Case Report: Electroencephalography in a neonate with isolated sulfite oxidase deficiency – a case report and literature review

Isolated sulfite oxidase deficiency (ISOD) is a rare autosomal recessive neuro-metabolic disorder caused by a mutation in the sulfite oxidase (SUOX) gene situated on chromosome 12. Due to the deficiency of this mitochondrial enzyme (sulfite oxidase), the oxidative degradation of toxic sulfites is disrupted. The most common form of this disease has an early onset (classical ISOD) in the neonatal period, with hypotonia, poor feeding and intractable seizures, mimicking hypoxic-ischaemic encephalopathy. The evolution is rapidly progressive to severe developmental delay, microcephaly and early death. Unfortunately, there is no effective treatment and the prognosis is very poor. In this article, we described the evolution of early continuous electroencephalography (EEG) in a case of ISOD with neonatal onset, as severely encephalopathic background, with refractory seizures and distinct delta-beta complexes. The presence of the delta-beta complexes might be a diagnostic marker in ISOD. We also performed a literature review of published cases of neonatal ISOD that included EEG monitoring.

Whole exome sequencing identified a homozygous novel mutation in SUOX gene causes extremely rare autosomal recessive isolated sulfite oxidase deficiency and literature review

Background: Isolated sulfite oxidase deficiency (ISOD) is the rarest types of life-threatening neurometabolic disorders characterized by neonatal intractable seizures and severe developmental delay with an autosomal recessive mode of inheritance. ISOD is extremely rare and till date only 32 mutations have been identified and reported worldwide. Germline mutation in SUOX gene causes ISOD. Methods: Here, we investigated a 5-days old Chinese female child, presented with intermittent tremor or seizures of limbs, neonatal encephalopathy, subarachnoid cyst and haemorrhage, dysplasia of corpus callosum, neonatal convulsion, respiratory failure, cardiac failure, hyperlactatemia, severe metabolic acidosis, hyperglycemia, hyperkalemia, moderate anemia, atrioventricular block and complete right bundle branch block. Results: Whole exome sequencing identified a novel homozygous transition (c.1227G>A) in exon 6 of the SUOX gene in the proband. This novel homozygous variant leads to the formation of a truncated sulfite oxidase (p.Trp409*) of 408 amino acids. Hence, it is a loss-of-function variant. Proband’s father and mother is carrying this novel variant in a heterozygous state. This variant was not identified in 200 ethnically matched normal healthy control individuals. Conclusions: Our study not only expand the mutational spectrum of SUOX gene associated ISOD, but also strongly suggested the application of whole exome sequencing for identifying candidate genes and novel disease-causing mutations.

Novel Compound Heterozygous Pathogenic Variants in SUOX Cause Isolated Sulfite Oxidase Deficiency in a Chinese Han Family

AimTo explore the clinical imaging, laboratory and genetic characteristics of a newborn boy with isolated sulfite oxidase deficiency (ISOD) in a Chinese mainland cohort.MethodsHomocysteine and uric acid in plasma and cysteine and total homocysteine in the blood spot were assessed in a Chinese newborn patient with progressive encephalopathy, tonic seizures, abnormal muscle tone, and feeding difficulties. Whole exome sequencing and Sanger sequencing facilitated an accurate diagnosis. The pathogenicity predictions and conservation analysis of the identified mutations were conducted by bioinformatics tools.ResultsLow total homocysteine was detected in the blood spot, while homocysteine and uric acid levels were normal in the plasma. S-sulfocysteine was abnormally elevated in urine. A follow-up examination revealed several progressive neuropathological findings. Also, intermittent convulsions and axial dystonia were observed. However, the coordination of sucking and swallowing was slightly improved. A novel paternal nonsense variant c.475G > T (p.Glu159∗) and a novel maternal missense variant c.1201A > G (p.Lys401Glu) in SUOX were identified in this case by co-segregation verification.ConclusionThis is the second report of early-onset ISOD case in a non-consanguineous Chinese mainland family. Combined with the clinical characteristics and biochemical indexes, we speculated that these two novel pathogenic variants of the SUOX gene underlie the cause of the disease in this patient. Next-generation sequencing (NGS) and Sanger sequencing provided reliable basis for clinical and prenatal diagnoses of this family, it also enriched the mutation spectrum of the SUOX gene.

