A Clinical Assessment Study in X-Linked Myotubular Myopathy (XLMTM) Subjects

Inclusion Criteria: - Subject has a diagnosis of XLMTM resulting from a confirmed mutation in the MTM1 gene - Subject is male - Subject is aged less than 4 years - Subject requires some mechanical ventilatory support (eg, ranging from 24 hours per day full time mechanical ventilation, to noninvasive support such as continuous positive airway pressure [CPAP] or bilevel positive airway pressure [BiPAP] during sleeping hours) - Access to subject's medical records - Signed informed consent by the parent(s) or legally authorized representative(s) (LAR) (when applicable) - Subject and parent(s) or LAR are willing and able to comply with study visits and study procedures Exclusion Criteria: - Subject is participating in an interventional study designed to treat XLMTM - Subject born <35 weeks gestation who is still not to term as per corrected age - Subject has a clinically important condition, or life-threatening disease other than XLMTM, in the opinion of the investigator - Subject has received pyridostigmine or any medication to treat XLMTM within 30 days of enrollment