General description

Sulfite oxidase deficiency is a severe neurological disorder caused by a defect in the SUOX gene, which follows an autosomal recessive inheritance pattern. This condition results in the loss or reduction of sulfite oxidase activity, an enzyme responsible for converting sulfite into sulfate. The accumulation of toxic sulfite and a deficiency of sulfate lead to significant neurological damage, affecting the brain, liver, and lungs.

Most affected individuals present symptoms in the neonatal period, often experiencing intractable seizures within the first 72 hours after birth. Other common symptoms include severe psychomotor developmental delay, muscle tone abnormalities—such as hypotonia combined with limb hypertonia—feeding difficulties, and vomiting. Additional neurological manifestations include involuntary movements such as myoclonus, athetosis, and dystonia, as well as cerebral palsy-like symptoms in milder cases. Infants who survive beyond the neonatal period may develop progressive microcephaly and lens dislocation.

Visual impairments, including strabismus, blindness, and retinal degeneration, are frequently observed. Crystalluria, characterized by the presence of sulfate or cystine crystals in urine, is another key feature. A related disorder, Molybdenum cofactor deficiency (MOCOD), arises from pathogenic variants in the MOCS1 or MOCS2 genes. Since molybdenum cofactor is essential for sulfite oxidase function, its deficiency results in a clinical presentation similar to sulfite oxidase deficiency. It is difficult to distinguish sulfite oxidase deficiency and molybdenum cofactor deficiency on imaging.

References

1. Dublin, Arthur B., John K. Hald, and Sandra L. Wootton-Gorges. "Isolated sulfite oxidase deficiency: MR imaging features." American journal of neuroradiology 23.3 (2002): 484-485.