Clinical and molecular genetic aspects of idiopathic epilepsies

The epilepsies are a heterogenic group of common neurological disorders,
affecting about 3% of the population at some point in their lives. Epilepsy can
be caused by structural or metabolic brain defects, but more than 40 % of
epilepsy patients have no underlying aetiology except for a genetic
predisposition. These *idiopathic* epilepsy syndromes often have a complex
inheritance pattern. In most cases several genetic factors, together with
environmental factors, influence the development of the epileptic phenotype.
Some cases are inherited in a Mendelian way in which case a mutation in 1 gene
is responsible for the epileptic phenotype.
Careful clinical study of individuals and families combined with the powerful
techniques of molecular genetic analyses has led to major breakthroughs in our
understanding of epilepsy, particularly of the idiopathic variants. Initially
the most significant advances in the domain of genetics of epilepsy have been
made in extended multiplex families with autosomal dominant inheritance of the
epileptic phenotype. However, recent technological advances have opened novel
avenues to study patients with a presumably idiopathic form of epilepsy who
lack a family history of similarly affected individuals. These patients often
have a severe form of epilepsy that is difficult to control and often mental
deterioration occurs leading to an epileptic encephalopathy. These catastrophic
forms of epilepsy put a large burden on the well-being of the child and the
family. Apart from the care of the affected child, parents are often confronted
with the uncertainty about the recurrence risk in case of later pregnancies.
To date about 40 loci and causal mutations in 15 genes have been identified for
inherited forms of epilepsy but these findings only explain the epilepsy in a
minority of idiopathic epilepsy patients underscoring the huge genetic
heterogeneity of the idiopathic epilepsies and the urgent need for additional
studies.

(1) Identification of novel loci and genes in which mutations are responsible
for the development of inherited epileptic syndromes.
(2) Establishing genotype-phenotype correlations; defining the yield of
mutation screenings in specific patient cohorts; drawing guidelines for
diagnostic mutation screening in the Dutch population of idiopathic epilepsy
patients with a focus on severe idiopathic epilepsies with early onset.

To achieve this a collaboration will be started between the clinical team of
the epilepsy centre Kempenhaeghe in the Netherlands (head of research Prof. P.
Boon) and the research team of Neurogenetics of Prof. P. De Jonghe of the
University of Antwerp in Belgium.


Collaboration is planned with het group of child neurologists of the azM
Maastricht and the Neurogenetics group of Prof. D. Lindhout of the UMC Utrecht.
When these collaborations will be formalized, an amendment will be submitted.

A. Collecting and clinical characterization of patient material
Blood samples and clinical data of Dutch families followed in Kempenhaeghe will
be collected prospectively. Special attention will be dedicated to the
collection of multiplex families, but also to smaller nuclear families with
variable phenotypes for project B (cfr. infra) or to isolated patient with
idiopathic epilepsies for project C (cfr. infra). To every patient or, in case
of children or mentally retarded patients, to their legal representative
informed consent will be asked and signed. Patients will always be allowed
minimal two weeks of time to decide about their collaboration to the study.
In the research lab of Neurogenetics in Antwerp DNA samples of Belgian patients
with idiopathic epilepsy have been collected during the last few years.
Relevant samples will be selected for this project, and additional patients
from Belgium will be included.

B. identification of new loci: delineation of candidate regions and gene
identification
This part will be done in the first place in big muliplex families with an
epileptic phenotype that has a Mendelian inheritance. Within the epilepsy
centre of Kempenhaeghe such families will be recruted, clinically described and
blood will be drawn for analysis. Secondly in the Neurogenetics group of Prof.
De Jonghe and in international literature several loci for epilepsy have been
described in families. Often these are private loci that until now only have
been described in a single family. To confirm these loci and to make them
smaller so that the amount of positional en functional candidate genes is
reduced, it's necessary that additional families are found that also link to
these loci.
Besides the classical linkage analyses we will also perform Comparative Genome
Hybridization (CGH) in patients with complex phenotypes in which epilepsy is an
important part. The underlying hypothesis is that deletions and duplications of
chromosomal regions with dosage-sensitive genes can be responsible for such
complex disease phenotypes. For this subproject we will select patients with a
combination of epilepsy, dysmorphia and mental retardation.

C. Mutation analysis in known epilepsy genes.
The analysis of mutations in known epilepsy genes will focus in this project on
severe idiopathic epilepsies with early onset. In this population we will
screen for STXBP1 (recently described in ohtahara syndrome), KCNQ2 and SCN2A
mutation (responsible for BFNS and BFNIS, but apparently also present in
atypical early onset epilepsy syndromes).
Performing these mutation analyses in cohorts of patients with a phenotype
similar to the patients in which the gene was originally described will give us
an idea of the relative frequency of these mutations. These data will make it
possible to say something about the usefulness of diagnostic screening of this
gene. The mutation analysis will also be extended to a broader phenotype to see
if mutations in these genes are also responsible for other epileptic syndromes.
Finally we will screen for GLUT1-transporter mutations in patients on a
ketogenic diet with epilepsy of unknown origin. The hypothesis is that in the
group of patients that respond well several patients carry a mutation in this
gene.

For this research project 1 blood sample has to be taken. Where possible this
will be done at the moment an already planned blood test is done, so that this
is actually not an extra procedure.
Performing a blood test can be unpleasant because it involves a puncture with a
needle. There is a small risk of a hematome. There exists also a risk that
participating in this study causes concerns about the heritability of the
disease. If this is the fact the patient can contact the investigator who can
refer the patient to a geneticist.

Minors and incapacitated adults will also be included in the study. This is
necessary because:
1. In a very big subset of patients with a severe early onset epileptic
encephalopathy a genetic cause is suspected. Especially in this group the
detection of an underlying genetic cause is important. This are patients in
which genetic counselling (recurrence risk in siblings) is very important for
parents. Furthermore a genetic diagnose makes that no more unnecessary
investigations are planned, and that parents can be informed about prognosis.
These patients often do not reach the adult age, and for this this study has to
be done in minors.
2. Part of this study will be done with the technique CGH( comparitive genome
hybridization) in which deletions/duplications are detected in patients with a
"contiguous gene syndrome". These patients have a complex phenotype, consisting
of mental retardation, dysmorphia and, in case of this study, epilepsy.