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Impaired Axon Initial Segment Structure and Function in a Model of ARHGEF9 Developmental and Epileptic Encephalopathy

Wang et al., PNAS. 2024.

https://www.pnas.org/doi/10.1073/pnas.2400709121

Researchers developed a mouse model carrying the G55A missense variant identified in ARHGEF9 patients with severe epilepsy and neurodevelopmental phenotypes. Using male Arhgef9G55A mice, this study examined behavioral, molecular, and electrophysiological phenotypes in the Arhgef9G55A model of developmental and epileptic encephalopathies (DEE). Researchers found that the G55A variant causes disruption of inhibitory postsynaptic organization and axon initial segment (AIS) architecture, leading to impairment of both synaptic transmission and action potential generation. The effects of Arhgef9G55A on neuronal function affect both intrinsic and synaptic excitability and preferentially impair AIS. These findings indicate a novel pathological mechanism of DEE and represent a unique example of a neuropathological condition converging from AIS dysfunctions. Supported by ORIP (U54OD020351, U54OD030187, U54OD020351, S10OD026974) and NINDS.

De Novo Variants in FRYL Are Associated With Developmental Delay, Intellectual Disability, and Dysmorphic Features

Pan et al., The American Journal of Human Genetics. 2024.

https://www.cell.com/ajhg/fulltext/S0002-9297(24)00039-9

FRY-like transcription coactivator (FRYL) belongs to a Furry protein family that is evolutionarily conserved from yeast to humans, and its functions in mammals are largely unknown. Investigators report 13 individuals who have de novo heterozygous variants in FRYL and one individual with a heterozygous FRYL variant that is not confirmed to be de novo. The individuals present with developmental delay; intellectual disability; dysmorphic features; and other congenital anomalies in cardiovascular, skeletal, gastrointestinal, renal, and urogenital systems. Using fruit flies, investigators provide evidence that haploinsufficiency in FRYL likely underlies a disorder in humans with developmental and neurological symptoms. Supported by ORIP (U54OD030165), NHLBI, NICHD, and NCATS.