Development of Gene Therapy Approaches to Cerebellar CACNA1A disorders

About This Grant

Project Summary/Abstract CACNA1A diseases are due to pathogenic mutations in the 1 subunit of the CaV2.1 channel that cause a range of neurodevelopmental and neurological disorders, including ataxia, epilepsy, migraine, autism, and cerebellar degeneration. Although CACNA1A dysfunction impacts multiple brain structures in the developing brain, one of the most devastating manifestations are CACNA1A cerebellar disorders, which cause severe movement problems and episodic dykinesia due to cerebellar dysfunction and progressive atrophy. CACNA1A cerebellar disorders result in dysfunction and degeneration of Purkinje cells, which provide the sole inhibitory output of the cerebellar cortex, regulating motor coordination and unleashing frequent generalized forebrain seizures in childhood. Despite decades of research that has identified causative mutations in CACNA1A, no cure and no therapeutic strategies that treat the root cause of CACNA1A disorders exist. Therefore, to stop cerebellar dysfunction and improve the quality of life of individuals who suffer from CACNA1A disorders, novel therapies must be developed. Vector gene therapy approaches are an attractive strategy to treat CACNA1A disorders, however, the large 7.5 kilobase (kb) size of the CACNA1A protein coding sequence presents a severe delivery challenge as it exceeds the ~5 kb packaging capacity of AAV which severely limits the use of AAV in treating CACNA1A disorders. Helper Dependent Adenoviral vectors (HdAd) are devoid of all viral genes, have a large carrying capacity (~36 kb) and provide long-term gene expression without toxicity after a single administration in multiple preclinical animal models and in Phase I human trials. Thus, HdAd holds extraordinary promise as a viral vector to treat CACNA1A disorders. However, its use to treat CACNA1A cerebellar disorders has not been explored. Building on our decade of experience with HdAd vectors in the central nervous system, we created a novel HdAd vector that transduces Purkinje Cells in a validated preclinical humanized mouse model. We propose to restore Cacna1a function in mouse Purkinje cells that have been selectively deleted for Cacna1a and which replicating the human loss of function phenotype. We will test our novel viral vectors and delivery approaches, in this conditional mouse model to develop approaches for long-term expression of CACNA1A in Purkinje cells, and correlate transfection patterns with rigorous analysis of cerebellar and EEG phenotypes. If successful, this project will provide a critical path to a cure of human CACA1A disorders.