Organization of the mevalonate kinase (MVK) gene and identification of novel mutations causing mevalonic aciduria and hyperimmunoglobulinaemia D and periodic fever syndrome

Mevalonic aciduria (MA) and hyperimmunoglobulinaemia D and periodic fever syndrome (HIDS) are two autosomal recessive inherited disorders both caused by a deficient activity of the enzyme mevalonate kinase (MK) resulting from mutations in the encoding MVK gene. Thus far, disease-causing mutations only could be detected by analysis of MVK cDNA. We now describe the genomic organization of the human MVK gene. It is 22 kb long and contains 11 exons of 46 to 837 bp and 10 introns of 379 bp to 4.2 kb. Three intron-exon boundaries were confirmed from natural splice variants, indicating the occurrence of exon skipping. Sequence analysis of 27 HIDS and MA patients confirmed all previously reported genotypes based on cDNA analysis and identified six novel nucleotide substitutions resulting in missense or nonsense mutations, providing new insights in the genotype/phenotype relation between HIDS and MA.     

Molecular analysis of MVK mutations and enzymatic activity in hyper-IgD and periodic fever syndrome

Hyperimmunoglobulinaemia D and periodic fever syndrome (HIDS) is an autosomal recessive inflammatory disorder characterised by recurrent episode of fever associated with lymphadenopathy, abdominal distress, joint involvement and skin lesions. We recently demonstrated that mutations in the mevalonate kinase gene (MVK) are associated with HIDS. Direct DNA sequencing was done to screen the entire coding region of MVK in 25 unrelated patients with HIDS. Mutations were detected in the coding region of the gene including 11 missense mutations, one deletion, the absence of expression of one allele, as well as three novel polymorphisms. Seven of these mutations are novel. The large majority of the patients were compound heterozygotes for two mutations. Of these, V377I (G-->A) is the most common mutation occurring in 20 unrelated patients and was found to be associated with I268T in six patients. Mutations were associated with a decrease of mevalonate kinase (MK) (ATP:mevalonate 5-phosphotransferase, EC 2.7.I.36) enzymatic activity but not as profound as in mevalonic aciduria, a syndrome also caused by a deficient activity of MK. In HIDS the mutations are located all along the protein which is different from mevalonic aciduria where MK mutations are mainly clustered to a same region of the protein. On the basis of this study, we propose that the diagnostic screen of MVK in HIDS should be first directed on V377I and I268T mutations. Three patients are also described to illustrate the genotypic and phenotypic overlap with mevalonic aciduria.     

Carrier frequency of the V377I (1129G>A) MVK mutation,associated with Hyper-IgD and periodic fever syndrome,in the Netherlands

Hyper-IgD and periodic fever syndrome (HIDS) and mevalonic aciduria (MA) are two autosomal recessive disorders that both are caused by a deficient activity of the enzyme mevalonate kinase (MK) due to mutations in the encoding gene (MVK). The most frequently occurring MVK mutation, V377I (1129G>A), has been identified exclusively in HIDS patients. Other common mutations have been associated with both HIDS and MA. To estimate the incidence of MK deficiency in the Netherlands, we determined the carrier frequency of the V377I mutation in genomic DNA extracted from anonymised newborn screening cards by PCR-RFLP. We found 14 carriers among 2138 analysed samples (1 : 153). Based on the V377I allele frequency of 42% in patients diagnosed with MK deficiency, the carrier frequency of any MVK mutation in the Dutch population can be calculated as 1 : 65. This predicts a disease incidence between 1 in 5196 and 1 in 53 656, which is far more than actually observed. Although under-diagnosis of patients with MK deficiency remains possible, this discrepancy probably is due to a reduced penetrance of V377I homozygosity. Analysis of the distribution of the V377I allele within patients carrying MVK mutations revealed that this was not according to the Hardy-Weinberg equilibrium principle, most probably due to an under-representation of V377I homozygotes in HIDS. Homozygotes for V377I might exhibit a much milder phenotype of MK deficiency or no disease-phenotype at all.     

