Sulfite Oxidase Deficiency
Patient Information
Characteristics
Background and History
This is an enzymatic disorder known only since the 1960s. It is quite rare and only a few families have been reported.
Clinical Correlations
Sulfur containing compounds appear in the urine as a result of a defect in an enzyme, sulfite oxidase, required in sulfur metabolism. This leads to severe neurological problems such as unsteadiness, random, purposeless movements and language difficulties. About 80% of patients have significant developmental delays. Newborns often have seizures and difficulty breathing. Some children exhibit irritability and restlessness, feeding problems, and mild spasticity. Some patients have dislocation of the lens in the eye, a condition known as ectopia lentis. However, there seems to be considerable variability of clinical disease as some patients that are diagnosed later have a milder course.
Genetics
Inheritance
This is an autosomal recessive disorder which requires the presence of two mutations, one from each parent. No symptoms occur in the carrier parents.
Pedigree
Autosomal recessive
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
Diagnosis and Prognosis
Most cases have an early onset of symptoms during early childhood. Symptoms of delayed development and a general ‘floppiness’ may be seen and are often accompanied by agitation and feeding problems. A pediatric neurologist may find increased levels of sulfite in the urine. Not enough patients have been evaluated for long enough to determine the optimum treatment but a low protein diet and restriction of sulfur containing amino acids has been reported to result in improved neurological functions, at least for a short time in a few individuals.
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