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SGIP1 encodes a protein Src homology 3-domain growth factor receptor-bound 2-like endophilin interacting protein 1. It is involved in the regulation of clathrin-mediated endocytosis along with having a role in energy homeostasis in neuronal systems. We generated an isogenic human induced pluripotent stem cell (iPSC) line with a biallelic frameshift variant in SGIP1. This exon has been shown to be subject to alternative splicing, leading to an isoform lacking 24 amino acids that are present in the longest SGIP isoform. The newly generated iPSC line will be helpful to dissect the differential properties of the two SGIP isoforms.
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Intellectual disability (ID) is a diverse neurodevelopmental condition and almost half of the cases have a genetic etiology. SGIP1 acts as an endocytic protein that influences the signaling of receptors in neuronal systems related to energy homeostasis through its interaction with endophilins. This study focuses on the generation and characterization of induced pluripotent stem cells (iPSC) from two unrelated patients due to a frameshift variant (c.764dupA, NM_032291.4) and a splice donor site variant (c.74 + 1G > A, NM_032291.4) in the SGIP1 gene.
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Homocigoto , Células Madre Pluripotentes Inducidas , Discapacidad Intelectual , Humanos , Células Madre Pluripotentes Inducidas/metabolismo , Discapacidad Intelectual/genética , Discapacidad Intelectual/patología , Masculino , Femenino , Línea Celular , NiñoRESUMEN
We describe the phenotype of 22 male patients (20 probands) carrying a hemizygous missense variant in MED12. The phenotypic spectrum is very broad ranging from nonspecific intellectual disability (ID) to the three well-known syndromes: Opitz-Kaveggia syndrome, Lujan-Fryns syndrome, or Ohdo syndrome. The identified variants were randomly distributed throughout the gene (p = 0.993, χ2 test), but mostly outside the functional domains (p = 0.004; χ2 test). Statistical analyses did not show a correlation between the MED12-related phenotypes and the locations of the variants (p = 0.295; Pearson correlation), nor the protein domain involved (p = 0.422; Pearson correlation). In conclusion, establishing a genotype-phenotype correlation in MED12-related diseases remains challenging. Therefore, we think that patients with a causative MED12 variant are currently underdiagnosed due to the broad patients' clinical presentations.
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Blefarofimosis , Discapacidad Intelectual , Discapacidad Intelectual Ligada al Cromosoma X , Masculino , Humanos , Complejo Mediador/genética , Discapacidad Intelectual Ligada al Cromosoma X/genética , Discapacidad Intelectual/diagnóstico , Discapacidad Intelectual/genética , Blefarofimosis/genética , Mutación Missense/genética , Fenotipo , SíndromeRESUMEN
SLITRK2 is a single-pass transmembrane protein expressed at postsynaptic neurons that regulates neurite outgrowth and excitatory synapse maintenance. In the present study, we report on rare variants (one nonsense and six missense variants) in SLITRK2 on the X chromosome identified by exome sequencing in individuals with neurodevelopmental disorders. Functional studies showed that some variants displayed impaired membrane transport and impaired excitatory synapse-promoting effects. Strikingly, these variations abolished the ability of SLITRK2 wild-type to reduce the levels of the receptor tyrosine kinase TrkB in neurons. Moreover, Slitrk2 conditional knockout mice exhibited impaired long-term memory and abnormal gait, recapitulating a subset of clinical features of patients with SLITRK2 variants. Furthermore, impaired excitatory synapse maintenance induced by hippocampal CA1-specific cKO of Slitrk2 caused abnormalities in spatial reference memory. Collectively, these data suggest that SLITRK2 is involved in X-linked neurodevelopmental disorders that are caused by perturbation of diverse facets of SLITRK2 function.