Hyper IgD syndrome (HIDS) associated with in vitro evidence of defective monocyte TNFRSF1A shedding and partial response to TNF receptor blockade with etanercept

Hereditary periodic fever syndromes comprise a group of distinct disease entities linked by the defining feature of recurrent febrile episodes. Hyper IgD with periodic fever syndrome (HIDS) is caused by mutations in the mevalonate kinase (MVK) gene. The mechanisms by which defects in the MVK gene cause febrile episodes are unclear and there is no uniformly effective treatment. Mutations of the TNFRSF1A gene may also cause periodic fever syndrome (TRAPS). Treatment with the TNFR-Fc fusion protein, etanercept, is effective in some patients with TRAPS, but its clinical usefulness in HIDS has not been reported. We describe a 3-year-old boy in whom genetic screening revealed a rare combination of two MVK mutations producing clinical HIDS as well as a TNFRSF1A P46L variant present in about 1% of the population. In vitro functional assays demonstrated reduced receptor shedding in proband's monocytes. The proband therefore appears to have a novel clinical entity combining Hyper IgD syndrome with defective TNFRSF1A homeostasis, which is partially responsive to etanercept.     

MVK gene abnormality and new approach to treatment of hyper IgD syndrome and periodic fever syndrome]

Hyper IgD and periodic fever syndrome (HIDS; OMIM 260920) is one of the hereditary autoinflammatory syndromes characterized by recurrent episodes of fever and inflammation.. HIDS is an autosomal recessive disorder characterized by recurrent fever attacks in early childhood. HIDS caused by mevalonate kinase (MK) mutations, also that is the gene of mevalonic aciduria (OMIM 251170). During febrile episodes, urinary mevalonate concentrations were found to be significantly elevated in patients. Diagnosis of HIDS was retrieving gene or measurement of the enzyme activity in peripheral blood lymphocyte in general. This of HIDS is an activity decline of MK, and a complete deficiency of MK becomes a mevalonic aciduria with a nervous symptom. The relation between the fever and inflammation of mevalonate or isoprenoid products are uncertain. The therapy attempt with statins, which is inhibited the next enzyme after HMG-CoA reductase, or inhibit the proinflammatory cytokines.     

Mutational spectrum and genotype-phenotype correlations in mevalonate kinase deficiency

Mevalonate kinase deficiency (MKD) is an autosomal recessive autoinflammatory disorder caused by mutations in the MVK gene resulting in deficient activity of mevalonate kinase (MK). Depending on the clinical severity, MKD may present as hyper-IgD and periodic fever syndrome (HIDS) or the more severe mevalonic aciduria (MA). We analyzed the MVK gene in 57 patients with MKD and found 39 different mutations including 15 novel mutations, expanding the total mutational spectrum of MKD to 63 mutations. To get more insight into the genotype-phenotype correlation in MKD, we studied the effect of selected missense mutations on MK protein stability and activity in various patient fibroblast cell lines. All MKD cell lines showed markedly decreased MK activities that correlated well with the clinical severity and, for most of the cell lines, with the amount of MK protein. When fibroblasts of MKD patients were cultured under conditions known to promote a more controlled protein folding, all cell lines of patients with the HIDS phenotype and few cell lines of patients with the MA phenotype showed an increase in the residual MK activity. This increase in enzyme activity correlates well with an increase in the MK protein levels in these cell lines, indicating that most of the mutations in MKD affect stability and/or folding of the MK protein rather than affecting the catalytic properties of the enzyme. The finding that the residual activity in MKD can be manipulated by environmental conditions may offer therapeutic options to alleviate or prevent the clinical symptoms associated with MKD.     

