Machine learning-based identification and characterization of 15 novel pathogenic SUOX missense mutations.

Isolated sulfite oxidase deficiency (ISOD) is a rare hereditary metabolic disease caused by absence of functional sulfite oxidase (SO) due to mutations of the SUOX gene. SO oxidizes toxic sulfite and sulfite accumulation is associated with neurological disorders, progressive brain atrophy and early death. Similarities of these neurological symptoms to abundant diseases like neonatal encephalopathy underlines the raising need to increase the awareness for ISOD. Here we report an interdisciplinary approach utilizing exome/genome data derived from gnomAD database as well as published variants to predict the pathogenic outcome of 303 naturally occurring SO missense variants and combining these with activity determination. We identified 15 novel ISOD-causing SO variants and generated a databank of pathogenic SO missense variants to support future diagnosis of ISOD patients. We found six inactive variants (W101G, H118Y, E197K, R217W, S427W, D512Y, Q518R) and seven (D110H, P119S, G121E, G130R, Y140C, R269H, Q396P, R459Q) with severe reduction in activity. Based on the Hardy-Weinberg-equilibrium and the combination of our results with published SO missense and protein truncating variants, we calculated the first comprehensive incidence rate for ISOD of 1 in 1,377,341 births and provide a pathogenicity score to 303 naturally occurring SO missense variants.

Hepatic Deficiency of Augmenter of Liver Regeneration Predisposes to Nonalcoholic Steatohepatitis and Fibrosis.

BACKGROUND AND AIMS: The augmenter of liver regeneration (ALR) protein is critical for lipid homeostasis and mitochondrial function. We investigated high-fat/high-carbohydrate (HF/HC) diet-induced nonalcoholic fatty liver disease (NAFLD) in wild-type (WT), hepatocyte-specific ALR-knockout (ALR-H-KO), and ALR-heterozygous (ALR-H-HET) mice. ALR was measured in serum of human nonalcoholic steatohepatitis (NASH) and NASH-induced cirrhosis (serum and liver). APPROACH AND RESULTS: HF/HC feeding decreased ALR expression in all groups of mice. The otherwise normal ALR-H-HET mice gained more weight and steatosis than WT mice when challenged metabolically with the HF/HC diet; ALR-H-KO mice gained the least weight and had the least steatosis. These findings were consistent with correspondingly increased triglycerides and cholesterol and altered expression of carnitine palmitoyltransferase 1a, sterol regulatory element-binding protein, acetyl coenzyme A carboxylase, and fatty acid synthase. All HF/HC-fed mice developed insulin resistance, the magnitude being lower in ALR-H-KO mice. HF/HC-fed ALR-H-HET mice were more resistant to glucose challenge than WT or ALR-H-KO mice. The frequency of tumor necrosis factor alpha-producing, interleukin 6 (IL6)-producing, and IL17-producing cells was greater in ALR-H-KO than ALR-H-HET and lowest in WT mice. HF/HC feeding did not increase their number in ALR-H-KO mice, and the increase in ALR-H-HET was greater than that in WT mice except for IL17 cells. Cluster of differentiation 25-positive (CD25+ ) forkhead box P3-positive CD4+ regulatory T-cell frequency was lower in ALR-H-HET than WT mice and further reduced in ALR-H-KO mice; HF/HC reduced regulatory T-cell frequency only in WT mice. HF/HC-fed ALR-H-HET, but not WT, mice developed fibrosis; and ALR-H-KO mice progressed to cirrhosis. White adipose tissue of HF/HC-fed ALR-deficient mice developed strong inflammation, indicating bidirectional interactions with the liver. Hepatic and serum ALR levels were significantly reduced in patients with NASH-cirrhosis. Serum ALR was also significantly lower in patients with NASH. CONCLUSIONS: Hepatic ALR deficiency may be a critical predisposing factor for aggressive NAFLD progression.

Effects of Srxn1 on growth and Notch signalling of astrocyte induced by hydrogen peroxide.

OBJECTIVE: To investigate the effect of Sulfiredoxin-1 (Srxn1) on astrocyte injury induced by hydrogen peroxide (H2O2). METHODS: Observing the changes of H2O2 on contents of lactate dehydrogenase (LDH), malondialdehyde (MDA), superoxide dismutase (SOD) and apoptosis after transfected Srxn1 siRNA into astrocytes. The protein expression of Notch 1, NICD and Hes1, the content of LDH and MDA, the activity of SOD and apoptosis rate of astrocytes after inhibiting or activation of Notch signalling pathway were detected by Western blot, ELISA and flow cytometry, respectively. RESULTS: Knockdown of Srxn1 could promote the secretion of LDH and MDA, decrease the activity of SOD and aggravate apoptosis of astrocytes induced by H2O2. The results of Western blot, ELISA assay and flow cytometry indicated that activation of the Notch signalling pathway attenuated the effect of Srxn1 on H2O2-induced oxidative damage and apoptosis of astrocytes. CONCLUSION: Srxn1 may protect astrocytes from oxidative stress injury induced by H2O2 by activation of Notch signalling pathway.

