Molecular basis of dimethylglycine dehydrogenase deficiency associated with pathogenic variant H109R

Summary  Dimethylglycine dehydrogenase (DMGDH) is a mitochondrial matrix flavoprotein that catalyses the demethylation of dimethylglycine to form sarcosine, accompanied by the reduction of the covalently bound FAD cofactor. Electron-transfer flavoprotein reoxidizes the reduced flavin and transfers reducing equivalents to the main mitochondrial respiratory chain through the enzyme ETF-ubiquinone oxidoreductase. DMGDH plays a prominent role in choline and 1-carbon metabolism. We have expressed the mature form of human DMGDH and the H109R variant identified in a DMGDH-deficient patient as N-terminally His₆-tagged proteins in E. coli. The enzymes were purified to homogeneity by nickel affinity and anion exchange chromatography. The presence of FAD in the wild-type enzyme was confirmed by spectrophotometric analysis. The H109R variant, however, had only 47% of the wild-type level of bound flavin as expressed in E. coli, indicating its reduced affinity for FAD As previously described for rat enzyme studies, the wild-type human enzyme exhibited two K _m values for N,N-dimethylglycine (K _m1 = 0.039 ± 0.010 mmol/L and K_m2 = 15.4 ± 1.2 mmol/L). The addition of 4 μmol/L tetrahydrofolate resulted in a slight decrease in specific activity and a substantial decrease in K _m2 (1.10 ± 0.55 mmol/L). The flavinated H109R variant protein exhibited a 27-fold decrease in specific activity and a 65-fold increase in K _m, explaining its pathogenicity. Additionally, the current expression system represents a significant improvement over a previously described rat DMGDH expression system and will enhance our ability to further study this important metabolic enzyme. Competing interests: None declared References to electronic databases: Dimethylglycine dehydrogenase: EC 1.5.99.2. Dimethylglycine dehydrogenase deficiency: OMIM 605850. Dimethylglycine oxidase structure: PDB 1PJ5.     

Variants in the sulphonylurea receptor gene: association of the exon 16–3t variant with Type II diabetes mellitus in Dutch Caucasians

Aims/hypothesis. We have analysed to what extent two previously reported single nucleotide polymorphisms in the sulphonylurea receptor gene (SUR1) are associated with Type II (non-insulin-dependent) diabetes mellitus in The Netherlands. Furthermore, we estimated haplotype frequencies in control and diabetic populations, including data extracted from three other studies. Methods. Subjects with Type II diabetes (n = 388) and normoglycaemic subjects (n = 336) were randomly selected from two population-based studies, the Hoorn and Rotterdam studies. DNA was typed for variants in exon 16 (-3c→t variant in the splice acceptor site) and exon 18 (Thr⁷⁵⁹Thr, ACC→ACT). Results. The genotype frequencies in both populations were similar. We observed an association of the exon 16–3t variant with Type II diabetes (allele frequencies 0.41 % vs 0.48 % in NGT and Type II diabetes, respectively, p = 0.01). There was no association between Type II diabetes and the variant in exon 18 or the combination of both variants (p > 0.5). A strong linkage disequilibrium between the exon 16 and exon 18 variants was observed in the diabetic groups but not, or less pronounced, in the control groups from the different studies. Haplotype estimation shows that several different risk haplotypes exist in different Caucasian populations. Conclusion/interpretation. The exon 16–3t allele of the SUR1 gene is associated with Type II diabetes in the Netherlands. Based on estimated haplotype frequencies in different Caucasian populations we conclude that multiple haplotypes on the SUR1 gene seem to confer a risk for developing Type II diabetes in Caucasians. [Diabetologia (1999) 42: 617–620] Received: 6 November 1998 and in final revised form: 14 January 1999     

Reduced second phase insulin secretion in carriers of a sulphonylurea receptor gene variant associating with Type II diabetes mellitus