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Trastornos del Neurodesarrollo , Sinapsis , Animales , Cognición , Hipocampo/fisiología , Ratones , Ratones Noqueados , Trastornos del Neurodesarrollo/genética , Trastornos del Neurodesarrollo/metabolismo , Sinapsis/metabolismoRESUMEN
Free oligosaccharides (fOSs) are soluble oligosaccharide species generated during N-glycosylation of proteins. Although little is known about fOS metabolism, the recent identification of NGLY1 deficiency, a congenital disorder of deglycosylation (CDDG) caused by loss of function of an enzyme involved in fOS metabolism, has elicited increased interest in fOS processing. The catabolism of fOSs has been linked to the activity of a specific cytosolic mannosidase, MAN2C1, which cleaves α1,2-, α1,3-, and α1,6-mannose residues. In this study, we report the clinical, biochemical, and molecular features of six individuals, including two fetuses, with bi-allelic pathogenic variants in MAN2C1; the individuals are from four different families. These individuals exhibit dysmorphic facial features, congenital anomalies such as tongue hamartoma, variable degrees of intellectual disability, and brain anomalies including polymicrogyria, interhemispheric cysts, hypothalamic hamartoma, callosal anomalies, and hypoplasia of brainstem and cerebellar vermis. Complementation experiments with isogenic MAN2C1-KO HAP1 cells confirm the pathogenicity of three of the identified MAN2C1 variants. We further demonstrate that MAN2C1 variants lead to accumulation and delay in the processing of fOSs in proband-derived cells. These results emphasize the involvement of MAN2C1 in human neurodevelopmental disease and the importance of fOS catabolism.
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Quistes del Sistema Nervioso Central/genética , Trastornos Congénitos de Glicosilación/genética , Hamartoma/genética , Discapacidad Intelectual/genética , Oligosacáridos/metabolismo , Péptido-N4-(N-acetil-beta-glucosaminil) Asparagina Amidasa/deficiencia , Polimicrogiria/genética , alfa-Manosidasa/genética , Adolescente , Alelos , Tronco Encefálico/metabolismo , Tronco Encefálico/patología , Línea Celular Tumoral , Quistes del Sistema Nervioso Central/metabolismo , Quistes del Sistema Nervioso Central/patología , Vermis Cerebeloso/metabolismo , Vermis Cerebeloso/patología , Niño , Preescolar , Trastornos Congénitos de Glicosilación/metabolismo , Trastornos Congénitos de Glicosilación/patología , Femenino , Feto , Glicosilación , Hamartoma/metabolismo , Hamartoma/patología , Humanos , Hipotálamo/metabolismo , Hipotálamo/patología , Discapacidad Intelectual/metabolismo , Discapacidad Intelectual/patología , Leucocitos/metabolismo , Leucocitos/patología , Masculino , Manosa/metabolismo , Péptido-N4-(N-acetil-beta-glucosaminil) Asparagina Amidasa/genética , Péptido-N4-(N-acetil-beta-glucosaminil) Asparagina Amidasa/metabolismo , Polimicrogiria/metabolismo , Polimicrogiria/patología , Lengua/metabolismo , Lengua/patología , alfa-Manosidasa/deficienciaRESUMEN
INTRODUCTION: Replication of the nuclear genome is an essential step for cell division. Pathogenic variants in genes coding for highly conserved components of the DNA replication machinery cause Meier-Gorlin syndrome (MGORS). OBJECTIVE: Identification of novel genes associated with MGORS. METHODS: Exome sequencing was performed to investigate the genotype of an individual presenting with prenatal and postnatal growth restriction, a craniofacial gestalt of MGORS and coronal craniosynostosis. The analysis of the candidate variants employed bioinformatic tools, in silico structural protein analysis and modelling in budding yeast. RESULTS: A novel homozygous missense variant NM_016095.2:c.341G>T, p.(Arg114Leu), in GINS2 was identified. Both non-consanguineous healthy parents carried this variant. Bioinformatic analysis supports its classification as pathogenic. Functional analyses using yeast showed that this variant increases sensitivity to nicotinamide, a compound that interferes with DNA replication processes. The phylogenetically highly conserved residue p.Arg114 localises at the docking site of CDC45 and MCM5 at GINS2. Moreover, the missense change possibly disrupts the effective interaction between the GINS complex and CDC45, which is necessary for the CMG helicase complex (Cdc45/MCM2-7/GINS) to accurately operate. Interestingly, our patient's phenotype is strikingly similar to the phenotype of patients with CDC45-related MGORS, particularly those with craniosynostosis, mild short stature and patellar hypoplasia. CONCLUSION: GINS2 is a new disease-associated gene, expanding the genetic aetiology of MGORS.
