Isolated sulphite oxidase deficiency: clinical and biochemical features in an Italian patient

Primary disorders of metabolism and disturbed fetal brain development

There exists a link between the in utero metabolic environment and the development of the fetal nervous system. Prenatal neurosonography offers a unique, noninvasive tool in the detection of developmental brain malformations and the ability to monitor changes over time. This article explores the association of malformations of cerebral development reported in association with inborn errors of metabolism, and speculates on potential mechanisms by which such malformations arise. The detection of cerebral malformations prenatally should lead to a search for both genetic etiologies and inborn errors of metabolism in the fetus. Improving the changes of an early diagnosis provides for timely therapeutic interventions and it is hoped a brighter future for affected children and their families.

Agenesis of the corpus callosum and cerebral anomalies in inborn errors of metabolism

Dysgenesis of the corpus callosum has been recognized as a marker for aberrant development of the central nervous system. It has been suggested that developmental defects of the corpus callosum may be more frequently encountered in patients with inborn errors of metabolism. The objectives of the present study were to determine the prevalence of developmental defects of the corpus callosum in patients attending a genetics-metabolic disorders clinic, to describe the spectrum of abnormalities in brain development in patients with confirmed inborn errors of metabolism and abnormalities of the corpus callosum as ascertained by neuroimaging and/or postmortem studies. Nineteen patients (10 males, 9 females) with confirmed metabolic diagnoses were identified by systematic search of the genetics clinic database. All 19 (100%) expressed variable degrees of hypoplasia, complete or partial agenesis (ACC). Abnormalities of head size were noted in 17/19 (89.5%). The majority 12/17 (70.5%) were associated with microcephaly, while macrocrania was noted in 5/17 (29.5%). Associated central nervous system (CNS) anomalies included abnormalities in ventricular morphology in 18/19 (94.7%), ventriculomegaly in 11/19 (63.1%), increased extraxial cerebrospinal fluid space in 11/19 (57.9%), changes in the gray matter (neuronal migration defects, porencephaly) in 9/19 (47.3%), white matter changes in 12/19 (63.1%) and abnormalities of the posterior fossa and hindbrain in 12/19 (63.1%). In patients with inborn errors of metabolism, dysgenesis of the corpus callosum serves as a marker for other developmental defects within the nervous system. We discuss here potential mechanisms by which metabolic defects affect diverse biochemical pathways, altering key neurobiological processes (e.g. defective cell membrane formation, cellular bioenergetics and cell-to-cell signaling), that eventually lead to structural abnormalities in the developing nervous system.

Magnetic resonance imaging and magnetic resonance spectroscopy in isolated sulfite oxidase deficiency

Isolated sulfite oxidase deficiency is a rare genetic neurometabolic disease. The first symptoms of this disorder (similar to symptoms of ischemic events) may lead to misdiagnosis and to subsequent birth of affected children in these families. This study characterizes the magnetic resonance (MR) imaging and (for the first time, to our knowledge) the MR spectroscopy features of isolated sulfite oxidase deficiency to provide a means for early and correct diagnosis. Three patients with isolated sulfite oxidase deficiency are studied who manifested intractable seizures and severe hypotonia in the immediate postnatal period with an unknown diagnosis, despite extensive workup. MR imaging and proton MR spectroscopy examinations were performed early in the neonatal period in 2 infants and after 5 months in the third infant. The prominent MR features were early cystic white matter damage, accompanied by profound cerebral atrophy in the third infant. Compared with hypoxic-ischemic disorder, MR findings in isolated sulfite oxidase deficiency demonstrate a more severe condition, without subsequent recovery. The MR spectroscopy studies indicate early onset of energetic and metabolic imbalance. Urine stick findings demonstrated high sulfite levels in 2 patients, and the final diagnosis was subsequently made based on molecular, biochemical, and genetic findings. Magnetic resonance imaging and MR spectroscopy measurements may help differentiate isolated sulfite oxidase deficiency from hypoxic-ischemic condition in patients in whom this diagnosis is not clinically suspected and may lead to further genetic antenatal inquiry that might prevent the birth of other infants affected with this severe and incurable congenital disease.

Isolated sulfite oxidase deficiency: a case report with a novel mutation and review of the literature

Isolated sulfite oxidase deficiency is a rare but devastating neurologic disease that usually presents in early infancy with seizures and alterations in muscle tone. Only 21 cases have been reported in the literature. We report a case of a newborn infant boy with isolated sulfite oxidase deficiency who presented with generalized seizures on his fourth day of life. Plasma total homocysteine was not detectable. Urinary sulfite, thiosulfate, and S-sulfocysteine levels were elevated. The patient began a low-methionine and low-cysteine diet and was treated with thiamine and dextromethorphan. However, he became increasingly microcephalic and was severely developmentally delayed. Mutation analysis of the sulfite oxidase gene revealed that the patient was homozygous for a novel 4-base pair deletion, and both of his parents were found to be heterozygous carriers of the same deletion. We reviewed the clinical, biochemical, neuroradiologic, and neuropathologic features in all published cases of isolated sulfite oxidase deficiency. Seizures or abnormal movements were prominent features in all cases. Developmental delays were reported in 17 cases. Ectopia lentis was detected in 9 cases. Clinical improvement with dietary therapy was seen in only 2 patients, both of whom presented after the age of 6 months and had relatively mild developmental delays. Plasma or urinary S-sulfocysteine levels were elevated in all cases. Urinary sulfite was detected in all except 1 case. Cerebral atrophy and cystic encephalomalacia were observed with neuroradiologic imaging and were noted in all 3 postmortem reports of isolated sulfite oxidase deficiency. The main alternative in the differential diagnosis of isolated sulfite oxidase deficiency is molybdenum cofactor deficiency.