Neuron Article Christianson Syndrome Protein NHE6 Modulates TrkB Endosomal Signaling Required for Neuronal Circuit Development Qing Ouyang,1,4 Sofia B. Lizarraga,1,4 Michael Schmidt,1 Unikora Yang,1 Jingyi Gong,1 Debra Ellisor,1 Julie A. Kauer,2 and Eric M. Morrow1,3,* 1Departments of Molecular Biology, Cell Biology and Biochemistry and Institute for Brain Science, Brown University, Laboratory for Molecular Medicine, 70 Ship Street, Providence, RI 02903, USA 2Departments of Molecular Pharmacology, Physiology and Biotechnology, and Neuroscience, Brown University, Providence, RI 02912, USA 3Developmental Disorders Genetics Research Program, Emma Pendleton Bradley Hospital and Department of Psychiatry and Human Behavior, Brown University Medical School, 1011 Veteran Memorial Parkway, East Providence, RI 02915, USA 4These authors contributed equally to this work *Correspondence:
[email protected] http://dx.doi.org/10.1016/j.neuron.2013.07.043 SUMMARY (Gilfillan et al., 2008). One of the pedigrees determined to have an NHE6 mutation by Gilfillan et al. was a large South African Neuronal arborization is regulated by cell-autono- pedigree previously reported by Christianson et al. (1999). mous and nonautonomous mechanisms including Christianson syndrome (CS) is now the commonly used term endosomal signaling via BDNF/TrkB. The endosomal for the condition associated with NHE6 mutations. In addition Na+/H+ exchanger 6 (NHE6) is mutated in a new to the symptoms described above, CS may also involve cranio- autism-related disorder. NHE6 functions to permit facial dysmorphology, ataxia, ophthalmoplegia, and cerebellar proton leak from endosomes, yet the mechanisms and brainstem atrophy. Christianson also described an associa- tion with autistic symptoms, including autistic regressions, as causing disease are unknown.