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Proteínas Cromosómicas no Histona , Microtia Congénita , Craneosinostosis , Micrognatismo , Proteínas de Ciclo Celular/genética , Proteínas Cromosómicas no Histona/genética , Proteínas Cromosómicas no Histona/metabolismo , Microtia Congénita/genética , Craneosinostosis/genética , Trastornos del Crecimiento/genética , Humanos , Micrognatismo/genética , Rótula/anomalías , Saccharomyces cerevisiae/genéticaRESUMEN
Intellectual disability (ID) can be caused by non-genetic and genetic factors, the latter being responsible for more than 1700 ID-related disorders. The broad ID phenotypic and genetic heterogeneity, as well as the difficulty in the establishment of the inheritance pattern, often result in a delay in the diagnosis. It has become apparent that massive parallel sequencing can overcome these difficulties. In this review we address: (i) ID genetic aetiology, (ii) clinical/medical settings testing, (iii) massive parallel sequencing, (iv) variant filtering and prioritization, (v) variant classification guidelines and functional studies, and (vi) ID diagnostic yield. Furthermore, the need for a constant update of the methodologies and functional tests, is essential. Thus, international collaborations, to gather expertise, data and resources through multidisciplinary contributions, are fundamental to keep track of the fast progress in ID gene discovery.
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Discapacidad Intelectual , Genómica , Humanos , Discapacidad Intelectual/diagnóstico , Discapacidad Intelectual/genéticaRESUMEN
EDEM3 encodes a protein that converts Man8GlcNAc2 isomer B to Man7-5GlcNAc2. It is involved in the endoplasmic reticulum-associated degradation pathway, responsible for the recognition of misfolded proteins that will be targeted and translocated to the cytosol and degraded by the proteasome. In this study, through a combination of exome sequencing and gene matching, we have identified seven independent families with 11 individuals with bi-allelic protein-truncating variants and one individual with a compound heterozygous missense variant in EDEM3. The affected individuals present with an inherited congenital disorder of glycosylation (CDG) consisting of neurodevelopmental delay and variable facial dysmorphisms. Experiments in human fibroblast cell lines, human plasma, and mouse plasma and brain tissue demonstrated decreased trimming of Man8GlcNAc2 isomer B to Man7GlcNAc2, consistent with loss of EDEM3 enzymatic activity. In human cells, Man5GlcNAc2 to Man4GlcNAc2 conversion is also diminished with an increase of Glc1Man5GlcNAc2. Furthermore, analysis of the unfolded protein response showed a reduced increase in EIF2AK3 (PERK) expression upon stimulation with tunicamycin as compared to controls, suggesting an impaired unfolded protein response. The aberrant plasma N-glycan profile provides a quick, clinically available test for validating variants of uncertain significance that may be identified by molecular genetic testing. We propose to call this deficiency EDEM3-CDG.
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Proteínas de Unión al Calcio/genética , Trastornos Congénitos de Glicosilación/genética , Retículo Endoplásmico/genética , alfa-Manosidasa/genética , Adolescente , Alelos , Proteínas de Unión al Calcio/deficiencia , Línea Celular , Niño , Preescolar , Trastornos Congénitos de Glicosilación/sangre , Discapacidades del Desarrollo/genética , Femenino , Glicoproteínas/sangre , Glicosilación , Humanos , Lactante , Discapacidad Intelectual/genética , Masculino , Mutación , Linaje , Polisacáridos/sangre , Deficiencias en la Proteostasis/genética , alfa-Manosidasa/deficienciaRESUMEN
PURPOSE: To elucidate the novel molecular cause in families with a new autosomal recessive neurodevelopmental disorder. METHODS: A combination of exome sequencing and gene matching tools was used to identify pathogenic variants in 17 individuals. Quantitative reverse transcription polymerase chain reaction (RT-qPCR) and subcellular localization studies were used to characterize gene expression profile and localization. RESULTS: Biallelic variants in the TMEM222 gene were identified in 17 individuals from nine unrelated families, presenting with intellectual disability and variable other features, such as aggressive behavior, shy character, body tremors, decreased muscle mass in the lower extremities, and mild hypotonia. We found relatively high TMEM222 expression levels in the human brain, especially in the parietal and occipital cortex. Additionally, subcellular localization analysis in human neurons derived from induced pluripotent stem cells (iPSCs) revealed that TMEM222 localizes to early endosomes in the synapses of mature iPSC-derived neurons. CONCLUSION: Our findings support a role for TMEM222 in brain development and function and adds variants in the gene TMEM222 as a novel underlying cause of an autosomal recessive neurodevelopmental disorder.