Deficiency in augmenter of liver regeneration accelerates liver fibrosis by promoting migration of hepatic stellate cell.

BACKGROUND: Augmenter of liver regeneration (ALR) protects liver from various injuries, however, the association of ALR with liver fibrosis, particularly its effect on hepatic stellate cells (HSC), remains unclear. In this study, we investigated the impact of ALR on the activation of HSC, a pivotal event in occurrence of liver fibrosis. METHODS: Liver fibrosis was induced in vivo in mice with heterozygous ALR knockdown (ALR-KD) by administration of CCl4 or bile duct ligation. The effect of ALR-KD and ALR-overexpression on liver fibrosis was studied in mice and in HSC cells as well. RESULTS: Hepatic collagen deposition and expression of α-smooth muscle actin (α-SMA) were significantly increased in the ALR-KD mice compared to wild-type mice. In vitro, ALR-shRNA resulted in the activation of HSC cell line (LX-2). Furthermore, ALR-shRNA promoted LX-2 cell migration, accompanied by increased filamentous actin (F-actin) assembly. The ALR-KD-mediated increase in HSC migration was associated with mitochondrial fusion, resulting in mitochondria elongation and enhancing ATP production. In contrast, ALR transfection (ALR-Tx) decelerated HSC migration and inhibited F-actin assembly, concomitantly enhancing mitochondrial fission and reducing ATP synthesis. Mechanically, stimulation of HSC migration by ALR-shRNA was attributed to the increased mitochondrial Ca2+ influx in HSCs. Treatment of ALR-shRNA-cells with Ruthenium Red (RuR), a specific inhibitor of mitochondrial calcium uniporter (MCU), significantly suppressed mitochondrial Ca2+ influx, HSC migration, mitochondrial fusion and ATP production. ALR-KD-induced HSC migration was verified in vitro in primary mouse HSCs. CONCLUSION: Inhibition of ALR expression aggravates liver fibrosis, probably via promoting HSC migration and mitochondrial fusion.

Isolated sulfite oxidase deficiency.

Isolated sulfite oxidase deficiency (ISOD) is a life-threatening, autosomal recessive disease characterized by severe neurological impairment. As no long-term effective treatment is available, distinction from other treatable diseases, such as molybdenum cofactor deficiency (MoCD) type A, should be made. We reviewed 47 patients (45 previously reported in the literature). Cases were reviewed for consanguinity, sex, age at onset, death, clinical findings (including spasticity, seizures, psychomotor retardation, feeding difficulties, ectopia lentis, microcephaly), laboratory findings [urinary sulfite, S-sulfocysteine (in plasma and urine), plasma cystine, total homocysteine, uric acid, and oxypurines in urine] and radiological findings (including cerebral/cerebellar atrophy, cystic white matter changes, ventriculomegaly). We also aligned the published SUOX gene mutations to the reference sequence NM_000456.2. Onset occurred mostly during the first 72 h of life (57%) and within the first year of life in all but two patients (96%). All patients presented with neurological abnormalities, such as neonatal axial hypotonia and/or peripheral hypertonia (100%), (pharmacoresistant) seizures (84%), or developmental delay (97%). Feeding problems were also common. As found in our review, measurement of homocysteine in plasma, amino acids in plasma/urine, and sulfite in fresh urine supports the diagnosis of ISOD. Analysis of uric acid (plasma) and oxypurines (urine) is useful to rule out MoCD. In all patients in whom brain magnetic resonance imaging/computed tomography (MRI/CT) was performed, brain abnormalities were found. The purpose of this literature review is to provide a thorough overview of clinical, neuroimaging, biochemical, and genetic findings of patients with ISOD.

Deceleration of liver regeneration by knockdown of augmenter of liver regeneration gene is associated with impairment of mitochondrial DNA synthesis in mice.

