A dominant disorder can occur when a person has a change, or disease-causing variant, in one copy of the gene associated with the condition. Dominant conditions are often inherited from an affected parent. Someone with a dominant condition (or variant that may lead to a dominant condition) has a 50% chance of passing down the changed copy of the gene and a 50% change of passing down the functional copy of the gene with each pregnancy. 

Sometimes, a disease-causing variant appears in an individual even though neither parent has that variant. Such occurrences, referred to as “de novo,” result from a new, random change in a sperm or egg cell, or in the fertilized egg itself.