Inborn errors of metabolism: a cause of abnormal brain development.

Brain malformations are caused by a disruption in the sequence of normal development by various environmental or genetic factors. By modifying the intrauterine milieu, inborn errors of metabolism may cause brain dysgenesis. However, this association is typically described in single case reports. The authors review the relationship between brain dysgenesis and specific inborn errors of metabolism. Peroxisomal disorders and fatty acid oxidation defects can produce migration defects. Pyruvate dehydrogenase deficiency, nonketotic hyperglycinemia, and maternal phenylketonuria preferentially cause a dysgenetic corpus callosum. Abnormal metabolism of folic acid causes neural tube defects, whereas defects in cholesterol metabolism may produce holoprosencephaly. Various mechanisms have been proposed to explain abnormal brain development in inborn errors of metabolism: production of a toxic or energy-deficient intrauterine milieu, modification of the content and function of membranes, or disturbance of the normal expression of intrauterine genes responsible for morphogenesis. The recognition of a metabolic disorder as the cause of the brain malformation has implications for both the care of the patient and for genetic counseling to prevent recurrence in subsequent pregnancies.