The extracellular matrix (ECM) of the brain comprises unique glycan "sulfation codes" that influence neurological function. Perineuronal nets (PNNs) are chondroitin sulfate-glycosaminoglycan (CS-GAG) containing matrices that enmesh neural networks involved in memory and cognition, and loss of PNN matrices is reported in patients with neurocognitive and neuropsychiatric disorders including Alzheimer's disease (AD). Using liquid chromatography tandem mass spectrometry (LC-MS/MS), we show that patients with a clinical diagnosis of AD-related dementia undergo a recoding of their PNN-associated CS-GAGs that correlates to Braak stage progression, hyperphosphorylated tau (p-tau) accumulation, and cognitive impairment. As these CS-GAG sulfation changes are detectable prior to the regional onset of classical AD pathology, they may contribute to the initiation and/or progression of the underlying degenerative processes and implicate the brain matrix sulfation code as a key player in the development of AD clinicopathology.

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Disorders of intestinal enteroendocrine cells (EEC) are a rare cause of congenital diarrhea and diabetes. The gene NEUROG3 is essential in EEC differentiation, and mutations in this gene lead to a paucity of EEC in the intestine and pancreas, often presenting clinically as congenital diarrhea and diabetes mellitus. We present the earliest known diagnosis of NEUROG3associated enteric endocrinopathy, which was identified on a neonatal diabetes genetic panel sent at 4 weeks of age. Our patient presented with severe diarrhea, malnutrition, electrolyte derangements, and neonatal diabetes. He was started on parenteral nutrition at 3 months of age for nutritional and hydration support and required long-acting insulin for his diabetes. We demonstrate significant reduction in EEC, including cells expressing glucagonlike peptide-1, in intestinal biopsies from our patient, raising the possibility that loss of glucagon-like peptide-1 contributes to NEUROG3-associated diarrhea and diabetes mellitus. This case advances our understanding of the presentation, diagnosis, and management of this rare disease.

Zika virus (ZIKV) infection during pregnancy can impair offspring hippocampal neurocircuit formation and cognitive function, but underlying mechanisms driving this neuronal miswiring remain unknown. During fetal development, axonal migration, pathfinding, and synaptogenesis are strongly influenced by extracellular chondroitin and dermatan sulfate‐glycosaminoglycans (CS/DS‐GAGs), which consist of six differentially sulfated isomers (CS‐A, B (DS), C, D, E, O). The relative abundance of these CS/DS isomers can influence functions ranging from circuit plasticity (CS‐C) and maturation (CS‐A, B) to axonal growth attraction (CS‐D) and repulsion (CS‐E). Using LC‐MS/MS to analyze the relative abundance of each CS/DS isomer in cortical and hippocampal tissue obtained from normal 145d fetal Macaca nemestrina nonhuman primates (NHP), a key difference between cortex and hippocampus included the presence of a less ‘mature’ glycan matrix environment in the latter region. This finding is supported by a 1.6‐fold increase in the neuroplastic CS‐C (p=0.002) and 1.7‐fold increase in the neuronal attractant CS‐D (p=0.0001) isomers, along with a 39%‐decrease in axonal repulsive CS‐E (p<0.0001), a 22%‐decrease in synapse stabilizing CS‐B/DS (p=0.06), and a 6%‐decrease in the matrix maturing CS‐A (p=0.02) isomers. The hippocampus also exhibited a 51%‐decrease in the nonsulfated CS‐O (p=0.0001) isomer compared to the adjacent cortex, with the resultant hypersulfation of hippocampal CS/DS‐GAGs (p=0.0001) predicted to increase binding of positively charged extracellular growth factors. These differences in CS/DS‐GAGs between brain regions suggest that whereas the cortex provides a matured matrix environment capable of supporting newly formed circuitry, hippocampal CS/DS‐GAGs retain a developmental sulfation patterning that allows for additional neuronal migration, axon growth, and synapse formation. With this background, we then tested whether 3rd trimester congenital ZIKV infection (fetal d120‐d124) in M. nemestrina influences offspring CS/DS‐GAG sulfation patterns 21d later. We found that whereas no change was observed in the cortex, offspring exposed to congenital ZIKV exhibited a 33%‐decrease in CS‐D (p=0.01) and a 1.5x‐increase in CS‐O (p=0.03) in the hippocampus. This ZIKV‐driven reduction of the axonal attractant CS‐D can be predicted to limit hippocampal neurocircuit formation, potentially exacerbated by reduced retention of growth factors resulting from the increase in nonsulfated CS‐O, which is consistent with previous evidence of reduced hippocampal neurocircuit formation after maternal ZIKV infection. Overall, these results imply that maternal ZIKV infection during late‐stage fetal neurodevelopment 1) targets the immature hippocampal CS/DS‐GAGs over the matured cortex, 2) identifies recoding of CS/DS‐GAGs as a novel target for ZIKV infection, and 3) offers a novel and plausible mechanism to explain the deleterious impact of maternal ZIKV on offspring development