Antenatal diagnosis of molybdenum cofactor deficiency

Total truncation of the molybdopterin/dimerization domains of SUOX protein in an Arab family with isolated sulfite oxidase deficiency

We ascertained a patient with the full-blown phenotype of isolated sulfite oxidase deficiency in a consanguineous Arab family. The proband's phenotype included the presence of intractable seizures in the neonatal period, some dysmorphic features, neuroradiologic findings reminiscent of hypoxic ischemic encephalopathy and rapidly progressive brain destruction leading to severe neurodevelopmental impairment. Biochemically, the patient excreted a large amount of S-sulfocysteine with normal amounts of xanthene and hypoxanthine and had normal plasma uric acid, which was consistent with isolated sulfite oxidase deficiency. We report the identification of the first Arab mutation in SUOX, the gene for sulfite oxidase enzyme, in the ascertained family. The newly identified Arab mutation in the SUOX gene (a single nucleotide deletion, del G1244) is predicted to cause a frame shift at amino acid 117 of the translated protein with the generation of a stop codon and total truncation of the molybdo-pterin- and the dimerizing-domain(s) of SUOX protein expressed from the mutant allele. The identification of this new Arab SUOX mutation should facilitate pre-implantation genetic diagnosis and selection of unaffected embryos for future pregnancy in the ascertained family with the mutation and related families with the same mutation.

An inborn error of metabolism presenting as hypoxic-ischemic insult

This case report profiles two children whose sole presentation is intractable seizures. The index case is a 1-year-old female. She presented to the emergency department with intractable seizures. Her initial metabolic evaluation was nonconclusive. Electroencephalogram was abnormal. Brain magnetic resonance imaging yielded a picture consistent with profound ischemic hypoxic injury. The second case was the 8-year-old brother of the index case. He suffered from intractable seizures since birth. On examination he was microcephalic with spastic quadriparesis and bilateral dislocation of lenses. Computed tomography of the brain revealed a low-density area in the white and cortical matter consistent with hypoxic-ischemic injury. His urinalysis for sulfocysteine produced findings consistent with isolated sulfite oxidase deficiency.

Molybdenum cofactor deficiency presenting with severe metabolic acidosis and intracranial hemorrhage

Molybdenum cofactor deficiency leads to combined deficiency of sulfite oxidase, xanthine dehydrogenase, and aldehyde oxidase enzyme activities. The major clinic symptom is intractable seizures seen soon after birth. No definite therapy is available. We report here a newborn with molybdenum cofactor deficiency-associated Dandy-Walker malformation who presented with severe lactic acidosis and intracranial hemorrhage.

Prenatal diagnosis of molybdenum cofactor deficiency and isolated sulfite oxidase deficiency

Molybdenum cofactor deficiency and isolated sulfite oxidase deficiency are autosomal recessive inborn errors of metabolism with severe neurological symptoms resulting from a lack of sulfite oxidase activity. The deficiencies can be diagnosed prenatally by monitoring sulfite oxidase activity in chorionic villus sampling (CVS) tissue. In those families in which the specific defects have been identified, diagnosis can be achieved by mutation analysis or linkage studies directed at affected genes. These include MOCS1, MOCS2 or GEPH, in cases of molybdenum cofactor deficiency, or SUOX in patients with isolated sulfite oxidase deficiency.

Molybdenum cofactor deficiency: report of three cases presenting as hypoxic-ischemic encephalopathy

We report three infants with the diagnosis of molybdenum cofactor deficiency. The key findings leading to diagnosis were neonatal seizures unresponsive to treatment, craniofacial dysmorphic features, hyperexcitability, low blood uric acid levels, and neuroimaging findings. The parents were consanguineous in two of these patients. The diagnosis was established by the presence of low blood uric acid levels, positive urine sulfite reaction, quantitative aminoacid analysis, and high-voltage electrophoresis of the urine sample showing a typical increase of S-sulfo-L-cysteine. Skin fibroblast cultures confirmed the diagnosis. Magnetic resonance imaging findings were suggestive of encephalomalacia with cystic changes due to hypoxic-ischemic encephalopathy. We conclude that molybdenum cofactor deficiency must be included in the differential diagnosis of patients presenting with intractable seizures in the newborn period who have computed tomography and magnetic resonance imaging findings reminiscent of those of hypoxic-ischemic encephalopathy, and the urine sulfite dipstick test can be a part of the evaluation of these infants in neonatal intensive care units.

Dietary therapy in two patients with a mild form of sulphite oxidase deficiency. Evidence for clinical and biological improvement

We report an attempt at dietetic therapy in two unrelated patients with isolated sulphite oxidase deficiency, with a mild clinical course and late onset of symptoms. In case 1, disease started at 15 months with an acute crisis of agitation, unexplained crying and restlessness following otitis. Case 2 was diagnosed at 10 months when she presented with slight motor delay and dislocation of lenses. In both cases, sulphite oxidase activity measured in fibroblasts was undetectable. Therapy consisted of a diet low in protein from natural foods (daily methionine intake 130-150 mg) and a synthetic amino acid mixture (50 g per day) without cystine and methionine (Xmet, Cys Maxamaid, SHS International Ltd). A comparison of clinical and biochemical parameters was made between the period before treatment and after 2 years of treatment. Restriction in protein and sulphur amino acids brought about a dramatic decrease of urinary thiosulphate and S-sulphocysteine. It also brought about a generalized hypoaminoacidaemia with a low plasma methionine and cystine in both patients. Furthermore, both patients grew normally with no signs of neurological deterioration, and there was evidence of progress in psychomotor development.