Abstract Aims/hypothesis. The sulphonylurea receptor is a subunit of the ATP-sensitive potassium channel in the pancreatic beta cell. Mutations at nt –3 of the splice acceptor site of exon 16 and a silent mutation in exon 18 of the gene for the sulphonylurea receptor (SUR1) associate with Type II (non-insulin-dependent) diabetes mellitus in several independent populations. We investigated whether these gene variants associate with changes in the pattern of glucose-stimulated insulin secretion.?Methods. Subjects who had normal glucose tolerance (n = 67) and subjects with an impaired glucose tolerance (n = 94), originating from two independent studies, were included in the study. Beta-cell function and insulin sensitivity were assessed by the hyperglycaemic clamp.?Results. Frequencies of the exon 16 –3t allele in the normal and impaired glucose tolerant groups were 46 % and 44 % respectively (p = NS). The more rare exon 18 T allele showed frequencies of 5 and 7 % respectively (p = NS). We observed an approximately 25 % reduced second-phase insulin secretion in carriers of the exon 16 –3t allele in both groups (p < 0.05). Estimates of insulin sensitivity did not show differences between carriers and non-carriers. The variant in exon 18 and the combined presence of variants in exon 16 and exon 18 were not associated with differences in insulin secretion or insulin sensitivity in our study groups.?Conclusion/interpretation. The diabetes associated exon 16 –3t variant of the SUR1 gene associates with a functional change of the beta cell as reflected by reduced second-phase insulin secretion in response to a standardized hyperglycaemia in normal and impaired glucose tolerant subjects. [Diabetologia (2000) 43: 515–519] Received: 5 July 1999 and in revised form: 24 November 1999     

The biochemistry, metabolism and inherited defects of the pentose phosphate pathway: A review

Summary  The recent discovery of two defects (ribose-5-phosphate isomerase deficiency and transaldolase deficiency) in the reversible part of the pentose phosphate pathway (PPP) has stimulated interest in this pathway. In this review we describe the functions of the PPP, its relation to other pathways of carbohydrate metabolism and an overview of the metabolic defects in the reversible part of the PPP. Competing interests: None declared Prof. Dr. Cornelis Jakobs was supervisor of this PhD project and Dr. Eduard A. Struys was co-supervisor References to electronic databases: Transaldolase: EC 2.2.1.2. Ribose-5-phosphate isomerase: EC 5.3.1.6. Xylitol dehydrogenase: EC 1.1.1.9. Glucose-6-phosphate dehydrogenase: EC 1.1.1.49. Transaldolase deficiency: OMIM #606003. Ribose-5-phosphate isomerase deficiency: OMIM #608611. Pentosuria: %260800. Glucose-6-phosphate dehydrogenase deficiency OMIM +305900. TALDO1: GenBank # NM_006755. RPIA: GenBank # NM_144563.

---

TAT gene mutation analysis in three Palestinian kindreds with oculocutaneous tyrosinaemia type II; characterization of a silent exonic transversion that causes complete missplicing by exon 11 skipping

Summary Deficiency of the hepatic cytosolic enzyme tyrosine aminotransferase (TAT) causes marked hypertyrosinaemia leading to painful palmoplantar hyperkeratoses, pseudodendritic keratitis and variable mental retardation (oculocutaneous tyrosinaemia type II or Richner–Hanhart syndrome). Parents may therefore seek prenatal diagnosis, but this is not possible by biochemical assays as tyrosine does not accumulate in amniotic fluid and TAT is not expressed in chorionic villi or amniocytes. Molecular analysis is therefore the only possible approach for prenatal diagnosis and carrier detection. To this end, we sought TAT gene mutations in 9 tyrosinaemia II patients from three consanguineous Palestinian kindreds. In two kindreds (7 patients), the only potential abnormality identified after sequencing all 12 exons and exon–intron boundaries was homozygosity for a silent, single-nucleotide transversion c.1224G > T (p.T408T) at the last base of exon 11. This was predicted to disrupt the 5′ donor splice site of exon 11 and result in missplicing. However, as TAT is expressed exclusively in liver, patient mRNA could not be obtained for splicing analysis. A minigene approach was therefore used to assess the effect of c.1224G > T on exon 11 splicing. Transfection experiments with wild-type and c.1224G > T mutant minigene constructs demonstrated that c.1224G > T results in complete exon 11 skipping, illustrating the utility of this approach for confirming a putative splicing defect when cDNA is unavailable. Homozygosity for a c.1249C > T (R417X) exon 12 nonsense mutation (previously reported in a French patient) was identified in both patients from the third kindred, enabling successful prenatal diagnosis of an unaffected fetus using chorionic villous tissue. Competing interests: None declared References to electronic databases: tyrosinaemia type II (OMIM +276600); hepatic cytosolic tyrosine aminotransferase (EC 2.6.1.5); GenBank: accession number for TAT mRNA, NM_000353; accession number for TAT genomic DNA, NC_000016.     

