GLOSSARY OF TERMS

To help our visitors better understand some of the more clinical sections of this website, we've provided a glossary of terms commonly used in descriptions of some autism research projects funded by the National Alliance for Autism Research as well as in some scientific explanations of autism spectrum disorders.

Allele: A normal variant of a gene. Both the long form and the short form of the serotonin transporter gene are normal variants, or alleles.

Autoregulation: A process whereby biological systems detect changes within, and makes adjustments accordingly.

Axon: A key component of a neuron (nerve cell), consisting of a single fiber, sometimes with branches near its end, which carries impulses from the cell body to other neurons or to effector organs (organs that produce an effect, such as contraction or secretion, in response to nerve stimulation).

Birth Cohort: A group of individuals born in the same year who share a common characteristic.

Brain Stem: One of the oldest parts of the brain in evolutionary terms and the lowest section, serving as a highway for messages between other parts of the brain and the spinal cord. The activities of the brain stem朿ontrol of vital functions, such as breathing and blood pressure朼re largely below the level of consciousness.

Brain Stem Tegmentum: The brain stem tegmentum is a transition zone from the spinal cord to the rest of the brain. Evolutionarily, it is the oldest part of the brain; developmentally it is the first part of the brain to form. Information from many senses杢aste, hearing, balance, plus senses of touch, pain and temperature from the inside and outside of the body enters the brain in the brain stem tegmentum, while motor impulses exit the tegmentum to control the eye muscles, facial muscles, larynx, tongue, and chewing and swallowing muscles. The brain stem tegmentum also controls levels of alertness as well as such basic functions as breathing and heart rate, both essential to survival.

Case-control Study Design: A type of epidemiologic study in which study subjects are selected on the basis of whether they do or do not have the disease being studied. Cases (subjects with the disease) are then compared to controls (study subjects without the disease).

Cerebellum: The "little brain"; sits just above the brain stem. Was previously thought to control movement and coordination, but is now known to be involved in "higher functions" as well, particularly shifting and orienting attention, and predicting and preparing biologically for upcoming movements (e.g., by altering cerebral blood flow levels).

Chromosome: Linear sequence of genes. Human beings have 46 chromosomes, arranged in 23 pairs, one from each parent.

Concordance Rate: The number or percentage of members of a study group that share a common trait, e.g. the number of identical twins in which both twins have autism.

Cytogenic: Producing or forming cells.

Developmental genes: Genes that turn on inside the embryo for a specific period in development, guide the formation of a structure or system, then turn off. Some of these resume activity later in life. They may be active in different regions of the body from those where they are active in development, and they may perform different functions from those served in the embryo. Other developmental genes are permanently inactivated after their brief period of expression in the embryo.

Dominant Gene: An allele (normal gene variant) that is expressed instead of the "recessive" allele for that same trait. In eye color, the allele for brown eyes is dominant over the allele for blue eyes: if you inherit one allele for brown eyes and one allele for blue eyes, you have brown eyes.

Embryogenesis: Formation and growth of the embryo.

Embryology: An embryologist studies development in the womb, and sometimes shortly after birth as well, but especially in the womb. The word "embryo" refers to the growing baby during the first trimester of development; "fetus" is used during the second and third trimesters.

Endoscopic: Performed by means of an endoscope, an instrument for the examination of hollow organs such as the bladder or the intestines.

Epidemiology: The study of the distribution and determinants of diseases in populations.

Etiology: The causes or origin of a disease or disorder.

Eye motility: The movement of the eye by the eye muscles. Eye motility requires an amazingly elaborate system of neural control involving many reflexes (automatic responses) as well as volitional control.

GABA (Gamma-aminobutyric acid): A neurotransmitter involved in anxiety. GABA is an inhibitory neurotransmitter now known to be involved in autism. It is also the neurotransmitter Xanax and Valium affect.

Ganglia: A cluster of neuron cell bodies usually outside the central nervous system.

Gene: The smallest physical unit of heredity. Geneticists estimate that we have 100,000 genes, all of them arranged on the 46 chromosomes. Each gene codes for one or more proteins.

Genotype: An individual's unique arrangement of his or her 100,000 genes.

Hippocampus: A part of the brain that is involved in learning and memory. Margaret Bauman has reported that, in autistic brains, the cells of the hippocampus are small and closely packed杙ossibly implying that they have not fully matured.

Hormone: A term for a chemical signal in the body. Some hormones are proteins (secretin and all of its relatives are proteins). Other hormones are not proteins or peptides at all, but instead are based on carbon rings. The steroid hormones, for example, such as cortisol, are not proteins. Whenever you see the term "hormone" think "signal." In other words the term "hormone" indicates a function rather than a particular structure or chemical content.

