Novel therapy for Non-Ketotic Hyperglycinemia

Non-Ketotic Hyperglycinemia (NKH) is a life-limiting inherited metabolic disease that becomes apparent in babies soon after birth with lethargy, breathing difficulties and neurological problems, including epilepsy. NKH causes profound delay in development, complex epilepsy and premature death, usually in early childhood. There is no cure for NKH and current treatments have limited effect. Hence, there is an urgent unmet need for new therapies. NKH is caused by a genetic alteration in a gene, glycine decarboxylase (GLDC), that encodes a component of a protein complex called the glycine cleavage system (GCS). Loss of GCS function prevents the normal breakdown of a small molecule called glycine in the body. As a result, glycine accumulates to harmful levels, and glycine breakdown products cannot be used in crucial metabolic reactions in the brain and liver. We have designed treatments that address both issues and tested these in a GLDC-deficient mouse model which recapitulates key features of NKH. We have developed gene therapy for NKH to introduce a ‘normal’ copy of the affected gene, encoding glycine decarboxylase (GLDC), into the cells in the patient’s body to provide the function that their own faulty copy does not have. We developed and optimised a vector based on components of adenoviral associated virus (AAV) to enable expression of GLDC in the brain and liver which are the key target tissues in NKH. Treatment of the NKH mouse model at neonatal stages showed long-lasting correction of metabolic abnormalities in the brain including normalisation of folate metabolism and lowering of glycine to normal levels. Treated mice showed 100% survival to 12 weeks of age. We monitored mice for up to 15 months and found no adverse effects of treatment. In summary, analysis of AAV-GLDC treated mice supports the hypothesis that this approach may be of therapeutic benefit in NKH. While we have shown normalisation of metabolic abnormalities and biomarkers, additional measures of effectiveness were not previously available in the GLDC-deficient mouse model. Therefore, in parallel with development of novel treatments we have carried out in depth phenotyping of the NKH mouse model, including analysis of metabolome, gene expression, neurological and behavioural abnormalities. These provided novel insight into the NKH disease process and, importantly, provide read-outs for testing effectiveness of therapies. In this project we will make use of these read-outs to test effectiveness of AAV-GLDC gene therapy using selected tests of neurological function and sensitivity to drug-induced seizures, which we found to discriminate between GLDC-deficient and unaffected mice. Demonstration of a protective effect will provide evidence to support next steps in translation progress towards a clinical trial. Another key step towards clinical trial, is transfer of AAV-GLDC vector production to a GMP (good manufacturing practise) facility for scale-up and manufacture using a process that would then be applicable for production of AAV9-GLDC for treatment of patients. We have engaged a GMP facility and initiated pilot manufacture of vector to de-risk process development. In the current project we will test the GMP-like vector in the NKH mouse model, to confirm activity. We have scheduled a regulatory advice meeting with MHRA to obtain advice on requirements for safety testing and clinical trial design. Overall, this project will provide supporting data for a funding application to support final stages of pre-clinical work, vector manufacture, pivotal safety study and first in child clinical trial.