Assessment of mitochondrial respiratory chain function in hyperphenylalaninaemia

Summary  Phenylketonuria (PKU) is an autosomal recessive disorder resulting in neurological and intellectual disability when untreated. However, even in treated patients there may be residual neurological impairment such as tremor. It has been suggested that the hyperphenylalaninaemia in patients with PKU reduces complex I (NADH:ubiquinone reductase) activity of the mitochondrial respiratory chain (MRC) and/or biosynthesis of coenzyme Q₁₀ (CoQ₁₀), which acts as an electron carrier in the MRC, leading to impaired energy metabolism in the brain of patients with PKU and hence the neurological pathology. The aim of this study was to elucidate the mechanism of phenylalanine (Phe) toxicity on the MRC. We compared mean plasma and blood-spot Phe and mononuclear CoQ₁₀ levels in 17 patients with PKU and a tremor compared to 22 patients without tremor. Human 1321N1 astrocytoma cells were exposed to hyperphenylalaninaemia by the addition of 300 or 900 μmol/L of Phe to the cell culture medium. Following 96 h of culture we measured complex I and citrate synthase activities and CoQ₁₀ level. Results showed no significant difference in Phe or CoQ₁₀ levels in patients with tremor compared to those without tremor. Further, hyperphenylalaninaemia did not cause a significant reduction in complex I activity or CoQ₁₀ biosynthesis, even when taking into account the mitochondrial enrichment of the cell samples by expressing complex I and CoQ₁₀ as a ratio to citrate synthase. In conclusion, the results of this study suggest that hyperphenylalaninaemia does not contribute to the pathophysiology of PKU by causing a decrease in MRC complex I activity and/or CoQ₁₀ biosynthesis. Competing interests: None declared References to electronic databases: Phenylketonuria: PKU. OMIM 261600. Citrate synthase: EC 4.1.3.7. Cytochrome oxidase: EC 1.9.3.1. Succinate:cytochrome-c oxidoreductase: EC 1.3.5.1 + EC 1.10.2.2. NADH:cytochrome-c oxidoreductase: EC 1.6.5.3 + EC 1.10.2.2. Hydroxymethylglutaryl-CoA reductase: EC 1.1.1.98. Ubiquinol:cytochrome-c oxidoreductase: EC 1.10.2.2. Succinate:ubiquinone reductase: EC 1.3.5.1. NADH:ubiquinone reductase: EC 1.6.5.3. Phenylalanine hydroxylase: EC 1.14.16.1.     

Multiple OXPHOS deficiency in the liver of a patient with CblA methylmalonic aciduria sensitive to vitamin B12

Summary  An adult patient with methylmalonic aciduria due to defective cobalamin synthesis (CblA) responsive to vitamin B₁₂ presented suddenly with severe visual impairment ascribed to optic atrophy followed by a fatal multiorgan failure and lactic acidosis but low methylmalonic acid in plasma and urine. Multiple deficiency of oxidative phosphorylation was found in the patient’s liver. We suggest that patients with B₁₂-sensitive methylmalonic aciduria who have a milder clinical course should be carefully monitored for long-term complications. Competing interests: None declared References to electronic databases: Methylmalonic aciduria (MMA): OMIM 251000, 277400, 251100 (CblA), 277410 (CblD), 251110 (CblB), 277380, 606169. Adenosylcobalamin: EC 2.7.7.62. Methylmalonyl-coenzyme A mutase (MUT): EC 5.4.99.2. Citrate synthase: EC 2.3.3.1. Succinate-CoA ligase (GDP-forming): EC 6.2.1.4. Succinate-CoA ligase (ADP-forming): EC 6.2.1.5. Succinate dehydrogenase (ubiquinone): EC 1.3.5.1. Fumarate hydratase: EC 4.2.1.2. ATP citrate synthetase: EC 2.3.3.8. Pyruvate dehydrogenase: EC 1.2.4.1. Pyruvate carboxylase: EC 6.4.1.1. Nucleoside-diphosphate kinase: EC 2.7.4.6. Presented at the Annual Symposium of the SSIEM, Lisbon, Portugal, 2–5 September 2008.     

