 samples representing 15 organs, ultimately profiling ~4 million single cells. We leveraged the literature and other atlases to identify and annotate hundreds of cell types and subtypes, both within and across tissues. Our analyses focused on organ-specific specializations of broadly distributed cell types (such as blood, endothelial, and epithelial), sites of fetal erythropoiesis (which notably included the adrenal gland), and integration with mouse developmental atlases (such as conserved specification of blood cells). These data represent a rich resource for the exploration of in vivo human gene expression in diverse tissues and cell types.


Assuntos
Cromatina/metabolismo , Feto/citologia , Feto/metabolismo , Perfilação da Expressão Gênica , Regulação da Expressão Gênica no Desenvolvimento , Análise de Célula Única , Atlas como Assunto , Humanos , Neurônios/metabolismo , Fatores de Transcrição/metabolismo
10.
J Clin Invest ; 130(8): 4423-4439, 2020 08 03.
Artigo em Inglês | MEDLINE | ID: mdl-32453716

RESUMO

Joubert syndrome (JBTS) is a recessive neurodevelopmental ciliopathy characterized by a pathognomonic hindbrain malformation. All known JBTS genes encode proteins involved in the structure or function of primary cilia, ubiquitous antenna-like organelles essential for cellular signal transduction. Here, we used the recently identified JBTS-associated protein armadillo repeat motif-containing 9 (ARMC9) in tandem-affinity purification and yeast 2-hybrid screens to identify a ciliary module whose dysfunction underlies JBTS. In addition to the known JBTS-associated proteins CEP104 and CSPP1, we identified coiled-coil domain containing 66 (CCDC66) and TOG array regulator of axonemal microtubules 1 (TOGARAM1) as ARMC9 interaction partners. We found that TOGARAM1 variants cause JBTS and disrupt TOGARAM1 interaction with ARMC9. Using a combination of protein interaction analyses, characterization of patient-derived fibroblasts, and analysis of CRISPR/Cas9-engineered zebrafish and hTERT-RPE1 cells, we demonstrated that dysfunction of ARMC9 or TOGARAM1 resulted in short cilia with decreased axonemal acetylation and polyglutamylation, but relatively intact transition zone function. Aberrant serum-induced ciliary resorption and cold-induced depolymerization in ARMC9 and TOGARAM1 patient cell lines suggest a role for this new JBTS-associated protein module in ciliary stability.


Assuntos
Anormalidades Múltiplas , Proteínas do Domínio Armadillo , Cerebelo/anormalidades , Cílios , Anormalidades do Olho , Doenças Renais Císticas , Retina/anormalidades , Proteínas de Peixe-Zebra , Peixe-Zebra , Anormalidades Múltiplas/genética , Anormalidades Múltiplas/metabolismo , Acetilação , Animais , Proteínas do Domínio Armadillo/genética , Proteínas do Domínio Armadillo/metabolismo , Sistemas CRISPR-Cas , Cerebelo/metabolismo , Cílios/genética , Cílios/metabolismo , Modelos Animais de Doenças , Anormalidades do Olho/genética , Anormalidades do Olho/metabolismo , Humanos , Doenças Renais Císticas/genética , Doenças Renais Císticas/metabolismo , Peptídeos/genética , Peptídeos/metabolismo , Retina/metabolismo , Peixe-Zebra/genética , Peixe-Zebra/metabolismo , Proteínas de Peixe-Zebra/genética , Proteínas de Peixe-Zebra/metabolismo
11.
Am J Hum Genet ; 106(5): 623-631, 2020 05 07.
Artigo em Inglês | MEDLINE | ID: mdl-32275884

