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Keywords
- 5-Oxoprolinase (1)
- 5-oxoprolinuria (1)
- AMT (1)
- Epilepsy (1)
- GLYCTK (1)
- Glutathione synthetase (1)
- Inborn errors of metabolism (1)
- Nonketotic hyperglycinemia (1)
- Pyroglutamic aciduria (1)
- d-Glycerate kinase deficiency (1)
BACKGROUND
Propionic acidemia is an inherited disorder caused by deficiency of propionyl-CoA carboxylase. Although it is one of the most frequent organic acidurias, information on the outcome of affected individuals is still limited.
STUDY DESIGN/METHODS
Clinical and outcome data of 55 patients with propionic acidemia from 16 European metabolic centers were evaluated retrospectively. 35 patients were diagnosed by selective metabolic screening while 20 patients were identified by newborn screening. Endocrine parameters and bone age were evaluated. In addition, IQ testing was performed and the patients' and their families' quality of life was assessed.
RESULTS
The vast majority of patients (>85%) presented with metabolic decompensation in the neonatal period. Asymptomatic individuals were the exception. About three quarters of the study population was mentally retarded, median IQ was 55. Apart from neurologic symptoms, complications comprised hematologic abnormalities, cardiac diseases, feeding problems and impaired growth. Most patients considered their quality of life high. However, according to the parents' point of view psychic problems were four times more common in propionic acidemia patients than in healthy controls.
CONCLUSION
Our data show that the outcome of propionic acidemia is still unfavourable, in spite of improved clinical management. Many patients develop long-term complications affecting different organ systems. Impairment of neurocognitive development is of special concern. Nevertheless, self-assessment of quality of life of the patients and their parents yielded rather positive results.
Historically, d-glyceric aciduria was thought to cause an uncharacterized blockage to the glycine cleavage enzyme system (GCS) causing nonketotic hyperglycinemia (NKH) as a secondary phenomenon. This inference was reached based on the clinical and biochemical results from the first d-glyceric aciduria patient reported in 1974. Along with elevated glyceric acid excretion, this patient exhibited severe neurological symptoms of myoclonic epilepsy and absent development, and had elevated glycine levels and decreased glycine cleavage system enzyme activity. Mutations in the GLYCTK gene (encoding d-glycerate kinase) causing glyceric aciduria were previously noted. Since glycine changes were not observed in almost all of the subsequently reported cases of d-glyceric aciduria, this theory of NKH as a secondary syndrome of d-glyceric aciduria was revisited in this work. We showed that this historic patient harbored a homozygous missense mutation in AMT c.350C > T, p.Ser117Leu, and enzymatic assay of the expressed mutation confirmed the pathogeneity of the p.Ser117Leu mutation. We conclude that the original d-glyceric aciduria patient also had classic NKH and that this co-occurrence of two inborn errors of metabolism explains the original presentation. We conclude that no evidence remains that d-glyceric aciduria would cause NKH.
BACKGROUND
Glutaric aciduria type 1 (GA1) is an inborn error in the metabolism of the amino acids tryptophan, lysine and hydroxylysine due to mutations in the GCDH gene coding for glutaryl-CoA dehydrogenase. Affected individuals often suffer from an encephalopathic crisis in infancy or childhood which results in acute striatal injury leading to a severe dystonic-dyskinetic movement disorder. Isobutyryl-coenzyme dehydrogenase (IBD) is an enzyme encoded by the ACAD8 gene and involved in the catabolism of the branched-chain amino acid valine. Both GA1 and IBD deficiency can be detected by expanded newborn screening using tandem-mass spectrometry, if they are considered screening targets.
METHODS
Tandem-mass spectrometry and gas-chromatography with mass-selective detection were used for the assessment of key metabolites in body fluids of a patient with abnormal findings in newborn screening. Mutations were investigated by direct sequencing and by restriction fragment lengths analysis. Valine metabolism was studied in vitro in immortalized lymphocytes.