Microarray analysis of multiple candidate genes and associated plasma proteins for nephropathy secondary to type 2 diabetes among Chinese individuals

Aims/hypothesis  Evolving research suggests that common and rare alleles jointly constitute the genetic landscape of complex disease. We studied the association between 43 pathway-related candidate genes with ‘intermediate phenotype’ (i.e. corresponding plasma protein) and diabetic nephropathy in a customised microarray of 1,536 SNPs. Methods  In this case–control study of type 2 diabetic Chinese individuals with and without diabetic nephropathy, cases (n = 545) were defined on the basis of a spot urinary albumin/creatinine ratio (ACR) > 113 mg/mmol; the value for controls (n = 503) was ACR < 3.3 mg/mmol. Genotyping was performed using Illumina GoldenGate assay. Results  No single nucleotide polymorphism (SNP) remained significant in single locus analysis after correction for multiple testing. Therefore, we explored the best ∼1% SNPs. Of these 13 SNPs, four clustered to a 5′ end NADPH oxidase homologue 4 (NOX4) haplotype (GGCC frequency = 0.776) with estimated OR for diabetic nephropathy of 2.05 (95% CI 1.04–4.06) (heterozygous) and 2.48 (1.27–4.83) (homozygous) (p = 0.0055). The haplotype was correlated with plasma Cu/Zn superoxide dismutase (SOD) concentration, suggesting increased oxidative burden. Endothelin-1 SNP (rs1476046G>A, frequency = 0.252) was correlated with plasma C-terminal pro-endothelin-1 concentrations with an estimated OR for diabetic nephropathy of (heterozygous) 1.26 (0.96–1.66) and (homozygous) 1.87 (1.13–3.12) (p = 0.0072). Nitric oxide synthase 1 (NOS1) 5′ haplotype (TGTC frequency = 0.38) also revealed a suggestive association with diabetic nephropathy: heterozygous 1.26 (0.95–1.67), homozygous 1.57 (1.04–2.35) (p = 0.0073). A rare NADPH oxidase homologue 1 (NOX1)-coding non-synonymous SNP (Arg315His, frequency = 0.006) was found exclusively among cases. Conclusions/interpretation  Our preliminary observations suggest that common haplotypes from NOX4 and endothelin-1 SNP correlated with plasma Cu/Zn SOD and C-terminal pro-endothelin-1 concentrations, respectively, and might have conferred diabetic nephropathy susceptibility. Common NOS1 and rare NOX1 variants also revealed a suggestive association with diabetic nephropathy. Future studies to validate our observation are needed. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorised users.     

Genetic variations in the pancreatic ATP-sensitive potassium channel, β-cell dysfunction, and susceptibility to type 2 diabetes

The KCNJ11 and ABCC8 genes encode the components of the pancreatic ATP-sensitive potassium (KATP) channel, which regulates insulin secretion by β-cells and hence could be involved in the pathogenesis of type 2 diabetes (T2D). The KCNJ11 E23K and ABCC8 exon 31 variants have been studied in 127 Russian T2D patients and 117 controls using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) approach. The KCNJ11 E23 variant and the ABCC8 exon 31 allele A were associated with higher risk of T2D [Odds ratio (OR) of 1.53 (P = 0.023) and 2.41 (P = 1.95 × 10⁻⁵)], respectively. Diabetic carriers of the ABCC8 G/G variant had reduced 2 h glucose compared to A/A + A/G (P = 0.031). The G/G genotype of ABCC8 was also significantly associated with increased both fasting and 2 h serum insulin in diabetic and non-diabetic patients. A HOMA-β value characterizing the β-cell homeostasis was higher in the non-diabetic carriers homozygous for G/G (98.0 ± 46.9) then for other genotypes (HOMA-β = 85.6 ± 45.5 for A/A + A/G, P = 0.0015). The KCNJ11 E23K and ABCC8 exon 31 variants contribute to susceptibility to T2D diabetes, glucose intolerance and altered insulin secretion in a Russian population.     

