What Causes Down Syndrome?

Trisomy 21 (Down Syndrome) is the model human phenotype for all genome gain-dosage imbalance situations, including microduplications. Years after the sequencing of chromosome 21, the discovery of functional genomics and the creation of multiple cellular and mouse models provided an unprecedented opportunity to demonstrate the molecular consequences of genome dosage imbalance. It was stated years ago that Down syndrome, caused by meiotic separation of chromosome 21 in humans, is associated with advanced maternal age, but defining and understanding other risk factors is insufficient. Commonly referred to as Down syndrome (DS) in humans, trisomy 21 is the most cited genetic cause of mental retardation. In about 95% of cases, the extra chromosome occurs as a result of meiotic non- nondisjunction (NDJ) or abnormal separation of chromosomes. In most of these cases the error occurs during maternal oogenesis, especially in meiosis I

Germline Pathogenic Variants Identified by Targeted Next-Generation Sequencing of Susceptibility Genes in Pheochromocytoma and Paraganglioma

The aim of this study was to evaluate germline variant frequencies of pheochromocytoma and paraganglioma targeted susceptibility genes with next-generation sequencing method. Germline DNA from 75 cases were evaluated with targeted next-generation sequencing on an Illumina NextSeq550 instrument. KIF1B, RET, SDHB, SDHD, TMEM127, and VHL genes were included in the study, and Sanger sequencing was used for verifying the variants. The pathogenic/likely pathogenic variants were in the VHL, RET, SDHB, and SDHD genes, and the diagnosis rate was 24% in this study. Three different novel pathogenic variants were determined in five cases. This is the first study from Turkey, evaluating germline susceptibility genes of pheochromocytoma and paraganglioma with a detection rate of 24% and three novel variants. All patients with pheochromocytoma and paraganglioma need clinical genetic testing with expanded targeted gene panels for higher diagnosis rates

Mechanisms of Aneuploidy

Aneuploidy is a very common occurrence in humans and occurs in an estimated 20–40% of all pregnancies. It is the most prominent cause of miscarriages and congenital defects in humans and is the main obstacle to infertility treatment. The vast majority of aneuploidies are caused by maternal meiotic non-disjunction errors. High levels of recombination errors were observed in studies on fetal oocytes. This suggests that some oocytes are more prone to not being separated due to events occurring before birth. Cell cycle checkpoints that work in the meiotic phase and metaphase-anaphase transition work more moderately in women than in men. As a result, while there are abnormal cells that have been sorted out in spermatogenesis, in females these cells can escape the actual control and ultimately give rise to aneuploid eggs

Methylation of RARß is a new clinical biomarker for treatment in higher-grade gliomas

Background: The dysregulation of various pathways and cellular processes contributes to the carcinogenic transition from low-grade gliomas to high-grade gliomas. The altered tumor microenvironment, altered epigenetic state, and high mutation heterogeneity are critical factors in glial tumors. The morphogen retinoic acid (RA) controls the homeostasis, regeneration, and development of the brain. RA receptor (RAR) gene methylation has been shown in different types of glial tumors. Aims and Objectives: This study assessed the RARß gene as a potential therapeutic target in gliomas. Materials and Methods: Using in silico methods, potential drugs targeting the RARß gene were compared based on temozolomide's effectiveness in treating gliomas. Results and Conclusion: Computational techniques can be used to identify drug-mediated pathways. This in silico study holds promise for RARB and RARB-targeted treatment strategies in gliomas

RAR beta gene methylation is a candidate for primary glioblastoma treatment planning.

Background: We screened RAR beta methylation in primary glioblastoma multiforme (GBM) and the results were evaluated based on the clinical data and treatment type

A large posterior encephalocele associated with severe ventriculomegaly, cerebellar atrophy and transposition of the great arteries

Posterior encephalocele is a neural tube defect, which is a sac-like protrusion of the neural tissue and cerebrospinal fluid through a defect in the occipital bone. This embryonic anomaly may coexist with cortical dysplasia, agenesis of the corpus callosum, hydrocephalus, microcephaly, craniofacial abnormalities, ventricular and atrial septal defect. We report a case of a large posterior encephalocele in a fetus accompanied by unexpected major abnormalities including transposition of the great arteries, severe ventriculomegaly and cerebellar atrophy. Postnatal surgical corrections of the posterior encephalocele and then of the transposition of the great arteries were performed but the neonate died 2 months after delivery

Long-range cis-regulatory elements controlling GDF6 expression are essential for ear development

Molecular mechanisms governing the development of the mammalian cochlea, the hearing organ, remain largely unknown. Through genome sequencing in 3 subjects from 2 families with nonsyndromic cochlear aplasia, we identified homozygous 221-kb and 338-kb deletions in a noncoding region on chromosome 8 with an approximately 200-kb overlapping section. Genomic location of the overlapping deleted region started from approximately 350 kb downstream of GDF6 , which codes for growth and differentiation factor 6. Otic lineage cells differentiated from induced pluripotent stem cells derived from an affected individual showed reduced expression of GDF6 compared with control cells. Knockout of Gdf6 in a mouse model resulted in cochlear aplasia, closely resembling the human phenotype. We conclude that GDF6 plays a necessary role in early cochlear development controlled by cis -regulatory elements located within an approximately 500-kb region of the genome in humans and that its disruption leads to deafness due to cochlear aplasia