Chromodomain-helicase-DNA-binding protein 2 is an enzyme that in humans is encoded by the CHD2 gene. [5] [6]
Chromodomain-helicase-DNA-binding protein 2 is an enzyme that in humans is encoded by the CHD2 gene. [5] [6]
The CHD family of proteins is characterized by the presence of chromo (chromatin organization modifier) domains and SNF2-related helicase/ATPase domains. CHD genes alter gene expression possibly by modification of chromatin structure thus altering access of the transcriptional apparatus to its chromosomal DNA template. CHD2 catalyzes the assembly of chromatin into periodic arrays; and the N-terminal region of CHD2, which contains tandem chromodomains, serves an auto-inhibitory role in both the DNA-binding and ATPase activities of CHD2. [7] Alternatively spliced transcript variants encoding distinct isoforms have been found for this gene. [6]
De novo mutations and deletions in this gene have been associated with cases of epileptic encephalopathies. [8] [9] [10] [11] [12]
CHD2 epilepsy is increasingly being identified as a subpopulation of Lennox-Gastaut Syndrome. [13] [14]
CHD2 myoclonic encephalopathy is a condition characterized by recurrent seizures (epilepsy), abnormal brain function (encephalopathy), and intellectual disability. Epilepsy begins in childhood, typically between ages 6 months and 4 years. Each individual may experience a variety of seizure types, most commonly myoclonic seizures. [15]
Recently, de novo mutations or deletions in CHD2 has been linked to intellectual disability [16] and to autism. [17] [18] [19] Researchers found 27 genes which abolish function of the corresponding protein — in at least two people with autism, and 6 genes are mutated in three or more people with autism. These six genes — CHD8, DYRK1A, ANK2, GRIN2B, DSCAM and CHD2 — are the strongest autism candidates identified so far.
Syndromes associated with mutations or deletions in CHD2 can be devastating. Families of individuals with CHD2 mutations or deletions can join the CHD2 research and support group on Facebook [20] or find information and support through the non-profit organization Coalition to Cure CHD2. [21]
Lennox–Gastaut syndrome (LGS) is a complex, rare, and severe childhood-onset epilepsy. It is characterized by multiple and concurrent seizure types, cognitive dysfunction, and slow spike waves on electroencephalogram (EEG). Typically, it presents in children aged 3–5 years and can persist into adulthood. It has been associated with several gene mutations, perinatal injuries, congenital infections, brain tumors/malformations, and genetic disorders such as tuberous sclerosis and West syndrome. The prognosis for LGS is poor with a 5% mortality in childhood and persistent seizures into adulthood (80%–90%).
The heritability of autism is the proportion of differences in expression of autism that can be explained by genetic variation; if the heritability of a condition is high, then the condition is considered to be primarily genetic. Autism has a strong genetic basis, although the genetics of autism are complex and it is unclear whether autism spectrum disorder (ASD) is explained more by multigene interactions or by rare mutations with major effects.
22q13 deletion syndrome, also known as Phelan–McDermid syndrome (PMS), is a genetic disorder caused by deletions or rearrangements on the q terminal end of chromosome 22. Any abnormal genetic variation in the q13 region that presents with significant manifestations (phenotype) typical of a terminal deletion may be diagnosed as 22q13 deletion syndrome. There is disagreement among researchers as to the exact definition of 22q13 deletion syndrome. The Developmental Synaptopathies Consortium defines PMS as being caused by SHANK3 mutations, a definition that appears to exclude terminal deletions. The requirement to include SHANK3 in the definition is supported by many but not by those who first described 22q13 deletion syndrome.
Generalized epilepsy with febrile seizures plus (GEFS+) is a syndromic autosomal dominant disorder where afflicted individuals can exhibit numerous epilepsy phenotypes. GEFS+ can persist beyond early childhood. GEFS+ is also now believed to encompass three other epilepsy disorders: severe myoclonic epilepsy of infancy (SMEI), which is also known as Dravet's syndrome, borderline SMEI (SMEB), and intractable epilepsy of childhood (IEC). There are at least six types of GEFS+, delineated by their causative gene. Known causative gene mutations are in the sodium channel α subunit genes SCN1A, an associated β subunit SCN1B, and in a GABAA receptor γ subunit gene, in GABRG2 and there is another gene related with calcium channel the PCDH19 which is also known as Epilepsy Female with Mental Retardation. Penetrance for this disorder is estimated at approximately 60%.
Dravet syndrome, previously known as severe myoclonic epilepsy of infancy (SMEI), is an autosomal dominant genetic disorder which causes a catastrophic form of epilepsy, with prolonged seizures that are often triggered by hot temperatures or fever. It is very difficult to treat with anticonvulsant medications. It often begins before 1 year of age, with 6 months being the age that seizures, characterized by prolonged convulsions and triggered by fever, usually begin.
CDKL5 is a gene that provides instructions for making a protein called cyclin-dependent kinase-like 5 also known as serine/threonine kinase 9 (STK9) that is essential for normal brain development. Mutations in the gene can cause deficiencies in the protein. The gene regulates neuronal morphology through cytoplasmic signaling and controlling gene expression. The CDKL5 protein acts as a kinase, which is an enzyme that changes the activity of other proteins by adding a cluster of oxygen and phosphorus atoms at specific positions. Researchers are currently working to determine which proteins are targeted by the CDKL5 protein.
