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Case Report/Case Series |

Infantile Spasms and Hyperekplexia Associated With Isolated Sulfite Oxidase Deficiency

J. Lloyd Holder Jr, MD, PhD1; Satish Agadi, MD1; William Reese, BA2; Catherine Rehder, PhD2; Michael M. Quach, MD1
[+] Author Affiliations
1Division of Neurology and Developmental Neuroscience, Department of Pediatrics, Baylor College of Medicine, Texas Children’s Hospital, Houston
2Clinical Molecular Diagnostic Laboratory, Duke University Health System, Durham, North Carolina
JAMA Neurol. 2014;71(6):782-784. doi:10.1001/jamaneurol.2013.5083.
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Importance  Isolated sulfite oxidase deficiency (ISOD) causes severe intellectual disability, epilepsy, and shortened life expectancy. Intractable seizures are invariable in children with ISOD; however, to our knowledge, infantile spasms with a corresponding hypsarrhythmia pattern on electroencephalogram have never been reported. In addition, the nonepileptic paroxysmal movement disorder hyperekplexia has not previously been reported with ISOD.

Observations  We describe an infant with ISOD who initially presented with neonatal seizures, diffusion restriction noted on magnetic resonance imaging, and elevated serum S-sulfocysteine consistent with ISOD. A homozygous mutation in the SUOX gene was identified, confirming the diagnosis. Uniquely, this patient developed a profound accentuated startle response that did not have a corresponding electrographic change on electroencephalogram consistent with hyperekplexia. This was followed by a change in the child’s electroencephalogram to the chaotic pattern of hypsarrhythmia and brief tonic seizures with attenuation of the hypsarrhythmia pattern characteristic of infantile spasms.

Conclusions and Relevance  The evolution of seizures associated with ISOD is poorly characterized because of the small number of patients. We report what we believe to be the first case of a child with ISOD who developed infantile spasms and hyperekplexia. This expands the phenotypes associated with ISOD and also should caution clinicians to not assume that all abnormal movements are seizures.

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Figure 1.
Neuroimaging and Neurophysiological Findings

A, Magnetic resonance image diffusion-weighted image axial section at 5 days of age. B, Magnetic resonance spectroscopy findings for the basal ganglia. Note the elevated lactate peak at 1.3 ppm. The peak values (left to right) are myo-inositol (mI), creatinine (Cr), glucose (Glx), mI, choline (Cho), Cr, N-acetylaspartic acid (NAA), Glx, and NAA. AU indicates arbitrary units. C, Sagittal section of a noncontrast computed tomography image of the head when the infant was aged 5 months. The arrowhead indicates the area of micromineralization. D, Electroencephalogram at 15 months with hypsarrhythmia background. EKG indicates electrocardiogram (red line); LOC-ROC, left-right ocular canthus (as a measure of muscle movement) (blue line).

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Figure 2.
Electropherogram of the SUOX Gene Mutation

Homozygous mutation of the SUOX gene in exon 2 resulting in the substitution of arginine for lysine at position 322 (c.965 A>G; p. Lys322Arg), indicated with the arrow. The reference sequence used was GenBank Accession number NT_029419.11.

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