Whole exome sequencing identified novel mutation in SUOX gene causes extremely rare autosomal recessive isolated sulfite oxidase deficiency

BackgroundIsolated sulfite oxidase deficiency (ISOD) is the rarest types of life-threatening neurometabolic disorders characterized by neonatal intractable seizures and severe developmental delay with an autosomal recessive mode of inheritance. ISOD is extremely rare and only 29 mutations have been identified and reported worldwide. Germline mutation in SUOX gene causes ISOD. MethodsHere, we investigated a 5-days old Chinese girl, presented with intermittent tremor or seizures of limbs, neonatal encephalopathy, subarachnoid cyst and haemorrhage, dysplasia of corpus callosum, neonatal convulsion, respiratory failure, cardiac failure, hyperlactatemia, severe metabolic acidosis, hyperglycemia, hyperkalemia, moderate anemia, atrioventricular block and complete right bundle branch block. Karyotype and chromosomal microarray analysis were performed and identified no chromosomal abnormalities in the proband. Whole exome sequencing was performed for the proband. Sanger sequencing was performed for the proband and her family members. ResultsWhole exome sequencing identified a novel heterozygous deletion (c.1406_1421delCCTGGCAGGTGGCTAA) and a previously reported heterozygous substitution (c.1200C>G) in exon 6 of the SUOX gene in the proband. The novel heterozygous deletion leads to frameshift (p.Thr469Serfs*20) which results into the formation of a truncated sulfite oxidase of 488 amino acids. The substitution leads to a premature stop codon (p.Tyr400*) followed by the formation of a truncated sulfite oxidase of 399 amino acids. Hence, both the variants are loss-of-function variants. The proband’s father and mother is carrying the substitution and deletion in a heterozygous state respectively. These two variants were not identified in the elder brother of the proband as well as in the 100 healthy individuals. ConclusionHere, we reported the first variant of SUOX gene associated ISOD in Chinese population. Our study not only expand the mutational spectrum of SUOX gene associated ISOD, but also strongly suggested the application of whole exome sequencing for identifying the novel disease-causing mutation in candidate genes.

Whole exome sequencing identified novel mutation in SUOX gene causes extremely rare autosomal recessive isolated sulfite oxidase deficiency

BackgroundIsolated sulfite oxidase deficiency (ISOD) is the rarest types of life-threatening neurometabolic disorders characterized by neonatal intractable seizures and severe developmental delay with an autosomal recessive mode of inheritance. ISOD is extremely rare and only 29 mutations have been identified and reported worldwide. Germline mutation in SUOX gene causes ISOD. MethodsHere, we investigated a 5-days old Chinese girl, presented with intermittent tremor or seizures of limbs, neonatal encephalopathy, subarachnoid cyst and haemorrhage, dysplasia of corpus callosum, neonatal convulsion, respiratory failure, cardiac failure, hyperlactatemia, severe metabolic acidosis, hyperglycemia, hyperkalemia, moderate anemia, atrioventricular block and complete right bundle branch block. Karyotype and chromosomal microarray analysis were performed and identified no chromosomal abnormalities in the proband. Whole exome sequencing was performed for the proband. Sanger sequencing was performed for the proband and her family members. ResultsWhole exome sequencing identified a novel heterozygous deletion (c.1406_1421delCCTGGCAGGTGGCTAA) and a previously reported heterozygous substitution (c.1200C>G) in exon 6 of the SUOX gene in the proband. The novel heterozygous deletion leads to frameshift (p.Thr469Serfs*20) which results into the formation of a truncated sulfite oxidase of 488 amino acids. The substitution leads to a premature stop codon (p.Tyr400*) followed by the formation of a truncated sulfite oxidase of 399 amino acids. Hence, both the variants are loss-of-function variants. The proband’s father and mother is carrying the substitution and deletion in a heterozygous state respectively. These two variants were not identified in the elder brother of the proband as well as in the 100 healthy individuals. ConclusionHere, we reported the first variant of SUOX gene associated ISOD in Chinese population. Our study not only expand the mutational spectrum of SUOX gene associated ISOD, but also strongly suggested the application of whole exome sequencing for identifying the novel disease-causing mutation in candidate genes.