Temperature dependence of mutant mevalonate kinase activity as a pathogenic factor in hyper-IgD and periodic fever syndrome

Hyper-IgD and periodic fever syndrome (HIDS) and mevalonic aciduria are autosomal recessive disorders characterized by recurrent episodes of fever and generalized inflammation. Both syndromes are caused by specific mutations in the gene encoding mevalonate kinase (MK), resulting in a depressed enzymatic activity mainly due to reduced protein levels. We studied the effect of temperature on the activity of wild-type and several mutant MKs in fibroblasts. All fibroblast cell lines from HIDS patients and harbouring the common V377I MVK allele displayed substantially higher MK activities at 30 degrees C as compared to 37 degrees C. As shown by temperature inactivation experiments this resulted in a protein nearly as stable as in control cell lines, indicating that primarily the maturation of the protein is affected. Accordingly, when HIDS cell lines were cultured at 39 degrees C, MK activity decreased further. This triggered a compensatory increase in 3-hydroxy-3-methylglutaryl-CoA reductase activity, indicating that MK becomes progressively rate-limiting. A similar phenomenon occurs in vivo. MK activity in peripheral blood mononuclear cells drops 2-8-fold when HIDS patients experience febrile attacks. Our results suggest that minor elevations in temperature can set off a chain of events with MK becoming progressively rate-limiting, leading to a temporary deficiency of isoprenoid end-products, which induces inflammation and fever.     

MVK mutations and associated clinical features in Italian patients affected with autoinflammatory disorders and recurrent fever

Autosomal recessive autoinflammatory disorder caused by mutations of the mevalonate kinase gene (MVK), leading to mild, incomplete MK enzyme deficiency (MKD), has been known so far as Hyper-IgD and periodic fever syndrome (HIDS) and regarded as mostly occurring in Northern Europe. Here we report the results of the molecular characterization of the first Italian series of patients affected with autoinflammatory disorders and periodic fever. A total of 13 different mutations, scattered throughout the MVK coding region, were identified in either homozygous or compound heterozygous state in 15 patients. The mutation leading to the V377I amino-acid change, already described also in other series, resulted the most common with a frequency of 50% of all MKD alleles. Among the other mutations, eight had never been described before, including an interstitial deletion of 19 nucleotides in exon 2. In addition to these nucleotide changes, private and polymorphic MVK variants have been detected in the patients under analysis and checked also in a set of control individuals. Clinical features are reported for each of the 15 MKD patients, and life-threatening infections and systemic amyloidosis presented as unexpected MKD-related complications. Our study demonstrates that MKD is a common cause of recurrent fever also in the Italian population, where it is associated with both a wide spectrum of previously unreported MVK mutations and peculiar phenotypic features.     

Intermittent Neutropenia as an Early Feature of Mild Mevalonate Kinase Deficiency

A 15-month-old boy, born to Iranian consanguineous parents presented with intermittent neutropenia interspersed with episodes of fever and leukocytosis since early infancy. No ELA2 mutations were found and the bone marrow study was normal. At age 4 years he progressed to more typical attacks of periodic attacks of fever, abdominal pain, oral aphthous ulcers, cutaneous rash and leukocytosis. The clinical and laboratory features were compatible with the mild form of mevalonate kinase deficiency, usually named “Hyper-IgD and periodic fever syndrome” (HIDS). Genomic sequencing of the mevalonate kinase (MVK) gene revealed homozygous missense mutation (p.Val377Ile). On demand dexamethasone resulted in a rapid amelioration of febrile episodes. The presentation of intermittent neutropenia has not been reported in HIDS and deserves more attention in large patient cohorts.     

