Genetic Testing 101: What Parents Need to Know

If your child has symptoms of an inherited condition or one that might be caused by a spontaneous gene mutation, your doctor may recommend genetic testing.

Marni Falk, MD, clinical geneticist and Executive Director of Mitochondrial Medicine, a Frontier Program at Children’s Hospital of Philadelphia (CHOP), recently summarized the basics of genetic testing for families in a patient resource published in JAMA Pediatrics. In the article, co-authored by Megan Moreno, MD, of the University of Wisconsin-Madison, Dr. Falk shares key information about genetic testing at CHOP.

When might genetic testing be recommended?

Genetic mutations can contribute to a wide range of health issues in children, including:

• Developmental disabilities
• Delays of motor, speech or cognitive function
• Structural birth defects (anomalies in one or multiple organs)
• Problems with vision or hearing
• Movement disorders
• Seizures
• Chronic behavior or mood problems
• Immune disorders resulting in frequent illness
• Heart rhythm problems
• Poor growth
• Hormone problems

If your child has symptoms of a condition linked to a genetic disorder, your child's doctor may recommend genetic testing to confirm a diagnosis and refine treatment plans.

Even if a child or adult has no unusual health symptoms, a family history of genetic disease can be a reason to recommend genetic testing.

How are genetic disorders inherited?

Different genetic disorders are inherited in different ways, and more is being learned every year about how specific gene mutations can lead to varying health symptoms.

• Some conditions, known as autosomal recessive diseases, occur only when both parents are carriers of the gene mutation. Carriers typically have no symptoms of the condition. A child born to two parents who are carriers of a genetic condition has a 25 percent chance of inheriting the condition, a 50 percent chance of becoming a carrier, and a 25 percent chance of not having the mutation at all.
• Other conditions, known as autosomal dominant diseases, can be inherited from just one parent, who may have similar or less severe symptoms. If the parent’s symptoms are mild, they may not be recognized until a child has a more severe form of the disease. These conditions may also result from new — or spontaneous — gene mutations, without being inherited from either parent.
• Conditions caused by a mutation in a gene on the X chromosome, known as X-linked diseases, typically affect boys more severely than girls. A mother may not be aware that she has the condition until symptoms appear in her son.
• Other genetic conditions result from mutations in the mitochondrial DNA. These can cause functional problems in nearly any body system. They can be inherited by both boys and girls from their mother (who may or may not have symptoms), or the conditions can be caused by new mutations in the child, without being inherited.

What is genetic testing and how might it be helpful?

Genetic testing is the microscopic examination of the genetic material in fluid or tissue samples. Blood samples are most often used, but other fluid or tissue samples may be used in genetic testing for some conditions. New technologies have made gene analysis faster and more efficient, and insurance companies increasingly cover diagnostic genetic tests for children.

“Medical genetic testing is very different from the mail-order tests used to identify ancestral origins and risk factors for adult disease,” Dr. Falk explains. “Genetic testing for medical diagnosis involves careful examination of the child’s entire set of genes to identify unique mutations in particular genes relevant to their specific medical problems.”

More than 7,000 genes have now been identified in which mutations are associated with diverse medical disorders. This growing knowledge has demonstrated that many genetic syndromes and diseases can have a wide range of symptoms, which often overlap with each other. Finding the specific causal gene mutation in any one patient — essentially a needle in the genetic haystack — enables doctors to make a firm clinical diagnosis, which can lead to improved treatment or targeted therapies.

Establishing a clear genetic diagnosis can also help lift the emotional burden parents may feel because of a child’s illness, wondering if something they did caused the condition or if there is something more they could be doing to fix the problem.

“Gene mutations are happening all the time in all people through no factors they can control, sometimes inherited and sometimes occurring new in the cells of the affected child,” says Dr. Falk. “That can be therapeutic for parents to understand.”

Knowing the specific cause of a genetic condition can also remove the fear of the unknown surrounding future reproductive choices for parents, the child, siblings and extended family members, and may lead to improved medical care for others in the family.

Even with these benefits, the decision to pursue genetic testing should not be made lightly. Genetic counseling with an experienced healthcare professional is recommended before testing. If testing is done, results should be discussed with a clinical genetics professional, who can interpret the often complex findings. Genetic test results must also be considered in the context of each child’s unique medical problems. Two children can have an identical gene mutation and present with very different symptoms, requiring very different treatments, or they can have the same symptoms but from very different genetic causes.