Possible involvement of NADPH oxidase and JNK in homocysteine-induced oxidative stress and apoptosis in human umbilical vein endothelial cells

Hyperhomocysteinemia is an independent risk factor for cardiovascular diseases, although the mechanism leading to vascular dysfunction is not clear. The aim of this study was to examine the effect of homocysteine (Hcy) on oxidative stress and apoptosis in human umbilical vein endothelial cells (HUVECs). HUVECs were challenged for 24 h with Hcy (10 μM-3 mM) in the presence of various stress signaling inhibitors, including the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor apocynin (100 μM), the p38 mitogen-activated protein kinase inhibitor SB203580 (2.5 μM), the extracellular signal-regulated kinase inhibitor U0126 (2.5 μM), the stress-activated protein kinase (SAPK)/c-Jun NH₂-terminal kinase (JNK) inhibitor JNK inhibitor II (10 μM), and antioxidants α-tocopherol (5 μg/mL) and N-acetyl cysteine (NAC, 2 mM). Reactive oxygen species (ROS) were detected using 5-(6)-chloromethyl-2′,7′-dichlorodihydrofluorescein diacetate. Apoptosis was evaluated by 4′,6′-diamidino-2′-phenylindoladihydrochloride staining, annexin-V phosphatidyl-serine/propidium iodide, and caspase-3 assay. NADPH oxidase and SAPK/JNK signal were evaluated with immunoblotting. Hcy significantly enhanced ROS generation and apoptosis after 24-h incubation. Apocynin prevented Hcy-induced ROS generation but only partially restored Hcy-induced apoptosis. JNK inhibitor II, α-tocopherol, and NAC partially reduced Hcy-induced apoptosis, although SB203580 and U0126 had no effect. Immunoblotting analysis confirmed upregulation of NADPH oxidase and SAPK/JNK signaling. Collectively, our results suggested that Hcy may induce oxidative stress and apoptosis through an NADPH oxidase and/or JNK-dependent mechanisms(s). The first two authors contributed equally to this work.     

Characterization of an apparently synonymous F5 mutation causing aberrant splicing and factor V deficiency

Coagulation factor V (FV) deficiency is a rare autosomal recessive bleeding disorder. We investigated a patient with severe FV deficiency (FV:C < 3%) and moderate bleeding symptoms. Thrombin generation experiments showed residual FV expression in the patient's plasma, which was quantified as 0.7 ± 0.3% by a sensitive prothrombinase‐based assay. F5 gene sequencing identified a novel missense mutation in exon 4 (c.578G>C, p.Cys193Ser), predicting the abolition of a conserved disulphide bridge, and an apparently synonymous variant in exon 8 (c.1281C>G). The observation that half of the patient's F5 mRNA lacked the last 18 nucleotides of exon 8 prompted us to re‐evaluate the c.1281C>G variant for its possible effects on splicing. Bioinformatics sequence analysis predicted that this transversion would activate a cryptic donor splice site and abolish an exonic splicing enhancer. Characterization in a F5 minigene model confirmed that the c.1281C>G variant was responsible for the patient's splicing defect, which could be partially corrected by a mutation‐specific morpholino antisense oligonucleotide. The aberrantly spliced F5 mRNA, whose stability was similar to that of the normal mRNA, encoded a putative FV mutant lacking amino acids 427–432. Expression in COS‐1 cells indicated that the mutant protein is poorly secreted and not functional. In conclusion, the c.1281C>G mutation, which was predicted to be translationally silent and hence neutral, causes FV deficiency by impairing pre‐mRNA splicing. This finding underscores the importance of cDNA analysis for the correct assessment of exonic mutations.     

