Glossary
ABA
An acronym for applied behavior analysis. ABA is a therapeutic intervention for children with autism and other pervasive developmental disorders.
affected individual
An individual who manifests symptoms of a particular condition.
amniocentesis
The surgical insertion of a hollow needle through the abdominal wall and into the uterus of a pregnant woman to obtain amniotic fluid especially to examine the fetal chromosomes for an abnormality and for the determination of sex.
Angelman syndrome
A developmental disorder that can be caused by deletions of the maternal copy of chromosome 15q11-q13. Characteristic features of this condition include developmental delay or mental retardation, severe speech impairment, seizures, small head size (microcephaly) and problems with movement and balance (ataxia). People with Angelman syndrome typically have a happy, excitable demeanor with frequent smiling, excessive laughter and hand-flapping movements. Some affected individuals also have unusually fair skin and light-colored hair.
ataxia
The shaky and unsteady movements that result from the brain’s failure to regulate the body’s posture and the strength and direction of movements.
ATP10A gene (also referred to as ATP10C)
The ATP10A gene makes a protein that is thought to be involved in moving calcium in and out of cells. It is expressed by the brain and most people with idic(15) chromosomes carry two additional copies of the gene while most children with interstitial duplications have one extra copy.
autism spectrum disorder
Autism spectrum disorder (ASD) is a pervasive developmental disorder characterized by severe deficits in social interaction and communication, by an extremely limited range of activities and interests, and often by the presence of repetitive, stereotyped behaviors. ASD is defined by a certain set of behaviors that can range from the very mild to the severe.
centromere
The constricted region near the center of a human chromosome. This is the region of the chromosome where the p arm and q arm are joined to one another.
chromosome
Chromosomes are the structures that hold our genes. More specifically, chromosomes are long pieces of DNA contained in the nucleus of cells. Chromosomes come in pairs. For most people each cell in their body has 23 pairs of chromosomes (for a total of 46). Each parent contributes one half of each chromosome pair to their child. It is possible to tell the chromosomes apart by their size and their “banding pattern.” The banding pattern is a result of a chemical staining process used in the laboratory to help researchers see the chromosomes more easily. Each chromosome is divided into two sections or “arms.” The short arm is called the “p” arm and the long arm is called the “q” arm. The bands on each arm are numbered. When researchers study the chromosomes (a process called chromosome analysis) they try to determine if there are any missing or extra pieces of the chromosomes.
chromosome 15q11.2-13.1 duplication syndrome
Chromosome 15q11.2-13.1 duplication syndrome (Dup15q) is a clinically identifiable syndrome which results from duplications of chromosome 15q11.2-13.1. These duplications most commonly occur in one of two forms. These include an extra isodicentric 15 chromosome, abbreviated idic(15), or an interstitial duplication 15. When the extra genetic material comes from the paternal chromosome, a child may have normal development. However, when the duplicated material comes from the maternal chromosome, developmental problems are often the result. In most cases of chromosome 15q11.2-13.1 duplication syndrome, the chromosome duplication is not inherited but occurred as a random event during early embroyonic development.
chromosome band
When chromosomes at a particular stage in cell division are stained, using one of several types of preparations, a specific pattern of light and dark stripes (bands) appear which can aid in identifying the chromosome and evaluating its structure.
comparative genomic hybridization (CGH)
A method of examining multiple locations on a chromosome simultaneously to identify genetic imbalance caused by the gain or loss of chromosomal material ranging in size from a whole chromosome to a tiny fraction of a single chromosomal band.
cytogenetics
The study of the structure, function, and abnormalities of human chromosomes.
de novo
A chromosome abnormality that occurred in the individual and was not inherited from the parents.
echolalia
Echolalia is an unconventional verbal behavior that is common among children with autism spectrum disorders. Echolalia occurs when the child repeats verbal information stated by others (e.g., people’s conversational exchanges, videos, books read aloud, songs, etc.).
