Project description:Calmodulin is an intracellular Ca2+ sensor that regulates numerous cellular processes through binding effector proteins and changing their activity. Humans have three calmodulin paralogs, CALM1, CALM2 and CALM3, encoding identical proteins, and missense variants in all three are included in the ACMG recommendations for reporting of secondary findings related to early onset sudden cardiac death caused by arrhythmias long QT syndrome and CPVT. Recently, a subset of individuals with de novo variants in calmodulin genes were described who also presented with neurologic phenotypes. Here we report two individuals with the same de novo variant c.419A>T in CALM1 or CALM2 that may generate a 5’ splice donor gain and/or a missense change p.E140V. These individuals share hypotonia, motor delay, intellectual disability, and abnormal electroencephalograms but lack cardiac arrhythmia/electrocardiogram abnormalities of previously described CALM-associated disease, suggesting the variant causes phenotypic expansion beyond the known Mendelian phenotypes. RNA-seq of the CALM1 proband blood’s sample revealed that most transcripts from the variant allele showed usage of the new splice site or intron retention, without NMD, resulting in frameshifted C-terminal truncations, while a minority resulted in production of the p.E140V missense protein. We modeled the CALM1/2 p.E140V variant as well as a known arrhythmia variant, CALM1 p.E141G, using the C. elegans ortholog cmd-1. We found that cmd-1 E140V displayed both qualitative and quantitative differences in phenotype from E141G, indicating distinct genetic mechanisms. Together, these findings support CALM1/2 phenotypic expansion, with c.419A>T p.E140V resulting in neurologic, but not arrhythmia phenotypes.
Project description:Genetic evidence indicates that microglial dysfunctions contribute to the development and progression of various neurologic diseases, emphasizing microglia replacement as a promising therapeutic strategy. However, traditional bone marrow transplantation (BMT) aimed at replenishing brain microglia faces challenges due to low efficiency and potential brain injury from preconditioning with irradiation or chemotherapy. Moreover, the BM-derived cells that migrate to the brain fail to replicate the characteristics of resident microglia. Here, we present a simple yet highly effective microglia transplantation strategy devoid of any conditioning, termed "Tri-Cyclic Microglial Depletion for Transplantation" (TCMDT). This approach leverages three cycles of microglial depletion using the CSF1R inhibitor PLX3397, creating a critical window for the efficient engraftment of exogenous microglia. Notably, transplanting primary cultured microglia via the TCMDT strategy achieves their full restoration to the identity and functions of native microglia. To evaluate the therapeutic potential, we applied our strategy to a Sandhoff disease mouse model, a form of neurodegenerative lysosomal storage disorder (LSD) caused by Hexb deficiency. The results revealed that our strategy facilitated the efficient replacement of deficient microglia, leading to a notable decrease in neurodegeneration and an enhancement in motor performance. Similarly, in an Alzheimer's disease (AD) mouse model carrying the Trem2 R47H mutation, our transplantation strategy corrected microglial dysfunction and alleviated AD-related pathology. Overall, our study presents a practical approach for microglia replacement that is simple, efficient, and safe, offering significant therapeutic potential for treating microglia-associated disorders.