Ritscher-Schinzel syndrome can be characterized as an endosomal recyclinopathy

Ritscher-Schinzel syndrome (RSS) is a congenital malformation syndrome characterized by cerebellar, cardiac, and craniofacial malformations and phenotypes associated with liver, skeletal, and kidney dysfunction. The genetic cause of RSS remains to be fully defined, and limited information is available regarding the root cause of the multiple tissue phenotypes. Causative mutations in the Commander multiprotein assembly are an emerging feature of this syndrome. Commander organizes the sorting nexin-17 (SNX17)-dependent recycling of hundreds of integral membrane proteins through the endosomal network. Here, we identify previously unrecognized cohorts of patients with RSS that we genetically and clinically analyzed to identify causative genes in the copper metabolic murr1 domain-containing (COMMD) proteins COMMD4, COMMD9, and coiled-coil domain containing 93 (CCDC93) subunits of the Commander complex. Using interactome analysis, we determined that these mutations disrupted Commander assembly and, through cell surface proteomics, that this reduces tissue-specific presentation of cell surface integral membrane proteins essential for kidney, bone, and brain development. We established that these integral proteins contained ΦxNPxY/F or ΦxNxxY/F sorting motifs in their cytoplasmic-facing domains (where Φ is a hydrophobic residue and x is any residue) that are recognized by SNX17 to drive their Commander-dependent endosomal recycling. Last, through generation of mouse models of RSS, we show replication of RSS-associated clinical phenotypes including proteinuria, skeletal malformation, and neurological impairment. Our data establish RSS as a "recyclinopathy" that arises from a dysfunction in the Commander endosomal recycling pathway.