EEG
An abbreviation for electroencephalogram, a technique for studying the electrical current within the brain. Electrodes are attached to the scalp. Wires attach these electrodes to a machine which records the electrical impulses. The results are either printed out or displayed on a computer screen. Different patterns of electrical impulses can denote various problems in the brain including different forms of epilepsy. Most EEGs see only a moment in time within the brain, and can catch only gross abnormalities in function. An overnight EEG is designed to check the electrical activity in the brain of a sleep-deprived patient, increasing the chance that seizure activity will be revealed. Also available are 24- or 48-hour EEGs, which measure electrical activity over one or two days, usually using mobile EEG units.
epilepsy
Describes a pattern of repeated seizures. Epilepsy occurs when nerve cells in the brain fire electrical impulses at a rate of up to four times higher than normal. This causes a sort of electrical storm in the brain, known as a seizure. Chromosome 15q duplications cause epilepsy in over half of affected individuals. Medication controls seizures for the majority of affected individuals.
FISH
An acronym standing for fluorescence in situ hybridization. FISH is a process which vividly paints chromosomes or portions of chromosomes with fluorescent molecules. This technique is useful for identifying chromosomal abnormalities and gene mapping.
GABA
GABA stands for gamma-amino butyric acid, and it is a neurotransmitter in the brain. Neurotransmitters are used by nerve cells to communicate with other nerve cells. When GABA is released from a nerve cell, it can communicate with another neighboring nerve cell by binding to a protein called the GABAA receptor, which is present on the surface of the neighboring nerve cell. When GABA communicates with other nerve cells, it causes them not to respond to other stimulatory signals in the brain. Thus, GABA is considered an inhibitory neurotransmitter. The overall effect of GABA and GABAA receptors is to stabilize the activity of nerve cells. There are 3 GABA receptor genes in the region that is commonly duplicated in Dup15q syndrome. Many seizure medications target the GABAergc system to try to inhibit seizure activity.
gene
Genes are very small structures inside almost every cell of the body. Genes are the instructions, or blueprints, that tell our body how to grow and develop, build necessary proteins, and thus determine an individual’s characteristics, such as eye color and blood type. It is estimated that there are about 35,000 genes in a human.
genetic counseling
A short-term educational session involving an individual or family, that includes: evaluation to confirm, diagnose, or exclude a genetic condition; discussion of natural history and the role of heredity; identification of medical management issues; calculation and communication of genetic risks; provision of or referral for psychosocial support. Genetic counseling provides patients with information about their condition and helps them make informed decisions.
genotype
The genetic identity of an individual. The genotype describes the genetic makeup of an individual, not the outward characteristics.
genotype-phenotype correlation
The association between the presence of a certain genetic mutations (genotype) and the resulting pattern of abnormalities (phenotype).
hippotherapy
A treatment method involving horses as a means of working on physical, occupational, and speech-language goals. Impairments that can be improved with hippotherapy include: impaired balance responses, coordination, communication, or sensimotor function difficulties; poor postural control; and decreased mobility.
hypertonia
A condition marked by an abnormal increase in muscle tension and a reduced ability of a muscle to stretch.
hypotonia
Decreased tone of skeletal muscles, often described as floppiness. Hypotonia is a common finding in chromosome 15q11.2-13.1 duplication syndrome. Treatment is via physical therapy. In some cases braces may be needed to permit a full range of movement despite hypotonia.
isodicentric 15 [idic(15)]
Isodicentric chromosome 15 is the scientific name for a specific type of chromosome abnormality. Individuals with isodicentric chromosome 15 have 47 chromosomes (sometimes more) instead of the typical 46 chromosomes. The extra chromosome is made up of material from chromosome 15. When the extra genetic material comes from the paternal chromosome, a child may have normal development. However, when the duplicated material comes from the maternal chromosome, developmental problems are often the result. Most commonly, the region called 15q11-q13 is the portion of chromosome 15 duplicated.
interstitial duplication 15 [int dup(15)]
People born without an extra chromosome but who have a segment of duplicated material within chromosome 15 are said to have an interstitial duplication chromosome 15. Most often this is the same section (15q11-13) that makes up the extra chromosome in idic(15). For this reason, people with interstitial duplications of 15q and those with idic(15) share similar characteristics. For both conditions, there is a wide range of severity from one person to the next; as a group however, people with interstitial duplication 15 tend to have milder symptoms than those with idic(15).
karyotype
The chromosomal complement of an individual, including the number of chromosomes and any abnormalities. The term is also used to refer to a photograph of an individual’s chromosomes.
mosaicism or mosaic
The occurrence of two or more cell lines with different genetic or chromosomal constitutions within a single individual.
