Eichner radiation

Eichner radiation is a form of exotic radiation emitted by certain sources, including the energy alien who impregnated Deanna Troi and the resulting child Ian Troi. 

Research conducted at the Vulcan Science Academy in the late 2370s showed that sustained exposure to Eichner radiation can cause erratic mutations in mitochondrial DNA, where "sustained" was defined as longer than four hours. As Deanna Troi had gestated Ian Troi for thirty-six hours, the radiation caused subtle and random genetic defects in her unreleased ova.

Although Doctor Katherine Pulaski had previously found no damage to Troi's systems from the experience, USS Titan Chief Medical Officer Shenti Yisec Eres Ree concluded that the tests had been performed on purely hormonal and cellular analysis rather than the deeper tests which were not performed until Troi miscarried her second pregnancy.