Chromosome 15q partial deletion is a rare human genetic disorder, caused by a chromosomal aberration in which the long ("q") arm of one copy of chromosome 15 is deleted, or partially deleted. Like other chromosomal disorders, this increases the risk of birth defects, developmental delay and learning difficulties, however, the problems that can develop depend very much on what genetic material is missing. If the mother's copy of the chromosomal region 15q11-13 is deleted, Angelman syndrome (AS) can result. The sister syndrome Prader-Willi syndrome (PWS) can result if the father's copy of the chromosomal region 15q11-13 is deleted. The smallest observed region that can result in these syndromes when deleted is therefore called the PWS/AS critical region. In addition to deletions, uniparental disomy of chromosome 15 also gives rise to the same genetic disorders, indicating that genomic imprinting must occur in this region.
A small supernumerary marker chromosome (sSMC) is an abnormal extra chromosome. It contains copies of parts of one or more normal chromosomes and like normal chromosomes is located in the cell's nucleus, is replicated and distributed into each daughter cell during cell division, and typically has genes which may be expressed. However, it may also be active in causing birth defects and neoplasms. The sSMC's small size makes it virtually undetectable using classical cytogenetic methods: the far larger DNA and gene content of the cell's normal chromosomes obscures those of the sSMC. Newer molecular techniques such as fluorescence in situ hybridization, next generation sequencing, comparative genomic hybridization, and highly specialized cytogenetic G banding analyses are required to study it. Using these methods, the DNA sequences and genes in sSMCs are identified and help define as well as explain any effect(s) it may have on individuals.
Beta waves, or beta rhythm, are neural oscillations (brainwaves) in the brain with a frequency range of between 12.5 and 30 Hz. Several different rhythms coexist, with some being inhibitory and others excitory in function.
Chromosome 15 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 15 spans about 99.7 million base pairs and represents between 3% and 3.5% of the total DNA in cells. Chromosome 15 is an acrocentric chromosome, with a very small short arm, which contains few protein coding genes among its 19 million base pairs. It has a larger long arm that is gene rich, spanning about 83 million base pairs.
Epileptic spasms is an uncommon-to-rare epileptic disorder in infants, children and adults. One of the other names of the disorder, West syndrome, is in memory of the English physician, William James West (1793–1848), who first described it in an article published in The Lancet in 1841. The original case actually described his own son, James Edwin West (1840–1860). Other names for it are "generalized flexion epilepsy", "infantile epileptic encephalopathy", "infantile myoclonic encephalopathy", "jackknife convulsions", "massive myoclonia" and "Salaam spasms". The term "infantile spasms" can be used to describe the specific seizure manifestation in the syndrome, but is also used as a synonym for the syndrome itself. West syndrome in modern usage is the triad of infantile spasms, a pathognomonic EEG pattern, and developmental regression – although the international definition requires only two out of these three elements.
22q13 deletion syndrome, 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.
Juvenile myoclonic epilepsy (JME), also known as Janz syndrome or impulsive petit mal, is a form of hereditary, idiopathic generalized epilepsy, representing 5–10% of all epilepsy cases. Typically it first presents between the ages of 12 and 18 with myoclonic seizures. These events typically occur after awakening from sleep, during the evening or when sleep-deprived. JME is also characterized by generalized tonic–clonic seizures, and a minority of patients have absence seizures. It was first described by Théodore Herpin in 1857. Understanding of the genetics of JME has been rapidly evolving since the 1990s, and over 20 chromosomal loci and multiple genes have been identified. Given the genetic and clinical heterogeneity of JME some authors have suggested that it should be thought of as a spectrum disorder.
Ring chromosome 20, ring-shaped chromosome 20 or r(20) syndrome is a rare human chromosome abnormality where the two arms of chromosome 20 fuse to form a ring chromosome. The syndrome is associated with epileptic seizures, behaviour disorders and intellectual disability.
Isodicentric 15, also called marker chromosome 15 syndrome, idic(15), partial tetrasomy 15q, or inverted duplication 15, is a chromosome abnormality in which a child is born with extra genetic material from chromosome 15. People with idic(15) are typically born with 47 chromosomes in their body cells, instead of the normal 46. The extra chromosome, which is classified as a small supernumerary marker chromosome, is made up of a piece of chromosome 15 that has been duplicated end-to-end like a mirror image. It is the presence of this extra genetic material that is thought to account for the symptoms seen in some people with idic(15). Individuals with idic(15) have a total of four copies of this chromosome 15 region instead of the usual two copies. The term isodicentric refers to a duplication and inversion of a centromere-containing chromosomal segment.
In molecular biology, SNORD115 is a non-coding RNA (ncRNA) molecule known as a small nucleolar RNA which usually functions in guiding the modification of other non-coding RNAs. This type of modifying RNA is usually located in the nucleolus of the eukaryotic cell which is a major site of snRNA biogenesis. HBII-52 refers to the human gene, whereas RBII-52 is used for the rat gene and MBII-52 is used for naming the mouse gene.