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Discapacidad Intelectual , Trastornos del Neurodesarrollo , Humanos , Discapacidad Intelectual/genética , Trastornos del Neurodesarrollo/genética , Linaje , Secuenciación del ExomaRESUMEN
We describe an infant female with a syndromic neurodevelopmental clinical phenotype and increased chromosome instability as cellular phenotype. Genotype characterization revealed heterozygous variants in genes directly or indirectly linked to DNA repair: a de novo X-linked HDAC8 pathogenic variant, a paternally inherited FANCG pathogenic variant and a maternally inherited BRCA2 variant of uncertain significance. The full spectrum of the phenotype cannot be explained by any of the heterozygous variants on their own; thus, a synergic contribution is proposed. Complementation studies showed that the FANCG gene from the Fanconi Anaemia/BRCA (FA/BRCA) DNA repair pathway was impaired, indicating that the variant in FANCG contributes to the cellular phenotype. The patient's chromosome instability represents the first report where heterozygous variant(s) in the FA/BRCA pathway are implicated in the cellular phenotype. We propose that a multigenic contribution of heterozygous variants in HDAC8 and the FA/BRCA pathway might have a role in the phenotype of this neurodevelopmental disorder. The importance of these findings may have repercussion in the clinical management of other cases with a similar synergic contribution of heterozygous variants, allowing the establishment of new genotype-phenotype correlations and motivating the biochemical study of the underlying mechanisms.
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Proteína BRCA1/genética , Proteína BRCA2/genética , Inestabilidad Cromosómica , Proteína del Grupo de Complementación G de la Anemia de Fanconi/genética , Histona Desacetilasas/genética , Trastornos del Neurodesarrollo/patología , Fenotipo , Proteínas Represoras/genética , Daño del ADN , Reparación del ADN , Femenino , Humanos , Recién Nacido , Mutación , Trastornos del Neurodesarrollo/genéticaRESUMEN
Eukaryotic translation elongation factor 2 (eEF2) is a key regulatory factor in gene expression that catalyzes the elongation stage of translation. A functionally impaired eEF2, due to a heterozygous missense variant in the EEF2 gene, was previously reported in one family with spinocerebellar ataxia-26 (SCA26), an autosomal dominant adult-onset pure cerebellar ataxia. Clinical exome sequencing identified de novo EEF2 variants in three unrelated children presenting with a neurodevelopmental disorder (NDD). Individuals shared a mild phenotype comprising motor delay and relative macrocephaly associated with ventriculomegaly. Populational data and bioinformatic analysis underscored the pathogenicity of all de novo missense variants. The eEF2 yeast model strains demonstrated that patient-derived variants affect cellular growth, sensitivity to translation inhibitors and translational fidelity. Consequently, we propose that pathogenic variants in the EEF2 gene, so far exclusively associated with late-onset SCA26, can cause a broader spectrum of neurologic disorders, including childhood-onset NDDs and benign external hydrocephalus.
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Quinasa del Factor 2 de Elongación/genética , Exoma , Heterocigoto , Hidrocefalia/patología , Mutación , Trastornos del Neurodesarrollo/patología , Niño , Preescolar , Humanos , Hidrocefalia/etiología , Hidrocefalia/metabolismo , Masculino , Trastornos del Neurodesarrollo/etiología , Trastornos del Neurodesarrollo/metabolismo , Fenotipo , Secuenciación del ExomaRESUMEN
In a patient with Usher syndrome and atypical muscle complaints, we have identified two separate variants in MYO7A andNEB genes by exome sequencing. The homozygous variants in these two recessive genes could explain the full phenotype of our patient.
