Hyperimmunoglobulinaemia D And Periodic Fever Syndrome Research Articles

Mevalonate kinase deficiency in 2016

Mevalonate kinase deficiency is a rare, autosomal recessive, auto-inflammatory disease. This results from mutations in the gene MVK coding for the enzyme mevalonate kinase. This enzyme is involved in cholesterol and isoprenoids synthesis. Depending partially of the residual activity of the mevalonate kinase, the clinical spectrum realizes a continuum which extends from the mild phenotype of the hyperimmunoglobulinemia D and periodic fever syndrome (HIDS) to a lethal form of mevalonic aciduria. The HIDS is characterized by recurrent episodes of fever with an intense inflammatory syndrome, accompanied with lymphadenopathy, abdominal pain, diarrhea, arthralgia, hepatomegaly, splenomegaly and skin rash. The first attack more frequently takes place in the first year of life, even during the neonatal period, where it can be confused with a maternofetal infection. There is furthermore in mevalonate aciduria a psychomotor retardation, a failure to thrive, a cerebellar ataxia, a dysmorphic syndrome and a reduction of the visual acuity. The diagnosis is based on the mevalonic aciduria during febrile attack. Genetics confirm the diagnosis in more than 80% of the cases. The dosage of IgD, low sensitive and specific, has no interest. There is no reference treatment. The less severe forms can be treated by non-steroidal anti-inflammatory drugs or steroids during febrile attacks. The most severe patients can be treated by biotherapy: antagonists of IL-1, TNF-α and IL-6.

Homozygosity for the V377I mutation in mevalonate kinase causes distinct clinical phenotypes in two sibs with hyperimmunoglobulinaemia D and periodic fever syndrome (HIDS)

ObjectiveMevalonate kinase (MVK) deficiency is a rare autosomal recessive auto-inflammatory disorder characterised by recurring episodes of fever associated with multiple non-specific inflammatory symptoms and caused by mutations in the MVK...

Quantification of mevalonate-5-phosphate using UPLC-MS/MS for determination of mevalonate kinase activity

ObjectivesMevalonate kinase deficiency, a rare autosomal recessive autoinflammatory disease, is caused by mutations in the MVK gene encoding mevalonate kinase (MK). MK catalyzes the phosphorylation of mevalonic acid to mevalonate-5-phosphate (MVAP) in the pathway of isoprenoid and sterol synthesis. The disease phenotype correlates with residual activity ranging from <0.5% for mevalonic aciduria to 1–7% for the milder hyperimmunoglobulinemia D and periodic fever syndrome (HIDS). Hence, assessment of loss-of-function requires high accuracy measurements. We describe a method using isotope dilution UPLC-MS/MS for precise and sensitive determination of MK activity. Design and methodsWild-type MK and the variant V261A, which is associated with HIDS, were recombinantly expressed in Escherichia coli. Enzyme activity was determined by formation of MVAP over time quantified by isotope dilution UPLC-MS/MS. The method was validated according to the FDA Guidance for Bioanalytical Method Validation. ResultsSensitivity for detection of MAVP by UPLC-MS/MS was improved by derivatization with butanol–HCl (LLOQ, 5.0fmol) and the method was linear from 0.5 to 250μmol/L (R2>0.99) with a precision of ≥89% and an accuracy of ±2.7%. The imprecision of the activity assay, including the enzymatic reaction and the UPLC-MS/MS quantification, was 8.3%. The variant V261A showed a significantly decreased activity of 53.1%. ConclusionAccurate determination of MK activity was enabled by sensitive and reproducible detection of MVAP using UPLC-MS/MS. The novel method may improve molecular characterization of MVK mutations, provide robust genotype–phenotype correlations, and accelerate compound screening for drug candidates restoring variant MK activity.

TLR2/TLR4-dependent exaggerated cytokine production in hyperimmunoglobulinaemia D and periodic fever syndrome.

