Researchers examined 100 people suffering from herniated disks in their backs  Five of them were found to have a defect in a particular gene  The researchers also examined 100 people who had no problems with the disks in their backs; none had the genetic defect
They concluded that the genetic defect increases the likelihood of herniated disks
When the researchers examined the families of the 5 subjects who had the defective gene, they found that 30 family members also had the defective gene, and each of them suffered from herniated disks.