TRAPPC10 is a specific subunit of the TRAPP (transport protein particle) II complex that functions in intracellular vesicle trafficking and membrane tethering 1. The protein contains a Longin domain that may contribute to the Rab11-GEF activity ascribed to TRAPP-II 2. TRAPPC10 interacts with TRAPPC9, another key TRAPP II component, and this interaction is essential for complex stability - studies show that TRAPPC10 deficiency leads to concomitant reduction of TRAPPC9 levels 1. Loss of TRAPPC10 function causes membrane trafficking defects that can be rescued by wild-type but not mutant constructs 1. Biallelic loss-of-function variants in TRAPPC10 cause a severe microcephalic neurodevelopmental disorder characterized by developmental delay, intellectual disability, microcephaly, and behavioral abnormalities including autistic traits 31. The mechanism involves premature protein termination leading to nonsense-mediated decay and loss of functional TRAPPC10 protein 3. Knockout mouse models recapitulate the human phenotype, showing neuroanatomical brain defects and microcephaly similar to findings in TRAPPC9 knockout mice 1. These findings establish TRAPPC10 as critical for normal brain development and highlight the importance of TRAPP II complex function in neurodevelopmental processes.