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A coenzyme that assists in processing the first step of the urea cycle and activates carbamoyl phosphate synthetase 1.

Nasogastric (NG) tube

A flexible tube that is passed through the nose and down through the nasopharynx and esophagus into the stomach. It can be used to remove the contents of the stomach, including air, small objects and fluid. It can also be used to place contents into the stomach, such as nutrients.

Natural history

The progression of a disease process in an individual over time, in the absence of treatment.

Neonatal-onset disorder

Severe, catastrophic disorder with life-threatening symptoms occurring in the neonatal period resulting from null/zero enzyme mutations or severely impaired enzyme activity.

Neural Tube Defects

Neural tube defects are birth defects that can occur early in pregnancy when the spinal cord, brain, and related structures do not form properly. Several types of neural tube defects exist, including spina bifida and anencephaly (having little or no brain matter). Also known as NTDs.



An abnormal decrease in the number of neutrophils in the blood.

Newborn screening

Testing performed on newborn babies to detect a wide variety of disorders. Typically, testing is performed on a blood sample obtained from a heel prick when the baby is two or three days old. In the United States, newborn screening is mandatory for several different genetic disorders, though the exact set of required tests differs from state to state.


NICU (Neonatal Intensive Care Unit)

A specialized department in a hospital that provides intensive-care medicine to newborns.

Night terrors

Night terrors are episodes of fear, flailing and screaming while asleep. Night terrors often are paired with sleepwalking.


An atmospheric gas that forms many compounds in the body (such as proteins) and is a component of all living cells.

Non-invasive prenatal screening (NIPS)

Also known as Non-invasive prenatal testing (NIPT). NIPS is a screening test offered during pregnancy that screens for a limited number of genetic conditions. The technology is different than tradition prenatal screening tests, like maternal serum screening or ultrasound screening because it uses cell–free DNA found in the mother’s blood to test for specific chromosome changes in the fetus.

Non-invasive prenatal testing (NIPT)

See Non-invasive prenatal screening (NIPS)

Non-verbal learning disability

A learning disorder characterized primarily by challenges in processing non-verbal information while verbal skills are normal.


See Neural Tube Defects

Nuchal translucency screening

This screening measures the thickness of the back of the fetus’s neck between 11 and 14 weeks. This information, combined with the mother’s age and the results of the serum screen, helps health care providers determine the fetus’s potential risk for chromosomal abnormalities and other problems. Also known as NT measurement.


Obsessive compulsive disorder (OCD)

Anxiety disorder consisting of obsessions (repeated, upsetting, unwanted thoughts) and compulsions (repeated activities that bring no pleasure and are not productive, but are meant to make the unwanted thoughts go away)


Obstetrics focuses on care of women during pregnancy, childbirth, and the recuperative period following delivery.


Odd Chain Fatty Acid

Fatty acids with an odd number of carbon atoms.

Oppositional defiant disorder

A compulsive pattern of disobedient, hostile, & defiant behaviors towards authority figures.

Oral medication

Medication taken by mouth.

Organic Acidemia

Inherited disorders of amino acid catabolism in which toxic substances are produced as a result of an enzymatic blockage.


Functions in the urea cycle and acts to change citrulline to arginine.

Ornithine transcarbamylase deficiency

Also called OTC deficiency. A urea cycle disorder resulting from an enzyme deficiency of ornithine transcarbamylase.


The roof of the mouth


Panel gene test

Genetic testing that usually targets a specific disease by testing for multiple genes at once known to be associated with that condition (example, breast or colon cancer). The test helps to determine disease-causing mutations in conditions that can have several different genetic causes.

Partial Activity

Not completely active, may be missing vital components.

Patent Ductus Arteriosis

See Ductus Arteriosis

PCV (pneumococcal conjugate) vaccine

An immunization that protects against a type of bacteria that is a common cause of pneumonia and ear infections. This type of bacteria can also cause more serious illnesses, such as meningitis and bacteremia (infection in the blood stream). Infants and toddlers are given 4 doses of the vaccine. The vaccine may also be used in older children who are at risk for pneumococcal infection.


See Ductus Arteriosis


The probability (likelihood) of a trait, feature, or disease being present in an individual with a genetic predisposition. Complete penetrance means the trait, feature, or disease is always present in all individuals with a given genetic variant. Incomplete penetrance means the trait, feature, or disease is present in some individuals but not all. The penetrance of a trait, feature, or disease may increase with age for some genetic disorders.


See Maternal-Fetal Medicine Specialist

Pervasive Developmental Disorder (PDD)

Refers to a group of disorders characterized by delays in the development of socialization and communication skills, including Asperger's, Rett's and Autism among others.


The complete observable characteristics of a group, including anatomical, physiological, and biochemical traits as determined by genetic makeup.


Normally formed from phenylacetate and glutamine and excreted in the urine.


The midline groove in the upper lip that runs from the top of the lip to the nose. The way the philtrum appears is determined genetically. In some syndromes, this groove is shortened.



The organ that nourishes the developing fetus in the uterus.



Liquid part of the blood in which blood cells are suspended.

Preconception Care

The care a woman gets before she becomes pregnant.



Pregnancy is a period of up to 41 weeks typically in which a woman carries a fetus inside of her.


Pregnancy Loss

Pregnancy loss or miscarriage is the spontaneous loss of a fetus before the 20th week of pregnancy.


Pregnancy ultrasound

An imaging test that uses sound waves to see how a baby is developing in the womb. It is also used to check the female pelvic organs during pregnancy. A pregnancy ultrasound may be done in the first trimester to:

  • Confirm a normal pregnancy
  • Determine the baby's age
  • Look for problems, such as ectopic pregnancies or the chances for a miscarriage
  • Determine the baby's heart rate
  • Look for multiple pregnancies (twins, triplets, etc.)
  • Identify problems of the placenta, uterus, cervix, and ovaries

A pregnancy ultrasound may also be done in the second and third trimesters to:

  • Determine the baby's age, growth, position, and sometimes gender
  • Identify any developmental problems
  • Look for multiple pregnancies (twins, triplets, etc.)
  • Look at the placenta, amniotic fluid, and pelvis



Before birth.

Prenatal care

The care a woman gets during pregnancy. Early and regular prenatal visits with a health care provider are important for the health of both the mother and the fetus.


Prenatal Tests

Tests used during pregnancy to check your and your baby's health. These tests may include but are not limited to amniocentesis, ultrasound exam, chorionic villus sampling (CVS), first trimester screen, and maternal serum screening.


Preterm labor and birth

The length of time that a normal human pregnancy lasts (the full term of a pregnancy) is about 40 weeks, or just more than 9 months, from the start of the last menstrual period to childbirth. Labor that begins before 37 weeks is called preterm labor (or early labor). An infant born before 37 weeks is considered a preterm birth.



In genetics, the right of people to restrict access to their genetic information.



An individual with a particular disorder who causes a study of his hereditary and genetic factors to determine if other members of the family have the same disease or carry it.


The likely outcome or course of a disease; the chance of recovery or recurrence.



Essential to all living cells, simplified by body processes to simple alpha-amino acids. Twenty different amino acids are commonly found in proteins and each protein has a unique, genetically defined amino acid sequence which determines its specific shape and function.


Nearest to the point of reference.

Pulmonary Stenosis

A heart valve disorder that involves the pulmonary valve. This valve separates the right ventricle (one of the chambers in the heart) and the pulmonary artery. The pulmonary artery carries oxygen-poor blood to the lungs. Stenosis, or narrowing, occurs when the valve cannot open wide enough. As a result, less blood flows to the lungs.



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