Microcephaly, WDR62, and how to analyze recessive epilepsy families

Success rate. What is in an exome? There are lots of rare and unknown variants that are hard to make sense of unless we can ask a specific question or have further data to limit the number of genes that we look at. Genetic studies in recessive diseases with limited candidate genes to consider might represent one of the most straightforward cases. In a recent paper in BMC Neurology, the genetic cause of a recessive epilepsy/intellectual disability syndrome in a consanguineous family presenting with primary microcephaly was solved using a single exome of an affected individual. Was this just lucky or can this strategy be applied to any recessive family with a reasonable chance? Continue reading

CNTN2 mutations and autosomal recessive cortical myoclonic tremor with epilepsy

Epilepsy & Tremor. The familial occurrence of epileptic seizures and chronic, non-progressive myoclonic tremor represents a peculiar genetic epilepsy syndrome for which the gene still remains elusive. Several families have been reported with autosomal dominant inheritance, and linkage to chromosomes 2, 5 and 8 have been reported. Now, the story regarding this familial syndrome gets even more enigmatic. In a recent paper in Brain, Stogmann and collaborators identify CNTN2 as the causative gene for a recessive form of cortical myoclonic tremor with epilepsy. Continue reading

Exome sequencing corrects diagnosis in autosomal recessive disorders

The amazing powers of exome sequencing – a disclaimer. We have recently blogged frequently on the power of exome sequencing in monogenic disorders. Dixon-Salazar now describe in “Exome Sequencing Can Improve Diagnosis and Alter Patient Management” the usefulness of exome sequencing in disease identification in autosomal recessive disorders. Their overall yield is a novel gene discovery in 22/118 probands and a different diagnosis than the initial in 10/118 patients. While title and abstract suggest that exome sequencing is a cure-all improving patient diagnosis and altering patient management, it should be pointed out that this manuscript exclusively deals with autosomal recessive disorders. Only two novel genes out of 20 are described, leaving the reader with little chance to investigate their claim. Many of their families were selected from countries with a high consanguinity including Morocco, where state-of-the-art diagnostic facilities are difficult to access for some patients. The only change in patient management resulting from the altered diagnosis was stopping supplementary Vitamin E in a family with a SPG11 mutation previously thought to have ataxia with vitamin E deficiency. What the altered direction of therapy in a family with a newly identified a-mannosidase type 1 entails, is left for the reader to imagine. The corresponding reference refers to a paper on stem cell transplant as a definitive treatment option, which will probably not be a treatment option for this family from Islamabad, Pakistan. The paper rather shows that exome sequencing is of use in autosomal recessive disorders and might yield surprises. Continue reading