Hepatic stimulator substance, also known as augmenter of liver regeneration (ALR), is a novel hepatic mitogen that stimulates liver regeneration after partial hepatectomy (PH). Recent work has indicated that a lack of ALR expression inhibited liver regeneration in rats, and the mechanism seems to be related to increased cell apoptosis. The mitochondria play an important role during liver regeneration. Adequate ATP supply, which is largely dependent on effective mitochondrial biogenesis, is essential for progress of liver regeneration. However, ALR gene expression during liver regeneration, particularly its function with mitochondrial DNA synthesis, remains poorly understood. In this study, ALR expression in hepatocytes of mice was suppressed with ALR short-hairpin RNA interference or ALR deletion (knockout, KO). The ALR-defective mice underwent PH, and the liver was allowed to regenerate for 1 wk. Analysis of liver growth and its correlation with mitochondrial biogenesis showed that both ALR mRNA and protein levels increased robustly in control mice with a maximum at days 3 and 4 post-PH. However, ALR knockdown inhibited hepatic DNA synthesis and decelerated liver regeneration after PH. Furthermore, both in the ALR-knockdown and ALR-KO mice, expression of mitochondrial transcription factor A and peroxisome proliferator-activated receptor-γ coactivator-1α were reduced, resulting in impaired mitochondrial biogenesis. In conclusion, ALR is apparently required to ensure appropriate liver regeneration following PH in mice, and deletion of the ALR gene may delay liver regeneration in part due to impaired mitochondrial biogenesis.

Microarray analysis unmasked paternal uniparental disomy of chromosome 12 in a patient with isolated sulfite oxidase deficiency.

BACKGROUND: In the investigation of a proband with a biochemical diagnosis of isolated sulfite oxidase deficiency, we identified a homozygous nonsense mutation of the SUOX gene in the proband. However, the mutation was only detected in the father and not the mother. Deletion of the SUOX gene of the mother and paternal disomy of chromosome 12, where the SUOX gene is located, were suspected in view that allele dropout of the mother non-amplified wild-type allele is unlikely. METHODS: To distinguish the two possible causes, we performed a genome wide microarray analysis in the patient and parents using high-density single-nucleotide microarrays. Whole genome allele sharing of the genomes of the patient and parents were performed by dChip. RESULTS: In the proband, the whole genome scan showed loss of heterozygosity (LOH) of the entire chromosome 12. However, the LOH is copy neutral and deletion of the SUOX gene of the mother was thus excluded. On whole genome allele sharing analysis, the proband showed a high degree of allele sharing with the father and a very low allele sharing with the mother only in chromosome 12. The cause of the homozygosity of the mutation of the patient is UPD (12) pat. CONCLUSIONS: To the best of our knowledge, this study is the first UPD (12) pat causing isolated sulfite oxidase deficiency in humans. Even with one parent being a carrier of an autosomal recessive disease, a fetus with the autosomal recessive disease is still possible. This will have clinical impact on genetic counseling.

Urinary AASA excretion is elevated in patients with molybdenum cofactor deficiency and isolated sulphite oxidase deficiency.

Analysis of α-aminoadipic semialdehyde is an important tool in the diagnosis of antiquitin deficiency (pyridoxine-dependent epilepsy). However continuing use of this test has revealed that elevated urinary excretion of α-aminoadipic semialdehyde is not only found in patients with pyridoxine-dependent epilepsy but is also seen in patients with molybdenum cofactor deficiency and isolated sulphite oxidase deficiency. This should be taken into account when interpreting the laboratory data. Sulphite was shown to inhibit α-aminoadipic semialdehyde dehydrogenase in vitro.

Sulfiredoxin protein is critical for redox balance and survival of cells exposed to low steady-state levels of H2O2.

Sulfiredoxin (Srx) is an enzyme that catalyzes the reduction of cysteine sulfinic acid of hyperoxidized peroxiredoxins (Prxs). Having high affinity toward H2O2, 2-Cys Prxs can efficiently reduce H2O2 at low concentration. We previously showed that Prx I is hyperoxidized at a rate of 0.072% per turnover even in the presence of low steady-state levels of H2O2. Here we examine the novel role of Srx in cells exposed to low steady-state levels of H2O2, which can be achieved by using glucose oxidase. Exposure of low steady-state levels of H2O2 (10-20 µm) to A549 or wild-type mouse embryonic fibroblast (MEF) cells does not lead to any significant change in oxidative injury because of the maintenance of balance between H2O2 production and elimination. In contrast, loss-of-function studies using Srx-depleted A549 and Srx-/- MEF cells demonstrate a dramatic increase in extra- and intracellular H2O2, sulfinic 2-Cys Prxs, and apoptosis. Concomitant with hyperoxidation of mitochondrial Prx III, Srx-depleted cells show an activation of mitochondria-mediated apoptotic pathways including mitochondria membrane potential collapse, cytochrome c release, and caspase activation. Furthermore, adenoviral re-expression of Srx in Srx-depleted A549 or Srx-/- MEF cells promotes the reactivation of sulfinic 2-Cys Prxs and results in cellular resistance to apoptosis, with enhanced removal of H2O2. These results indicate that Srx functions as a novel component to maintain the balance between H2O2 production and elimination and then protects cells from apoptosis even in the presence of low steady-state levels of H2O2.

