Cases related to genetic mutations and metabolic abnormalities have also been described, although at least some of these cases also exhibited associated structural malformations. Even in some cases when no structural

lesion was evident on cranial imaging, postmortem examinations demonstrated evidence of a migration disorder or dysgenesis that was not previously appreciated on neuroimaging [3] and [16]. A variety of structural malformations have been associated with Ohtahara syndrome, including hemimegalencephaly [11] and [17], agenesis of the corpus callosum [3] and [8], porencephaly [8], agenesis of the mamillary bodies [18], and dentato-olivary dysplasia [17]. Hypoxic injury [3], cortical dysplasias, and cerebral migration disorders are also frequently described [16], [19] and [20]. Metabolic disorders that were reported to accompany E7080 Ohtahara syndrome include BAY 80-6946 in vivo nonketotic hyperglycinemia [3], cytochrome C oxidase deficiency [21], pyridoxine dependency, carnitine palmitoyltransferase deficiency [11], and a case of Leigh encephalopathy [22]. More recently, a patient with biotinidase deficiency [23] and two patients with mitochondrial respiratory chain complex I deficiency were described [24] and [25]. One of the patients with respiratory

chain complex I deficiency also manifested microcephaly, thinning of the corpus callosum, and cortical atrophy [24]. The other patient with a similar complex 1 deficiency demonstrated normal cranial imaging [25]. Deficiencies in cytochrome C oxidase or respiratory chain complex I may result in energy depletion during development, in turn leading to demyelination and abnormalities in neuronal migration [26]. Underlying genetic mutations have been increasingly reported with Ohtahara syndrome. Mutations in the syntaxin binding protein 1 (STXBP1) gene, for example, have been described in Ohtahara syndrome since 2008 [27]. A proportion of patients with known

Ohtahara syndrome is now thought to manifest underlying STXBP1 mutations, although the exact number of such patients has varied from study to study, ranging from 10-13% [28] and [29] to 38% in the original report [27]. Similarly, mutations of the Aristaless-related homeobox (ARX) gene Adenosine triphosphate have also been associated with Ohtahara syndrome [30], [31] and [32]. In keeping with the close relationship between the age-dependent epileptic encephalopathies, mutations in both ARX and STXBP1 have also been described in patients with West syndrome [28], [29] and [31]. Finally, two reports described patients with Ohtahara syndrome who had mutations in the solute carrier family 25 (SLC25A22) gene. Both patients were born to consanguinous parents [33]. As with the metabolic disturbances, the mechanisms by which these genetic abnormalities cause Ohtahara syndrome are thought to be related to brain dysgenesis or neuronal dysfunction.