Clinical Guidance

Isolated sulfite oxidase deficiency (ISOD), a rare inborn error of metabolism of sulfur-containing amino acids, comprises a spectrum ranging from classic early-onset (severe) disease to late-onset (mild) disease .

Classic ISOD

Classic ISOD typically manifests within few hours to days of life with intractable seizures, feeding difficulties, and rapidly progressive encephalopathy . The clinical features resemble that of neonatal hypoxic ischemic encephalopathy. Almost all affected infants are born after uncomplicated pregnancy. Of note, sustained abdominal trembling resembling vibration of mobile phones (interpreted as fetal seizures) has been reported in the third trimester in one instance . Delivery is usually uncomplicated, although Apgar scores may be depressed.

Diagnostic Criteria

Suggestive Findings

Classic early-onset (severe) and late-onset (mild) isolated sulfite oxidase deficiency (ISOD) should be suspected in infants with the following clinical, neuroimaging, and supportive laboratory findings.

Clinical Features

Classic ISOD

Source: GeneReviews — "Isolated Sulfite Oxidase Deficiency"

Management Guidelines

Evaluations Following Initial Diagnosis

To establish the extent of disease and/or needs in an individual with a diagnosis of isolated sulfite oxidase deficiency (ISOD), the following evaluations are recommended:

• Complete neurologic assessment by a pediatric neurologist

Surveillance Guidelines

Periodic assessment by the multidisciplinary team with particular attention to the following:

• Nutritional status

• Neurologic status including evaluation of dosages of anti-seizure medication and their side effects

• Degree of spasticity and related complications, including scoliosis