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De novo mutation

A genetic change in the DNA that happens for the first time in a patient, i.e., the parents do not carry the change.

De-identified data

Data from which identifiers are removed from the health information, mitigating privacy risks to individuals and thereby supporting the secondary use of data for comparative effectiveness studies, policy assessment, life sciences research, and other endeavors.



A lower amount than necessary for functioning.


Excessive loss of water from the body or from an organ or body part, as from illness or fluid deprivation.


A type of mutation involving the loss of genetic material. It can be small, involving a single missing DNA base pair, or large, involving a piece of a chromosome.


Developmental delay

Developmental Delay means a delay in one or more of the following areas of childhood development as measured by appropriate diagnostic instruments and standard procedures. Areas of assessment include:

  • Cognitive development
  • Physical development, including vision and hearing
  • Communication development
  • Social and/or emotional development
  • Adaptive development, including eating skills, dressing and toileting skills and other areas of personal responsibility

Developmental Disabilities

A chronic mental or physical impairment that results in decreased ability of an individual to reach appropriate age-level developmental goals.


Developmental evaluation

See Developmental screening and Developmental monitoring

Developmental milestones

Skills such as taking a first step, smiling for the first time, and waving "bye bye" are called developmental milestones. Children reach milestones in how they play, learn, speak, behave, and move (crawling, walking, etc.).


Developmental monitoring

Your child’s growth and development are kept track of through a partnership between you and your health professional. At each well-child visit the doctor looks for developmental delays or problems and talks with you about any concerns you might have. This is called developmental monitoring (or surveillance). Any problems noticed during developmental monitoring should be followed-up with developmental screening.

Children with special health care needs should have developmental monitoring and screening just like those without special needs. Monitoring healthy development means paying attention not only to symptoms related to the child’s condition, but also to the child’s physical, mental, social, and emotional well-being.


Developmental screening

Developmental screening is a short test to tell if a child is learning basic skills when he or she should, or if there are delays. Developmental screening can also be done by other professionals in health care, community, or school settings.

The doctor might ask you some questions or talk and play with the child during an examination to see how he or she plays, learns, speaks, behaves, and moves. A delay in any of these areas could be a sign of a problem.

The American Academy of Pediatrics recommends that all children be screened for developmental delays and disabilities during regular well-child doctor visits at:

  • 9 months
  • 18 months
  • 24 or 30 months

Additional screening might be needed if a child is at high risk for developmental problems due to preterm birth, low birthweight, or other reasons.

If your child’s doctor does not routinely check your child with this type of developmental screening test, you can ask that it be done.


Developmental survelliance

See Developmental monitoring

Diagnostic test

Is used to confirm a diagnosis when a person has signs or symptoms that suggest a genetic disease. The particular genetic test used depends on the disease for which a person is tested. For example, if a patient has physical features that suggest Down Syndrome, a chromosomal test is used to see if the patient has an extra copy of chromosome 21. To test for Duchenne muscular dystrophy, a gene test is done to look for missing sections in the dystrophin gene.



Deoxyribonucleic acid (DNA) is the chemical inside the nucleus of all cells that carries the genetic instructions for making living organisms.

DNA sequencing (genome sequencing)

A multistage process that includes cloning, physical mapping, subcloning, determination of the DNA sequence of the nucleotide bases and information analysis. Sometimes the entire gene is decoded and sometimes only the most important parts are. Different people can have slightly different sequences (variants) with little or no impact on how well the gene works. However, some errors in a gene's sequence can have serious consequences.


An allele that is almost always expressed, even if only one copy is present. See Autosomal dominance


Dosage sensitive

Genes where the amount of gene product (protein) is dependent on the number of working copies a person has of a particular gene. For most genes, we have two copies. In a person with an extra or missing copy of the dosage sensitive gene(s), there can be an impact on the health and development of that person.

