Revisiting I-BAR Proteins at Central Synapses

MTSS2-Related Disorder: Refining the Phenotype in Four New Cases and Literature Review

MTSS2 encodes a protein highly expressed in the central nervous system, with a crucial role in neurodevelopment. The de novo recurrent variant c.2011C>T (p.Arg671Trp) was first identified in 2022 as cause of Intellectual Developmental Disorder with ocular anomalies and distinctive facial features (OMIM#620086). We present clinical data about four new unrelated patients harboring the MTSS2 recurrent variant c.2011C>T (p.Arg671Trp). Common clinical features included developmental delay (particularly affecting language skills), mild intellectual disability, learning disabilities, microcephaly, non-specific brain MR findings and facial dysmorphisms. Other features were hypotonia, psychiatric disorders, generalized febrile or afebrile seizures with generalized epileptic anomalies on EEG, growth delay, skeletal anomalies, feeding difficulties (particularly affecting chewing), and poor coordination. Rare manifestations included hearing loss, ocular, gastrointestinal, genitourinary, and cardiovascular anomalies. To date, only six cases were documented in literature. Neurodevelopmental disorder with intellectual disability, microcephaly, and dysmorphisms are the main features of the disease. This study elaborates on the clinical manifestations, exploring the characterization of both neurologic and extra-neurologic comorbidities, proposing a possible association with cardiac and renal malformations. We suggest that MTSS2 could be linked to a predominantly neurological but multisystem disorder.

Neurodevelopmental disorder-associated mutations in TAOK1 reveal its function as a plasma membrane remodeling kinase

Mutations in TAOK1, which encodes a serine-threonine kinase, are associated with both autism spectrum disorder (ASD) and neurodevelopmental delay (NDD). Here, we investigated the molecular function of this evolutionarily conserved kinase and the mechanisms through which TAOK1 mutations may lead to neuropathology. We found that TAOK1 was abundant in neurons in the mammalian brain and remodeled the neuronal plasma membrane through direct association with phosphoinositides. Our characterization of four NDD-associated TAOK1 mutations revealed that these mutants were catalytically inactive and were aberrantly trapped in a membrane-bound state, which induced abnormal membrane protrusions. Expression of these TAOK1 mutants in cultured mouse hippocampal neurons led to abnormal growth of the dendritic arbor. The coiled-coil region carboxyl-terminal to the kinase domain was predicted to fold into a triple helix, and this region directly bound phospholipids and was required for both membrane association and induction of aberrant protrusions. Autophosphorylation of threonine-440 and threonine-443 in the triple-helical region by the kinase domain blocked the plasma membrane association of TAOK1. These findings define TAOK1 as a plasma membrane remodeling kinase and reveal the underlying mechanisms through which TAOK1 dysfunction may lead to neurodevelopmental disorders.