Genetic Services

Genetics is the study of the patterns of inheritance—how traits and characteristics are passed from parents to their children. Humans have an estimated 25,000 different genes that each controls a specific function of the body. These genes have collections of DNA that make up our chromosomes (linear structures in the nucleus of cells). Nearly every cell in our body contains 46 chromosomes arranged in 23 pairs.

Genes are lined up on the chromosomes in specific positions and locations. Although these locations are the same for each pair of chromosomes, the DNA content of those genes may be similar or different. Just as traits, such as blue eyes and curly hair, are passed from the genetic information of the parents to a baby, inherited diseases and abnormalities can also be passed on. Some disorders are autosomal recessive, meaning that one copy of an abnormal gene must be received from both parents, for the child to be affected. Other disorders are autosomal dominant, meaning one copy of an abnormal gene may come from only one parent for the disorder to occur. Other genetic conditions can happen spontaneously, meaning the genetic change happened in a child randomly at the time of conception and was not inherited from either parent.

When a gene is abnormal, or when entire chromosomes are missing or duplicated (also known as aneuploidy), defects in the structure or function of the body’s organs or systems can occur. Mutations in a specific gene can result in a specific disorder, such as cystic fibrosis, which is a recessive genetic disease. Meanwhile, abnormalities in a specific chromosome can result in conditions such as Down syndrome, a condition that occurs when a baby receives three copies of the #21 chromosome.

There are approximately 25,000 genes contained on the 46 chromosomes in each cell of the human body. This means that one chromosome contains thousands of genes. A person can have normal chromosomes in number and structure but have a mutation in one or more of the genes on the chromosomes. This is called a single gene defect. Similarly, a person can have normal genes but have a chromosome abnormality, which is when pieces of a chromosome are missing or duplicated. This is an important distinction to make. Testing for single gene disorders and chromosome abnormalities uses different technologies. Your genetics doctor can provide more information.

The following is a general checklist of characteristics that may indicate a child has a genetic defect. This is not an all-inclusive list. When two or more of these items are found, there may be a need for a genetic evaluation of the child.

Birth Defects

• Cataracts
• Cleft lip and/or cleft palate
• Congenital heart defects
• Contractures (stiff joints)
• Diaphragmatic hernia
• Genital malformations
• Genitourinary malformations
• Structural eye abnormalities (coloboma, glaucoma, cataracts)
• Craniosynostosis (misshapen skull)
• Missing or extra fingers or toes
• Missing or incomplete arms or legs
• Spina bifida or open spine defects

Chronic Diseases

• Bleeding disorders
• Childhood cancers
• Kidney or urinary tract disease
• Slow growth or short stature
• Cystic fibrosis
• Sickle cell disease
• Thalassemias

Developmental Problems

• Autism
• Developmental delay or disability
• Failure to thrive
• Large size (macrosomia)
• Learning disability
• Loss of developmental skills
• Low muscle tone (hypotonia)
• Mental illness
• Intellectual disability
• Speech problems
• Seizures

Sensory Deficits

• Extreme farsightedness
• Extreme nearsightedness
• Bilateral hearing loss
• Retinal or other visual problems

Physical Features

• Ear abnormalities
• Unusually shaped eyes
• Facial features that are unusual or are very different from other family members
• Brittle or sparse hair
• Excessive body hair
• White patch(es) of hair
• Large or small tongue
• Misshapen teeth
• Missing or extra teeth
• Loose or stiff joints
• Unusually tall or short stature
• Webbing between fingers or toes
• Excessive skin over the body
• Unusual birthmarks
• Increased or decreased sweating

Family History of a Genetic Disorder
We recommend a genetics evaluation if a first-degree or second-degree relative of a child has a genetic condition. A genetics evaluation is recommended prior to any testing of the child.

Each child should be evaluated on an individual basis since some of these features, when isolated, are found in the general population and are not associated with a genetic disease. Symptoms of genetic diseases may resemble other conditions or medical problems. Always talk to your doctor for a diagnosis and a complete list of characteristics.

A genetics evaluation involves meeting with a geneticist and genetic counselor(s) to review the following:

• Your child’s medical history
• Your child’s birth history
• Your family tree going back three generations
• A head-to-toe physical examination.

The purpose of a genetics evaluation is to identify an underlying genetic condition in order to provide information to your family, as well as to provide genetic counseling about the risk of recurrence. Once a genetic evaluation is complete, we may or may not recommend genetic testing, depending on the condition that we suspect your child has.

After your child’s genetic evaluation, our genetic specialist may recommend a genetic test, and will explain the test in easy-to-understand terms. The following genetic tests are commonly used for children.

Diagnostic Testing
Most of the genetic tests performed on children at CHOC are done for diagnostic reasons. Diagnostic testing is used to identify or confirm the diagnosis of a disease or condition in a person or a family. Diagnostic genetic testing often gives a “yes” or “no” answer, but not always. This testing can be helpful in determining the course of a disease and the choice of treatment or support. Examples of diagnostic testing include chromosome analysis–which looks for chromosomes that are extra or missing–and gene testing (sequencing), which determines if the molecular sentence of a gene is correct (i.e. if the letters of DNA in the gene are in the appropriate order). To test chromosomes, we use a sample of blood. For testing genes, we may take samples of a child’s blood or saliva, or swab the inside a child’s cheek (buccal swab).

Newborn Screenings
Screenings are performed on newborns soon after birth at every hospital in California. This screening tests for about 80 different genetic conditions. If a baby tests positive for any of these conditions, the test results are sent to labs throughout the state for further evaluation, including the CHOC Children’s Metabolics Lab. From there, the metabolics team at CHOC, along with the genetics team, is available to help you manage any condition that your baby may have. Learn more about metabolic tests at birth.

Prenatal Screening and Prenatal Diagnosis
Prenatal screening and diagnosis methods are used to diagnose a genetic disease or condition in the developing fetus. This includes maternal serum screening, prenatal ultrasound (sonograms), amniocentesis, chorionic villus sampling (CVS), and percutaneous umbilical blood sampling (PUBS). Learn more about prenatal genetic screening and prenatal diagnostic testing.

In most cases, no, genetic conditions cannot be prevented or avoided. Most genetic conditions occur at the time of conception. Some are inherited from a parent(s) and others happen spontaneously for the first time in a child. These defects are not caused by an action or inaction on the parents’ part either before or during the pregnancy.

Yes. Every human has millions of variances in their DNA when compared to other humans. Many genetic conditions may have different features even among affected people within the same family. We are all unique and not everyone will have the same lifetime experience. Some genetic conditions may not manifest in every person who has a genetic change or mutation. However, knowing about an underlying genetic condition is important so that parents know if there is a risk for the condition to be passed on to future generations.