Down syndrome

Down syndrome is a set of cognitive and physical symptoms that result from having an extra chromosome 21 or an extra piece of that chromosome. It is the most common chromosomal cause of mild to moderate intellectual disabilities. People with Down syndrome also have some distinct physical features, such as a flat-looking face, and they are at risk for a number of other health conditions. Also known as Trisomy 21.


DTaP vaccine

An immunization against diphtheria, tetanus, and pertussis (whooping cough) that is one of the recommended childhood immunizations. Five DTaP vaccines are recommended, usually given to children at ages 2 months, 4 months, 6 months, 15-18 months, and 4-6 years.

Ductus arteriosis

(also known as patent ductus arteriosis or PDA) - a condition in which the ductus arteriosus does not close. (The word "patent" means open.) The ductus arteriosus is a blood vessel that allows blood to go around the baby's lungs before birth. Soon after the infant is born and the lungs fill with air, the ductus arteriosus is no longer needed. It usually closes in a couple of days after birth. PDA leads to abnormal blood flow between the aorta and pulmonary artery, two major blood vessels that carry blood from the heart.



A duplication occurs when part of a chromosome is copied (duplicated) abnormally, resulting in extra genetic material from the duplicated segment.


Early Intervention Services

Research shows that early intervention treatment services can greatly improve a child’s development. Early intervention services help children from birth through 3 years of age (36 months) learn important skills. Services include therapy to help the child talk, walk, and interact with others. The Individuals with Disabilities Education Act (IDEA) says that children younger than 3 years of age (36 months) who are at risk of having developmental delays, might be eligible for early intervention treatment services even if the child has not received a formal diagnosis. These services are provided through an early intervention system in each state.



Any of various ions, such as sodium or chloride, required by cells to regulate the electric charge and flow of water molecules across the cell membrane. The primary ions of electrolytes are sodium, potassium, calcium, magnesium, chloride, phosphate and bicarbonate.


Caused by an abnormal condition of the structure or function of the tissues in the brain, especially chronic, destructive or degenerative conditions such as hyperammonemia, metabolic or mitochondrial disorders.

Enzymatic Assay

Laboratory methods for measuring enzymatic activity.


A protein molecule that helps other organic molecules enter into chemical reactions with one another but is itself unaffected by these reactions.

Epicanthal folds

Skin of the upper eyelid, from the nose to the inner side of the eyebrow, that covers the inner corner (canthus) of the eye. The presence of an epicanthal fold is normal in people of Asiatic descent. An epicanthal fold is also common in children with Down syndrome. Epicanthal folds may also be seen in young children of any race before the bridge of the nose begins to elevate.




The origins of a disease.

Expressive language disorder

A condition in which a child has lower than normal ability in vocabulary, producing complex sentences, and remembering words. However, children with this disorder may have the normal language skills needed to understand verbal or written communication.



Measure for describing the range of phenotypic expression is called expressivity. Expressivity measures the extent to which a given genotype is expressed at the phenotypic level. Different degrees of expression in different individuals may be due to variation in the allelic constitution of the rest of the genome or to environmental factors.



A cell that is present in connective tissue and active in making and secreting collagen. Skin cells.

First trimester

Weeks 1-12 of a pregnancy.


First trimester screen

Blood is drawn to test for PAPP-A and free beta-hCG (or hCG) and may be combined with performing a nuchal translucency ultrasound. This test will provide the risk for Down syndrome as well as other chromosomal problems.



See Fluorescence in situ hybridization

Fluorescence in situ hybridization

Also called FISH, is a technique used to visualize and map the genetic material in an individual's cells, including specifc genes or portions of genes. This is important for understanding a variety of chromosomal abnormalities and other genetic mutations. Unlike most other techniques used to study chromosomes, FISH does not have to be performed on cells that are actively dividing.

fMRI (Functional magnetic resonance imaging)

A diagnostic imaging technique used in brain mapping to measure the tiny metabolic changes that take place in an active part of healthy, diseased, or injured brains. During an fMRI examination, the patient will perform a particular task during the imaging process, causing increased metabolic activity in the area of the brain responsible for the task which is then recorded on MRI images.


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