Medical Genetics It may be that they are carriers of the condition or that the genetic problem occurred for the first time in the cells that gave rise to the baby Known genetic causes account for about 25 per cent of all abnormalitiesMedical Genetics It may be that they are carriers of the condition, or that the genetic problem occurred for the first time in the cells that gave rise to the baby. Known genetic causes account for about 25 per cent of all abnormalities