Neurexins (NRXN) are a family of presynaptic cell adhesion proteins that have roles in connecting neurons at the synapse. They are located mostly on the presynaptic membrane and contain a single transmembrane domain. The extracellular domain interacts with proteins in the synaptic cleft, most notably neuroligin, while the intracellular cytoplasmic portion interacts with proteins associated with exocytosis. Neurexin and neuroligin "shake hands," resulting in the connection between the two neurons and the production of a synapse. Neurexins mediate signaling across the synapse, and influence the properties of neural networks by synapse specificity. Neurexins were discovered as receptors for α-latrotoxin, a vertebrate-specific toxin in black widow spider venom that binds to presynaptic receptors and induces massive neurotransmitter release. In humans, alterations in genes encoding neurexins are implicated in autism and other cognitive diseases, such as Tourette syndrome and schizophrenia.
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.
The GABAA beta-2 subunit is a protein that in humans is encoded by the GABRB2 gene. It combines with other subunits to form the ionotropic GABAA receptors. GABA system is the major inhibitory system in the brain, and its dominant GABAA receptor subtype is composed of α1, β2, and γ2 subunits with the stoichiometry of 2:2:1, which accounts for 43% of all GABAA receptors. Alternative splicing of the GABRB2 gene leads at least to four isoforms, viz. β2-long (β2L) and β2-short. Alternatively spliced variants displayed similar but non-identical electrophysiological properties. GABRB2 is subjected to positive selection and known to be both an alternative splicing and a recombination hotspot; it is regulated via epigenetic regulation including imprinting and gene and promoter methylation GABRB2 has been associated with a number of neuropsychiatric disorders, and found to display altered expression in cancer.
Gamma-aminobutyric acid (GABA) A receptor, alpha 5, also known as GABRA5, is a protein which in humans is encoded by the GABRA5 gene.
GABAA receptor-γ3, also known as GABRG3, is a protein which in humans is encoded by the GABRG3 gene.
Angelman syndrome (AS) is a genetic disorder that mainly affects the nervous system. Symptoms include a small head and a specific facial appearance, severe intellectual disability, developmental disability, limited to no functional speech, balance and movement problems, seizures, and sleep problems. Children usually have a happy personality and have a particular interest in water. The symptoms generally become noticeable by one year of age.
Autism spectrum disorder (ASD) refers to a variety of conditions typically identified by challenges with social skills, communication, speech, and repetitive sensory-motor behaviors. The 11th International Classification of Diseases (ICD-11), released in January 2021, characterizes ASD by the associated deficits in the ability to initiate and sustain two-way social communication and restricted or repetitive behavior unusual for the individual's age or situation. Although linked with early childhood, the symptoms can appear later as well. Symptoms can be detected before the age of two and experienced practitioners can give a reliable diagnosis by that age. However, official diagnosis may not occur until much older, even well into adulthood. There is a large degree of variation in how much support a person with ASD needs in day-to-day life. This can be classified by a further diagnosis of ASD level 1, level 2, or level 3. Of these, ASD level 3 describes people requiring very substantial support and who experience more severe symptoms. ASD-related deficits in nonverbal and verbal social skills can result in impediments in personal, family, social, educational, and occupational situations. This disorder tends to have a strong correlation with genetics along with other factors. More research is identifying ways in which epigenetics is linked to autism. Epigenetics generally refers to the ways in which chromatin structure is altered to affect gene expression. Mechanisms such as cytosine regulation and post-translational modifications of histones. Of the 215 genes contributing, to some extent in ASD, 42 have been found to be involved in epigenetic modification of gene expression. Some examples of ASD signs are specific or repeated behaviors, enhanced sensitivity to materials, being upset by changes in routine, appearing to show reduced interest in others, avoiding eye contact and limitations in social situations, as well as verbal communication. When social interaction becomes more important, some whose condition might have been overlooked suffer social and other exclusion and are more likely to have coexisting mental and physical conditions. Long-term problems include difficulties in daily living such as managing schedules, hypersensitivities, initiating and sustaining relationships, and maintaining jobs.
Chromosomal deletion syndromes result from deletion of parts of chromosomes. Depending on the location, size, and whom the deletion is inherited from, there are a few known different variations of chromosome deletions. Chromosomal deletion syndromes typically involve larger deletions that are visible using karyotyping techniques. Smaller deletions result in Microdeletion syndrome, which are detected using fluorescence in situ hybridization (FISH)
CDKL5 deficiency disorder (CDD) is a rare genetic disorder caused by pathogenic variants in the gene CDKL5.
Syndromic autism denotes cases of autism spectrum disorder that are associated with a broader medical condition, generally a syndrome. Cases without such association, which account for the majority of total autism cases, are known as non-syndromic autism.
