Functional birth defects related to how a body part/structure works D Central Nervous System problems, e.g. Down syndrome Sensory problems, e.g. blindness Metabolic disorders, e. g, phenylketonuria(PKU Degenerative disorders, e.g. muscular dystrophyFunctional Birth Defects  related to how a body part/structure works  Central Nervous System problems, e.g. Down syndrome  Sensory problems, e.g. blindness  Metabolic disorders, e.g., phenylketonuria (PKU)  Degenerative disorders, e.g. muscular dystrophy