Utility of Exogenous Ketones and Modified Atkins Diet in a Child With GSD VII (Tarui Disease)

Glycogen storage disease VII (GSD VII), also known as Tarui disease, is caused by a deficiency of the skeletal muscle enzyme, phosphofructokinase (PFK). Classical GSD VII is characterised by reduced exercise capacity and exercise-induced myopathic symptoms, exacerbated with carbohydrate intake. No recommended medical or dietary therapy currently exists to improve exercise symptomology in GSD VII. An 11-year-old female was recommended four trial dietary therapies for 8 weeks each: (1) usual diet, (2) 150 mg/kg exogenous ketones pre-exercise, (3) modified Atkins diet (MAD), (4) MAD and pre-exercise ketones. Clinical assessments comprised cardiopulmonary exercise test, anthropometry, biochemical tests including creatine kinase (CK), quality of life (QoL), heart rate (HR) monitoring and subjective symptom reports. Exogenous ketones improved exercise capacity demonstrated by reduced HR for equivalent exercise workload, and participation in higher intensity exercise for longer duration. MAD improved QoL physical domain score by 29%, normalised CK and halved the number of symptoms reported per 'physically active day'. Dissatisfaction with MAD resulted in unintentional weight loss, and a 20% reduction in QoL emotional domain score, leading to the patient declining the fourth study phase. This study is the first to demonstrate a beneficial effect of exogenous ketones, and separately, MAD, in a child with GSD VII. Exogenous ketones or MAD could be recommended under medical and dietetic supervision in GSD VII. However, consideration must be given to the potential negative impact of MAD on weight and emotional health. Further interventional studies are warranted in this condition.