Detection of chromosomal breakpoints in patients with developmental delay and speech disorders.

Delineating candidate genes at the chromosomal breakpoint regions in the apparently balanced chromosome rearrangements (ABCR) has been shown to be more effective with the emergence of next-generation sequencing (NGS) technologies. We employed a large-insert (7-11 kb) paired-end tag sequencing technology (DNA-PET) to systematically analyze genome of four patients harbouring cytogenetically defined ABCR with neurodevelopmental symptoms, including developmental delay (DD) and speech disorders. We characterized structural variants (SVs) specific to each individual, including those matching the chromosomal breakpoints. Refinement of these regions by Sanger sequencing resulted in the identification of five disrupted genes in three individuals: guanine nucleotide binding protein, q polypeptide (GNAQ), RNA-binding protein, fox-1 homolog (RBFOX3), unc-5 homolog D (C.elegans) (UNC5D), transmembrane protein 47 (TMEM47), and X-linked inhibitor of apoptosis (XIAP). Among them, XIAP is the causative gene for the immunodeficiency phenotype seen in the patient. The remaining genes displayed specific expression in the fetal brain and have known biologically relevant functions in brain development, suggesting putative candidate genes for neurodevelopmental phenotypes. This study demonstrates the application of NGS technologies in mapping individual gene disruptions in ABCR as a resource for deciphering candidate genes in human neurodevelopmental disorders (NDDs).

Genome-wide analysis reveals methyl-CpG-binding protein 2-dependent regulation of microRNAs in a mouse model of Rett syndrome.

MicroRNAs (miRNAs) are a class of small, noncoding RNAs that function as posttranscriptional regulators of gene expression. Many miRNAs are expressed in the developing brain and regulate multiple aspects of neural development, including neurogenesis, dendritogenesis, and synapse formation. Rett syndrome (RTT) is a progressive neurodevelopmental disorder caused by mutations in the gene encoding methyl-CpG-binding protein 2 (MECP2). Although Mecp2 is known to act as a global transcriptional regulator, miRNAs that are directly regulated by Mecp2 in the brain are not known. Using massively parallel sequencing methods, we have identified miRNAs whose expression is altered in cerebella of Mecp2-null mice before and after the onset of severe neurological symptoms. In vivo genome-wide analyses indicate that promoter regions of a significant fraction of dysregulated miRNA transcripts, including a large polycistronic cluster of brain-specific miRNAs, are DNA-methylated and are bound directly by Mecp2. Functional analysis demonstrates that the 3' UTR of messenger RNA encoding Brain-derived neurotrophic factor (Bdnf) can be targeted by multiple miRNAs aberrantly up-regulated in the absence of Mecp2. Taken together, these results suggest that dysregulation of miRNAs may contribute to RTT pathoetiology and also may provide a valuable resource for further investigations of the role of miRNAs in RTT.