Absence of evidence – where are the recessive epilepsy genes?

E2. When we work up a new-onset epileptic encephalopathy in clinical practice, there is a discrepancy between what we know and what we do. While we know that we have an almost 30% chance to find a causative de novo mutation in any of the known epilepsy genes, we usually think about a possible underlying inherited metabolic disorder when we order our first round of tests. However, the full phenotypic spectrum is often unknown and the question remained how many of these inherited metabolic disorders are missed. In our recent publication of the E2 consortium, we looked for evidence of inherited genetic disorders in patients with epileptic encephalopathies. Follow us on our journey that led to a negative answer, but uncovered a complexity in finding inherited diseases that we did not anticipate. Continue reading

AP4S1 in fever-associated epilepsies and spastic paraplegia

Peds vs. adult. Sometimes it makes a fundamental difference in diagnosis whether a patient is seen in a pediatric setting or by an adult specialist later in life. Here is the most recent example from our consortium, which was just published in Human Molecular Genetics: what initially looked like recessive inheritance with intellectual disability and a peculiar fever-associated epilepsy syndrome eventually turned out to be the second reported family of the novel spastic paraplegia gene AP4S1. This raises the question of how much we are missing if we are looking at the wrong point in time. Let’s have a look at how genetics can help us see an overlap of diseases where we usually don’t have a chance to. Continue reading

Imbalance of a rare second messenger – FIG4 mutations in polymicrogyria

Brain malformations. Various brain malformations are thought to have a genetic basis, and several genes have already been identified. Polymicrogyria is a particular form of congenital brain malformation due to an excessive number of small and sometimes malformed gyri. In a recent publication in Neurology, mutations in FIG4 are described in a familial form of polymicrogyria. However, the FIG4 gene is no stranger in the field of neurogenetics. Continue reading

TBC1D24, DOORS Syndrome, and the unexpected heterogeneity of recessive epilepsies

The return of TBC1D24. In 2010, the TBC1D24 gene was the first gene for human epilepsies to be discovered through next generation sequencing techniques. Ever since, this gene has been a mystery, as the phenotypes of the families with recessive mutations in this gene varied widely. Now, a recent paper in Lancet Neurology finds recessive TBC1D24 mutations in a large proportion of patients with DOORS syndrome, a rare distinct autosomal recessive syndrome with deafness, onychodystrophy, osteodystrophy, intellectual disability (mental retardation), and seizures. This finding demonstrates that we have only just scratched the surface of the complicated genetic architecture of human epilepsies. Continue reading