The enlarging spectrum of focal cortical dysplasias.

Abstract

This scientific commentary refers to ‘PI3K/AKT pathway mutations cause a spectrum of brain malformations from megalencephaly to focal cortical dysplasia’, by Jansen et al. (doi: 10.1093/brain/awv045). Focal malformations of cortical development, including focal cortical dysplasia (FCD), are among the most common causes of intractable epilepsy in children. In this issue of Brain , Jansen and colleagues provide evidence that hemimegalencephaly (HMEG) and FCD type IIa result from mosaic mutations in components of the PI3K/Akt/mTOR (mammalian target of rapamycin) pathway, i.e. PI3KCA , AKT3 , or PTEN , in 4/33 patients using targeted screening of a panel of PI3K , AKT , and PTEN genes (Jansen et al. , 2015). These individuals suffered from intractable seizures, and exhibited radiographic and histopathologically defined evidence of either HMEG or FCD. An additional single case of dysplastic megalencephaly (DMEG) was linked to PI3KCA. In the remaining 29 patients with HMEG, or FCD type I, type IIa, or type IIb, no mutations were identified. The phosphorylation profile of components of the PI3K/Akt/mTOR signalling pathway showed that phosphorylation of Akt at threonine (T)308 and serine (S)473 was enriched in all HMEG and FCD cases, and in conjunction with measured Akt kinase activity, could distinguish mutation-positive dysplasia cortex, mutation-negative dysplasia cortex, and non-dysplasia epilepsy cortex. In conclusion, Jansen et al. suggest that FCD, HMEG and DMEG comprise a spectrum of developmental malformations linked to the PI3K/Akt/mTOR pathway. Focal malformations of the cerebral cortex have been reported since the 1800s, with the first description of HMEG by Sims in 1835 and tuberous sclerosis complex by Bourneville in 1880. In 1957, Crome published a short pathological report describing abnormally ‘large neurons’ in the brains of three patients with intractable epilepsy within areas of ‘ulegyria’, which set the conceptual stage for the index report of focal dysplasia of the …