RESUMO

Nucleoporins (NUPs) are an essential component of the nuclear-pore complex, which regulates nucleocytoplasmic transport of macromolecules. Pathogenic variants in NUP genes have been linked to several inherited human diseases, including a number with progressive neurological degeneration. We present six affected individuals with bi-allelic truncating variants in NUP188 and strikingly similar phenotypes and clinical courses, representing a recognizable genetic syndrome; the individuals are from four unrelated families. Key clinical features include congenital cataracts, hypotonia, prenatal-onset ventriculomegaly, white-matter abnormalities, hypoplastic corpus callosum, congenital heart defects, and central hypoventilation. Characteristic dysmorphic features include small palpebral fissures, a wide nasal bridge and nose, micrognathia, and digital anomalies. All affected individuals died as a result of respiratory failure, and five of them died within the first year of life. Nuclear import of proteins was decreased in affected individuals' fibroblasts, supporting a possible disease mechanism. CRISPR-mediated knockout of NUP188 in Drosophila revealed motor deficits and seizure susceptibility, partially recapitulating the neurological phenotype seen in affected individuals. Removal of NUP188 also resulted in aberrant dendrite tiling, suggesting a potential role of NUP188 in dendritic development. Two of the NUP188 pathogenic variants are enriched in the Ashkenazi Jewish population in gnomAD, a finding we confirmed with a separate targeted population screen of an international sampling of 3,225 healthy Ashkenazi Jewish individuals. Taken together, our results implicate bi-allelic loss-of-function NUP188 variants in a recessive syndrome characterized by a distinct neurologic, ophthalmologic, and facial phenotype.


Assuntos
Alelos , Encéfalo/anormalidades , Proteínas de Drosophila/genética , Anormalidades do Olho/genética , Cardiopatias Congênitas/genética , Mutação com Perda de Função/genética , Complexo de Proteínas Formadoras de Poros Nucleares/genética , Transporte Ativo do Núcleo Celular , Animais , Núcleo Celular/metabolismo , Pré-Escolar , Dendritos/metabolismo , Dendritos/patologia , Drosophila melanogaster , Anormalidades do Olho/mortalidade , Feminino , Fibroblastos , Genes Recessivos , Cardiopatias Congênitas/mortalidade , Humanos , Lactente , Recém-Nascido , Judeus/genética , Masculino , Complexo de Proteínas Formadoras de Poros Nucleares/deficiência , Convulsões/metabolismo , Síndrome , beta Carioferinas/metabolismo
13.
Brain ; 143(1): 55-68, 2020 01 01.
Artigo em Inglês | MEDLINE | ID: mdl-31834374

RESUMO

MN1 encodes a transcriptional co-regulator without homology to other proteins, previously implicated in acute myeloid leukaemia and development of the palate. Large deletions encompassing MN1 have been reported in individuals with variable neurodevelopmental anomalies and non-specific facial features. We identified a cluster of de novo truncating mutations in MN1 in a cohort of 23 individuals with strikingly similar dysmorphic facial features, especially midface hypoplasia, and intellectual disability with severe expressive language delay. Imaging revealed an atypical form of rhombencephalosynapsis, a distinctive brain malformation characterized by partial or complete loss of the cerebellar vermis with fusion of the cerebellar hemispheres, in 8/10 individuals. Rhombencephalosynapsis has no previously known definitive genetic or environmental causes. Other frequent features included perisylvian polymicrogyria, abnormal posterior clinoid processes and persistent trigeminal artery. MN1 is encoded by only two exons. All mutations, including the recurrent variant p.Arg1295* observed in 8/21 probands, fall in the terminal exon or the extreme 3' region of exon 1, and are therefore predicted to result in escape from nonsense-mediated mRNA decay. This was confirmed in fibroblasts from three individuals. We propose that the condition described here, MN1 C-terminal truncation (MCTT) syndrome, is not due to MN1 haploinsufficiency but rather is the result of dominantly acting C-terminally truncated MN1 protein. Our data show that MN1 plays a critical role in human craniofacial and brain development, and opens the door to understanding the biological mechanisms underlying rhombencephalosynapsis.


Assuntos
Anormalidades Múltiplas/genética , Anormalidades Craniofaciais/genética , Deficiência Intelectual/genética , Transtornos do Desenvolvimento da Linguagem/genética , Malformações do Sistema Nervoso/genética , Transativadores/genética , Proteínas Supressoras de Tumor/genética , Anormalidades Múltiplas/diagnóstico por imagem , Adolescente , Artéria Basilar/anormalidades , Artéria Basilar/diagnóstico por imagem , Artérias Carótidas/anormalidades , Artérias Carótidas/diagnóstico por imagem , Vermis Cerebelar/anormalidades , Vermis Cerebelar/diagnóstico por imagem , Cerebelo/anormalidades , Cerebelo/diagnóstico por imagem , Criança , Pré-Escolar , Estudos de Coortes , Hibridização Genômica Comparativa , Anormalidades Craniofaciais/diagnóstico por imagem , Feminino , Fibroblastos/metabolismo , Humanos , Imageamento Tridimensional , Lactente , Imageamento por Ressonância Magnética , Masculino , Pessoa de Meia-Idade , Mutação , Malformações do Sistema Nervoso/diagnóstico por imagem , Degradação do RNAm Mediada por Códon sem Sentido , Polimicrogiria/diagnóstico por imagem , Polimicrogiria/genética , RNA-Seq , Reação em Cadeia da Polimerase em Tempo Real , Síndrome , Tomografia Computadorizada por Raios X , Sequenciamento Completo do Exoma , Sequenciamento Completo do Genoma
14.
Am J Med Genet A ; 182(1): 229-249, 2020 01.
Artigo em Inglês | MEDLINE | ID: mdl-31710777