Proline impairs energy metabolism in cerebral cortex of young rats

In the present study we investigated the effect of acute hyperprolinemia on some parameters of energy metabolism, including the activities of succinate dehydrogenase and cytocrome c oxidase and ¹⁴CO₂ production from glucose and acetate in cerebral cortex of young rats. Lipid peroxidation determined by the levels of thiobarbituric acid-reactive substances, as well as the influence of the antioxidants α-tocopherol plus ascorbic acid on the effects elicited by Pro on enzyme activities and on the lipid peroxidation were also evaluated. Wistar rats of 12 and 29 days of life received one subcutaneous injection of saline or proline (12.8 or 18.2 μmol/g body weight, respectively) and were sacrificed 1 h later. In another set of experiments, 5- and 22-day-old rats were pretreated for a week with daily intraperitoneal administration of α-tocopherol (40 mg/kg) plus ascorbic acid (100 mg/kg) or saline. Twelve hours after the last injection, rats received one injection of proline or saline and were sacrificed 1 h later. Results showed that acute administration of proline significantly reduced cytochrome c oxidase activity and increased succinate dehydrogenase activity and ¹⁴CO₂ production in cerebral cortex, suggesting that Pro might disrupt energy metabolism in brain of young rats. In addition, proline administration increased the thiobarbituric acid-reactive substances levels, which were prevented by antioxidants. These findings suggest that mitochondrial dysfunction and oxidative stress may be important contributors to the neurological dysfunction observed in some hyperprolinemic patients and that treatment with antioxidants may be beneficial in this pathology.     

3-Hydroxyisobutyrate aciduria and mutations in the <Emphasis Type="Italic">ALDH6A1</Emphasis> gene coding for methylmalonate semialdehyde dehydrogenase

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.     

Pathogenesis of CNS involvement in disorders of amino and organic acid metabolism

Summary Inherited disorders of amino and organic acid metabolism have a high cumulative frequency, and despite heterogeneous aetiology and varying clinical presentation, the manifestation of neurological disease is common. It has been demonstrated for some of these diseases that accumulating pathological metabolites are directly involved in the manifestation of neurological disease. Various pathomechanisms have been suggested in different in vitro and in vivo models including an impairment of brain energy metabolism, an imbalance of excitatory and inhibitory neurotransmission, altered transport across the blood–brain barrier and between glial cells and neurons, impairment of myelination and disturbed neuronal efflux of metabolic water. This review summarizes recent knowledge on pathomechanisms involved in phenylketonuria, glutaric aciduria type I, succinic semialdehyde dehydrogenase deficiency and aspartoacylase deficiency with examples, highlighting general as well as disease-specific concepts and their putative impact on treatment. Competing interests: None declared References to electronic databases: Phenylketonuria: OMIM #261600. Glutaric aciduria type I: OMIM #231670. Succinic semialdehyde dehydrogenase deficiency: OMIM #271980. Aspartoacylase disease (Canavan–van Bogaert–Bertrand disease): OMIM #271900. Phenylalanine hydroxylase: EC 1.14.16.1. Glutaryl-CoA dehydrogenase: EC 1.3.99.7. Succinic semialdehyde dehydrogenase: EC 1.2.1.16. Aspartoacylase: EC 3.5.1.15. Presented at the Annual Symposium of the SSIEM, Hamburg, 4–7 September 2007     

Novel NF1 gene mutation in a Japanese patient with neurofibromatosis type 1 and a gastrointestinal stromal tumor

Many mutations of the NF1 gene have been reported in patients with neurofibromatosis type 1 (NF1); however, there have been no documented NF1 gene mutations in Japanese NF1 patients. In the present study, we used the polymerase chain reaction (PCR) and DNA sequencing analysis to characterize the NF1 gene in a 53-year-old Japanese patient with NF1 who suffered from neurofibroma, pheochromocytoma, and gastrointestinal stromal tumor (GIST). Direct sequence analyses revealed a single base substitution in the splicing donor site of intron 6 (IVS6 888+1, G → A) in one NF1 allele, resulting in an altered splice site (ss) in the mutated allele. Splicing at the cryptic 5′ ss in the mutated allele generated mRNA with an insertion of 60 nucleotides. In addition, we screened for mutations in exons 9, 11, 13, and 17 of the c-kit gene in GIST and the succinate dehydrogenase subunit D (SDHD) gene in the pheochromocytoma, but we did not detect any somatic mutations. We report here the first case of an NF1 patient with four neoplasms: neurofibroma, pheochromocytoma, astrocytoma and GIST. Our results suggest that the molecular pathogenesis of GISTs in NF1 patients is different from that in non-NF1 patients.