WASHC5 encodes a core component of the WASH complex, a nucleation-promoting factor that recruits and activates the Arp2/3 complex to induce actin polymerization at endosomal membranes 12. This activity is essential for endosome fission and tubulation during endosomal sorting and trafficking 3. WASHC5 also regulates protein recycling through CAV1-dependent mechanisms and maintains integrin-mediated cell adhesion 3. Pathogenic WASHC5 variants cause two distinct genetic disorders. Autosomal recessive mutations cause Ritscher-Schinzel syndrome 1 (RTSCS1), characterized by craniofacial dysmorphism, macrocephaly, developmental delay, intellectual disability, ataxic gait, and cardiovascular/cerebellar malformations 45. Autosomal dominant mutations cause hereditary spastic paraplegia type SPG8 (SPG8), presenting with progressive leg spasticity and weakness with variable age of onset 67. SPG8-associated mutations impair endosomal fission and CAV1-dependent cell adhesion 3. WASHC5 functions within a broader trafficking network coordinating with the CCC and Retriever complexes 8. Disease mechanisms involve disrupted endosomal homeostasis and abnormal ER function affecting skeletal, cardiac, and nervous system development 5. The WASH complex's role in maintaining protein abundance through inhibition of lysosomal degradation appears critical for cellular pathogenesis 3.