The exosome is a multi-protein complex, required for the degradation of AU-rich element (ARE) containing messenger RNAs (mRNAs). EXOSC8 is an essential protein of the exosome core, as its depletion causes a severe growth defect in yeast. Here we show that homozygous missense mutations in EXOSC8 cause progressive and lethal neurological disease in 22 infants from three independent pedigrees. Affected individuals have cerebellar and corpus callosum hypoplasia, abnormal myelination of the central nervous system or spinal motor neuron disease. Experimental downregulation of EXOSC8 in human oligodendroglia cells and in zebrafish induce a specific increase in ARE mRNAs encoding myelin proteins, showing that the imbalanced supply of myelin proteins causes the disruption of myelin, and explaining the clinical presentation. These findings show the central role of the exosomal pathway in neurodegenerative disease.

We investigated the functions of Akt during vascular development and remodeling by using an inducible endothelial cell-specific driver of the dominant-active myrAkt. We found that sustained signaling in response to overexpression of myrAkt led to embryonic lethality, edema, and vascular malformations. In addition to the morphological malformations, the vascular phenotype was consistent with a failure in remodeling, such that the normal patterning and vessel hierarchy was disturbed. Examination of the well studied retinal vasculature during the remodeling phases revealed that transient expression of myrAkt was capable of altering the normal response to oxygen-induced remodeling without causing vascular malformations. These findings suggest that physiological levels of Akt signaling modulated microvascular remodeling and support the hypothesis that, although Akt may be required for vascular growth and homeostasis, appropriate downregulation is also an essential aspect of normal vascular patterning.Akt͞PKB ͉ angiogenesis ͉ retina E ndothelial cell survival and apoptosis have been studied extensively with respect to micro-and macrovascular disease in diabetes, cardiovascular disease, sepsis, and after transplant surgery (1). As a desired effect of therapy, endothelial cell apoptosis has been explored in response to antiangiogenic treatments for cancer (2). Less attention has been paid to the control of endothelial cell apoptosis during development, although it has been proposed to explain the overall decrease in microvascular density associated with microvascular remodeling.Much of the classical work on microvascular remodeling has been done in the developing retina because of its planar architecture and accessibility, because the expansion and remodeling of this vascular bed is postnatal. A series of elegant studies have clearly established VEGF-A as a driver of vascular expansion in this organ in both development (3, 4) and pathological neovascularization (5-7) as well as a regulator of endothelial cell survival during the remodeling process (8). In the retina, VEGF-A is provided largely by the astrocytes, which enter the retina through the optic disk and spread radially toward the periphery in advance of blood vessel formation (3, 9). The astrocytes are exquisitely sensitive to oxygen levels and strongly induce VEGF-A in hypoxic regions of the retina (10, 11). As the astrocytes and expand radially across the retina, they attract the endothelium to follow and lay a scaffold on which blood vessels form, in part due to the molecular attraction of VEGFR-2 expressed on endothelial cell filopodia with sequestered VEGF on the astrocyte surface (9). Once the new blood vessels bring oxygen to the formerly hypoxic regions of the retina, local VEGF-A levels drop. These events initiate the remodeling process where vessel regression is coordinated with pericyteinduced stabilization (12,13). This coordination of oxygeninduced VEGF-A reduction and pericyte stabilization has led to the hypothesis that the balance in survival sig...

Whole exome sequencing has become a pivotal methodology for rapid and cost-effective detection of pathogenic variations in Mendelian disorders. A major challenge of this approach is determining the causative mutation from a substantial number of bystander variations that do not play any role in the disease etiology. Current strategies to analyze variations have mainly relied on genetic and functional arguments such as mode of inheritance, conservation, and loss of function prediction. Here, we demonstrate that disease-network analysis provides an additional layer of information to stratify variations even in the presence of incomplete sequencing coverage, a known limitation of exome sequencing. We studied a case of Hereditary Spastic Paraparesis (HSP) in a single inbred Palestinian family. HSP is a group of neuropathological disorders that are characterized by abnormal gait and spasticity of the lower limbs. Forty-five loci have been associated with HSP and lesions in 20 genes have been documented to induce the disorder. We used whole exome sequencing and homozygosity mapping to create a list of possible candidates. After exhausting the genetic and functional arguments, we stratified the remaining candidates according to their similarity to the previously known disease genes. Our analysis implicated the causative mutation in the motor domain of KIF1A, a gene that has not yet associated with HSP, which functions in anterograde axonal transportation. Our strategy can be useful for a large class of disorders that are characterized by locus heterogeneity, particularly when studying disorders in single families.[Supplemental material is available for this article. The sequencing and genotyping data from this study have been submitted to the NCBI dbGaP (http://www.ncbi.nlm.nih.gov/gap) and at http://cancan.cshl.edu/hsp/.]Whole exome sequencing has ushered in a renaissance in identifying pathogenic variations in monogenic diseases. The approach enables a rapid and cost-effective detection from a small number of individuals, and has proved useful for a wide range of clinical settings (Choi et al.

Mutations in clinically manifest as SDS-like phenotype. Similar to the molecular pathology of SDS, mutant EFL1 proteins do not promote the release of cytoplasmic Tif6 from the 60S subunit, likely preventing the formation of mature ribosomes.

Liver damage is typically inferred from serum measurements of cytoplasmic liver enzymes. DNA molecules released from dying hepatocytes are an alternative biomarker, unexplored so far, potentially allowing for quantitative assessment of liver cell death. Here we describe a method for detecting acute hepatocyte death, based on quantification of circulating, cell-free DNA (cfDNA) fragments carrying hepatocyte-specific methylation patterns. We identified 3 genomic loci that are unmethylated specifically in hepatocytes, and used bisulfite conversion, PCR, and massively parallel sequencing to quantify the concentration of hepatocyte-derived DNA in mixed samples. Healthy donors had, on average, 30 hepatocyte genomes/ml plasma, reflective of basal cell turnover in the liver. We identified elevations of hepatocyte cfDNA in patients shortly after liver transplantation, during acute rejection of an established liver transplant, and also in healthy individuals after partial hepatectomy. Furthermore, patients with sepsis had high levels of hepatocyte cfDNA, which correlated with levels of liver enzymes aspartate aminotransferase (AST) and alanine aminotransferase (ALT). Duchenne muscular dystrophy patients, in which elevated AST and ALT derive from damaged muscle rather than liver, did not have elevated hepatocyte cfDNA. We conclude that measurements of hepatocyte-derived cfDNA can provide specific and sensitive information on hepatocyte death, for monitoring human liver dynamics, disease, and toxicity.