A single gene condition is caused by a change, known as a mutation, in a particular gene which causes that gene to function improperly or not function at all. Single gene conditions are inherited and passed through families. Examples of single gene conditions include cystic fibrosis, spinal muscular atrophy (SMA), hemophilia, and Tay-Sachs disease. In many cases, couples are ‘carriers’ of a gene mutation that does not affect their health, but puts their children at risk of inheriting the genetic condition.