The autoinflammatory hyperimmunoglobulinaemia D and periodic fever syndrome (HIDS) is characterized by recurrent episodes of fever and inflammation. As part of the mevalonate kinase deficiency spectrum, it is caused by MVK mutations, resulting in decreased mevalonate kinase activity in the isoprenoid pathway. Although IL-1β is considered a major cytokine in its pathogenesis, IL-1 blockade is not successful in a proportion of patients. We aimed to further characterize the pro-inflammatory cytokine profile of HIDS. Peripheral blood mononuclear cells from HIDS patients and healthy donors were incubated with several stimuli. Cytokine concentrations were detected by ELISA. To analyse mRNA and protein expression, we performed quantitative RT-PCR and western blot, respectively. We observed significant differences in cytokine production when cells were incubated with ligands for Toll-like receptor 2 (TLR2), TLR4 and nucleotide-binding oligomerization domain-containing 2 (NOD2). The increased ratio between active and inactive caspase-1 protein in HIDS patients could explain why these cells are more easily triggered to secrete IL-1β. This is apparently not regulated at the transcriptional level, since expression levels of caspase-1 and IL-1β mRNA were similar in patients and controls. Both anakinra and tocilizumab treatment resulted in decreased inflammation, both ex vivo as well as in vivo. The increased cytokine secretion in HIDS is specific for TLR2, TLR4 and NOD2 ligation. Although IL-1β is important in the HIDS pathology, our data suggest it is a multicytokine disease. A more rigorous clinical trial is required to determine whether IL-6 receptor blockade may be considered in patients not responding to anakinra treatment.

Sterol metabolism disorders and neurodevelopment—an update

Cholesterol has numerous quintessential functions in normal cell physiology, as well as in embryonic and postnatal development. It is a major component of cell membranes and myelin, and is a precursor of steroid hormones and bile acids. The development of the blood brain barrier likely around 12-18 weeks of human gestation makes the developing embryonic/fetal brain dependent on endogenous cholesterol synthesis. Known enzyme defects along the cholesterol biosynthetic pathway result in a host of neurodevelopmental and behavioral findings along with CNS structural anomalies. In this article, we review sterol synthesis disorders in the pre- and post-squalene pathway highlighting neurodevelopmental aspects that underlie the clinical presentations and course of Smith-Lemli-Opitz Syndrome (SLOS), mevalonic aciduria (MVA) or the milder version hyper-immunoglobulinemia D and periodic fever syndrome (HIDS), Antley-Bixler syndrome with genital anomalies and disordered steroidogenesis (ABS1), congenital hemidysplasia with icthyosiform nevus and limb defects (CHILD) syndrome, CK syndrome, sterol C4 methyl oxidase (SC4MOL) deficiency, X-linked dominant chondrodysplasia punctata 2(CDPX2)/ Conradi Hunermann syndrome, lathosterolosis and desmosterolosis, We also discuss current controversies and share thoughts on future directions in the field.

Incidence and clinical features of hyperimmunoglobulinemia D and periodic fever syndrome (HIDS) and spectrum of mevalonate kinase (MVK) mutations in German children

Autoinflammatory diseases (AIDs) are characterized by recurrent, self-limiting systemic inflammation. Disorders include hereditary recurrent fever (HRF) syndromes such as hyperimmunoglobulinemia D and periodic fever syndrome (HIDS). To determine the incidence of HIDS and report clinical and genetic characteristics together with the underlying MVK genotypes in German children, a prospective active surveillance was conducted in Germany during a period of 3 years. Monthly inquiries were sent to 370 children's hospitals by the German Paediatric Surveillance Unit (Clinic-ESPED, n1) and to two laboratories (Laboratory-ESPED, n2) performing genetic analyses. Inclusion criteria were a MVK mutation-positive patient ≤16 years of age with more than three self-limiting episodes of fever >38.5°C associated with increased inflammation markers. Clinical, epidemiological, and genetic data were assessed via questionnaires. Eight out of 16 patients were identified in Clinic-ESPED (n1) and 15 of 16 in Laboratory-ESPED (n2). Clinical and laboratory surveys overlapped in 7 of 16 cases. Incidence of HIDS was estimated to be 0.39 (95% CI: 0.22, 0.64) per 10(6) person-years. HIDS symptoms generally started in infancy with recurrent fever episodes lasting 3-12 (median, 4.5) days and recurring every 1-12 weeks. Fever was accompanied by abdominal pain, vomiting, diarrhea, cervical lymphadenopathy, and sometimes by headache, skin and joint symptoms. The patients carried 11 different MVK mutations mostly in compound heterozygosity (75%, 12 out of 16). The most frequent mutation was p.Val377Ile (81%, 13 out of 16). In Germany, the incidence of HIDS is very low with 0.39 per 10(6) person-years.

