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An individual's collection of chromosomes. The term also refers to a laboratory technique that produces an image of an individual's chromosomes. The karyotype is used to look for abnormal numbers or structures of chromosomes.



A test to examine chromosomes in a sample of cells, which can help identify genetic problems as the cause of a disorder or disease. This test can:

  • Count the number of chromosomes
  • Look for structural changes in chromosomes

Certain problems can be identified through the number or arrangement of the chromosomes. See also Karyotype.


Ketone or Ketone Bodies

A ketone is an intermediate product of the breakdown of fats in the body; any of three compounds (acetoacetic acid, acetone, and/or beta-hydroxybutyric acid) found in excess in blood and urine of persons with metabolic disorders. Ketones are used as a measure of metabolic instability in patients with propionic acidemia.


A pathological increase in the production of ketone bodies. Ketosis is a stage in metabolism occurring when the liver has been depleted of stored glycogen and switches to a fasting mode such as occurs during sleep, during dieting, and during the body's response to starvation. In propionic acidemia, a measure of metabolic instability.

Laboratory geneticist

A doctoral-level board certified genetic professional who works in a laboratory setting. Generally, a laboratory geneticist works in one specialty area of genetic testing, including cytogenetics, molecular genetics, or biochemical genetics. This person is generally responsible for the interpretation and communication of genetic test results in their area of practice.

Learning disabilities


Learning disabilities are disorders that affect the ability to understand or use spoken or written language, do mathematical calculations, coordinate movements, or direct attention.


Legal guardian

An individual who is authorized under applicable state or local law to consent on behalf of a child to general medical care.





A large vascular organ in the body that causes important changes in substances in the body in order for the body to use these substances.

Low blood pressure

A condition in which blood pressure during and after each heartbeat is much lower than usual, preventing the heart, brain, and other parts of the body from getting enough blood. Also known as hypotension.


An essential amino acid.


Increased head circumference. The measured distance around the widest part of the skull is larger than expected for the child's age and background.


Maternal serum screen

A screening test done at 15 to 20 weeks to detect higher risk of:

  • Chromosomal disorders, including Down syndrome and trisomy 18
  • Neural tube defects, such as spina bifida

Based on test results, your doctor may suggest other tests to diagnose a disorder. See also Quad Screen


Maternal-Fetal Medicine Specialist

Also known as a perinatologist, an OB/GYN physician who has received additional training and specializes in the care of pregnant women who are at higher risk for certain types of complications. These complications can include medical issues, such as diabetes or hypertension, or pregnancy-related issues, such as preeclampsia or multiple gestations, or prenatally diagnosed conditions.

Metabolic Acidosis

Decreased pH and bicarbonate concentration of the body fluids caused either by the accumulation of excess acids stronger than carbonic acid or by abnormal losses of bicarbonate from the body. A metabolic derangement of acid-base balance where the blood pH is abnormally low.

Metabolic Pathway

The sequence by which the chemical changes in living cells provide energy for vital processes in the body.


Any substance produced by metabolic action or necessary for metabolic process. In UCDs and PA, certain metabolites can reach toxic levels, others can be abnormally low.


Amino acid found in most proteins and essential for nutrition. Restricted amino acid for patients with propionic acidemia.

Microarray technology

A developing technology used to study the expression of many genes at once. It involves placing thousands of gene sequences in known locations on a glass slide called a gene chip. A sample containing DNA or RNA is placed in contact with the gene chip. Complementary base pairing between the sample and the gene sequences on the chip produces light that is measured. Areas on the chip producing light identify genes that are expressed in the sample.



A medical condition in which the circumference of the head is smaller than normal because the brain has not developed properly or has stopped growing.




A term that describes an abnormally small lower jaw.



The spontaneous loss of a fetus before the 20th week of pregnancy. (Pregnancy losses after the 20th week are called preterm deliveries.) A miscarriage may also be called a "spontaneous abortion." This refers to naturally occurring events, not to medical abortions or surgical abortions.


Mitochondrial Disorder

Mitochondria, located in the cells, convert oxygen and food into energy. A mitochondrial disorder occurs when this conversion doesn't work properly and can damage or kill blood cells, resulting in systems shutting down. Primary onset in childhood, also sometimes in adults.

MMR (measles, mumps, rubella) vaccine

A vaccination that protects against the measles, mumps and rubella. It is often given to children before they begin school.


A combination of tiny, invisible particles in the body that are bonded together.


When different cells in the same organ or tissue have different genetic make up. For example, some cells carrying a mutation in the OTC gene, while other cells do not.

MRI (magnetic resonance imaging)

A diagnostic radiology technique that uses magnetism, radiowaves, and a computer to produce images of body structures.


An unusual change in genetic material occurring spontaneously or by induction, which changes the original expression (function or purpose) of the gene.


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