We describe the case of 10-year-old twin girls, who were born to nonconsanguineous parents and showed pes equinovarus, infantile spasms, and severe psychomotor retardation. Neither patient showed marked microcephaly. Neuroimaging revealed a simplified gyral pattern in the bilateral frontotemporal areas, a reduced volume of cerebral white matter, and a thin corpus callosum in both patients. The cerebral cortex presented with significant thickness in the anterior temporal region at the age of 10 years, which suggest that the simplified gyri can evolve into the pachygyria during postnatal period. These cases may represent a hereditary brain malformation with a distinct pattern of abnormal cortical gyration. The age-dependent change in appearance of dysgenetic cortex should be further explored in cases with brain malformations.