RESULTS
Following accumulation of acylcarnitines C5DC and C4, of 3-hydroxyglutaric acid and isobutyrylglycine in body fluids, sequence analysis in the GCDH gene revealed homozygosity for a missense mutation in exon 6, c.482G>A, p.Arg161Gln, which had been reported in GA1 before. In the ACAD8 gene a novel mutation c.841+3G>C was identified, which results in loss of exon 7 and predicts a premature stop of translation. Impaired valine degradation was corroborated by the increased post-load level of acylcarnitine C4 in lymphocytes.
CONCLUSION
The molecular basis of two inborn errors of metabolism in a newborn was elucidated. The metabolite studies underline the use of urinary C4 acylcarnitine as a sensitive marker of IBD deficiency. A functional test of IBD activity in lymphocytes may replace more invasive fibroblast studies. In view of the combination of two organic acidurias, which may both affect the level of free carnitine, careful follow-up including regular assessment of the carnitine status of the patient appears prudent.
Sulfite oxidase is a mitochondrial enzyme encoded by the SUOX gene and essential for the detoxification of sulfite which results mainly from the catabolism of sulfur-containing amino acids. Decreased activity of this enzyme can either be due to mutations in the SUOX gene or secondary to defects in the synthesis of its cofactor, the molybdenum cofactor. Defects in the synthesis of the molybdenum cofactor are caused by mutations in one of the genes MOCS1, MOCS2, MOCS3 and GEPH and result in combined deficiencies of the enzymes sulfite oxidase, xanthine dehydrogenase and aldehyde oxidase. Although present in many ethnic groups, isolated sulfite oxidase deficiency and molybdenum cofactor deficiency are rare inborn errors of metabolism, which makes awareness of key clinical and laboratory features of affected individuals crucial for early diagnosis. We report clinical, radiologic, biochemical and genetic data on a Brazilian and on a Turkish child with sulfite oxidase deficiency due to the isolated defect and impaired synthesis of the molybdenum cofactor, respectively. Both patients presented with early onset seizures and neurological deterioration. They showed no sulfite oxidase activity in fibroblasts and were homozygous for the mutations c.1136A>G in the SUOX gene and c.667insCGA in the MOCS1 gene, respectively. Widely available routine laboratory tests such as assessment of total homocysteine and uric acid are indicated in children with a clinical presentation resembling that of hypoxic ischemic encephalopathy and may help in obtaining a tentative diagnosis locally, which requires confirmation by specialized laboratories.
Aminoacylase 1 (ACY1) deficiency is a recently described inborn error of metabolism. Most of the patients reported so far have presented with rather heterogeneous neurologic symptoms. At this moment, it is not clear whether ACY1 deficiency represents a true metabolic disease with a causal relationship between the enzyme defect and the clinical phenotype or merely a biochemical abnormality. Here we present a patient identified in the course of selective screening for inborn errors of metabolism (IEM). The patient was diagnosed with autistic syndrome and admitted to the Children's Memorial Health Institute (CMHI) for metabolic evaluation. Organic acid analysis using gas chromatography-mass spectrometry (GC-MS) revealed increased urinary excretion of several N-acetylated amino acids, including the derivatives of methionine, glutamic acid, alanine, glycine, leucine, isoleucine, and valine. In Epstein-Barr virus (EBV)-transformed lymphoblasts, ACY1 activity was deficient. The mutation analysis showed a homozygous c.1057C>T transition, predicting a p.Arg353Cys substitution. Both parents were heterozygous for the mutation and had normal results in the organic acid analysis using GC-MS. This article reports the findings of an ACY1-deficient patient presenting with autistic features.
