For example, the clinical heterogeneity associated with the Ala467Thr mutation in the mitochondrial polymerase-γ (POLG) gene illustrates how identical homozygous mutations can give rise to a wide range of phenotypes, from Alpers-Huttenlocher syndrome to peripheral neuropathy and ophthalmoplegia 70. The gene discussed is POLG; the disease is ophthalmoplegia.