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Recurrent somatic variants in SPOP are cancer specific; endometrial and prostate cancers result from gain-of-function and dominant-negative effects toward BET proteins, respectively. By using clinical exome sequencing, we identified six de novo pathogenic missense variants in SPOP in seven individuals with developmental delay and/or intellectual disability, facial dysmorphisms, and congenital anomalies. Two individuals shared craniofacial dysmorphisms, including congenital microcephaly, that were strikingly different from those of the other five individuals, who had (relative) macrocephaly and hypertelorism. We measured the effect of SPOP variants on BET protein amounts in human Ishikawa endometrial cancer cells and patient-derived cell lines because we hypothesized that variants would lead to functional divergent effects on BET proteins. The de novo variants c.362G>A (p.Arg121Gln) and c. 430G>A (p.Asp144Asn), identified in the first two individuals, resulted in a gain of function, and conversely, the c.73A>G (p.Thr25Ala), c.248A>G (p.Tyr83Cys), c.395G>T (p.Gly132Val), and c.412C>T (p.Arg138Cys) variants resulted in a dominant-negative effect. Our findings suggest that these opposite functional effects caused by the variants in SPOP result in two distinct and clinically recognizable syndromic forms of intellectual disability with contrasting craniofacial dysmorphisms.
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Mutación Missense , Trastornos del Neurodesarrollo/genética , Proteínas Nucleares/genética , Proteínas Represoras/genética , Adolescente , Niño , Preescolar , Facies , Femenino , Humanos , Lactante , Discapacidad Intelectual/genética , Masculino , Cráneo/anomalías , Adulto JovenRESUMEN
PURPOSE: To delineate the genotype-phenotype correlation in individuals with likely pathogenic variants in the CLTC gene. METHODS: We describe 13 individuals with de novo CLTC variants. Causality of variants was determined by using the tolerance landscape of CLTC and computer-assisted molecular modeling where applicable. Phenotypic abnormalities observed in the individuals identified with missense and in-frame variants were compared with those with nonsense or frameshift variants in CLTC. RESULTS: All de novo variants were judged to be causal. Combining our data with that of 14 previously reported affected individuals (n = 27), all had intellectual disability (ID), ranging from mild to moderate/severe, with or without additional neurologic, behavioral, craniofacial, ophthalmologic, and gastrointestinal features. Microcephaly, hypoplasia of the corpus callosum, and epilepsy were more frequently observed in individuals with missense and in-frame variants than in those with nonsense and frameshift variants. However, this difference was not significant. CONCLUSIONS: The wide phenotypic variability associated with likely pathogenic CLTC variants seems to be associated with allelic heterogeneity. The detailed clinical characterization of a larger cohort of individuals with pathogenic CLTC variants is warranted to support the hypothesis that missense and in-frame variants exert a dominant-negative effect, whereas the nonsense and frameshift variants would result in haploinsufficiency.
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Epilepsia , Discapacidad Intelectual , Microcefalia , Variación Biológica Poblacional , Cuerpo Calloso , Epilepsia/genética , Humanos , Discapacidad Intelectual/genética , Microcefalia/genética , FenotipoRESUMEN
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
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BACKGROUND: Eight different deletions and point variants of the X-chromosomal gene CNKSR2 have been reported in families with males presenting intellectual disability (ID) and epilepsy. Obligate carrier females with a frameshift variant in the N-terminal protein coding part of CNKSR2 or with a deletion of the complete gene are not affected. Only for one C-terminal nonsense variant, two carrier females were mildly affected by seizures without or with mild motor and language delay. METHODS: Exome sequencing was performed in one female child of a Dutch family, presenting seizures, mild ID, facial dysmorphisms, and abnormalities of the extremities. Potential causative variants were validated by Sanger sequencing. X-chromosome-inactivation (XCI) analysis was performed by methylation-sensitive PCR and fragment-length analysis of the androgen-receptor CAG repeat polymorphism. RESULTS: We identified a de novo variant, c.2304G>A (p.(Trp768*)), in the C-terminal protein coding part of the X-chromosomal gene CNKSR2 in a female patient with seizures and mild ID. Sanger sequencing confirmed the presence of this nonsense variant. XCI analysis showed a mild skewing of X inactivation (20:80) in the blood of our patient. Our variant is the second C-terminal-affecting CNKSR2 variant described in neurologically affected females. CONCLUSION: Our results indicate that CNKSR2 nonsense variants in the C-terminal coding part can result in ID with seizures in female variant carriers.