Isolated sulfite oxidase deficiency: review of two cases in one family

OBJECTIVE

The authors describe two cases of isolated sulfite oxidase deficiency found in one family. This is a rare autosomal-recessive disorder presenting at birth with seizures, severe neurologic disease, and ectopia lentis. It can be easily missed with metabolic screening; however, the finding of lens subluxation stresses the importance of ophthalmic assessment in making the diagnosis.

DESIGN

Two observational case reports.

INTERVENTION/METHODS

Ophthalmic assessment, biochemical assay for specific urinary and plasma metabolites, magnetic resonance imaging, and gene sequencing were used to make the diagnosis of the disease in the proband. The diagnosis was subsequently recognized in a previously affected sibling after the postmortem neuropathology was reviewed. Mutation analysis was performed on cultured fibroblasts from the proband to identify and categorize the specific mutation responsible for the disease in the family. From this, future prenatal detection of sulfite oxidase deficiency is possible.

MAIN OUTCOME MEASURES

The diagnosis of sulfite oxidase deficiency was established in this family, enabling appropriate genetic counseling and recurrence risk estimation.

RESULTS

Point mutations were found in both alleles of the sulfite oxidase gene in the proband. The first is a 623C-->A mutation, which predicts an A208D substitution, and the second is a 1109C-->A, which predicts an S370Y substitution. Both residues A208D and S370Y are critical for sulfite oxidase activity.

CONCLUSIONS

Isolated sulfite oxidase deficiency is a rare heritable disease for which mutation analysis can allow accurate prenatal screening. It often is difficult to diagnose by clinical presentation alone, but the critical finding of lens subluxation accompanying seizures and diffuse neurologic disease in an infant should alert the physician to the diagnosis.

Localization of a gene for molybdenum cofactor deficiency, on the short arm of chromosome 6, by homozygosity mapping

Molybdenum cofactor deficiency (MoCoD) is a fatal disorder manifesting, shortly after birth, with profound neurological abnormalities, mental retardation, and severe seizures unresponsive to any therapy. The disease is a monogenic, autosomal recessive disorder, and the existence of at least two complementation groups suggests genetic heterogeneity. In humans, MoCoD leads to the combined deficient activities of sulfite oxidase, xanthine dehydrogenase, and aldehyde oxidase. By using homozygosity mapping and two consanguineous affected kindreds of Israeli-Arab origin, including five patients, we demonstrated linkage of a MoCoD gene to an 8-cM region on chromosome 6p21.3, between markers D6S1641 and D6S1672. Linkage analysis generated the highest combined LOD-score value, 3.6, at a recombination fraction of 0, with marker D6S1575. These results now can be used to perform prenatal diagnosis with microsatellite markers. They also provide the only tool for carrier detection of this fatal disorder.

Molybdenum: an essential trace element

Molybdenum is found in most foods, with legumes, dairy products, and meats being the richest sources. This metal is considered essential because it is part of a complex called molybdenum cofactor that is required for the three mammalian enzymes xanthine oxidase (XO), aldehyde oxidase (AO), and sulfite oxidase (SO). XO participates in the metabolism of purines, AO catalyzes the conversion of aldehydes to acids, and SO is involved in the metabolism of sulfur-containing amino acids. Molybdenum deficiency is not found in free-living humans, but deficiency is reported in a patient receiving prolonged total parenteral nutrition with clinical signs characterized by tachycardia, headache, mental disturbances, and coma. The biochemical abnormalities in this acquired molybdenum deficiency include very low levels of uric acid in serum and urine (low XO activity) and low inorganic sulfate levels in urine (low SO activity). Inborn errors of isolated deficiencies of XO, SO, and molybdenum cofactor are described. Although XO deficiency is relatively benign, patients with isolated deficiencies of SO or molybdenum cofactor exhibit mental retardation, neurologic problems, and ocular lens dislocation. These abnormalities seem to be caused by the toxicity of sulfite and/or inadequate amounts of inorganic sulfate available for the formation of sulfated compounds present in the brain. XO and AO may also participate in the inactivation of some toxic substances, inasmuch as studies suggest that molybdenum deficiency is a factor in the higher incidence of esophageal cancer in populations consuming food grown in molybdenum-poor soil.

Molybdenum cofactor deficiency

We describe a new case of molybdenum cofactor deficiency, an underrecognized inborn error of metabolism that results in neonatal seizures and neurologic abnormalities. Characteristic biochemical defects in affected individuals include hypouricemia, elevated urine sulfate (detectable by dipstick), and elevated S-sulfocysteine (detectable by anion exchange chromatography). This disorder should be considered in the differential diagnosis of neonatal seizures.

Molybdenum cofactor deficiency in two siblings: diagnostic difficulties

Two siblings with molybdenum cofactor deficiency are presented. They showed clinical, biochemical and neuroradiological features very similar to those of the few previously described cases. Difficulties in diagnosis are emphasised.

Prenatal diagnosis of molybdenum cofactor deficiency by assay of sulphite oxidase activity in chorionic villus samples

Molybdenum cofactor deficiency is characterized by the absence of sulphite oxidase, xanthine dehydrogenase and aldehyde oxidase, the three known enzymes in man that require the cofactor for their activity. Prenatal diagnosis of the deficiency may be performed by assay of sulphite oxidase activity in cultured amniocytes. However, the activity in amniocytes is low and large numbers of cells are required for reliable assessment. We show that sulphite oxidase is present at high levels in chorionic villi obtained at 10-14 weeks gestation and can be assayed directly in the biopsy sample without cell culture. This assay has been applied to two pregnancies at risk for molybdenum cofactor deficiency with successful diagnoses of an unaffected and an affected fetus.