Hyperimmunoglobulinemia D and periodic fever syndrome

Hyperimmunogloblinemia D and periodic fever syndrome (HIDS) is inherited autoinflammatory syndrome caused by deficiency of the mevalonate kinase (MK), which is involved in metabolism of cholesterol. The disease is characterized as periodic fever from early infancy accompanied by elevated serum C-reactive protein. Since clinical symptoms such as abdominal symptom, skin rash, and arthritis are common to other autoinflammatory disease, the diagnosis of HIDS during clinical work is difficult for the physicians without suspicion of HIDS for infants suffering from fever of unknown origin. Moreover, serum IgD levels are not high during infancy conflicting to the name of the disease, which is often misunderstood in the clinicians. Thus, the diagnosis of HIDS in Japan is bothering, depending on the lack of correct recognition of the disease and on the lack of commercially available examination for the disease. It is important for clinicians, especially pediatricians to update current knowledge about HIDS and to learn the appropriate way to the definitive diagnosis of HIDS, because HIDS patients exist also in Japan and the specific therapies for HIDS would be developed in the near future.     

In Silico Prediction of the Effects of Mutations in the Human Mevalonate Kinase Gene: Towards a Predictive Framework for Mevalonate Kinase Deficiency

Mevalonate kinase (MVK) catalyses the phosphorylation of mevalonate. Deficiency of MVK is associated with two rare periodic fever syndromes, mevalonic aciduria (MA), a severe form and hyper‐immunoglobulin‐D syndrome (HIDS), a milder form. An in silico approach was used to analyse the physicochemical and structural effects of 47 disease‐associated variants of MVK. A further 20 variants, which are present in human genome databases, were also analysed. Variants associated with MA are clustered into a “hotspot” consisting of residues 8–35 and 234–338 and tended to result in a prediction of severely reduced protein stability. Four of the uncharacterised variants, p.H24P, p.G198R, p. R253W, and p.G335S, were likely to be associated with MA. This method could be used as the basis for initial predictions of severity when new MVK variants are discovered.     

A severe autosomal-dominant periodic inflammatory disorder with renal AA amyloidosis and colchicine resistance associated to the MEFV H478Y variant in a Spanish kindred: an unusual familial Mediterranean fever phenotype or another MEFV-associated periodic inflammatory disorder?

Familial Mediterranean fever (FMF) is an autosomal recessive disease characterized by recurring short attacks of fever and serositis. Secondary AA amyloidosis is the worst complication of the disease and often determines the prognosis. The MEFV gene, on chromosome 16p13.3, is responsible for the disease and around 30 mutations have been reported to date. Colchicine is the standard FMF treatment today, and prevents both attacks and amyloid deposition in 95% of patients. Here we describe a three-generation Spanish kindred with five family members affected by a severe periodic inflammatory disorder associated with renal AA amyloidosis and colchicine unresponsiveness. Clinical diagnosis of definite FMF disease was made based on the Tel-Hashomer criteria set. Genetic analyses revealed that all subjects were heterozygous for the new H478Y MEFV variant, segregating with the disease. In addition, mutations in the TNFRSF1A and CIAS1/PYPAF1/NALP3 genes, related to the dominantly inherited autoinflammatory periodic syndromes, were ruled out. However, the dominant inheritance of the disease, the long fever episodes with a predominant joint involvement, and the resistance to colchicine in these patients raise the question of whether the periodic syndrome seen in this kindred is a true FMF disease with unusual manifestations or rather another MEFV-associated periodic syndrome. We conclude that the new H478Y MEFV mutation is the dominant pathological variant causing the inflammatory periodic syndrome in this kindred and that full-length analyses of the MEFV gene are needed to obtain an adequate diagnosis of patients with clinical suspicion of a hereditary periodic fever syndrome, especially those from non-ancestral populations.     

Hyper-immunoglobulin A in the hyperimmunoglobulinemia D syndrome

The hyperimmunoglobulinemia D syndrome (HIDS) is an autosomal recessive disorder characterized by recurrent febrile attacks with abdominal, articular, and skin manifestations. Apart from elevated immunoglobulin D (IgD) levels (>100 IU/ml), there are high IgA levels in the majority of cases. Mutations in the gene encoding mevalonate kinase constitute the molecular defect in HIDS. The cause of elevated IgA concentrations in HIDS patients remains to be elucidated. We studied the hyper-IgA response in serum of a group of HIDS patients. Elevated IgA concentrations result from increased IgA1 concentrations. IgA and IgA1 concentrations correlated significantly with IgD concentrations, and levels of IgA polymers were significantly higher than the levels in healthy donors. These results indicate a continuous, presumably systemic, stimulation of IgA in HIDS patients.     

