De novo variants in MPP5 cause global developmental delay and behavioral changes
2020
MPP5 is a highly conserved apical complex protein essential for cell polarity, fate and survival. Defects in cell polarity are associated with neurologic disorders including autism and microcephaly. MPP5 is essential for neurogenesis in animal models, but human variants leading to neurologic impairment have not been described. We identified three patients with heterozygous MPP5 de novo variants (DNV) and global developmental delay (GDD), and compared their phenotypes and MRIs to ascertain how MPP5 DNV lead to GDD. All three patients with MPP5 DNV experienced GDD with language delay/regression and behavioral changes. MRIs ranged from normal to decreased gyral folding and microcephaly. The effects of MPP5 depletion on developing brain was assessed by creating a heterozygous (het) murine model with CNS-specific nestin-Cre drivers (het CKO). In the het CKO model, Mpp5 depletion led to microcephaly, decreased cerebellar volume and cortical thickness. Het CKO mice had decreased ependymal cells and Mpp5 at the apical surface of cortical ventricular zone compared to wild type. Het CKO mice also failed to maintain progenitor pools essential for neurogenesis. The proportion of cortical cells undergoing apoptotic cell death increased, suggesting that cell death reduces progenitor population and neuron number. Het CKO mice also showed behavioral changes, similar to our patients. To our knowledge, this is the first report to show that variants in MPP5 are associated with GDD, behavioral abnormalities and language regression/delay. Murine modeling shows that neurogenesis is likely altered in these individuals, with cell death and skewed cellular composition playing significant roles.
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