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see Chromosomal Microarray

ADHD (Attention deficit hyperactivity disorder)

A behavior disorder originating in childhood in which the essential features are signs of developmentally inappropriate inattention, impulsivity, and hyperactivity. Although most individuals have symptoms of both inattention and hyperactivity-impulsivity, one or the other pattern may be predominant. The disorder is more frequent in males than females. Onset is in childhood. Symptoms often attenuate during late adolescence although a minority experience the full complement of symptoms into mid-adulthood. (From DSM-IV)


Affected individual

Referring to an individual who manifests symptoms of a particular condition.


Alpha-fetoprotein (AFP)

A fetal blood protein present abnormally in adults with some forms of cancer (as of the liver) and normally in the amniotic fluid of pregnant women but with very low levels tending to be associated with Down syndrome in the fetus and very high levels with neural tube defects (as spina bifida) in which the tube remains open.


Amino Acids

When proteins are digested in the diet, amino acids remain - amino acids are either essential (obtained through diet) or non-essential (made by the body from the essential amino acids). Amino acids are the building blocks of proteins, which are formed by linking amino acids together in chains. Amino acids are either essential (must be consumed through the diet) or nonessential (made by the body from the essential amino acids). There are eight essential amino acids and twelve non-essential amino acids.


A by-product of protein metabolism.


A test sometimes done during pregnancy that looks for birth defects and genetic problems in the developing baby. Amniocentesis removes a small amount of fluid from the sac that surrounds the baby in the womb (uterus). It is usually done in a doctor's office or medical center.

The health care provider inserts a long, thin needle through your belly and into the womb. A small amount of fluid (about 4 teaspoons) is removed from the sac surrounding the baby.

The fluid is sent to a laboratory, where:
• Genetic studies are done.
• Levels of alpha-fetoprotein are measured.
• Other tests may be done.



The occurrence of one or more extra or missing chromosomes leading to an unbalanced chromosome complement, or, any chromosome number that is not an exact multiple of the haploid number.


Anion Gap

The difference between the sum of cations and anions found in plasma or serum. The anion gap is used to aid in the differential diagnosis of metabolic acidosis. It is calculated by subtracting the chloride and bicarbonate levels from the sodium plus potassium levels.

Anxiety disorder

A psychological disorder characterized by a persistent and disabling feeling of apprehension or fear.


A non-essential amino acid produced in the normal urea cycle by the transfer of a nitrogen atom from aspartate to citrulline. Pharmaceutical-grade arginine supplementation is used in all the urea cycle disorders except arginase deficiency, which is characterized by high levels of arginine in the blood.

Argininosuccinate lyase (ASL) deficiency

A urea cycle disorder that results in defective cleavage of ASA, leading to an accumulation of ASA in cells and an excessive excretion of ASA in urine (arginosuccinic aciduria).

Argininosuccinate or Argininosuccinic Acid

Arginosuccinic acid (ASA) is an acid formed as an intermediate during the urea cycle in a reaction involving aspartic acid and adenosine triphosphate.

Argininosuccinate synthetase deficiency

A urea cycle disorder that results in accumulation of excessive ammonia and citrulline. Also called Citrullinemia.

array based copy number analysis (aCNA)

see Chromosomal Microarray

array CGH

see Chromosomal Microarray

Ashkenazi Jewish carrier screening

Genetic carrier screening in individuals with ancestors who were born in eastern Europe (Ashkenazi Jewish descent). Certain inherited diseases are more prevalent in individuals of Ashkenazi Jewish descent. Carriers do not have the disease, but are at increased risk to have children with these conditions.


A non-essential amino acid.


An assessment of characteristics (as in weight, measure, or quality).


Showing no symptoms, as in asymptomatic carriers for Ornithine transcarbamylase (OTC) deficiency.


A developmental brain disorder characterized by impaired social interactions, communication problems, and repetitive behaviors. Symptoms usually appear before the age of three. The exact cause of autism is not known, however, it is likely influenced by genetics. Autism is one of a group of related developmental disorders called autism spectrum disorders (ASDs). Other ASDs include Asperger syndrome and Rett syndrome.


Autism spectrum disorders (ASDs)

A group of developmental disabilities that can cause significant social, communication and behavioral challenges. See Autism


Autosomal dominant

A pattern of inheritance characteristic of some genetic diseases. "Autosomal" means that the gene in question is located on one of the numbered, or non-sex, chromosomes. "Dominant" means that a single copy of the disease-associated mutation is enough to cause the disease. This is in contrast to a recessive disorder, where two copies of the mutation are needed to cause the disease. Huntington's disease is a common example of an autosomal dominant genetic disorder.


Autosomal Recessive Inherited Disorder

A characteristic or disorder occurring when an individual receives two copies of a gene for that condition, one from the mother and one from the father.


