Congenital myopathy with internal nuclei and atypical cores is a rare genetic skeletal muscle disease characterized by neonatal hypotonia, distal more than proximal muscle weakness, progressive exercise intolerance with prominent myalgias, and mild-to-moderate overall motor impairment with preserved ambulation. Face, extraocular, cardiac, and respiratory muscles are unaffected. Mild cognitive impairment is also noted in most patients. The disease is Monarch Disease Ontology identifier MONDO_0013890 (congenital myopathy with internal nuclei and atypical cores). Also known as: CNM4, centronuclear myopathy 4, centronuclear myopathy type 4, myopathy, centronuclear, type 4.