MRI
A MRI (or magnetic resonance imaging) scan is a radiology technique that uses magnetism, radio waves, and a computer to produce images of body structures. The MRI scanner is a tube surrounded by a giant circular magnet. The patient is placed on a moveable bed which is inserted into the magnet. The magnet creates a strong magnetic field that is combined with a beam of radio waves to produce a faint signal that can be detected by the receiver portion of the MRI scanner. The receiver information is processed by a computer, and an image is then produced. The image and resolution produced by MRI is quite detailed and can detect tiny changes of structures within the body.
p arm
Each chromosomes has a “p” arm and a “q” arm; p (petit) is the short arm of the chromosome. Some of the chromosomes like 13, 14, and 15 have very small p arms. When a karyotype is made the p arm is always shown on the top. The p arm is separated from the q arm by a region known as the centromere, which is a pinched area of the chromosome.
phenotype
The observable traits or characteristics of an individual, for example hair color, weight, or the presence or absence of a condition such as cognitive impairments, autism or seizures.
Prader-Willi/Angelman critical region (PWACR)
The specific portion of a chromosome that, when altered in some way (deleted, duplicated, or otherwise mutated), produces the characteristic set of phenotypic abnormalities associated with a particular syndrome or disorder. The critical region on chromosome 15 is on the q arm and extends from 15q11–13. A maternal deletion of this region will cause Angelman Syndrome, a paternal deletion will cause Prader-Willi Syndrome and a duplication will cause chromosome 15q11.2-13.1 duplication syndrome.
Prader-Willi syndrome
A developmental disorder caused by a deletion of the paternal copy of chromosome 15q11-q13. Prader-Willi Syndrome affects many parts of the body. In infancy, this condition is characterized by weak muscle tone (hypotonia), feeding difficulties, poor growth, and delayed development. Beginning in childhood, affected individuals develop an insatiable appetite and chronic overeating (hyperphagia), obesity, and short stature. People with Prader-Willi syndrome typically also have mental retardation or learning disabilities and behavioral problems. Some affected individuals also have unusually fair skin and light-colored hair.
q arm
Each chromosomes has a “p” arm and a “q” arm; q is the long arm of the chromosome. When a karyotype is made the q arm is always put on the bottom and the p on the top. The arms are separated by a region known as the centromere, which is a pinched area of the chromosome.
ring chromosome
A ring chromosome can happen in two ways. In one instance the ends of the p and q arms break off and then stick to each other. Second, the ends of the p and q arm stick together (fusion), usually without loss of material. However the ring can cause problems when the cell divides and can cause problems for the individual. It is also possible to have a ring and be apparently healthy with no delays in development. As with all chromosome abnormalities it depends on what is actually found, the size of the ring, how much material was lost, which chromosomes are involved etc.
seizure
Uncontrolled electrical activity in the brain, which may produce a physical convulsion, minor physical signs, thought disturbances, or a combination of symptoms. The type of symptoms and seizures depend on where the abnormal electrical activity takes place in the brain, what its cause is, and such factors as an individual’s age and general state of health.
syndrome
The group or recognizable pattern of symptoms or abnormalities that indicate a particular trait or disease. Chromosome 15q11.2-13.1 duplication syndrome was first recognized as a syndrome in the scientific literature in 2005.
UBE3A gene
The UBE3A gene encodes a protein that is involved in degradation of other proteins in the cell. Loss of protein product arising from errors in the gene or deletion of the gene causes Angelman syndrome. UBE3A is expressed by many cells in the body (which actually express both copies of the gene) and nerve cells in the brain, which only use the maternal copy. This gene is present in 4 copies in most children with idic(15) and 3 copies in most patients with interstitial duplications.