Chromodomain-helicase-DNA-binding protein 7 also known as ATP-dependent helicase CHD7 is an enzyme that in humans is encoded by the CHD7 gene.
Gamma-aminobutyric acid receptor subunit beta-3 is a protein that in humans is encoded by the GABRB3 gene. It is located within the 15q12 region in the human genome and spans 250kb. This gene includes 10 exons within its coding region. Due to alternative splicing, the gene codes for many protein isoforms, all being subunits in the GABAA receptor, a ligand-gated ion channel. The beta-3 subunit is expressed at different levels within the cerebral cortex, hippocampus, cerebellum, thalamus, olivary body and piriform cortex of the brain at different points of development and maturity. GABRB3 deficiencies are implicated in many human neurodevelopmental disorders and syndromes such as Angelman syndrome, Prader-Willi syndrome, nonsyndromic orofacial clefts, epilepsy and autism. The effects of methaqualone and etomidate are mediated through GABBR3 positive allosteric modulation.
Nav1.1, also known as the sodium channel, voltage-gated, type I, alpha subunit (SCN1A), is a protein which in humans is encoded by the SCN1A gene.
Synaptic Ras GTPase-activating protein 1, also known as synaptic Ras-GAP 1 or SYNGAP1, is a protein that in humans is encoded by the SYNGAP1 gene. SYNGAP1 is a ras GTPase-activating protein that is critical for the development of cognition and proper synapse function. Mutations in humans can cause intellectual disability, epilepsy, autism and sensory processing deficits.
Chromodomain-helicase-DNA-binding protein 8 is an enzyme that in humans is encoded by the CHD8 gene.
Chromodomain-helicase-DNA-binding protein 9 is an enzyme that in humans is encoded by the CHD9 gene.
Mitochondrially encoded tRNA lysine also known as MT-TK is a transfer RNA which in humans is encoded by the mitochondrial MT-TK gene.
Mitochondrially encoded tRNA proline also known as MT-TP is a transfer RNA that in humans is encoded by the mitochondrial MT-TP gene.
Pitt–Hopkins syndrome (PTHS) is a rare genetic disorder characterized by developmental delay, epilepsy, distinctive facial features, and possible intermittent hyperventilation followed by apnea. As more is learned about Pitt–Hopkins, the developmental spectrum of the disorder is widening, and can also include difficulties with anxiety, autism, ADHD, and sensory disorders. It is associated with an abnormality within chromosome 18; specifically, it is caused by an insufficient expression of the TCF4 gene.
Early myoclonic encephalopathy (EME) is a neonatal-onset epilepsy syndrome with multiple seizure types including myoclonic seizure. The electroencephalographic recording is abnormal with a suppression-burst pattern. On most occasions the seizures are drug-resistant. After several months, the seizure pattern may develop into infantile spasms. The neurological exam is very abnormal with a significant risk of early death. Various genetic and metabolic disorders are responsible. At present, EME and Ohtahara syndrome are recorded as distinct patterns in the categorization of epilepsies. It is a severe types of epilepsy syndrome associated with high level of resistance to treatment and a high risk for cognitive impairment.
People with epilepsy may be classified into different syndromes based on specific clinical features. These features include the age at which seizures begin, the seizure types, and EEG findings, among others. Identifying an epilepsy syndrome is useful as it helps determine the underlying causes as well as deciding what anti-seizure medication should be tried. Epilepsy syndromes are more commonly diagnosed in infants and children. Some examples of epilepsy syndromes include benign rolandic epilepsy, childhood absence epilepsy and juvenile myoclonic epilepsy. Severe syndromes with diffuse brain dysfunction caused, at least partly, by some aspect of epilepsy, are also referred to as epileptic encephalopathies. These are associated with frequent seizures that are resistant to treatment and severe cognitive dysfunction, for instance Lennox-Gastaut syndrome and West syndrome.
SYNGAP1-related intellectual disability is a monogenetic developmental and epileptic encephalopathy that affects the central nervous system. Symptoms include intellectual disability, epilepsy, autism, sensory processing deficits, hypotonia and unstable gait.
17q12 microdeletion syndrome, also known as 17q12 deletion syndrome, is a rare chromosomal anomaly caused by the deletion of a small amount of material from a region in the long arm of chromosome 17. It is typified by deletion of the HNF1B gene, resulting in kidney abnormalities and renal cysts and diabetes syndrome. It also has neurocognitive effects, and has been implicated as a genetic factor for autism and schizophrenia.
Malignant migrating partial seizures of infancy (MMPSI) is a rare epileptic syndrome that onsets before 6 months of age, commonly in the first few weeks of life. Once seizures start, the site of seizure activity repeatedly migrates from one area of the brain to another, with few periods of remission in between. These seizures are 'focal', meaning they do not affect both sides of the brain at the same time. These continuous seizures cause damage to the brain, hence the descriptor 'malignant.'