Angelman syndrome (AS) is a neurodevelopmental disorder characterized by severe intellectual and developmental disability, sleep disturbance, seizures, jerky movements (especially hand-flapping), frequent laughter or smiling, and usually a happy demeanor.
AS is a classic example of genomic imprinting in that it is caused by deletion or inactivation of genes on the maternally inherited chromosome 15 while the paternal copy, which may be of normal sequence, is imprinted and therefore silenced. The sister syndrome, Prader–Willi syndrome, is caused by a similar loss of paternally inherited genes and maternal imprinting.
AS is named after a British pediatrician, Harry Angelman, who first described the syndrome in 1965. An older, alternative term for AS, “happy puppet syndrome”, is generally considered pejorative and stigmatizing so it is no longer the accepted term. People with AS are sometimes referred to as “angels”, both because of the syndrome’s name and because of their youthful, happy appearance.
Amit Rakhit, MD, Chief Medical and Portfolio Officer at Ovid Therapeutics, discusses OV101, a compound that was originally developed to treat insomnia, but is now being studed in Angelman and Fragile X syndromes. OV101 (gaboxadol) is believed to be the only delta (δ)-selective GABAA receptor agonist in development and the first investigational drug to specifically target the disruption of tonic inhibition that is thought to be the underlying cause of certain neurodevelopmental disorders.
OV101 has been demonstrated in laboratory studies and animal models to selectively activate the δ-subunit of GABAA receptors, which are found in the extrasynaptic space (outside of the synapse), and thereby impact neuronal activity through tonic inhibition.
Ovid is developing OV101 for the treatment of Angelman syndrome and Fragile X syndrome to potentially restore tonic inhibition and relieve several of the symptoms of these disorders. In preclinical studies, it was observed that OV101 improved symptoms of Angelman syndrome and Fragile X syndrome. To date, gaboxadol has been tested in over 4,000 patients (approximately 950 patient-years of exposure) and was observed to have favorable safety and bioavailability profiles. The FDA granted orphan drug designation for OV101 for the treatment of both Angelman syndrome and Fragile X syndrome. The United States Patent and Trademark Office has granted Ovid two patents directed to methods of treating Angelman syndrome using OV101.
The issued patents expire in 2035, without regulatory extensions. Fragile X syndrome is the most common inherited form of intellectual disability and autism, with a prevalence of 1 in 3,600 to 4,000 males and 1 in 4,000 to 6,000 females in the United States. Individuals with Fragile X syndrome often have a range of behavioral challenges, such as cognitive impairment, anxiety, mood swings, hyperactivity, attention deficit, poor sleep, self-injury and heightened sensitivity to various stimuli, such as sound. Additionally, individuals with Fragile X syndrome are prone to comorbid medical issues including seizures and sleep disturbance. Fragile X syndrome results from mutations in the FMR1 gene, which blocks expression of the Fragile X Mental Retardation Protein (FMRP), an important protein in GABA synthesis.
There are no FDA-approved therapies for Fragile X syndrome, and treatment primarily consists of behavioral interventions and pharmacologic management of symptoms. In studies of individuals with Fragile X syndrome and in experimental models, extrasynaptic GABA levels are abnormally reduced, and there is also dysregulation of GABA receptors. This ultimately contributes to a decrease in tonic inhibition, causing the brain to become inundated with signals and lose the ability to separate background noise from critical information.