PCDH17 and Down syndrome: In a study performed by the Anton lab, the conditional knockdown of the Joubert Syndrome-associated gene Arl13b in cultured deep cerebellar nuclei (DCN) neurons led to reduced dynamic axonal branching, aberrant growth cone morphology with altered filopodia-lamellipodia balance (i.e., numerous longer filopodial protrusions), as well as impaired axon-axon adhesion associated with reduced recruitment of the protocadherin-17 (Pcdh17) to axon-axon contacts (Guo et al., 2019; Figure 3, bottom and middle).