RESUMO

Joubert syndrome (JS) is a recessive neurodevelopmental disorder defined by a characteristic cerebellar and brainstem malformation recognizable on axial brain magnetic resonance imaging as the "Molar Tooth Sign". Although defined by the neurological features, JS is associated with clinical features affecting many other organ systems, particularly progressive involvement of the retina, kidney, and liver. JS is a rare condition; therefore, many affected individuals may not have easy access to subspecialty providers familiar with JS (e.g., geneticists, neurologists, developmental pediatricians, ophthalmologists, nephrologists, hepatologists, psychiatrists, therapists, and educators). Expert recommendations can enable practitioners of all types to provide quality care to individuals with JS and know when to refer for subspecialty care. This need will only increase as precision treatments targeting specific genetic causes of JS emerge. The goal of these recommendations is to provide a resource for general practitioners, subspecialists, and families to maximize the health of individuals with JS throughout the lifespan.


Assuntos
Anormalidades Múltiplas/epidemiologia , Cerebelo/anormalidades , Anormalidades do Olho/epidemiologia , Pessoal de Saúde , Doenças Renais Císticas/epidemiologia , Transtornos do Neurodesenvolvimento/epidemiologia , Retina/anormalidades , Anormalidades Múltiplas/genética , Anormalidades Múltiplas/patologia , Anormalidades Múltiplas/terapia , Tronco Encefálico/patologia , Cerebelo/patologia , Anormalidades do Olho/genética , Anormalidades do Olho/patologia , Anormalidades do Olho/terapia , Diretrizes para o Planejamento em Saúde , Humanos , Rim/patologia , Doenças Renais Císticas/genética , Doenças Renais Císticas/patologia , Doenças Renais Císticas/terapia , Fígado/patologia , Transtornos do Neurodesenvolvimento/genética , Transtornos do Neurodesenvolvimento/patologia , Transtornos do Neurodesenvolvimento/terapia , Retina/patologia
15.
Am J Hum Genet ; 105(3): 606-615, 2019 09 05.
Artigo em Inglês | MEDLINE | ID: mdl-31474318

RESUMO

Cerebellar malformations are diverse congenital anomalies frequently associated with developmental disability. Although genetic and prenatal non-genetic causes have been described, no systematic analysis has been performed. Here, we present a large-exome sequencing study of Dandy-Walker malformation (DWM) and cerebellar hypoplasia (CBLH). We performed exome sequencing in 282 individuals from 100 families with DWM or CBLH, and we established a molecular diagnosis in 36 of 100 families, with a significantly higher yield for CBLH (51%) than for DWM (16%). The 41 variants impact 27 neurodevelopmental-disorder-associated genes, thus demonstrating that CBLH and DWM are often features of monogenic neurodevelopmental disorders. Though only seven monogenic causes (19%) were identified in more than one individual, neuroimaging review of 131 additional individuals confirmed cerebellar abnormalities in 23 of 27 genetic disorders (85%). Prenatal risk factors were frequently found among individuals without a genetic diagnosis (30 of 64 individuals [47%]). Single-cell RNA sequencing of prenatal human cerebellar tissue revealed gene enrichment in neuronal and vascular cell types; this suggests that defective vasculogenesis may disrupt cerebellar development. Further, de novo gain-of-function variants in PDGFRB, a tyrosine kinase receptor essential for vascular progenitor signaling, were associated with CBLH, and this discovery links genetic and non-genetic etiologies. Our results suggest that genetic defects impact specific cerebellar cell types and implicate abnormal vascular development as a mechanism for cerebellar malformations. We also confirmed a major contribution for non-genetic prenatal factors in individuals with cerebellar abnormalities, substantially influencing diagnostic evaluation and counseling regarding recurrence risk and prognosis.