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Proteínas Adaptadoras Transductoras de Señales/genética , Discapacidad Intelectual/diagnóstico , Convulsiones/diagnóstico , Encéfalo/diagnóstico por imagen , Niño , Codón sin Sentido , Femenino , Humanos , Discapacidad Intelectual/genética , Imagen por Resonancia Magnética , Convulsiones/genética , Secuenciación del Exoma , Inactivación del Cromosoma XRESUMEN
Glypicans are a family of cell-surface heparan sulfate proteoglycans that regulate growth-factor signaling during development and are thought to play a role in the regulation of morphogenesis. Whole-exome sequencing of the Australian family that defined Keipert syndrome (nasodigitoacoustic syndrome) identified a hemizygous truncating variant in the gene encoding glypican 4 (GPC4). This variant, located in the final exon of GPC4, results in premature termination of the protein 51 amino acid residues prior to the stop codon, and in concomitant loss of functionally important N-linked glycosylation (Asn514) and glycosylphosphatidylinositol (GPI) anchor (Ser529) sites. We subsequently identified seven affected males from five additional kindreds with novel and predicted pathogenic variants in GPC4. Segregation analysis and X-inactivation studies in carrier females provided supportive evidence that the GPC4 variants caused the condition. Furthermore, functional studies of recombinant protein suggested that the truncated proteins p.Gln506∗ and p.Glu496∗ were less stable than the wild type. Clinical features of Keipert syndrome included a prominent forehead, a flat midface, hypertelorism, a broad nose, downturned corners of mouth, and digital abnormalities, whereas cognitive impairment and deafness were variable features. Studies of Gpc4 knockout mice showed evidence of the two primary features of Keipert syndrome: craniofacial abnormalities and digital abnormalities. Phylogenetic analysis demonstrated that GPC4 is most closely related to GPC6, which is associated with a bone dysplasia that has a phenotypic overlap with Keipert syndrome. Overall, we have shown that pathogenic variants in GPC4 cause a loss of function that results in Keipert syndrome, making GPC4 the third human glypican to be linked to a genetic syndrome.
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Sordera/congénito , Enfermedades Genéticas Ligadas al Cromosoma X/genética , Enfermedades Genéticas Ligadas al Cromosoma X/patología , Variación Genética , Glipicanos/genética , Deformidades Congénitas de las Extremidades Inferiores/genética , Deformidades Congénitas de las Extremidades Inferiores/patología , Adulto , Niño , Preescolar , Sordera/genética , Sordera/patología , Femenino , Humanos , Lactante , Masculino , Linaje , Fenotipo , Adulto JovenRESUMEN
PURPOSE: To investigate the effect of different DEAF1 variants on the phenotype of patients with autosomal dominant and recessive inheritance patterns and on DEAF1 activity in vitro. METHODS: We assembled a cohort of 23 patients with de novo and biallelic DEAF1 variants, described the genotype-phenotype correlation, and investigated the differential effect of de novo and recessive variants on transcription assays using DEAF1 and Eif4g3 promoter luciferase constructs. RESULTS: The proportion of the most prevalent phenotypic features, including intellectual disability, speech delay, motor delay, autism, sleep disturbances, and a high pain threshold, were not significantly different in patients with biallelic and pathogenic de novo DEAF1 variants. However, microcephaly was exclusively observed in patients with recessive variants (p < 0.0001). CONCLUSION: We propose that different variants in the DEAF1 gene result in a phenotypic spectrum centered around neurodevelopmental delay. While a pathogenic de novo dominant variant would also incapacitate the product of the wild-type allele and result in a dominant-negative effect, a combination of two recessive variants would result in a partial loss of function. Because the clinical picture can be nonspecific, detailed phenotype information, segregation, and functional analysis are fundamental to determine the pathogenicity of novel variants and to improve the care of these patients.
