De novo mutations (DNMs) in protein-coding genes are a well-established cause of developmental disorders (DD). However, known DD-associated genes only account for a minority of the observed excess of such DNMs. To identify novel DD-associated genes, we integrated healthcare and research exome sequences on 31,058 DD parent-offspring trios, and developed a simulation-based statistical test to identify gene-specific enrichments of DNMs. We identified 285 significantly DD-associated genes, including 28 not previously robustly associated with DDs. Despite detecting more DD-associated genes than in any previous study, much of the excess of DNMs of protein-coding genes remains unaccounted for. Modelling suggests that over 1,000 novel DD-associated genes await discovery, many of which are likely to be less penetrant than the currently known genes. Research access to clinical diagnostic datasets will be critical for completing the map of dominant DDs.
Research Article 3703 IntroductionEndosomal protein sorting has a vital role in a number of physiologically important processes including antigen presentation, macromolecular nutrient uptake, growth factor receptor signaling and downregulation, autophagy and lysosome biogenesis (for reviews, see Sadowski et al., 2009;Saksena and Emr, 2009;Sann et al., 2009;Seaman, 2008;Lee et al., 2008). Recent studies of inherited diseases have identified several examples of genes encoding proteins that function in endosomal protein sorting that, when mutated, result in a range of pathologies. A notable example is hereditary spastic paraplegias (HSP), the hallmark of which is a selective distal axonopathy. There is a striking localisation of many of the HSP-encoded proteins to the endosome, including the microtubule-severing protein spastin, the ubiquitin-ligase-interacting protein spartin, and NIPA1, a membrane protein that mediates bone morphogenic protein signaling at the endosome (Tsang et al., 2009; for a review, see Salinas et al., 2008). Despite this concentration of HSP proteins at endosomes, in most cases their function is unknown.Much of the core machinery that carries out endosomal protein sorting is conserved in evolution, for example, the retromer complex (for reviews, see Attar and Cullen, 2009;Verges, 2008;Collins, 2008;Bonifacino and Hurley, 2008). Retromer mediates endosometo-Golgi retrieval of lysosomal and vacuolar hydrolase receptors (e.g. the cation-independent mannose 6 phosphate receptor, CIMPR) along with other physiologically significant membrane proteins including wntless, which functions in WNT secretion, and SORL1, a protein that is genetically linked to late-onset Alzheimer's disease (Arighi et al., 2004;Seaman, 2004;Eaton, 2008;Nielsen et al., 2007;Rogaeva et al., 2007).The retromer complex was first identified in yeast where it comprises five proteins encoded by vacuolar protein sorting (VPS) genes. The heteropentameric retromer complex can be functionally dissected into two subcomplexes: a cargo-selective complex formed from a conserved trimer of Vps35p, Vps29p and Vps26p and a 'structural complex' formed from a dimer of the sorting nexin (SNX) proteins Vps5p and Vps17p (Seaman et al., 1998). In mammals, SNX1, SNX2 with SNX5 and SNX6 provide the 'structural' role and can tubulate membranes through the C-terminal Bin, amphiphysin and Rvs (BAR) domains present in these proteins (Carlton et al., 2004;Wassmer et al., 2007). Additionally, SNX5 and SNX6 interact with the microtubule cytoskeleton via the p150glued protein that binds to dynein, thereby linking endosomal protein sorting to microtubules (Wassmer et al., 2009;Hong et al., 2009).The interaction between the SNX component of retromer and p150glued is an example of how retromer-interacting proteins facilitate retromer in mediating endosome-to-Golgi retrieval. In yeast, the SNX3 homologue Grd19p binds to Ftr1p to sort Ftr1p into the retromer pathway (Strochlic et al., 2008). In mammalian cells, the EPS15 homology domain protein, EHD1, interacts ...
We have identified a missense mutation in the motor domain of the neuronal kinesin heavy chain gene KIF5A, in a family with hereditary spastic paraplegia. The mutation occurs in the family in which the SPG10 locus was originally identified, at an invariant asparagine residue that, when mutated in orthologous kinesin heavy chain motor proteins, prevents stimulation of the motor ATPase by microtubule-binding. Mutation of kinesin orthologues in various species leads to phenotypes resembling hereditary spastic paraplegia. The conventional kinesin motor powers intracellular movement of membranous organelles and other macromolecular cargo from the neuronal cell body to the distal tip of the axon. This finding suggests that the underlying pathology of SPG10 and possibly of other forms of hereditary spastic paraplegia may involve perturbation of neuronal anterograde (or retrograde) axoplasmic flow, leading to axonal degeneration, especially in the longest axons of the central nervous system.
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