Assuntos
Cerebelo/anormalidades , Cerebelo/diagnóstico por imagem , Estudos de Coortes , Feminino , Humanos , Masculino , Gravidez
16.
Am J Med Genet A ; 179(9): 1783-1790, 2019 09.
Artigo em Inglês | MEDLINE | ID: mdl-31294511

RESUMO

Rare individuals with 20p11.2 proximal deletions have been previously reported, with a variable phenotype that includes heterotaxy, biliary atresia, midline brain defects associated with panhypopituitarism, intellectual disability, scoliosis, and seizures. Deletions have ranged in size from 277 kb to 11.96 Mb. We describe a newborn with a de novo 2.7 Mb deletion of 20p11.22p11.21 that partially overlaps previously reported deletions and encompasses FOXA2. Her clinical findings further expand the 20p11.2 deletion phenotype to include severe midline cranial and intracranial defects such as aqueductal stenosis with hydrocephalus, mesencephalosynapsis with diencephalic-mesencephalic junction dysplasia, and pyriform aperture stenosis. We also report one individual with a missense variant in FOXA2 who had abnormal glucose homeostasis, panhypopituitarism, and endodermal organ dysfunction. Together, these findings support the critical role of FOXA2 in panhypopituitarism and midline defects.


Assuntos
Encéfalo/anormalidades , Constrição Patológica/genética , Fator 3-beta Nuclear de Hepatócito/genética , Hipopituitarismo/genética , Encéfalo/diagnóstico por imagem , Encéfalo/fisiopatologia , Deleção Cromossômica , Cromossomos Humanos Par 20/genética , Constrição Patológica/diagnóstico por imagem , Constrição Patológica/fisiopatologia , Predisposição Genética para Doença , Humanos , Hidrocefalia/diagnóstico por imagem , Hidrocefalia/genética , Hidrocefalia/fisiopatologia , Hipopituitarismo/diagnóstico por imagem , Hipopituitarismo/fisiopatologia , Recém-Nascido , Mutação de Sentido Incorreto/genética , Fenótipo , Córtex Piriforme/diagnóstico por imagem , Córtex Piriforme/fisiopatologia
17.
Am J Hum Genet ; 104(1): 35-44, 2019 01 03.
Artigo em Inglês | MEDLINE | ID: mdl-30554721

RESUMO

Baratela-Scott syndrome (BSS) is a rare, autosomal-recessive disorder characterized by short stature, facial dysmorphisms, developmental delay, and skeletal dysplasia caused by pathogenic variants in XYLT1. We report clinical and molecular investigation of 10 families (12 individuals) with BSS. Standard sequencing methods identified biallelic pathogenic variants in XYLT1 in only two families. Of the remaining cohort, two probands had no variants and six probands had only a single variant, including four with a heterozygous 3.1 Mb 16p13 deletion encompassing XYLT1 and two with a heterozygous truncating variant. Bisulfite sequencing revealed aberrant hypermethylation in exon 1 of XYLT1, always in trans with the sequence variant or deletion when present; both alleles were methylated in those with no identified variant. Expression of the methylated XYLT1 allele was severely reduced in fibroblasts from two probands. Southern blot studies combined with repeat expansion analysis of genome sequence data showed that the hypermethylation is associated with expansion of a GGC repeat in the XYLT1 promoter region that is not present in the reference genome, confirming that BSS is a trinucleotide repeat expansion disorder. The hypermethylated allele accounts for 50% of disease alleles in our cohort and is not present in 130 control subjects. Our study highlights the importance of investigating non-sequence-based alterations, including epigenetic changes, to identify the missing heritability in genetic disorders.