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Proteínas de Unión al ADN/genética , Discapacidades del Desarrollo/genética , Discapacidad Intelectual/genética , Microcefalia/genética , Factores de Transcripción/genética , Adolescente , Adulto , Alelos , Trastorno Autístico/genética , Trastorno Autístico/patología , Niño , Preescolar , Discapacidades del Desarrollo/patología , Exoma/genética , Femenino , Estudios de Asociación Genética , Humanos , Discapacidad Intelectual/patología , Trastornos del Desarrollo del Lenguaje/genética , Trastornos del Desarrollo del Lenguaje/patología , Masculino , Microcefalia/patología , Mutación Missense/genética , Adulto JovenRESUMEN
Intellectual disability (ID), megalencephaly, frontal predominant pachygyria, and seizures, previously called "thin" lissencephaly, are reported to be caused by recessive variants in CRADD. Among five families of different ethnicities identified, one homozygous missense variant, c.509G>A p.(Arg170His), was of Finnish ancestry. Here we report on the phenotypic variability associated for this potential CRADD founder variant in 22 Finnish individuals. Exome sequencing was used to identify candidate genes in Finnish patients presenting with ID. Targeted Sanger sequencing and restriction enzyme analysis were applied to screen for the c.509G>A CRADD variant in cohorts from Finland. Detailed phenotyping and genealogical studies were performed. Twenty two patients were identified with the c.509G>A p.(Arg170His) homozygous variant in CRADD. The majority of the ancestors originated from Northeastern Finland indicating a founder effect. The hallmark of the disease is frontotemporal predominant pachygyria with mild cortical thickening. All patients show ID of variable severity. Aggressive behavior was found in nearly half of the patients, EEG abnormalities in five patients and megalencephaly in three patients. This study provides detailed data about the phenotypic spectrum of patients with lissencephaly due to a CRADD variant that affects function. High inter- and intrafamilial phenotypic heterogeneity was identified in patients with pachygyria caused by the homozygous CRADD founder variant. The phenotype variability suggests that additional genetic and/or environmental factors play a role in the clinical presentation. Since frontotemporal pachygyria is the hallmark of the disease, brain imaging studies are essential to support the molecular diagnosis for individuals with ID and a CRADD variant.
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Proteína Adaptadora de Señalización CRADD/genética , Efecto Fundador , Predisposición Genética a la Enfermedad/genética , Lisencefalia/genética , Mutación Missense , Encéfalo/diagnóstico por imagen , Encéfalo/metabolismo , Encéfalo/patología , Salud de la Familia , Femenino , Finlandia , Geografía , Homocigoto , Humanos , Lisencefalia/diagnóstico por imagen , Lisencefalia/patología , Imagen por Resonancia Magnética/métodos , Masculino , Linaje , Fenotipo , Secuenciación del ExomaRESUMEN
PURPOSE: To characterize new molecular factors implicated in a hereditary congenital facial paresis (HCFP) family and otosclerosis. METHODS: We performed exome sequencing in a four-generation family presenting nonprogressive HCFP and mixed hearing loss (HL). MEPE was analyzed using either Sanger sequencing or molecular inversion probes combined with massive parallel sequencing in 89 otosclerosis families, 1604 unrelated affected subjects, and 1538 unscreened controls. RESULTS: Exome sequencing in the HCFP family led to the identification of a rare segregating heterozygous frameshift variant p.(Gln425Lysfs*38) in MEPE. As the HL phenotype in this family resembled otosclerosis, we performed variant burden and variance components analyses in a large otosclerosis cohort and demonstrated that nonsense and frameshift MEPE variants were significantly enriched in affected subjects (p = 0.0006-0.0060). CONCLUSION: MEPE exerts its function in bone homeostasis by two domains, an RGD and an acidic serine aspartate-rich MEPE-associated (ASARM) motif inhibiting respectively bone resorption and mineralization. All variants associated with otosclerosis are predicted to result in nonsense mediated decay or an ASARM-and-RGD-truncated MEPE. The HCFP variant is predicted to produce an ASARM-truncated MEPE with an intact RGD motif. This difference in effect on the protein corresponds with the presumed pathophysiology of both diseases, and provides a plausible molecular explanation for the distinct phenotypic outcome.