D-glyceric aciduria is a rare inborn error of serine and fructose metabolism that was first described in 1974. Most affected individuals have presented with neurological symptoms. The molecular basis of D-glyceric aciduria is largely unknown; possible causes that have been discussed are deficiencies of D-glycerate dehydrogenase, triokinase, and D-glycerate kinase. In 1989, van Schaftingen has reported decreased D-glycerate kinase activity in the liver of a single patient with D-glyceric aciduria. However, this analysis has not been performed in other affected individuals, and the underlying defect has remained unknown on the gene level until now. We report three patients with deficiency of D-glycerate kinase. They are of Serbian, Mexican, and Turkish origin and include the patient initially reported in 1974. All had homozygous mutations in exon 5 of the GLYCTK gene encoding D-glycerate kinase: c.1448delT (p.Phe483SerfsX2), c.1478T>G (p.Phe493Cys), or c.1558delC (p.Leu520CysfsX108). Transient overexpression of the variant GLYCTK genes in HEK293 cells clearly showed loss of enzyme activity and immunoreactivity when compared to the reference enzyme. Our work has revealed mutations in the GLYCTK gene as the cause of D-glycerate kinase deficiency and D-glyceric aciduria and provides a noninvasive approach for further diagnostic workup and research.
Primary 5-oxoprolinuria (pyroglutamic aciduria) is caused by a genetic defect in the γ-glutamyl cycle, affecting either glutathione synthetase or 5-oxoprolinase. While several dozens of patients with glutathione synthetase deficiency have been reported, with hemolytic anemia representing the clinical key feature, 5-oxoprolinase deficiency due to OPLAH mutations is less frequent and so far has not attracted much attention. This has prompted us to investigate the clinical phenotype as well as the underlying genotype in patients from 14 families of various ethnic backgrounds who underwent diagnostic mutation analysis following the detection of 5-oxoprolinuria.
In all patients with 5-oxoprolinuria studied, bi-allelic mutations in OPLAH were indicated. An autosomal recessive mode of inheritance for 5-oxoprolinase deficiency is further supported by the identification of a single mutation in all 9/14 parent sample sets investigated (except for the father of one patient whose result suggests homozygosity), and the absence of 5-oxoprolinuria in all tested heterozygotes. It is remarkable, that all 20 mutations identified were novel and private to the respective families.
Clinical features were highly variable and in several sib pairs, did not segregate with 5-oxoprolinuria. Although a pathogenic role of 5-oxoprolinase deficiency remains possible, this is not supported by our findings. Additional patient ascertainment and long-term follow-up is needed to establish the benign nature of this inborn error of metabolism. It is important that all symptomatic patients with persistently elevated levels of 5-oxoproline and no obvious explanation are investigated for the genetic etiology.
3-hydroxyisobutyric aciduria is an organic aciduria with a poorly understood biochemical basis. It has previously been assumed that deficiency of 3-hydroxyisobutyrate dehydrogenase (HIBADH) in the valine catabolic pathway is the underlying enzyme defect, but more recent evidence makes it likely that individuals with 3-hydroxyisobutyryic aciduria represent a heterogeneous group with different underlying mechanisms, including respiratory chain defects or deficiency of methylmalonate semialdehyde dehydrogenase. However, to date methylmalonate semialdehyde dehydrogenase deficiency has only been demonstrated at the gene level for a single individual. We present two unrelated patients who presented with developmental delay and increased urinary concentrations of 3-hydroxyisobutyric acid. Both children were products of consanguineous unions and were of European or Pakistani descent. One patient developed a febrile illness and subsequently died from a hepatoencephalopathy at 2 years of age. Further studies were initiated and included tests of the HIBADH enzyme in fibroblast homogenates, which yielded normal activities. Sequencing of the ALDH6A1 gene (encoding methylmalonate semialdehyde dehydrogenase) suggested homozygosity for the missense mutation c.785 C > A (S262Y) in exon 7 which was not found in 210 control alleles. Mutation analysis of the ALDH6A1 gene of the second patient confirmed the presence of a different missense mutation, c.184 C > T (P62S), which was also identified in 1/530 control chromosomes. Both mutations affect highly evolutionarily conserved amino acids of the methylmalonate semialdehyde dehydrogenase protein. Mutation analysis in the ALDH6A1 gene can reveal a cause of 3-hydroxyisobutyric aciduria, which may present with only slightly increased urinary levels of 3-hydroxyisobutyric acid, if a patient is metabolically stable.