Assuntos
Anormalidades Múltiplas/genética , Metilação de DNA/genética , Epigênese Genética/genética , Éxons/genética , Mutação , Pentosiltransferases/genética , Expansão das Repetições de Trinucleotídeos/genética , Alelos , Southern Blotting , Estudos de Coortes , Feminino , Humanos , Lactente , Recém-Nascido , Masculino , Linhagem , Sulfitos/metabolismo , Síndrome
18.
Am J Med Genet C Semin Med Genet ; 178(4): 432-439, 2018 12.
Artigo em Inglês | MEDLINE | ID: mdl-30580482

RESUMO

Rhombencephalosynapsis (RES) is a unique cerebellar malformation characterized by fusion of the cerebellar hemispheres with partial or complete absence of a recognizable cerebellar vermis. Subsets of patients also have other brain malformations such as midbrain fusion with aqueductal stenosis, characteristic craniofacial features (prominent forehead, flat midface, hypertelorism, ear abnormalities), and somatic malformations (heart, kidney, spine, and limb defects). Similar to known genetic brain malformations, the RES cerebellar malformation is highly stereotyped, yet no genetic causes have been identified. Here, we outline our current understanding of the genetic basis for RES, discuss limitations, and outline future approaches to identifying the causes of this fascinating brain malformation.


Assuntos
Doenças Cerebelares/diagnóstico , Doenças Cerebelares/genética , Cerebelo/anormalidades , Transtornos do Crescimento/diagnóstico , Rombencéfalo/anormalidades , Transtornos do Crescimento/genética , Humanos , Rombencéfalo/patologia
19.
Am J Hum Genet ; 103(6): 1009-1021, 2018 12 06.
Artigo em Inglês | MEDLINE | ID: mdl-30471716

RESUMO

To date, mutations in 15 actin- or microtubule-associated genes have been associated with the cortical malformation lissencephaly and variable brainstem hypoplasia. During a multicenter review, we recognized a rare lissencephaly variant with a complex brainstem malformation in three unrelated children. We searched our large brain-malformation databases and found another five children with this malformation (as well as one with a less severe variant), analyzed available whole-exome or -genome sequencing data, and tested ciliogenesis in two affected individuals. The brain malformation comprised posterior predominant lissencephaly and midline crossing defects consisting of absent anterior commissure and a striking W-shaped brainstem malformation caused by small or absent pontine crossing fibers. We discovered heterozygous de novo missense variants or an in-frame deletion involving highly conserved zinc-binding residues within the GAR domain of MACF1 in the first eight subjects. We studied cilium formation and found a higher proportion of mutant cells with short cilia than of control cells with short cilia. A ninth child had similar lissencephaly but only subtle brainstem dysplasia associated with a heterozygous de novo missense variant in the spectrin repeat domain of MACF1. Thus, we report variants of the microtubule-binding GAR domain of MACF1 as the cause of a distinctive and most likely pathognomonic brain malformation. A gain-of-function or dominant-negative mechanism appears likely given that many heterozygous mutations leading to protein truncation are included in the ExAC Browser. However, three de novo variants in MACF1 have been observed in large schizophrenia cohorts.


Assuntos
Orientação de Axônios/genética , Movimento Celular/genética , Sequência Conservada/genética , Proteínas dos Microfilamentos/genética , Mutação/genética , Neurônios/patologia , Zinco/metabolismo , Adolescente , Tronco Encefálico/patologia , Criança , Pré-Escolar , Cílios/genética , Feminino , Humanos , Lisencefalia/genética , Masculino , Microtúbulos/genética , Malformações do Sistema Nervoso/genética
20.
Handb Clin Neurol ; 154: 267-286, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29903444

RESUMO

The approach to identifying a genetic cause in patients with cerebellar disorders relies on history, examination, consultation, and testing, combined with specialized expertise because they are rare and genetically diverse. Cerebellar disorders can be caused by a variety of DNA alterations including single-nucleotide changes, small insertions or deletions, larger copy number variants, and nucleotide repeat expansions, exhibiting autosomal-recessive, autosomal-dominant (inherited and de novo), X-linked, and mitochondrial modes of inheritance. Imaging findings and a variety of neurologic and nonneurologic clinical features can help direct genetic testing and choose the most appropriate strategy. Clinical and genetic diagnoses are complementary, each providing distinct information for the care of the patient. In this chapter, we provide an overview of inheritance modes for different cerebellar disorders and the variety of genetic testing and tools that are currently available to reach a genetic diagnosis, including conventional and next-generation sequencing, classic, molecular and virtual cytogenetics, testing for repeat expansions, and other techniques. Practical examples are presented in both the text and accompanying vignettes.


Assuntos
Doenças Cerebelares/genética , Testes Genéticos , Mutação/genética , Humanos
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