RESUMEN
Major Facilitator Superfamily Domain containing 2a (MFSD2A) is an essential endothelial lipid transporter at the blood-brain barrier. Biallelic variants affecting function in MFSD2A cause autosomal recessive primary microcephaly 15 (MCPH15, OMIM# 616486). We sought to expand our knowledge of the phenotypic spectrum of MCPH15 and demonstrate the underlying mechanism of inactivation of the MFSD2A transporter. We carried out detailed analysis of the clinical and neuroradiological features of a series of 27 MCPH15 cases, including eight new individuals from seven unrelated families. Genetic investigation was performed through exome sequencing (ES). Structural insights on the human Mfsd2a model and in-vitro biochemical assays were used to investigate the functional impact of the identified variants. All patients had primary microcephaly and severe developmental delay. Brain MRI showed variable degrees of white matter reduction, ventricular enlargement, callosal hypodysgenesis, and pontine and vermian hypoplasia. ES led to the identification of six novel biallelic MFSD2A variants (NG_053084.1, NM_032793.5: c.556+1G>A, c.748G>T; p.(Val250Phe), c.750_753del; p.(Cys251SerfsTer3), c.977G>A; p.(Arg326His), c.1386_1435del; p.(Gln462HisfsTer17), and c.1478C>T; p.(Pro493Leu)) and two recurrent variants (NM_032793.5: c.593C>T; p.(Thr198Met) and c.476C>T; p.(Thr159Met)). All these variants and the previously reported NM_032793.5: c.490C>A; p.(Pro164Thr) resulted in either reduced MFSD2A expression and/or transport activity. Our study further delineates the phenotypic spectrum of MCPH15, refining its clinical and neuroradiological characterization and supporting that MFSD2A deficiency causes early prenatal brain developmental disruption. We also show that poor MFSD2A expression despite normal transporter activity is a relevant pathomechanism in MCPH15.
Asunto(s)
Agenesia del Cuerpo Calloso/genética , Discapacidades del Desarrollo/genética , Microcefalia/genética , Mutación , Simportadores/genética , Adolescente , Adulto , Agenesia del Cuerpo Calloso/diagnóstico por imagen , Agenesia del Cuerpo Calloso/patología , Niño , Preescolar , Discapacidades del Desarrollo/diagnóstico por imagen , Discapacidades del Desarrollo/patología , Femenino , Células HEK293 , Humanos , Lactante , Imagen por Resonancia Magnética , Masculino , Microcefalia/diagnóstico por imagen , Microcefalia/patología , Dominios Proteicos , Simportadores/química , Simportadores/metabolismo , SíndromeRESUMEN
Ataxia with oculomotor apraxia type 4 (AOA4) is a rare autosomal recessive, PNKP -related disorder delineated in 2015 in Portugal. We diagnosed AOA4 by next generation sequencing (NGS) followed by Sanger's sequencing in three boys from two unrelated Belarusian families. In both families, one of the heterozygous PNKP mutations was c.1123G>T, common in Portuguese patients; biallelic mutations, c.1270_1283dup14 and c.1029+2T>C, respectively, were novel. These are the first reported AOA4 Slavic cases and the first with a "Portuguese" PNKP mutation outside Portugal. Distinction in two brothers was microcephaly but their disease was not severe in contrast to PNKP -related "microcephaly, seizures, and developmental delay" and reported cases with features of both phenotypes.
Asunto(s)
Anomalías Múltiples/diagnóstico , Anomalías Múltiples/genética , Empalme Alternativo , Estudios de Asociación Genética , Predisposición Genética a la Enfermedad , Variación Genética , Proteínas/genética , Análisis Mutacional de ADN , Estudios de Asociación Genética/métodos , Humanos , Linaje , Federación de Rusia , Ultrasonografía PrenatalRESUMEN
Intellectual disability is the most common developmental disorder caused by chromosomal aberrations as well as single-nucleotide variants (SNVs) and small insertions/deletions (indels). Here we report identification of a novel, probably pathogenic mutation in the WHSC1 gene in a patient case with phenotype overlapping the features of Wolf-Hirschhorn syndrome. Deletions involving WHSC1 (Wolf-Hirschhorn syndrome candidate 1 gene) were described earlier in patients with Wolf-Hirschhorn syndrome. However, to our knowledge, single-point mutations in WHSC1 associated with any intellectual deficiency syndromes have not been reported. Using whole exome sequencing, we found a de novo nonsense mutation in WHSC1 (c.3412C>T, p.Arg1138Ter, NM_001042424.2) in patient with syndromic intellectual disability. This finding is challenging regarding a possible causative role of WHSC1 in intellectual disability syndromes, specifically Wolf-Hirschhorn syndrome. From the clinical standpoint, our finding suggests that next-generation sequencing along with chromosome microarray analysis (CMA) might be useful in genetic testing for patients with intellectual disability and dysmorphic features.