Patient with neonatal-onset chronic hepatitis presenting with mevalonate kinase deficiency with a novel MVK gene mutation

A Japanese girl with neonatal-onset chronic hepatitis and systemic inflammation was diagnosed with hyper-immunoglobulinemia D and periodic fever syndrome (HIDS). However, she lacked the typical HIDS features until the age of 32 months. She had compound heterozygous MVK mutations, H380R and A262P, the latter of which was novel. These findings suggest that HIDS patients could lack typical episodes of recurrent fever at the onset and that HIDS should be considered as a possible cause of neonatal-onset chronic hepatitis.

Translational research network and patient registry for auto-inflammatory diseases

Auto-inflammatory diseases (AIDs) are characterized by recurrent self-limiting systemic inflammation. In a multicentre effort, we set out to register genetic, epidemiological and clinical features as well as prognostic factors of these diseases by prospective longitudinal and long-term documentation, in order to define novel AIDs and to better understand treatment responses and outcome. In 2009, a federally funded clinical and research consortium (AID-Net) was established, including an online registry for AIDs (http://www.aid-register.uk-essen.de). Inclusion criteria are disease-associated mutations for hereditary periodic fever syndromes [FMF, hyperimmunoglobulinaemia D and periodic fever syndrome (HIDS), TNF receptor 1-associated periodic syndrome (TRAPS) and cryopyrin-associated periodic syndrome (CAPS)], or, alternatively, clinically confirmed AID, systemic-onset JIA (SoJIA) and periodic fever, aphthous stomatitis, pharyngitis and adenopathy (PFAPA) syndrome with unknown genetic background. Patients were recruited to the registry and patient material was deposited in biomaterial banks (DNA/serum). In addition, basic research projects were initiated that focus on molecular mechanisms of AID. During the first 9 months, 117 patients (65 males, 52 females; age 1-21 years) have been recorded and classified as FMF (n=84), HIDS (n=1), TRAPS (n=3) and CAPS (n=1); clinically confirmed AID (n=5); SoJIA (n=22); and PFAPA (n=1). One hundred and fifty blood samples of 18 patients were included in biomaterial banks. Recruitment and follow-up of patients with AID will enable us to comprehensively address the correlation between clinical and epidemiological data, genetics and biomarkers. The translational approach may help to identify genetic or inflammatory markers relevant for the course and outcome of diseases.

A Novel Missense Mutation in MVK Associated With MK Deficiency and Dyserythropoietic Anemia

Mevalonate kinase deficiency (MKD) is a rare inborn error of metabolism caused by mutations in the mevalonate kinase (MVK) gene. The clinical phenotype is variable, ranging from the hyperimmunoglobulinemia D and periodic fever syndrome (HIDS) to mevalonic aciduria (MA), a severe metabolic disease. We report here for the first time (to our knowledge) the case of a patient with MKD and congenital dyserythropoietic anemia. Clinical and laboratory characteristics of inflammatory attacks were compatible with HIDS, but mild dysmorphic features and elevated urinary mevalonic acid levels in the absence of an inflammatory attack suggested an intermediate phenotype between HIDS and MA. Genomic sequencing of the MVK gene revealed compound heterozygosity for a missense mutation previously described in MA (V310M) and a novel missense mutation (Y116H). By contrast, sequencing of the novel CDAII (SEC23B) gene revealed no mutations, suggesting that the bone marrow abnormalities were causally related to the MKD. Treatment with corticosteroids and colchicine directed at controlling the autoinflammatory disease resulted in improvement of the anemia.

