Table 2.

Disorders to Consider in the Differential Diagnosis of Isolated Sulfite Oxidase Deficiency (ISOD)

DiffDx DisorderGene(s)MOIFeatures of DiffDx Disorder
Overlapping w/ISODDistinguishing from ISOD
Molybdenum cofactor deficiency MOCS1
ARIntractable seizures & feeding difficulties in 1st few hrs to days of life; subsequent severe ID, spasticity, & seizures refractory to ASM↓ serum uric acid levels; ↑ urinary xanthine & hypoxanthine levels due to loss of function of xanthine dehydrogenase
Glycine encephalopathy GLDC
ARProgressive lethargy, hypotonia, & myoclonic jerks in 1st few hrs to days of life; subsequent profound ID & seizures refractory to ASM↑ glycine levels in plasma & CSF; on MRI: diffusion restriction of areas that are myelinating at birth (e.g., posterior limb of internal capsule & pericentral area)
Pyridoxine-dependent epilepsy ALDH7A1 ARSoon after birth: seizures refractory to ASMSeizures respond to large supplements of pyridoxine.
Pyridox(am)ine 5'-phosphate oxidase deficiency PNPO ARSoon after birth: seizures refractory to ASM & pyridoxineSeizures respond to pyridoxal-5’ phosphate.

ASM = anti-seizure medication; AR = autosomal recessive; DiffDx = differential diagnosis; ID = intellectual disability; MOI = mode of inheritance

From: Isolated Sulfite Oxidase Deficiency

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