 Hello, my name is Alex Besouk, my name is Ben Darbro, and I'm Vanith Mahajan. We are clinician scientists from the University of Iowa, and we will be discussing our manuscript in Human Mutation entitled Mutations in Extracellular Matrix Genes NID-1 and LAM-C1 Cause Autosomal Dominant Dandy Walker Melformation and Accipital Cephalocele. The Dandy Walker Melformation is characterized by variable cerebellar hypoplasia, meningeal anomalies, and accipital skull defects. In 2004, we described a three-generation pedigree that had variable Dandy Walker Melformation with accipital skull defects, indicated in this MRI by the white arrow, that appeared to be inherited in an autosomal dominant manner. The dark figures in the pedigree all represent individuals with the malformation. The skull defects appear as small outpouchings on the back of the head, circled here. Several other multi-generation pedigrees with autosomal dominant inheritance have been described in the last decade, including a family from India outlined in this pedigree, where we have a child, his father, and grandfather who all have the defects. Here is an example of the accipital cephalocele in this family, and here is an x-ray demonstrating the skull defect. To directly determine if a protein-coding mutation segregated with the Dandy Walker phenotype in the original pedigree, we re-examined this family by whole axome capture and massively parallel sequencing. Whole axome sequencing was performed for seven affected family members with cephalocele. Re-sequencing of putative segregating variants by Sanger sequencing in the entire pedigree revealed only a single mutation that was present in all 14 affected family members, all with Dandy Walker variant cerebellar vermal hypoplasia, and absent from 384 ethnically matched control chromosomes, or large genomic databases such as the 1000 Genomes Project and Exome Variant Server databases. The variation we found was a nonsense mutation in the gene NID or NID-1. The NID-1 protein coordinates extracellular matrix protein interactions. The family from India was also examined for NID-1 mutations by Sanger re-sequencing, however no NID-1 mutations were discovered. Since the functional consequence of the NID-1 stop mutation found in the first family was the deletion of several domains that interact with other extracellular matrix proteins, we investigated binding partner interactions that might be disrupted. A NID-1 interactome was generated and NID-1 interacting proteins were considered as candidate genes for the Indian family. The coding sequence for each of these genes was then interrogated following whole axome capture and massive parallel sequencing of family two. We found that only a single mutation from the NID-1 interactome segregated with the phenotype in the Indian Dandy-Walker family. This segregating variant corresponded to a missense mutation in the LAM-C1 gene. This gene encodes the laminin-gamma chain. This mutation was not found in any control database. The variant alters a 3-inning residue conserved throughout evolution. Since LAM-C1 was selected as a candidate gene based on its physical interaction with NID-1, we investigated how the mutation might disrupt this interaction by computational three-dimensional structural homology modeling of the involved domains in the context of the known interaction. The NID-1 stop mutation results in a loss of the entire G2 and G3 regions of NID-1, including the beta-propeller domain that directly interacts with LAM-C1. The LAM-C1 mutation occurs in the epidermal growth factor like 6-domain, a highly conserved rigid structure with four disulfide linkages compared to three dulcefide linkages of a typical EGF domain. This mutation maps to a four-residue beta sheet featured in red, one of only three short stretches in this domain with secondary structure. Normally, the buried 3-inning is constrained by a rigid disulfide leakage on either side, and mutation to a 25% larger residue such as methionine is predicted to significantly decrease the stability of the protein primarily due to steric clashes with neighboring residues. In addition to furthering our understanding of the genetics of dandy walker spectrum disorders, our study demonstrates several important aspects of combining next-generation sequencing technologies, proteomics, and tertiary structural modeling.