Abnormal IgD and IgA1 O-glycosylation in hyperimmunoglobulinaemia D and periodic fever syndrome

In order to determine the glycosylation pattern for IgD, and to examine whether there are changes in the pattern of IgD and IgA1 O-glycosylation in patients with hyperimmunoglobulinaemia D and periodic fever syndrome (HIDS) during acute febrile attacks and during periods of quiescence, serum was obtained from 20 patients with HIDS and 20 control subjects. In the HIDS group, serum was obtained either during an acute febrile episode (n = 9) or during a period of quiescence (n = 11). The O-glycosylation profiles of native and desialylated IgA1 and IgD were measured in an ELISA-type system using the lectins Helix aspersa and peanut agglutinin, which bind to alternative forms of O-glycan moieties. IgD is more heavily O-galactosylated and less O-sialylated than IgA1 in healthy subjects. HIDS is associated with more extensive O-galactosylation of IgD and a reduction in O-sialylation of both IgD and IgA1. These changes are present both during acute febrile attacks and periods of quiescence. The T cell IgD receptor is a lectin with binding affinity for the O-glycans of both IgD and IgA1. The observed changes in IgD and IgA1 O-glycosylation are likely to have a significant effect on IgD/IgA1–T cell IgD receptor interactions including basal immunoglobulin synthesis, and possibly myeloid IgD receptor-mediated cytokine release.

Long-Term Follow-Up, Clinical Features, and Quality of Life in a Series of 103 Patients With Hyperimmunoglobulinemia D Syndrome

The hyperimmunoglobulinemia D and periodic fever syndrome (HIDS), one of the autoinflammatory syndromes, is caused by mutations in the gene coding for mevalonate kinase (MVK). We conducted the current study to assess the genetic, laboratory, and clinical features as well as the complications and course of disease in patients with genetically confirmed HIDS. In addition, we studied the quality of life and course of life in a selection of patients. Follow-up data were obtained by a questionnaire sent to all physicians of patients in the International HIDS Database. In addition, we assessed the course of life and quality of life in Dutch patients aged >16 years using validated quality of life instruments. Data were obtained from 103 patients from 18 different countries. The median age of first attack was 6 months (range, 0-120 mo), with a median period of 9.9 years from onset of disease to diagnosis. The most frequent symptoms that accompanied attacks of fever were lymphadenopathy, abdominal pain, arthralgia, diarrhea, vomiting, skin lesions, and aphthous ulcers. Amyloidosis was a severe but infrequent complication (2.9%). The median serum IgD level was 400 U/mL. IgD levels were normal in 22% of patients. The 4 most prevalent mutations (V377I, I268T, H20P/N, P167L) accounted for 71.5% of mutations found. The frequency of attacks decreased with the patient's increasing age, although 50% of patients over the age of 20 years still had 6 or more attacks per year. Many drugs have been tried in HIDS. Some patients responded to high-dose prednisone (24.4% response). Anakinra and etanercept can also be effective (33.3% response). Quality of life was determined in a subgroup of patients (n = 28). Social functioning, general health perception, and vitality were significantly lower in patients with HIDS than in controls, as were autonomy and social development. In addition, HIDS had an adverse impact on educational achievements and employment status. In conclusion, HIDS is an early-onset disease that is accompanied by an array of inflammatory symptoms. Although the frequency of attacks decreases during the patient's life, many patients continue to have frequent attacks. HIDS impairs several aspects of quality of life.

