Acute Infantile Encephalopathy as Presentation of Succinic Semialdehyde Dehydrogenase Deficiency

Succinic semialdehyde dehydrogenase deficiency is a rare neurological disorder resulting from impaired gamma-aminobutyric acid metabolism. The syndrome typically presents as a static encephalopathy with developmental delays, hypotonia, and seizures.

A six-month-old previously healthy girl developed acute choreoathetosis and severe hypotonia in the setting of influenza A infection. In our database of 112 patients with succinic semialdehyde dehydrogenase deficiency, one additional patient was identified who presented with an acute illness (encephalopathy associated with bronchiolitis at age five months).

Urine organic acid and cerebrospinal fluid analyses confirmed elevated 4-hydroxybutyric acid in both cases, verified by enzymatic quantification in lymphocytes in the second patient. Brain magnetic resonance imaging scans in both cases showed bilateral symmetric T2 hyperintensities of globus pallidi. The lesions demonstrated restricted diffusion, consistent with acute symptom onset.

In contrast to most organic acidopathies, succinic semialdehyde dehydrogenase deficiency typically presents with nonprogressive global developmental delays. Here we report that succinic semialdehyde dehydrogenase deficiency can present fulminantly during a febrile illness as well as in the more common static fashion, thereby broadening the spectrum of onset patterns in this disorder.