Mechanisms of PiT2-loop7 Missense Mutations Induced Pi Dyshomeostasis / 神经科学通报·英文版

PiT2 is an inorganic phosphate (Pi) transporter whose mutations are linked to primary familial brain calcification (PFBC). PiT2 mainly consists of two ProDom (PD) domains and a large intracellular loop region (loop7). The PD domains are crucial for the Pi transport, but the role of PiT2-loop7 remains unclear. In PFBC patients, mutations in PiT2-loop7 are mainly nonsense or frameshift mutations that probably cause PFBC due to C-PD1131 deletion. To date, six missense mutations have been identified in PiT2-loop7; however, the mechanisms by which these mutations cause PFBC are poorly understood. Here, we found that the p.T390A and p.S434W mutations in PiT2-loop7 decreased the Pi transport activity and cell surface levels of PiT2. Furthermore, we showed that these two mutations attenuated its membrane localization by affecting adenosine monophosphate-activated protein kinase (AMPK)- or protein kinase B (AKT)-mediated PiT2 phosphorylation. In contrast, the p.S121C and p.S601W mutations in the PD domains did not affect PiT2 phosphorylation but rather impaired its substrate-binding abilities. These results suggested that missense mutations in PiT2-loop7 can cause Pi dyshomeostasis by affecting the phosphorylation-regulated cell-surface localization of PiT2. This study helps understand the pathogenesis of PFBC caused by PiT2-loop7 missense mutations and indicates that increasing the phosphorylation levels of PiT2-loop7 could be a promising strategy for developing PFBC therapies.

Anti-γ-aminobutyric acid type A receptor encephalitis: a new type of autoimmune encephalitis with prominent epilepsy / 中华神经科杂志

Objective To firstly report the clinical features,diagnosis and treatment response of patients with anti-γ-aminobutyric acid type A receptor (GABAAR) encephalitis in China,thus raising neurologists' awareness of this emerging type of autoimmune encephalitis.Methods Specific anti-GABAAR autoantibodies in the serum and cerebrospinal fluid (CSF) of patients with suspected autoimmune encephalitis but negative for commercial available antibody tests were detected by live cell-based assay (CBA).The clinical features,laboratory examinations and treatment of two cases of autoimmune encephalitis with anti-GABAAR autoantibodies were analyzed,who admitted to Huashan Hospital,Fudan University between 2013 and 2014.Results By using live CBA,serum and CSF of the two patients diagnosed with possible autoimmune encephalitis both contained autoantibodies targeted to the GABAAR.These two patients had onset symptom of seizure or refractory seizures.Memory impairment,psychiatric symptoms and decreased consciousness were also presented.One patient was combined with mass in anterior superior mediastinum.Both patients had multifocal cortical and subcortical T2 /fluid attenuated inversion recovery-weighted images hyperintensity signal on brain magnetic resonance imaging.The two patients had poor response to antiepileptic drugs,but showed noticeable recovery with sufficient immunotherapeutic treatments.Conclusions Anti-GABAAR encephalitis is characterized by prominent epilepsy and multifocal abnormalities on brain magnetic resonance imaging.Autoantibodies specifically against GABAAR could be detected by CBA in this group of patients.Early diagnosis and immunotherapy are critical to improve clinical symptoms and outcomes of the disease.