CACNA2D2, the ducky mouse, and what it takes to be an epilepsy gene

Subunit. Spontaneous mouse mutants help to identify candidate genes for disease mechanisms and have hinted at an important role for ion channels in epilepsy long before the first human channelopathies were identified. The ducky mouse has absence seizures and suffers from ataxia. A truncation mutation in CACNA2D2 could be identified in this phenotype, encoding for an auxiliary calcium channel subunit. This finding emphasizes the role of calcium channels in absence seizures and begs the question whether genetic variation in CACNA2D2 is also involved in human epilepsy. A recent publication in PLOS One now identifies the second recessive CACNA2D2 mutation in a patient with epileptic encephalopathy. But are two independent cases sufficient anymore to claim causality? Continue reading

C6orf70, neuronal migration and periventricular heterotopia

Radial migration. The fact that neurons find their place in the cortex during development is nothing short of a miracle. Many neurons originate in the subventricular zone, i.e. the area lining the ventricles. During brain development, these neurons subsequently climb outwards to their final positions using radial glia cells as scaffolds. If this delicate process is disturbed, neurons may be misplaced. Periventricular nodular heterotopia (PVNH) is a condition in which defects in neuronal migration result in ectopic neuronal nodules lining the ventricles. These nodules may result in a broad range of epilepsies, ranging from mild seizure disorders to intractable epilepsy with intellectual disability. Many cases of PVNH are assumed to be genetic, and FLNA and ARFGEF2 as known causative genes. However, the cause remains unknown in a significant number of patients. In a recent paper in Brain, C6orf70 is identified as a new candidate for PVNH using a clever combination of array CGH and exome sequencing. Continue reading