The X-linked form due to mutations in the myotubularin (MTM1) gene has been clinically well characterised and usually gives rise to a severe phenotype in males presenting at birth with marked weakness and hypotonia, external ophthalmoplegia and respiratory failure (Figure 1) [6-19]; a preceding family history of either male neonatal deaths or miscarriages is common. The gene discussed is MTM1; the disease is External ophthalmoplegia.