Welcome to Rare Variant Island

Gamification. Genetic epidemiology is probably one of the driest and most boring fields of genome science that you will encounter. However, there are some basic questions that keep on puzzling me. One of them is about rare variants: if we think of rare variants that are present in patients, but also in controls, how could a combination of rare variants ever fully explain a disease? What are the rules, what are the conditions for such a situation? I happened to play around with R yesterday, and caught by a wave of gaming spirit, I wanted to try and see. I created a virtual population with 1 million people where disease risk is almost fully explained by 300 rare variants – a little genetic SimCity that I will call Rare Variant Island. Follow me through some of the adventures in our new empire and see what happens. Continue reading

Epi25 – breaking the genetic sound barrier

25,000 genomes. The epilepsy community is currently preparing for the largest sequencing project in the epilepsies so far, responding to a call by the National Human Genome Research Institute (NHGRI). If funded, the Epi25 project will allow us to begin sequencing 25,000 individuals with epilepsy, helping us to achieve the next, necessary level for gene discovery in human epilepsies. Here are some of the reasons why we need Epi25 and why you should be part of it. Continue reading

Flickering lights, endophenotypes, and EEG genetics – CHD2 in photosensitivity

Heritable. Many epilepsy syndromes have signature EEG traits, and these traits are thought to have a strong genetic component. The endophenotype concept suggests that using these epilepsy-related traits in genetic studies will facilitate gene discovery, a concept that has failed us so far in epilepsy research, unfortunately. Now, in a recent publication in Brain, we were able to demonstrate that variants in CHD2 predispose to photosensitivity, an abnormal cortical response to flickering light. Finally, after several decades of persisting difficulties, there is some progress in the field of EEG genetics. Continue reading

EFHC1 – retiring an epilepsy gene

The era of gene retirement. As of 2015, the list of epilepsy genes has shrunk by one. EFHC1, a gene initially proposed to be a monogenic cause of Juvenile Myoclonic Epilepsy, is no longer an epilepsy gene. A recent study in Epilepsia finds that EFHC1 variants initially thought to be pathogenic are found in unaffected controls of the same ancestry. Follow us on one of the most perplexing journeys that modern day neurogenetics has to offer, and the retirement of the first epilepsy gene. Continue reading

TADA – a joint analysis of de novo and inherited risk factors in autism

Beyond de novo. One of the most robust ways to interpret exome data is the analysis of de novo mutations. However, in addition to the 1-2 de novo events that we can identify in every individual, there is a plethora of inherited variants that often look suspicious. Unfortunately, other than looking at monogenic recessive disorders, we are often incapable of understanding the importance of these inherited variants and tend to ignore them. A recent publication in Nature now overcomes this difficulty by applying a joint analysis of inherited and de novo variants in autism. Continue reading

The genetic architecture toolkit – modeling polygenic disease with rare variants

Architecture. Even though we often write about novel gene findings in the epilepsies, we assume that most epilepsies are complex genetic or polygenic. Polygenic inheritance suggests the genetic architecture is composed of multiple interacting genetic risk factors, each contributing a small proportion to the disease risk. However, when using the phrase genetic architecture, sometimes I am not quite sure what I actually mean by this. For example, how many genes are needed? This is why I wanted to build a model genetic architecture and explore what happens if we build a genetic disease solely from rare risk variants. Follow me to a brief back-of-the-envelope calculation of how this might work.

Continue reading

A polygenic trickle of rare disruptive variants in schizophrenia

Polygenic. Schizophrenia is a complex neurodevelopmental disorder that is assumed to be caused by a mixture of genetic and non-genetic factors. The genetic component in schizophrenia is thought to be polygenic, i.e. due to the interaction of multiple genetic factors. Rare variants may play a particular role in this presumable polygenic genetic architecture, but so far this component of the genetic morbidity has been hard to pin down. Now, a recent study in Nature explores the role of rare, disruptive mutations in schizophrenia using large-scale population-based exome sequencing. Let’s find out about a new level of exome-wide honesty and why even a gene with 10 disruptive mutations in cases and none in controls is only mentioned in passing. Continue reading

The age of mega-genomics, type 2 diabetes, and protective variants in SLC30A8

Sequence first. There are larger genetic studies but not too many. In a recent study in Nature Genetics, roughly 150,000 individuals were genotyped to assess the importance of rare, disruptive variants in SLC30A8 in type 2 diabetes. This genomic tour de force was made possible by available and curated databases that could be tapped to extract the necessary genetic information. Also, this study highlights some of the surprises that we can expect by mining the human genome for disease-related information. Rare, disruptive variants in SLC30A8 protect against type 2 diabetes. Let’s review why these rare, protective genetic factors might be particularly important for biomedical research and what kind of studies we need to identify them. Continue reading

GPHN deletions in IGE and mutation-dependent recessive inheritance

Bild1Living in Cologne is a little tough at the moment. Currently, we are in the middle of the Cologne Carnival, the world’s oldest carnival, which started in 1829. Until the upcoming Wednesday the entire city is one big festival. In addition to the 1 million Cologne citizens probably another million tourists will join. Due to this (positive) distraction I will write less than usual. However, I still consider this week’s publications noteworthy. Continue reading

Papers of the week – Encephalitis-antibodies, FAN1, Art and Parent-of-Origin Effects

Dennis' paper of the week

Biggest surprise this week: Imprinted genes interact with non-imprinted genes frequently. But first sequencing reports, statistical frameworks for rare variants analyzes and an impressive translational result.

A novel encephalitis with seizures and the analysis of the effects of antibodies. In their study published in LANCET NEUROLOGY Petit-Pedrol and coworkers characterized serum and CSF samples for antigens in 140 patients with encephalitis, seizures or status epilepticus as well as antibodies to unknown neurophil antigens. High titres of serum and CSF GABAA receptor antibodies are reported to be associated with a severe form of encephalitis with seizures, refractory status epilepticus, or both, which could be exploited for immunotherapy with 15 patients.

Continue reading