P.247 - New myotubular myopathy classification

The aim of a new classification for the myotubular myopathy (MTM) is to help having a better understanding of the severity and the burden of the different phenotypes of the disease. MTM is an X-linked congenital myopathy due to mutations in the MTM1 gene. MTM is classified as a rare and severe disease (incidence of 1/50.000 males). A prospective and longitudinal natural history study (NatHis-MTM) is conducted in Europe, USA and Canada in order to prepare upcoming clinical trials. MTM patients are currently classified into 3 groups (severe, moderate and mild) based on the clinical presentations described in case reports, but not on specific criteria. Our study suggests a new classification built on the baseline data of 39 patients enrolled in the European NatHis-MTM study. The ambulant status and the ventilation dependency are the two criteria, whereon the classification we propose will be based. Regarding the ambulant status, we decided to distinguish the acquisition and the loss of walking. Six different groups have been defined. Once the patients classified, their strength and function results collected from standardized tools and scales have been compared with the new classification. The overall classification fits with the MFM score and the quantified strength of handgrip that discriminates the patients groups. The advantage to classify patients is to define the severity of the disease and thus to anticipate more precisely the best patient care. It also helps to better define patients groups for future trials and for economic models.