Asunto(s)
Codón sin Sentido/genética , Predisposición Genética a la Enfermedad , N-Metiltransferasa de Histona-Lisina/genética , Discapacidad Intelectual/genética , Proteínas Represoras/genética , Síndrome de Wolf-Hirschhorn/genética , Secuencia de Aminoácidos , Secuencia de Bases , Femenino , N-Metiltransferasa de Histona-Lisina/química , Humanos , Lactante , Masculino , Linaje , Proteínas Represoras/químicaRESUMEN
Zinc chloride (0.01 mM kept for 3h) is not toxic to cultured cerebellar granule neurons (CGNs) while kainate (0.1mM kept for 3h) demonstrates some but very low toxicity towards these cells. Measurements of the relative intraneuronal zinc ion concentration showed that increase in [Zn(2+)](i) under the simultaneous action of ZnCl(2) and kainate was significantly stronger compared to their separate action. Simultaneous treatment of CGNs with kainate and zinc chloride caused the swelling of neuronal mitochondria and consequent intensive neuronal death, which was totally prevented by NBQX (an AMPA/kainate-receptors blocker) or ruthenium red (a mitochondrial Ca(2+) uniporter blocker). These data imply that Zn(2+) synergistically to kainate increase their separate toxic effects on mitochondria leading to rapid neuronal death.
Asunto(s)
Cerebelo/efectos de los fármacos , Cloruros/toxicidad , Agonistas de Aminoácidos Excitadores/toxicidad , Ácido Kaínico/toxicidad , Mitocondrias/efectos de los fármacos , Neuronas/efectos de los fármacos , Compuestos de Zinc/toxicidad , Zinc/toxicidad , Animales , Calcio/metabolismo , Células Cultivadas , Cerebelo/citología , Sinergismo Farmacológico , Ratas , Ratas Wistar , Zinc/metabolismoRESUMEN
Zinc chloride (0.02 mM, 3h) did not have any influence on the survival of cerebellar granule neurons (CGNs) incubated in balanced salt solution (BSS). However, in the absence of glucose ZnCl(2) caused severe neuronal damage, decreasing cell survival to 12±2%. Either the blockade of ionotropic glutamate NMDA-receptors with MK-801 or APV or supplementation the medium with ruthenium red (mitochondrial Ca(2+) uniporter blocker) almost entirely protected CGNs from the toxic effect of ZnCl(2) during glucose deprivation (GD). However, NBQX (AMPA/kainate glutamate receptor blocker) did not show protective effect. Measurements of intracellular calcium ions concentration using fluorescent probe (Fluo-4 AM) and zinc ions (FluoZin-3AM) demonstrated that 1.5h-exposure to GD induced intensive increase of Fluo-4 fluorescence and small increase of FluoZin-3 fluorescence in neurons. The supplementation of medium with ZnCl(2) caused equal increase of FluoZin-3 fluorescence at both GD and normoglycemia, whereas the potentiation of Fluo-4 fluorescence by zinc was observed only under GD and could be prevented by MK-801. However, neither MK-801 nor NBQX could influence [Zn(2+)](i) increase caused by zinc addition under GD, while ruthenium red did cause significant increase of [Zn(2+)](i). This data implies that zinc ions during GD induce an additional overload of CGNs with calcium ions that get transported through activated NMDA-channel. Zinc and calcium ions accumulate in mitochondria and amplify individual destructive action on these organelles leading to neuronal death.