Hyper-Immunoglobulin A in the Hyperimmunoglobulinemia D Syndrome

The hyperimmunoglobulinemia D syndrome (HIDS) is an autosomal recessive disorder characterized by recurrent febrile attacks with abdominal, articular, and skin manifestations. Apart from elevated immunoglobulin D (IgD) levels (>100 IU/ml), there are high IgA levels in the majority of cases. Mutations in the gene encoding mevalonate kinase constitute the molecular defect in HIDS. The cause of elevated IgA concentrations in HIDS patients remains to be elucidated. We studied the hyper-IgA response in serum of a group of HIDS patients. Elevated IgA concentrations result from increased IgA1 concentrations. IgA and IgA1 concentrations correlated significantly with IgD concentrations, and levels of IgA polymers were significantly higher than the levels in healthy donors. These results indicate a continuous, presumably systemic, stimulation of IgA in HIDS patients.     

Tumor necrosis factor receptor-associated periodic syndrome (TRAPS) in a Dutch family: evidence for a TNFRSF1A mutation with reduced penetrance

Mutations of the tumor necrosis factor receptor 1 (TNFRSF1A) gene underly susceptibility to a subset of autosomal dominant recurrent fevers (ADRFs). We report on a two-generation six-member Dutch family in which a novel R92P mutation and reduced plasma TNFRSF1A levels were found in all the children, including two who are unaffected. However, only the daughter proband and father exhibited a typical TNF-receptor associated periodic syndrome (TRAPS) phenotype. PCR-RFLP analysis revealed that the mutation was not present in 120 control chromosomes from unaffected Dutch individuals. As this R92P mutation is present in two unaffected carriers it appears to be less penetrant than previously reported TNFRSF1A mutations involving cysteine residues in the extracellular domains.     

Detection of a novel missense mutation in the mevalonate kinase gene in one Chinese family with DSAP

Disseminated superficial actinic porokeratosis (DSAP) is the most common form of porokeratosis and a severe chronic autosomal dominant cutaneous disorder with high genetic heterogeneity. Recently, the mevalonate kinase (MVK) gene has been identified as a candidate gene responsible for DSAP and multiple mutations have been reported. Here, we report identification of a novel missense mutation in the MVK gene in a Chinese family with DSAP. A 50-year-old male was diagnosed as proband of DSAP based on the clinical and histological findings, which show numerous hyperpigmented macules by physical examination and cornoid lamella by skin biopsy. Similar skin symptoms were also observed in his father, who died many years ago. We prepared genomic DNA from the proband, unaffected individuals from his family members, as well as 100 unrelated healthy controls. PCR was then conducted using the above genomic DNA as template and the MVK gene-specific primers. The PCR product was subjected to direct sequencing and the sequence was compared to that of MVK gene within the NCBI database. We detected a heterozygous C to G transition at nucleotide 643 in exon 7 of MVK gene of the proband. This will result in an amino acid change at codon 215 (P.Arg215Gly.), which is from an arginine codon (CGA) to a Glycine codon (GGA). We did not detect any mutation in the unaffected family members or the 100 unrelated healthy controls, demonstrating that this is a novel missense mutation in MVK gene and therefore, contributes to the molecular diagnosis of DSAP.     

