Testing a person’s DNA and then comparing it to two biologically related family members is called “trio testing.”  
 
Trio testing is valuable because it:

• increases the chance of finding the gene change causing the symptoms  
• decreases the chance of unclear or uncertain findings 

That’s because everyone has changes in their genes. Comparing the DNA of relatives makes it easier to figure out which genetic changes are causing your symptoms (and which are not). 

Samples from biological parents can provide the most information. However, other blood-related family members may also be considered if both biological parents are unable to provide a sample.