A chromosome not involved in sex determination. The diploid human genome consists of a total of 46 chromosomes: 22 pairs of autosomes, and 1 pair of sex chromosomes (the X and Y chromosomes).


Balanced rearrangement

A chromosome abnormality caused by a change in the position of chromosomal material between two or more chromosomes. Balanced rearrangements change the chromosomal gene order but do not remove or duplicate any of the DNA of the chromosomes.


Biochemical Pathway

Systems in the body that process molecules for useful purposes.


A vitamin Cofactor for carboxylase enzymes. Essential for metabolism of proteins, carbohydrates and fats.

Bipolar disease/manic depression

A psychiatric disorder marked by mood swings that range from of the lows of depression to the highs of mania, seen at the same time in some cases. Depression brings feelings of sadness, hopelessness and loss of interest in the activities that once brought pleasure. Mania brings a feeing of euphoria and energy, a time of great productivity. Mood shifts may occur only a few times a year, or as often as several times a day. Sometimes referred to as manic-depressive disorder.

Birth defect

A birth defect is a physical difference or abnormality that is present at birth. Birth defects can be caused by genetic mutations, unfavorable environments during pregnancy, or a combination of both. The effect of a birth defect can be mild, severe, or incompatible with life.


Branched Chain Amino Acid (BCAA)

L-Leucine, L-Isoleucine, L-Valine are essential amino acids because humans cannot survive unless they are present in the diet. They are easily converted to ATP, critical to energy and muscle metabolism. They aid in hemoglobin formation, which helps to stabilize blood sugar and lower elevated blood sugar levels. L-Leucine decreases blood sugar and boosts tissue healing, including bone. L-isoleucine is essential for hemoglobin formation and regulates blood sugar and energy levels. L-Valine acts as a natural stimulant and is involved in tissue regeneration and nitrogen balance. In urea cycle disorders, low levels of BCAA can trigger hyperammonemia.

Carbamyl phosphate synthetase deficiency

Also called CPS1 deficiency. A urea cycle disorder resulting from an enzyme deficiency of carbamyl phosphate synthetase. Caused by a mutation in the CPS1 gene.


Cardiomyopathy is a group of chronic disorders affecting the muscle of the heart resulting in impairment of the pumping function of the heart.


This essential fatty acid metabolism cofactor helps to move the fatty acid to the mitochondria from the cytoplasm of the cell.


Individuals carrying an abnormal gene that can be transmitted to their offspring. These individuals do not show evidence of the disorder.


The breakdown of lean muscle mass to obtain amino acids (for growth and development) and energy, resulting from inadequate supply in the diet. Results in excess production of ammonia. Any metabolic process by which organisms convert substances into excreted compounds

Cerebral edema

Accumulation of fluid in the tissues of the brain, ultimately causing coma.

Chromosomal Microarray

A type of genetic test which looks for gains or losses of genetic material (extra or missing pieces) which may impact a person's health or development.



A situation or disease with a long duration.



An amino acid produced from ornithine during the normal urea cycle and subsequently transformed to arginine by the transfer of a nitrogen atom from aspartate. L-citrulline is sometimes used in place of arginine supplementation in OTC deficiency.

Citrullinemia A urea cycle disorder which leads to excessive accumulation of ammonia and other toxins in the blood. Also known as argininosuccinate synthetase deficiency.

Clinical trial

Type of clinical research that follows a pre-defined plan or protocol. By taking part in clinical trials, participants can not only play a more active role in their own health care, but they can also access new treatments and help others by contributing to medical research.



See Copy Number Variation


A Cofactor is any substance that needs to be present in addition to an enzyme to catalyze a certain reaction.

Conduct disorder

A disorder of childhood and adolescence that involves chronic behavioral and emotional problems, characterized by defiant, impulsive, or antisocial behavior.


In genetics, the expectation that genetic material and the information gained from testing that material will not be available without the donor's consent.


Congenital conditions are those present from birth. Birth defects are described as being congenital. They can be caused by a genetic mutation, an unfavorable environment in the uterus, or a combination of both factors. See also Birth defect


Congenital heart defects

Conditions that are present at birth and can affect the structure of a baby's heart and the way it works. They are the most common type of birth defect. As medical care and treatment have advanced, infants with congenital heart defects are living longer and healthier lives. Many now are living into adulthood.



Difficult, incomplete, or infrequent evacuation of dry hardened feces from the bowels. Can cause elevation of ammonia in UCD and PA.

Copy number variation

A copy number variation (CNV) is when the number of copies of a particular gene varies from one individual to the next. Following the completion of the Human Genome Project, it became apparent that the genome experiences gains and losses of genetic material. The extent to which copy number variation contributes to human disease is not yet known. It has long been recognized that some cancers are associated with elevated copy numbers of particular genes.



Recurring or moving in cycles.


The study of the physical appearance of chromosomes.



Area of the cell where most of the chemical actions occur.


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