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Asparagine-linked glycosylation 13 homolog (ALG13) encodes a nonredundant, highly conserved, X-linked uridine diphosphate (UDP)-N-acetylglucosaminyltransferase required for the synthesis of lipid linked oligosaccharide precursor and proper N-linked glycosylation. De novo variants in ALG13 underlie a form of early infantile epileptic encephalopathy known as EIEE36, but given its essential role in glycosylation, it is also considered a congenital disorder of glycosylation (CDG), ALG13-CDG. Twenty-four previously reported ALG13-CDG cases had de novo variants, but surprisingly, unlike most forms of CDG, ALG13-CDG did not show the anticipated glycosylation defects, typically detected by altered transferrin glycosylation. Structural homology modeling of two recurrent de novo variants, p.A81T and p.N107S, suggests both are likely to impact the function of ALG13. Using a corresponding ALG13-deficient yeast strain, we show that expressing yeast ALG13 with either of the highly conserved hotspot variants rescues the observed growth defect, but not its glycosylation abnormality. We present molecular and clinical data on 29 previously unreported individuals with de novo variants in ALG13. This more than doubles the number of known cases. A key finding is that a vast majority of the individuals presents with West syndrome, a feature shared with other CDG types. Among these, the initial epileptic spasms best responded to adrenocorticotropic hormone or prednisolone, while clobazam and felbamate showed promise for continued epilepsy treatment. A ketogenic diet seems to play an important role in the treatment of these individuals. Fil: Ng, Bobby G.. Sanford Burnham Prebys Medical Discovery Institute; Estados Unidos Fil: Eklund, Erik A.. Sanford Burnham Prebys Medical Discovery Institute; Estados Unidos. Lund University; Suecia Fil: Shiryaev, Sergey A.. Sanford Burnham Prebys Medical Discovery Institute; Estados Unidos Fil: Dong, Yin Y.. University of Oxford; Reino Unido Fil: Abbott, Mary Alice. University of Massachusetts Medical School; Estados Unidos Fil: Asteggiano, Carla Gabriela. Universidad Católica de Córdoba; Argentina. Universidad Nacional de Córdoba. Facultad de Medicina. Centro de Estudios de las Metabolopatías Congénitas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina Fil: Bamshad, Michael J.. University of Washington; Estados Unidos Fil: Barr, Eileen. University of Emory; Estados Unidos Fil: Bernstein, Jonathan A.. University of Stanford; Estados Unidos Fil: Chelakkadan, Shabeed. Monash Children's Hospital; Australia Fil: Christodoulou, John. Sydney Medical School; Australia. University of Melbourne; Australia Fil: Chung, Wendy K.. Columbia University; Estados Unidos Fil: Ciliberto, Michael A.. University of Iowa; Estados Unidos Fil: Cousin, Janice. National Human Genome Research Institute ; Estados Unidos Fil: Gardiner, Fiona. University of Melbourne; Australia Fil: Ghosh, Suman. University of Florida; Estados Unidos Fil: Graf, William D.. University of Connecticut; Estados Unidos Fil: Grunewald, Stephanie. University College London; Estados Unidos Fil: Hammond, Katherine. University of Alabama at Birmingahm; Estados Unidos Fil: Hauser, Natalie S.. Inova, Fairfax Hospital Falls Church; Estados Unidos Fil: Hoganson, George E.. University Of Illinois At Chicago; Estados Unidos Fil: Houck, Kimberly M.. Baylor College of Medicine; Estados Unidos Fil: Kohler, Jennefer N.. University of Stanford; Estados Unidos Fil: Morava, Eva. Mayo Clinic; Estados Unidos Fil: Larson, Austin A.. University Of Colorado Anschutz Medical Campus.; Estados Unidos Fil: Liu, Pengfei. Baylor Genetics; Estados Unidos. Baylor College Of Medicine; Estados Unidos Fil: Madathil, Sujana. University of Iowa; Estados Unidos Fil: McCormack, Colleen. University of Stanford; Estados Unidos Fil: Meeks, Naomi J.L.. University Of Colorado Anschutz Medical Campus.; Estados Unidos Fil: Papazoglu, Gabriela Magali. Universidad Nacional de Córdoba. Facultad de Medicina. Centro de Estudios de las Metabolopatías Congénitas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina

ZMYND8 encodes a multidomain protein that serves as a central interactive hub for coordinating critical roles in transcription regulation, chromatin remodeling, regulation of super-enhancers, DNA damage response and tumor suppression. We delineate a novel neurocognitive disorder caused by variants in the ZMYND8 gene.An international collaboration, exome sequencing, molecular modeling, yeast two-hybrid assays, analysis of available transcriptomic data and a knockdown Drosophila model were used to characterize the ZMYND8 variants.ZMYND8 variants were identified in 11 unrelated individuals; 10 occurred de novo and one suspected de novo; 2 were truncating, 9 were missense, of which one was recurrent. The disorder is characterized by intellectual disability with variable cardiovascular, ophthalmologic and minor skeletal anomalies. Missense variants in the PWWP domain of ZMYND8 abolish the interaction with Drebrin and missense variants in the MYND domain disrupt the interaction with GATAD2A. ZMYND8 is broadly expressed across cell types in all brain regions and shows highest expression in the early stages of brain development. Neuronal knockdown of the DrosophilaZMYND8 ortholog results in decreased habituation learning, consistent with a role in cognitive function.We present genomic and functional evidence for disruption of ZMYND8 as a novel etiology of syndromic intellectual disability.

Whereas large-scale statistical analyses can robustly identify disease-gene relationships, they do not accurately capture genotype-phenotype correlations or disease mechanisms. We use multiple lines of independent evidence to show that different variant types in a single gene,SATB1, cause clinically overlapping but distinct neurodevelopmental disorders. Clinical evaluation of 42 individuals carryingSATB1variants identified overt genotype-phenotype relationships, associated with different pathophysiological mechanisms, established by functional assays. Missense variants in the CUT1 and CUT2 DNA-binding domains result in stronger chromatin binding, increased transcriptional repression and a severe phenotype. Contrastingly, variants predicted to result in haploinsufficiency are associated with a milder clinical presentation. A similarly mild phenotype is observed for individuals with premature protein truncating variants that escape nonsense-mediated decay and encode truncated proteins, which are transcriptionally active but mislocalized in the cell. Our results suggest that in-depth mutation-specific genotype-phenotype studies are essential to capture full disease complexity and to explain phenotypic variability.