Sodium Valproate for GSDV

Inclusion Criteria: * Male subjects and post-menopausal or infertile females * Diagnosed with GSDV and over 18 years of age * Normal serum carnitine level and acylcarnitine blood profile at screening visit Exclusion Criteria: * Children under the age of 18 years * People older than 64 years * Females of child bearing potential * Patients with Diabetes * Inflammatory disorders especially systemic lupus erythematosis. * A previous history of sensitivity/allergy to sodium valproate and its excipients * Patients treated with sodium valproate for epilepsy or a psychiatric disorder within the last 12 months prior to screening * Patients with pre-existing liver disease or a family history of severe liver disease affecting a first degree relative. Liver disease will be defined by abnormal liver biopsy. Patients with GSDV may have raised serum transaminases that originate from muscle but which may cause abnormal liver function tests measured in serum, this will not be a reason for exclusion. * Patients prescribed other anti-convulsant medication or any other medication known to interact with sodium valproate (see section 9.3). * Patients who are sensitive to local anaesthetics that would prevent muscle biopsy. * Subjects with any co-morbid illness or disability which would prevent an exercise assessment such as severe unstable/ untreated ischaemic heart disease, lower limb disability such as severe muscle weakness with muscle strength assessed as worse than MRC scale 3 in any pelvi…