are inventors on a provisional patent (PCT ref. no. SD2017-181-2PCT) filed by UC, San Diego that is titled "Assessing risk of de novo mutations in males".

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The structure of the human neocortex underlies species-specific features and is a reflection of intricate developmental programs. Here we analyzed neocortical cellular lineages through a comprehensive assessment of brain somatic mosaicism-which acts as a neutral recorder of lineage history. We employed deep whole genome and variant sequencing in a single postmortem neurotypical human brain across 25 anatomic regions and three distinct modalities: bulk geographies, sorted cell types, and single nuclei. We identified 259 mosaic variants, revealing remarkable differences in localization, clonal abundance, cell type specificity, and clade distribution. We identified a set of hierarchical cellular diffusion barriers, whereby the leftright axis separation of the neocortex occurs prior to anterior-posterior and dorsal-ventral axis separation. We also found that stochastic distribution is a driver of clonal dispersion, and that rules regarding cellular lineages and anatomical boundaries are often ignored. Our data provides a comprehensive analysis of brain somatic mosaicism across the human cerebral cortex, deconvolving clonal distributions and migration patterns in the human embryo.

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We analyzed 131 human brains (44 neurotypical, 19 with Tourette syndrome, 9 with schizophrenia, and 59 with autism) for somatic mutations after whole genome sequencing to a depth of more than 200×. Typically, brains had 20 to 60 detectable single-nucleotide mutations, but ~6% of brains harbored hundreds of somatic mutations. Hypermutability was associated with age and damaging mutations in genes implicated in cancers and, in some brains, reflected in vivo clonal expansions. Somatic duplications, likely arising during development, were found in ~5% of normal and diseased brains, reflecting background mutagenesis. Brains with autism were associated with mutations creating putative transcription factor binding motifs in enhancer-like regions in the developing brain. The top-ranked affected motifs corresponded to MEIS (myeloid ectopic viral integration site) transcription factors, suggesting a potential link between their involvement in gene regulation and autism.

Objectives Recently, defects in the protein kinase mTOR (mammalian target of rapamycin) and its associated pathway have been correlated with hemimegalencephaly (HME). mTOR acts as a central regulator of important physiological cellular functions such as growth and proliferation, metabolism, autophagy, death, and survival. This study was aimed at identifying specific variants in mTOR signaling pathway genes in patients diagnosed with HME. Methods Using amplicon and whole exome sequencing (WES) of resected brain and paired blood samples from five HME patients, we were able to identify pathogenic mosaic variants in the mTOR pathway genes MTOR, PIK3CA, and DEPDC5. Results These results strengthen the hypothesis that somatic variants in PI3K‐Akt‐mTOR pathway genes contribute to HME. We also describe one patient presenting with a pathogenic variant on DEPDC5 gene, which reinforces the role of DEPDC5 on cortical structural changes due to mTORC1 hyperactivation. These findings also provide insights into when in brain development these variants occurred. An early developmental variant is expected to affect a larger number of cells and to result in a larger malformation, whereas the same variant occurring later in development would cause a minor malformation. Significance In the future, numerous somatic variants in known or new genes will undoubtedly be revealed in resected brain samples, making it possible to draw correlations between genotypes and phenotypes and allow for a genetic clinical diagnosis that may help to predict a given patient's outcome.

Microtubules play a crucial role in the generation, migration and differentiation of nascent neurons in the developing vertebrate brain. Mutations in the constituents of microtubules, the tubulins, are known to cause an array of neurological disorders, including lissencephaly, polymicrogyria and microcephaly. In this study we explore the genetic and cellular mechanisms that cause TUBB5-associated microcephaly by exploiting two new mouse models: a conditional E401K knock-in, and a conditional knockout animal. These mice present with profound microcephaly due to a loss of upper-layer neurons that correlates with massive apoptosis and upregulation of p53. This phenotype is associated with a delay in cell cycle progression and ectopic DNA elements in progenitors, which is dependent on the dosage of functional Tubb5. Strikingly, we report ectopic Sox2-positive progenitors and defects in spindle orientation in our knock-in mouse line, which are absent in knockout animals. This work sheds light on the functional repertoire of Tubb5, reveals that the E401K mutation acts by a complex mechanism, and demonstrates that the cellular pathology driving TUBB5-associated microcephaly is cell death.

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