Simon is the Head of the Enzyme and Metabolic Laboratories at Great Ormond Street Hospital and holds the UCL Chair of Clinical Chemistry. He has a strong interest in the diagnosis and monitoring of patients with inherited metabolic disorders. This work is underpinned by a number of basic and translational research projects that are carried out in conjunction with the UCL Institute of Child Health. He has published over 150 papers in the area of mitochondrial, neurotransmitter and lysosomal disorders. Simon is also the Clinical Lead for the Neurometabolic Unit at the National Hospital, Queen Square (UCLH Foundation Trust).