TNF receptor-associated periodic syndrome (TRAPS) in Japan: clinical characterization, pathogenesis, diagnostic criteria, and treatment]

TNF receptor-associated periodic syndrome (TRAPS) is an autosomal dominant inherited disease characterized by prolonged episodes of periodic fever and localized inflammation. The hypothetical pathogenesis of TRAPS is defective TNF receptor 1 (TNFRSF1A) shedding from cell membranes in response to a stimulus including TNFalpha. This mechanism has recently been shown to account for a minor population of TRAPS patients and other mechanisms are reported to explain the disease, such as resistance to apoptosis, TNFRSF1A internalization, or TNFRSF1A misfolding and aggregation, leading to NF-kappaB activation and apoptosis. Until now 15 TRAPS patients from 5 pedigree including 5 different mutations (C30R, C30Y, T61I, C70S, C70G) had been reported in Japan. There were many sporadic cases of TRAPS without TNFRSF1A mutation in our epidemiological study. In this issue, we described the clinical characterization, pathogenesis, diagnostic criteria, and treatment of TRAPS according to our case and literature.     

Unexpected high frequency of P46L TNFRSF1A allele in sub-Saharan West African populations

TNF receptor-associated periodic syndrome (TRAPS) is an autosomal dominant disorder characterized by recurrent attacks of fever and serositis. To date, more than 30 mutations have been reported in TNFRSF1A, the responsible gene. In Caucasian populations, the P46L (c.224C>T) TNFRSF1A sequence variation is considered as a low-penetrance mutation because its allele frequency is similar in patients and controls ( approximately 1%). Whereas the spectrum of TNFRSF1A gene mutations has been well established in Caucasian and several Mediterranean populations, it remains unknown in sub-Saharan African populations. In this study, we found an unexpected high P46L allele frequency ( approximately 10%) in two groups from West Africa - a group of 145 patients with sickle cell anaemia and a group of 349 healthy controls. These data suggest that the P46L variant is rather a polymorphism than a TRAPS causative mutation. We propose that the P46L high frequency in West African populations could be explained by some biological advantage conferred to carriers.     

A novel Y331X nonsense mutation in TNFRSF1A gene in two unrelated Turkish families with periodic fever syndrome

The autoinflammatory disorders differ in severity, as well as age of onset, duration, and manifestations, but they all share some common features: recurring fever peaks, inflammation of serosal membranes, musculoskeletal involvement, varying types of skin rash, amyloidosis as a sequel of the disease. TRAPS is very rare in Turkish population and we present two unrelated Turkish children with similar clinical phenotypes and laboratory findings related with autoinflammatory disorders and with novel p. Y331X mutation in TNFRSF1A gene. Both of the patients were male and they had recurrent fever without abdominal pain and arthralgia. Full cDNA and exon–intron binding regions of TNFRSF1A, MEFV, MVK, CIAS1 genes were analysed by direct DNA sequencing methods in order to differentiate TRAPS, FMF, HIDS, CINCA/MWS/FCAS respectively. We screened ten exons of TNFRSF1A gene, and detected a heterozygous c.1080C>G nucleotide substitution in exon 10 in both of the unrelated patients, resulting p.Y360X nonsense (protein truncated) mutation. According to classical TNFRSF1A gene nomenclature and the agreement of 30th amino acid as the first one, it is accepted as p.Y331X. It was interesting to determine same mutations in fathers of two patients. In one of the cases, E148Q heterozygous mutation, which is one of the disease-causing mutations of MEFV gene, was detected. No nucleotide substitution was identified in exon and exon–intron splicing regions encoding 396 amino acid of MVK gene in both of the patients. In CIAS1 gene, two different nucleotide substitutions resulting synonymous amino acid mutation were detected in exon 3: c.[732G>A] and c.[786A>G] nucleotide substitutions and compatible p.A242A (according to c.DNA p.A244A) and p.R260R (according to c.DNA p.R262R) synonymous amino acid mutations. These nucleotide substitutions were also detected in parents and were reported to be normal variations in Turkish population. In conclusion, in Turkish patients, with dominantly inherited recurrent fever, TRAPS is a diagnosis worthy of attention and novel mutations have to be reported with phenotype associations.