Project Summary/Abstract Relatively little is known about SMARD1 and CMT2S and the disease-causing gene IGHMBP2 as it relates to disease development. Therapeutic options are, at best, minimal as no approved drugs exist. The objective of this project is to understand the consequences of disease-causing mutations in IGHMBP2 that result in SMA with Respiratory Distress (SMARD1) or Charcot Marie Tooth Type 2S (CMT2S). Towards this goal, we have generated six Ighmbp2 mouse models that are based on patient mutations in IGHMBP2. These models represent the first, patient-based models of SMARD1 and CMT2S. Importantly, we demonstrate that each mutation thus far studied demonstrates distinct disease phenotypes. These investigations are designed to further our understanding of IGHMBP2 and its functional significance in disease development by utilizing the Ighmbp2 mouse models and complementary approaches: genetics and biochemistry. Aim I of this proposal examines the phenotypic and molecular changes that result from Ighmbp2 mutations R604X and H922Y and the effect of these mutations on disease progression and therapeutic efficacy. Examining the similarities and differences between these mutations should provide valuable information towards what molecular alterations result in the more severe SMARD1 or less severe CMT2S. Therapeutic studies proposed will help us understand what aspects of disease pathology are altered and to what extent. Aim II utilizes biochemistry to investigate how these IGHMBP2 mutations effect IGHMBP2 function and the association of proteins in IGHMBP2 pathways. RNA and protein stability, protein binding affinity, ATPase and helicase activity and processivity for these mutants will be examined in the presence of absence of ABT1, a protein that binds IGHMBP2 and increases IGHMBP2 ATPase and helicase activity and processivity. It will be important to determine how each of these mutations alter IGHMBP2 biochemical function and how altered IGHMBP2 biochemical function relates to disease. Our previous studies suggest that IGHMBP2-ABT1 function in 47S pre- rRNA processing; Aim III expands on these studies. Our laboratory has developed reagents aimed at addressing IGHMBP2-ABT1 function in neuronal and non-neuronal contexts. 47S pre-rRNA processing will be examined in wild type and mutant contexts to determine whether and to what extent processing is altered. We will also ask whether any processing defects can be eliminated following therapeutic delivery of IGHMBP2 or ABT1. Each Aim of this proposal should provide independent relevant information towards understanding disease development and progression, IGHMBP2 biological processes and targets for therapeutic development. Determining the functional differences between IGHMBP2 mutations that result in SMARD1 versus CMT2S has important therapeutic implications since a subtle increase in functionality can have profound clinical implications. This proposal is a natural collaboration of MU invest...