Myoadenylate deaminase deficit (MAD, MIM#615511) is the most common cause of metabolic myopathies with an estimated prevalence of 1-2% in the general population. We report the case of a 39-year-old man suffering from severe skeletal muscle pain that had developed gradually for 4 years. A moderate increase in creatine kinase (CK) was the only biological sign observed. This study takes a closer look at a common but poorly known pathology and highlights the interest of the dynamic metabolic investigations carried out during exercise stress test with a cycle ergometer. Our non-invasive clinical and biological examination, at the interface between physiology and biology, disclosed the total absence of a physiological increase in plasma ammonia evocative of MAD. However, MAD was later confirmed by histochemistry and molecular studies, which revealed the presence of the recurrent homozygous pathogenic variant affecting the adenosine monophosphate deaminase 1 gene (AMPD1) in most patients with MAD.
Keywords: AMPD1; exercise stress testing; metabolic myopathies; myalgia; myoadenylate deaminase.