This need, historically, may correlate with increased preprandial irritability, lethargy, jitteriness, sweating, and, possibly, seizures, which are all symptomatic of hypoglycemia. Exaggerated lethargy accompanied by vomiting and acidosis with previous viral illness, often requiring intravenous fluid replacement therapy, frequently can be elicited on history. Although early development is usually normal, growth may be somewhat slow. Prior to acute clinical presentation, physical examination findings may be entirely normal or may be remarkable only for a growth rate that is below the norm. At acute presentation, the infant is likely to be tachypneic, somnolent, and have a mildly enlarged liver, which is due to fatty infiltration.
Neurological examination is nonspecific, without localizing signs.
If the infant has experienced a hypoglycemic seizure, distinguishing a postictal state from coma due to cerebral edema is vital. The most common mutation by far is called G985, referring to a substitution of a guanine for an adenine nucleotide at the 985th residue. Serum electrolytes may show depressed bicarbonate and an anion gap. Blood ammonia may be mildly to moderately elevated. These changes are suggestive of a mitochondrial oxidative disorder but are not specific to MCAD deficiency.