Sulfite oxidase (SO) deficiency, isolated or in association with xanthine oxidase (XO) deficiency. Molybdenum Cofactor Deficiency (MoCD).
Incidence
It is a rare metabolic disorder. It may occur SO defic. alone or SO-XO combined deficiency. Both disorders have AR inheritance. The SO enzyme require pterin-containing molybdenum cofactor. Deficit may occur by defect in enzyme or in the cofactor. When the factor is deficient, the condition is called Molybdenum Cofactor Deficiency (MoCD).
Clinical Characteristics
Neonatal feeding difficulties and intractable seizures since first weeks of life. The condition resemble severe Hypoxic Ischemic Encephalopathy (HIE) but no history or evidence of HIE such as normal or uneventful delivery. The initial clinical characteristics are intractable seizures, feeding difficulties, high-pitched cry, exaggerated startle reactions and change in tone, either hypertonia or hypotonia. Most patients develop spastic tetraplegia, axial hypotonia, microcephaly, severe developm. delay & growth retardation. Infantile spasms and choreoathetoid movements tend to occur. EEG abnormal. EEG may show burst-suppression pattern. Peculiar facial dysmorphism. Large coarse face, broad nasal bridge, enophtalmo, long philtrum, large ears, sagging skin, ectopia lentis (50%), Most patients die < 2 yrs age.
Precipitants
no
Provocation Tests
no
Diagnostic Procedures
EB(F,Liver). Use \\\'Sulfitest\\\' strips in fresh voided urine to detect sulfituria. Sulfite oxidize rapidly to sulfate in urine, so urine tested should be fresh. Aminoacid chromatography shows accumulation of thiosulfate, S-sulfocysteine & taurine. Labs at Mayo Clinic (1-800-533-1710) and Duke University (919-549-0445) have developed expedited biochemical testing for S-sulfocysteine (SSC). Very low amounts of sulfate, cystine and uric acid in urine. Sulfites and/or other key biomarkers include: a) elevated sulfites in urine. b) elevated S-sulfocysteine (SSC) in urine. c) low or undetectable uric acid (blood or urine test). d) Purine & pyrimidines panel (blood or urine test) showing high levels of xanthine and hypoxanthine. For the diagnosis of MoCD type A, a defect of MOCS1 gene is present. An increasing number of genetic panels for neonatal seizures and neonatal epileptic encephalopathies now include MOCS1 gene testing.