Disorder	Organ or system affected	Signs of metabolic instability	Neurodevelopmental effects (if not treated)
Amino acid
Homocystinuria	Eye, skeletal	Blood clots; long, thin, Marfan syndrome-like stature; dislocated lenses	Mental retardation, psychiatric problems
Maple syrup urine disease	CNS	Coma, ketoacidosis, lethargy, failure to thrive, poor feeding	Mental retardation
Phenylketonuria	CNS	Hyperactivity, seizures	Mental retardation, autism; risk of executive functioning deficits, slow reaction time, and depression; maternal phenylketonuria
Tyrosinemia type I	Liver	Liver disease	Motor deficits
Urea cycle
Arginase deficiency	CNS	Hyperammonemia	Developmental delay, motor deficits
Argininosuccinic acidemia	CNS, liver	Hyperammonemia	Developmental delay, motor deficits, mental retardation, behavioral problems
Citrullinemia	CNS	Hyperammonemia	Developmental delay, motor deficits, mental retardation, behavioral problems
Hyperornithinemia-hyperammonemia-homocitrullinuria syndrome (ornithine transport defect; secondary urea cycle defect)	CNS	Hyperammonemia	Learning disabilities, speech delay, poor visual-motor skills, irritability, aggression, attention-deficit/hyperactivity disorder