Concerted action of sulfiredoxin and peroxiredoxin I protects against alcohol-induced oxidative injury in mouse liver.

UNLABELLED: Peroxiredoxins (Prxs) are peroxidases that catalyze the reduction of reactive oxygen species (ROS). The active site cysteine residue of members of the 2-Cys Prx subgroup (Prx I to IV) of Prxs is hyperoxidized to cysteine sulfinic acid (Cys-SO(2) ) during catalysis with concomitant loss of peroxidase activity. Reactivation of the hyperoxidized Prx is catalyzed by sulfiredoxin (Srx). Ethanol consumption induces the accumulation of cytochrome P450 2E1 (CYP2E1), a major contributor to ethanol-induced ROS production in the liver. We now show that chronic ethanol feeding markedly increased the expression of Srx in the liver of mice in a largely Nrf2-dependent manner. Among Prx I to IV, only Prx I was found to be hyperoxidized in the liver of ethanol-fed wildtype mice, and the level of Prx I-SO(2) increased to ≈30% to 50% of total Prx I in the liver of ethanol-fed Srx(-/-) mice. This result suggests that Prx I is the most active 2-Cys Prx in elimination of ROS from the liver of ethanol-fed mice and that, despite the up-regulation of Srx expression by ethanol, the capacity of Srx is not sufficient to counteract the hyperoxidation of Prx I that occurs during ROS reduction. A protease protection assay revealed that a large fraction of Prx I is located together with CYP2E1 at the cytosolic side of the endoplasmic reticulum membrane. The selective role of Prx I in ROS removal is thus likely attributable to the proximity of Prx I and CYP2E1. CONCLUSION: The pivotal functions of Srx and Prx I in protection of the liver in ethanol-fed mice was evident from the severe oxidative damage observed in mice lacking either Srx or Prx I.

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.

The G473D mutation impairs dimerization and catalysis in human sulfite oxidase.

Among the mutations identified in patients with isolated sulfite oxidase deficiency, the G473D variant is of particular interest since sedimentation analysis reveals that this variant is a monomer, and the importance of the wild-type dimeric state of mammalian sulfite oxidase is not yet well understood. Analysis of recombinant G473D sulfite oxidase indicated that it is severely impaired both in the ability to bind sulfite and in catalysis, with a second-order rate constant 5 orders of magnitude lower than that of the wild type. To elucidate the specific reasons for the severe effects seen in the G473D variant, several other variants were created, including G473A, G473W, and the double mutant R212A/G473D. Despite the inability to form a stable dimer, the G473W variant had 5-fold higher activity than G473D and nearly wild-type activity at pH 7.0 when ferricyanide was the electron acceptor. In contrast, the R212A/G473D variant demonstrated some ability to oligomerize but had undetectable activity. The G473A variant retained the ability to dimerize and had steady-state activity that was comparable to that of the wild type. Furthermore, stopped-flow analysis of the reductive half-reaction of this variant yielded a rate constant nearly 3 times higher than that of the wild type. Examination of the secondary structures of the variants by CD spectroscopy indicated significant random-coil formation in G473D, G473W, and R212A/G473D. These results demonstrate that both the charge and the large size of an Asp residue in this position contribute to the severe effects seen in a patient with the G473D mutation, by causing partial misfolding and monomerization of sulfite oxidase and attenuating both substrate binding and catalytic efficiency during the reaction cycle.

Structural insights into sulfite oxidase deficiency.

Sulfite oxidase deficiency is a lethal genetic disease that results from defects either in the genes encoding proteins involved in molybdenum cofactor biosynthesis or in the sulfite oxidase gene itself. Several point mutations in the sulfite oxidase gene have been identified from patients suffering from this disease worldwide. Although detailed biochemical analyses have been carried out on these mutations, no structural data could be obtained because of problems in crystallizing recombinant human and rat sulfite oxidases and the failure to clone the chicken sulfite oxidase gene. We synthesized the gene for chicken sulfite oxidase de novo, working backward from the amino acid sequence of the native chicken liver enzyme by PCR amplification of a series of 72 overlapping primers. The recombinant protein displayed the characteristic absorption spectrum of sulfite oxidase and exhibited steady state and rapid kinetic parameters comparable with those of the tissue-derived enzyme. We solved the crystal structures of the wild type and the sulfite oxidase deficiency-causing R138Q (R160Q in humans) variant of recombinant chicken sulfite oxidase in the resting and sulfate-bound forms. Significant alterations in the substrate-binding pocket were detected in the structure of the mutant, and a comparison between the wild type and mutant protein revealed that the active site residue Arg-450 adopts different conformations in the presence and absence of bound sulfate. The size of the binding pocket is thereby considerably reduced, and its position relative to the cofactor is shifted, causing an increase in the distance of the sulfur atom of the bound sulfate to the molybdenum.

