Double Blind Crossover Trial of Ganaxolone in Patients with Fragile X Syndrome
$90,000 in 2014-2015
Previous FRAXA Awards:
$45,000 in 2010
$100,000 in 2007-8
$65,000 in 1999-2000
Clinical Trial Plan
with Anke Van Dijck, MD
We are conducting a double blind crossover trial to investigate whether ganaxolone can ameliorate clinical symptoms of patients with fragile X syndrome. In a crossover trial, each patient acts as his own control, receiving placebo for part of the trial, and active drug during a different part of the trial. This clinical trial will include 30 patients with fragile X syndrome in Antwerp, Belgium, and is expected to be complete within two years.
GABA A in Fragile X
Proper function of the nervous system requires both excitatory neurons and counterbalancing inhibitory neurons. Glutamate is the major excitatory neurotransmitter in the brain, and fragile X is closely associated with abnormalities at metabotropic glutamate receptors (mGluRs). However, inhibition is also clearly abnormal.
GABA-A receptors, the main inhibitory receptors in the brain, are implicated in processes disturbed in fragile X patients, including excessive neuronal excitability, leading to enhanced seizures susceptibility, anxiety, sleep, and learning and memory problems. The Kooy lab is studying the function of GABA (gamma-amino butyric acid) in fragile X, with a goal of developing treatments based on enhancement of inhibitory neurotransmission.
The Kooy lab previously showed that part of the clinical symptoms of the fragile X syndrome is due to a dysfunctional GABAergic system. Subsequent experiments showed that drugs that restore the GABAergic function can reduce symptoms of the disorder in animal models.
Ganaxolone is an investigational new drug under development by Marinus Pharmaceuticals and is one of a new class of drugs known as neurosteroids. It is a positive modulator of the GABA-A receptor and thus it can enhance the GABA neurotransmitter system, which studies have shown to be underactive in Fragile X. Ganaxolone is a synthetic neuroactive steroid related to allopregnanolone that has sedative, anxiolytic, and anticonvulsant effects. It is a potent and selective positive allosteric modulator of GABAA receptors. Ganaxolone protects against seizures in diverse animal models, including the pentylenetetrazol, 6 Hz and amygdala kindling models. Unlike for benzodiazepines, there is no tolerance to the anticonvulsant effects of ganaxolone.
Ganaxolone is being investigated for potential medical use in the treatment of epilepsy. It is well tolerated in human trials (with exposure of >900 patients), with the main side-effects being sedation, dizziness, and headache. Trials in adults with partial seizures and in infantile spasms have recently been completed. See http://en.wikipedia.org/wiki/Ganaxolone
Earlier Studies of the GABA A Receptor in Fragile X
by Frank Kooy, 4/1/2010
In previous studies we showed that the amount of GABAA receptors is significantly decreased in fragile X animal models and that this receptor is a suitable target for treatment. However, before drugs can be tested on human patients, the abnormalities of the GABAergic system observed in animal models need to be verified in human patients. Therefore, we propose to perform position emission tomography (PET), a functional imaging technology that is able to provide non-invasive in vivo assessment and quantification of GABAA receptor binding through injections of labelled flumazenil. A difference in GABAA receptor distribution between fragile X patients and controls will enforce our hypothesis that a dysfunction of the GABAergic system is responsible for the neurologic and behavioural problems seen in fragile X patients. Our research will thus strongly encourage drug trials on fragile X patients.
Background on the GABA A Receptor
by Frank Kooy, 9/30/2008
Absence of a single protein, FMRP, in fragile X patients leads to a cascade of molecular events in brain cells. To find out which other genes are involved the clinical symptoms, we have been looking for genes that are differentially expressed in fragile X syndrome. One of the genes specifically underexpressed is part of the GABAA receptor. As GABAA receptors are the main inhibitory receptors in the brain, involved in processes like anxiety, mood swings, sleep and cognition, processes also disturbed in fragile X patients, we followed up on this finding. In subsequent studies, we demonstrated abnormalities in expression levels of multiple parts of the GABAA receptor, both in the mouse model and in the fly model, indicating underexpression is an evolutionary conserved hallmark of fragile X syndrome. Our case for involvement of the GABAergic system in fragile X is supported by independent findings from other groups.
The purpose of this grant is twofold: first, we want to understand why and how absence of the fragile X protein results in underexpression of the GABA system. Second, we want to investigate whether drugs that work on the GABA system are able to influence the phenotype of the fragile X mouse model.
During the first year of our study, we analyzed the relative expression of many genes that are responsible for GABA synthesis, transport, clustering and degradation. Essentially all of these genes were under expressed in the fragile X syndrome, strengthening our hypothesis that the entire GABA system is down regulated in the disorder. In current animal experiments, we are now investigating whether drugs that reactivate the GABA system are able to correct some of the symptoms observed in patients, including epilepsy, hyper activity and anxiety. In initial experiments, we already verified that GABAergic drugs such as the neurosteroid alphaxolone are still effective in the knockout mice.
A second breakthrough in the first year of this project was the observation that the GABA receptor mRNAs that are down regulated are a part of the FMRP-mRNP complex. This means that FMRP binds GABA RNAs, possibly explaining why the GABAergic system is down regulated in fragile X syndrome. Planned experiments will follow up on this finding and aim to unravel the precise mechanism of GABAergic down regulation.