Hyperimmunoglobulinemia D and periodic fever syndrome; treatment with etanercept and follow-up

The hyperimmunoglobulinemia D and periodic fever syndrome (HIDS) is an autoinflammatory syndrome. It is caused by the mutations of the mevalonate kinase gene. There is no consensus for specific therapy of HIDS, but there are some case reports and studies in regards to its treatment with drugs like colchicine, steroids, nonsteroid anti-inflammatory drugs, simvastatin, anakinra, thalidomide, and etanercept. We are reporting a case evaluated for the complaints of abdominal pain and febrile episodes with massive hepatomegaly, not common finding on physical examination, its treatment with etanercept, and long-term follow-up.

Diagnostic value of serum immunoglobulinaemia D level in patients with a clinical suspicion of hyper IgD syndrome

The hyperimmunoglobulinaemia D and periodic fever syndrome (HIDS) was originally defined by the presence of a high serum level of immunoglobulin D associated with recurrent fever. Since the discovery of the mevalonate kinase gene (MVK) gene encoding the mevalonate kinase enzyme, most patients with a clinical diagnostic of HIDS are now found to have a mevalonate kinase deficiency based on metabolic and genetic data. We aimed to asses the value of a high IgD serum level for the diagnosis of HIDS in a cohort of patients with a phenotype of recurrent fever, and to characterize patients with a high IgD serum level without mevalonate kinase mutation. Main clinical and biological data of 50 patients who presented with clinical signs compatible with HIDS have been prospectively registered on a standard form. Clinical data have been analysed according the IgD serum level and the presence of MVK mutation. The metabolic and genetic data establishing the diagnosis of HIDS correlated in all cases. In this series of 50 patients, the sensitivity of a high IgD value for the diagnosis of HIDS is 0.79. In five patients with MVK mutation, IgD levels were found to be in the normal range. Likelihood ratios indicate that IgD measurement is not relevant for the diagnostic of HIDS. Most patients with a high serum IgD level and no MVK mutation have no definite diagnosis. The clinical relevance of the IgD measurement for the diagnosis of MKD in our population appears as poor, as reflected by likelihood ratios which are both close to 1.

Autoinflammatorische (Fieber-)Syndrome - Klinik, Genetik und Therapie

Fever is frequent during infancy and childhood. The cause is usually a common cold. In cases where the fever reoccurs at intervals for more than six months without an obvious reason, one has to consider the possibility that the child suffers from an autoinflammatory syndrome which is commonly also known as a periodic fever syndrome. This group of diseases is characterised by a multisystemic inflammation with leukocytosis, an elevation of the erythrocyte sedimentation rate, and increased C-reactive protein and amyloid A serum concentrations. Common symptoms of an attack are abdominal pain, myalgia, arthralgia, and skin rash. Fever is almost always present in children. The attack starts abruptly and can be triggered by external factors such as trauma, vaccination, stress, and menstruation. The fever persists for several days up to weeks and spontaneously resolves without therapy. It is, however, often difficult to make a definitive diagnosis based solely on the clinical presentation, because the symptoms accompanying the fever are mostly rather unspecific and typical for more than one of the autoinflammatory syndromes. It is therefore helpful to perform a genetic analysis to either confirm the suspicion or to rule out a specific diagnosis. Hereditary fever syndromes, for which gene defects are known, include familial Mediterranean fever (FMF), tumor necrosis factor receptor 1-associated periodic syndrome (TRAPS), hyperimmunoglobulinaemia D and periodic fever syndrome (HIDS), and the cryopyrin-associated periodic syndromes (CAPS). The most frequently observed fever syndrome in childhood is, however, the mostly transient periodic fever, aphthous stomatitis, pharyngitis, and adenitis (PFAPA) syndrome which appears not to be inherited.