Incidence: The number of new cases of disease occurring in a population over a period of time.

Innervation: In the case of muscles, this refers to their connection to nerve cells from the brain or spinal cord that signal the muscle to contract. Muscles deprived of their innervation cannot act. Similarly, skin deprived of its sensory connections to the nervous system sends no messages back. Thus, it is numb.

Motor neurons: The neurons that work the muscles. "Motor neurons" are so called because they are the motor of the muscle.

Macrocephaly: Excessive head size.

Neurogenesis: The development of nervous tissue. Neuron: The technical term for a brain cell (also called "nerve cell").

Neuropeptide: A peptide or polypeptide found in the brain.

Neurotransmitters: Neurotransmitters are chemical substances that nerve cells use to communicate. Parts of the neuron specialized for communication release the neurotransmitter which then affects the activity of another cell杣sually a nerve or muscle cell. Some neurotransmitters are "excitator", causing the next cell to fire, while others are "inhibitory", preventing the next cell from firing. Examples of neurotransmitters are serotonin, dopamine, acetylcholine, GABA and norepinephrine.

Oculomotor: Pertaining to or effecting movements of the eye.

Optokinetic nystagmus: Whenever normal eyes move, they do it in a slightly jerky, rather than completely smooth, motion. This is called nystagmus. The nystagmus that occurs when the eyes are following a moving target is called "optokinetic." Some people with autism appear to have abnormalities of optokinetic nystagmus.

Pathology: The scientific study of the nature of disease, especially of the structural and functional changes in tissues and organs of the body which cause or are caused by disease.

Phenotype: The expression of an individual's genotype杢his is the way the person actually looks and acts because of his or her genes. With HTT, the "genotype" is the tiny biological unit of DNA that makes up the gene; the "phenotype" is a slightly higher level of normal anxiety.

Peptide: A very short string of amino acids. These very short strings are called peptides because whenever two amino acids combine they expel a molecule of water and form a bond called a "peptide bond."

Polypeptide: Refers to more than two amino acids linked together.

Positron Emission Tomography (PET): A method of mapping brain activity in a living person.

Prevalence: The number of existing cases of a disease in a population at a given time.

Promoter: A substance that, in very small amounts, can increase the activity of a catalyst.

Protein: A polypeptide that is long enough to form a 3- dimensional structure. Secretin is a polypeptide with 27 amino acids that coils up into a helix, thus becoming a (very small) protein. The researcher who developed purification schemes for secretin and sequenced its amino acids, Victor Mutt of the Karolinska Institute in Stockholm, called secretin a "mini-protein." (Ironically, Mutt died a few weeks before the DATELINE broadcast.) Glucagon, another member of the secretin family, is also a small protein with a helical structure, and is sometimes called a "minimal protein." The key to the polypeptide/protein distinction is this: once a polypeptide is long enough to develop a 3-dimensional structure it is called a protein.

Purkinje cells: One of two major cell types in the cerebellum. Eighty to 85% of people with autism show a reduction in Purkinje cells.

Recessive Gene: An allele (normal gene variant) that is only expressed when both chromosomes have that allele. For a child to have blue eyes, he or she has to inherit the allele for blue eyes from both parents.

Selective Serotonin Reuptake Inhibitor (SSRI): A medication that blocks the "reuptake" of serotonin back inside the cell that has released it into the synapse. By blocking reuptake, SSRIs increase the amount of serotonin free and available in the synapse. There are currently four SSRI's: Prozac, Zoloft, Paxil, Luvox.

Serotonin: A major neurotransmitter involved in depression and anxiety. A quarter to a third of people with autism show abnormally high levels of serotonin in the blood.

Serotonin Transporter Gene (HTT): A normal gene that is involved in transporting serotonin into the cell. Ed Cook誷 team has found an association between autism and the short form of this gene.

Strabismus: Any deviation of the eyes from normal in position. Strabismus includes crossed eyes, or eyes in which one eye moves more to the side or not to the middle or vice versa. The gaze of the two eyes is not parallel.

Target: A term used by pharmaceutical companies to denote a protein or nucleic acid molecule that can potentially bind a drug molecule. Since the protein or nucleic acid acts as a control or checkpoint in some biochemical cascade, the binding of a candidate drug molecule can influence or modulate the disease-related process of interest. Serotonin reuptake inhibitors, for example, are drugs aimed at modulating the proteins responsible for serotonin transport across cell membranes.