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.

Effect of sulfite on cognitive function in normal and sulfite oxidase deficient rats.

Sulfites, which are commonly used as preservatives, are continuously formed in the body during metabolism of sulfur-containing amino acids. Sulfite is oxidized to sulfate ion by sulfite oxidase (SOX, EC. 1.8.3.1). The aim of this study was to investigate the possible toxic effects of sulfite on neurons by measuring active avoidance learning in normal and SOX-deficient rats. For this purpose, male albino rats used in this study were divided into eight groups such as control group (C), sulfite group (25 mg/kg) (S), vitamin E group (50 mg/kg) (E), sulfite (25 mg/kg)+vitamin E group (50 mg/kg) (SE), SOX-deficient group (D), deficient+vitamin E group (50 mg/kg) (DE), deficient+sulfite group (25 mg/kg) (DS) and deficient+sulfite (25 mg/kg)+vitamin E group (50 mg/kg) (DSE). Sulfite-induced impairment of active avoidance learning in SOX-deficient rats but not in normal rats. Sulfite had no effect on hippocampus TBARS levels in SOX normal groups. In SOX-deficient rats, TBARS levels were found to be significantly increased with sulfite exposure. Vitamin E reversed the observed detrimental effects of sulfite in the SOX-deficient rats on their hippocampal TBARS but not on their active avoidance learning. In conclusion, sulfite has neurotoxic effects in sulfite oxidase deficient rats, but this effect may not depend on oxidative stress.

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.

Determination of urinary S-sulphocysteine, xanthine and hypoxanthine by liquid chromatography-electrospray tandem mass spectrometry.

Molybdenum cofactor and isolated sulphite oxidase deficiencies are two related rare autosomal recessive diseases characterized by severe neurological abnormalities, dislocated lens and mental retardation. Determination of three biochemical markers S-sulphocysteine (SSC), xanthine (XAN) and hypoxanthine (HXAN) in urine is essential for a definitive diagnosis and identification of the exact defect. We developed a rapid liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the analysis of SSC, XAN and HXAN in urine. The analysis was carried out in the negative-ion selected-reaction monitoring mode. The turnaround time for the assay was 7 min. Linear calibration curves for the three biomarkers were obtained in the range of 12-480 micromol/L. The intra- and inter-day assay variations were <2.5%. Mean recoveries of SSC, XAN and HXAN added to urine at two significantly different concentrations were in the range 94.3-107.3%. At a normal SSC urine excretion value of 3.2 micromol/mmol creatinine, the signal-to-noise ratio was 337:1. This stable isotope dilution LC-MS/MS method is specific, rapid and simple, and provides definitive diagnosis for molybdenum cofactor and isolated sulphite oxidase deficiencies in very small volumes of urine. We have identified seven new cases of isolated sulphite oxidase deficiency from four Saudi families and one Sudanese family.

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

A patient with isolated sulphite oxidase deficiency presented with seizures at 12 h of life and followed a severe course, dying at 10 months of age. There was mild facial dysmorphism and the brain showed multiple cystic fibrosis.

New approaches towards laboratory diagnosis of isolated sulphite oxidase deficiency.

BACKGROUND: Molybdenum cofactor deficiency (resulting in combined deficiencies of the enzymes sulphite oxidase, xanthine dehydrogenase and aldehyde dehydrogenase) and isolated sulphite oxidase deficiency are inherited metabolic diseases which follow an autosomal recessive trait of inheritance. Detection of these diseases in selective screening for inborn errors of metabolism is not easy because relevant metabolites are either not routinely determined or are unstable. METHODS: We have searched for additional markers for these diseases and studied plasma total homocysteine (determined by enzyme immunoassay) and S-sulphonation of transthyretin (assessed by electrospray ionization mass spectrometry). RESULTS AND CONCLUSION: We found total homocysteine concentrations below the limit of quantification (<1 micromol/L) in all samples of patients with sulphite oxidase deficiency studied in this regard and that the proportion of S-sulphonated transthyretin is clearly increased in such samples. Our observations suggest additional tools for selective screening and diagnostic work-up of patients suspected of having sulphite oxidase deficiency.

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.