Hereditary periodic fever and reactive amyloidosis

Hereditary periodic fever syndromes (HPF) are a group of diseases characterised by recurrences of fever and inflammation separated by symptom-free intervals. Familial Mediterranean fever (FMF) is the most frequent entity within this group of disorders which further consists of hyperimmunoglobulinaemia D and periodic fever syndrome (HIDS), tumour necrosis factor receptor-associated periodic syndrome (TRAPS) and cryopyrin-associated periodic syndrome (CAPS). In recent years the causative genes have been identified. Reactive amyloidosis is a severe complication of HPFs. This is caused by deposition of fibrils that consist of the proteolytically cleaved acutephase protein serum amyloid A (SAA). Several factors have been identified that modulate the risk for developing amyloidosis, including SAA concentrations, polymorphisms in the SAA gene and ethnic origin. Furthermore, the risk of developing amyloidosis varies widely between the different HPFs. Colchicine is the cornerstone in the management of FMF, as it reduces the severity and frequency of attacks and is also effective in preventing amyloidosis. In the other HPFs, the introduction of anticytokine-based therapies is a promising new option in treating these inflammatory conditions and they potentially can prevent amyloidosis.

Identification of a novel mevalonate kinase gene mutation in combination with the common MVK V377I substitution and the low-penetrance TNFRSF1A R92Q mutation

The hyperimmunoglobulinemia D and periodic fever syndrome (HIDS) is an autosomal recessively inherited autoinflammatory disease caused by mutations in the mevalonate kinase (MVK) gene on chromosome 12q24, which lead to a depressed enzymatic activity of mevalonate kinase (MK). TNF-receptor associated periodic syndrome (TRAPS), on the other hand, is the most frequent autosomal dominantly inherited periodic fever syndrome due to mutations in exons 2-4 and 6 of the TNFRSF1A gene on chromosome 12p13.2. We describe a girl with heterozygosity for the common MVK V377I mutation and for a novel T(1132) --> C transition, leading to the exchange of serine (TCC) by proline (CCC) at amino-acid position 378. Interestingly, our patient presented only with mild clinical features typical of HIDS and slightly increased immunoglobulin D levels, but a distinctly diminished MK activity. The girl was also heterozygous for the TNFRSF1A R92Q low-penetrance mutation, which may have significant proinflammatory effects. However, at the time of presentation, the patient had no TRAPS-associated symptoms.

Hyperimmunoglobulinemia D and periodic fever syndrome (HIDS) in a child with normal serum IgD, but increased serum IgA concentration

This report describes a boy with hyperimmunoglobulinemia D and periodic fever syndrome (HIDS). The serum IgD level was normal, but the serum IgA concentration was markedly elevated. In addition, he had a history of orchitis on two occasions, a previously unreported manifestation of HIDS. This report expands the clinical and laboratory features associated with HIDS and serves to emphasize that a normal serum IgD level does not exclude the diagnosis of HIDS.

Clinical and molecular variability in childhood periodic fever with hyperimmunoglobulinaemia D.

The hyperimmunoglobulinaemia D and periodic fever syndrome (HIDS) was found recently to be caused by a deficiency of mevalonate kinase (MK). The aim of this study was to examine whether a relationship exists between the clinical expression of HIDS and the extent of MK deficiency. The medical records of children diagnosed with HIDS were reviewed for clinical features and serum immunoglobulin values. The mevalonic acid excretion in urine and MK enzyme activity in patients' cells were measured and the cDNA of the MVK gene was sequenced. Fifteen patients with recurrent fever and raised serum immunoglobulin (Ig) D were included. Their clinical features varied. Eleven patients had a deficiency of MK, caused by mutations in the MVK gene. One mutation (V377I) was common to all 11 patients. Nine patients were compound heterozygotes for V377I and various other MVK mutations. There was no apparent relationship between the observed mutations and the clinical features. Surprisingly, four boys had normal MK activity and no MVK mutations. Most HIDS patients have mutations in the MVK gene. The clinical variability observed cannot be explained by genotypic differences. Periodic fever and elevated IgD can result from other, still unknown, causes. Hence, testing for MK deficiency is necessary in patients with unexplained periodic fever.

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.

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.