A number of nonhereditary metabolic diseases must be distinguished from the hereditary ones in this period of life. Hypocalcemia is one of the most frequent causes of neonatal seizures; tetany, spasms, and tremulous movements are usually present. Its cause is unknown, but the disorder is easily corrected, with excellent prognosis. Symptomatic hypoglycemic reactions are frequent in neonates. Premature infants are the most susceptible. Seizures, tremulousness, and drowsiness occur with blood sugar levels of less than 30 mg/dL in the mature infant, and less than 20 mg/dL in the premature. Maternal toxemia and diabetes mellitus also predispose to hypoglycemia. Other causes of hypoglycemia are adrenal insufficiency, galactosemia, an idiopathic pancreatic islet-cell hyperplasia, the treatable fatty-acid beta-oxidation disorders, and a congenital deficiency of CSF glucose transport— causing persistent hypoglycorrhachia and refractory seizures unless blood glucose levels are kept high. The damaging effects of untreated hypoglycemia were well documented by Koivisto and colleagues. Also now identified is a disorder of CSF serine transport causing failure to thrive, severe developmental disability with spasticity and intractable epilepsy. The diagnosis is made by measuring CSF amino acids; treatment is with high-dose oral serine. Cretinism and idiopathic hypercalcemia are other recognizable entities that appear during this age period.
Aicardi has described a neonatal myoclonic syndrome, and Ohtahara has described a malignant neonatal seizure disorder. In some of the cases, the neonatal syndrome merged later with the West type of infantile spasms and the Lennox-Gastaut syndrome (see Chap. 15). Some of the cases had developmental abnormalities of the cerebrum, and severe developmental delay was the outcome. In other cases of this type, a familial coincidence was a feature; a metabolic defect has been suspected in these cases but never proved.
The hereditary metabolic diseases must also be distinguished from a number of other catastrophic disorders that occur at or soon after birth, such as asphyxia, perinatal ventricular hemorrhage with the respiratory distress syndrome of hyaline membrane disease, other hypotensive–hypoxic states, erythroblastosis fetalis with kernicterus, neonatal bacterial meningitis, meningoencephalitis (herpes simplex, cytomegalic inclusion disease, listeriosis, rubella, syphilis, and toxoplasmosis), and hemorrhagic disease of the newborn. These are described in Chap. 37, on the developmental diseases.