Genetic analysis of a child with Complex cortical dysplasia with other brain malformations type 6 due to a p.M73V variant of TUBB gene / 中华医学遗传学杂志

OBJECTIVE@#To explore the genetic basis for a child with multiple malformations.@*METHODS@#A child who had presented at Shanxi Provincial Children's Hospital in February 2021 was selected as the study subject. Clinical data of the patient was collected, and whole exome sequencing (WES) was carried out to screen pathogenic variants associated with the phenotype. Candidate variant was validated by Sanger sequencing of her family members.@*RESULTS@#The child had normal skin, but right ear defect, hemivertebral deformity, ventricular septal defect, arterial duct and patent foramen ovale, and separation of collecting system of the left kidney. Cranial MRI showed irregular enlargement of bilateral ventricles and widening of the distance between the cerebral cortex and temporal meninges. Genetic testing revealed that she has harbored a heterozygous variant of NM_178014.4: c.217A>G (p.Met73Val) in the TUBB gene, which was unreported previously and predicted to be likely pathogenic based on the guidelines from the American College of Medical Genetics and Genomics (ACMG). The child was diagnosed with Complex cortical dysplasia with other brain malformations 6 (CDCBM6).@*CONCLUSION@#CDCBM is a rare and serious disease with great genetic heterogeneity, and CDCBM6 caused by mutations of the TUBB gene is even rarer. Above finding has enriched the variant and phenotypic spectrum of the TUBB gene, and provided important reference for summarizing the genotype-phenotype correlation of the CDCBM6.

Genetic and clinical analysis of KIF2A gene variant in a Chinese patient with complex cortical dysplasia and other brain malformations / 中华医学遗传学杂志

OBJECTIVE@#To explore the genetic basis for a child featuring complex cortical dysplasia and other brain malformations (CDCBM3).@*METHODS@#Genomic DNA was extracted from peripheral blood samples from the patient and his parents. Whole exome sequencing (WES) was carried out for the family trio. Suspected variant was verified by Sanger sequencing.@*RESULTS@#The proband, a 1-year-and-2-month old Chinese boy, had presented with motor developmental delay, lissencephaly, severe cognitive impairments, absent speech and congenital laryngomalacia. WES revealed that he has harbored a heterozygous missense variant of the KIF2A gene, namely NM_001098511.2: c.952G>A, p.Gly318Arg (GRCh37/hg19). The highly conserved residue is located around the ATP nucleotide-binding pocket in the kinesin motor domain (PM1). The variant was not found in the Genome Aggregation Database and the 1000 Genomes Project (PM2), and was predicted to be deleterious on the gene product by multiple in silico prediction tools (PP3). This variant was unreported previously and was de novo in origin (PS2). Based on the ACMG guidelines, it was categorized as likely pathogenic (PS2+PM1+PM2+PP3). Furthermore, the congenital laryngomalacia found in our patient was absent in previously reported CDCBM3 cases.@*CONCLUSION@#The novel variant of the KIF2A gene probably underlay the disorders in the proband. Above finding has expanded the phenotypic and mutational spectrum of CDCBM3.

Analysis of TUBB2B gene variant in a fetus with complex cortical dysplasia with other brain malformations-7 / 中华医学遗传学杂志

OBJECTIVE@#To explore the genetic basis for a fetus with dysgenesis of corpus callosum and other brain malformations.@*METHODS@#Whole exome sequencing was carried out for the fetus and its parents. Suspected pathogenic variants were verified by Sanger sequencing.@*RESULTS@#A novel de novo missense variant c.758T>A (p.L253Q) of the TUBB2B gene was identified, which was unreported previously. Based on the guidelines from the American College of Medical Genetics, the c.758T>A variant was predicted to be likely pathogenic. Bioinformatics analysis predicted that the leucine at position 253 was highly conserved among various species, and the c.758T>A variant may impact the formation of hydrogen bonds between Leu253 and Asp249 and Met257 residues, which in turn may affect the combination of GTP/GDP and function of the TUBB2B protein.@*CONCLUSION@#The c.758T>A variant of the TUBB2B gene probably underlay the fetal malformations in this Chinese family. Above discovery has enriched the spectrum of TUBB2B gene variants and provided a basis for genetic counseling and prenatal diagnosis.

Epilepsias en las malformaciones del desarrollo cortical / Malformations of cortical development and epilepsy

Alrededor del 15% de las epilepsias en pediatría son fármaco-resistentes y en el 40% de este grupo la etiología es una malformación del desarrollo cortical (MDC). El esquema de clasificación actual de las MDC se basa en las etapas primarias de desarrollo de la proliferación celular, migración neuronal y organización cortical. Teniendo en cuenta la clínica y las alteraciones moleculares, se propuso una clasificación basada en la disrupción de las vías principales y el fenotipo neurorradiológico. Se dividió a las MDC en cuatro grupos: la megalencefalia y las displasias corticales focales; las tubulinopatías y lisencefalias; el espectro de las polimicrogirias y las heterotopías. Hasta el momento, más de 100 genes han sido asociados con uno o más tipos de MDC. Los mecanismos biológicos y genéticos incluyen la regulación del ciclo celular en varios estadios, división celular), apoptosis, diferenciación celular, función y estructura del citoesqueleto, migración neuronal y membrana basal. El espectro de síndromes epilépticos asociados con las MDC es amplio e incluye desde encefalopatías epilépticas de comienzo temprano a epilepsias focales de debut más tardío. Teniendo en cuenta que la evolución de la epilepsia hacia la refractariedad en las MDC es importante, el diagnóstico precoz y la elección de la mejor opción terapéutica influirán en el pronóstico de los pacientes.

Around 15% of childhood epilepsies are resistant to antiepileptic drugs, 40% of which are caused by malformations of cortical development (MCD). The current classification scheme for MCD is based on the primary developmental steps of cell proliferation, neuronal migration, and cortical organization. Considering the clinic and molecular alterations, a classification based on main pathways disruption and imaging phenotype has been proposed. MCD were divided into four groups: megalencephaly and focal cerebral dysplasia; tubulinopathies and lissencephalies; polymicrogyria syndromes and heterotopia syndromes. More than 100 genes have been reported to be associated with different types of MCD. Genetic and biological mechanisms include different stages of cell cycle regulation - especially cell division -, apoptosis, cell-fate specification, cytoskeletal structure and function, neuronal migration, and basement-membrane function. The associated epileptic syndromes are varied ranging from early-onset epileptic encephalopathies to focal epilepsies. As MCD are common causes of refractory epilepsy, a prompt diagnosis and the development of different therapeutic options in order to improve the outcome of the patients are essential.