Reduced half-life of holocarboxylase synthetase from patients with severe multiple carboxylase deficiency

Multiple carboxylase deficiency is a clinical condition caused by defects in the enzymes involved in biotin metabolism, holocarboxylase synthetase (HLCS) or biotinidase. HLCS deficiency is a potentially fatal condition if left untreated, although the majority of patients respond to oral supplementation of 10-20 mg/day of biotin. Patients who display incomplete responsiveness to this therapy have a poor long-term prognosis. Here we investigated cell lines from two such HLCS-deficient patients homozygous for the c.647T>G p.L216R allele. Growth of the patients' fibroblasts was compromised compared with normal fibroblasts. Also the patient cells were not sensitive to biotin-depletion from the media, and growth rates could not be restored by re-administration of biotin. The molecular basis for the HLCS deficiency was further investigated by characterisation of the p.L216R protein. The HLCS mRNA was detected in MCD and normal cell lines. However, protein and enzyme activity could not be detected in the patients' cells. In vitro kinetic analysis revealed that enzyme activity was severely compromised for recombinantly expressed p.L216R and could not be increased by additional biotin. Furthermore, the turn-over rate for the mutant protein was double that of wildtype HLCS. These results help provide a molecular explanation for the incomplete biotin-responsiveness of this p.L216R form of HLCS.     

Mutations in the holocarboxylase synthetase gene HLCS

Holocarboxylase synthetase (HLCS) deficiency is an autosomal recessive disorder. HLCS is an enzyme that catalyzes biotin incorporation into carboxylases and histones. Since the first report of the cDNA sequence, 30 mutations in the HLCS gene have been reported. Mutations occur throughout the entire coding region except exons 6 and 10. The types of mutations are one single amino acid deletion, five single nucleotide insertions/deletions, 22 missense mutations, and two nonsense mutations. The only intronic mutation identified thus far is c.1519+5G>A (also designated IVS10+5G>A), which causes a splice error. Several lines of evidence suggest that c.1519+5G>A is a founder mutation in Scandinavian patients. Prevalence of this mutation is about 10 times higher in the Faroe Islands than in the rest of the world. The mutations p.L237P and c.780delG are predominant only in Japanese patients. These are probably founder mutations in this population. Mutations p.R508W and p.V550M are identified in several ethic groups and accompanied with various haplotypes, suggesting that these are recurrent mutations. There is a good relationship between clinical biotin responsiveness and the residual activity of HLCS. A combination of a null mutation and a point mutation that shows less than a few percent of the normal activity results in neonatal onset. Patients who have mutant HLCS with higher residual activity develop symptom after the neonatal period and show a good clinical response to biotin therapy.     

Clinical findings and biochemical and molecular analysis of four patients with holocarboxylase synthetase deficiency

Holocarboxylase synthetase (HLCS) deficiency (HLCSD) is a rare autosomal recessive disorder of biotin metabolism. HLCS catalyzes the biotinylation of the four human biotin-dependent carboxylases. Using the newly available human genomic sequence, we report the map of HLCS genomic structure and the predicted exon/intron boundaries. Moreover, the molecular studies of four patients (two Italians, one Iranian, and one Australian) affected by HLCS deficiency are here reported. The clinical findings, the age of onset, and response to biotin treatment differed between our patients. The diagnosis was made by organic acid analysis and confirmed by enzymatic analysis in three patients. Six mutations in the HLCS gene were identified, including two novel (N511K and G582R) and four known missense mutations (L216R, R508W, V550M, and G581S). Five of the mutations are localized within the HLCS biotin-binding domain, whereas the L216R amino acid change is located in the N-terminal region outside of the putative biotin-binding domain. This mutation, previously reported in a heterozygous state, was detected for the first time in a patient with homozygous status. The patient's severe clinical phenotype and partial responsiveness to biotin support a genotype-phenotype correlation through the involvement of residues of the N-terminal region in a substrate specificity recognition or regulation of the HLCS enzyme.     

Effects of single-nucleotide polymorphisms in the human holocarboxylase synthetase gene on enzyme catalysis

Holocarboxylase synthetase (HLCS) is a biotin protein ligase, which has a pivotal role in biotin-dependent metabolic pathways and epigenetic phenomena in humans. Knockdown of HLCS produces phenotypes such as heat susceptibility and decreased life span in Drosophila melanogaster, whereas knockout of HLCS appears to be embryonic lethal. HLCS comprises 726 amino acids in four domains. More than 2500 single-nucleotide polymorphisms (SNPs) have been identified in human HLCS. Here, we tested the hypotheses that HLCS SNPs impair enzyme activity, and that biotin supplementation restores the activities of HLCS variants to wild-type levels. We used an in silico approach to identify five SNPs that alter the amino acid sequence in the N-terminal, central, and C-terminal domains in human HLCS. Recombinant HLCS was used for enzyme kinetics analyses of HLCS variants, wild-type HLCS, and the L216R mutant, which has a biotin ligase activity near zero. The biotin affinity of variant Q699R is lower than that of the wild-type control, but the maximal activity was restored to that of wild-type HLCS when assay mixtures were supplemented with biotin. In contrast, the biotin affinities of HLCS variants V96F and G510R are not significantly different from the wild-type control, but their maximal activities remained moderately lower than that of wild-type HLCS even when assay mixtures were supplemented with biotin. The V96 L SNP did not alter enzyme kinetics. Our findings suggest that individuals with HLCS SNPs may benefit from supplemental biotin, yet to different extents depending on the genotype.     

Holocarboxylase synthetase deficiency: novel clinical and molecular findings

Tammachote R, Janklat S, Tongkobpetch S, Suphapeetiporn K and Shotelersuk V. Holocarboxylase synthetase deficiency: novel clinical and molecular findings. Multiple carboxylase deficiency (MCD) is an autosomal recessive metabolic disorder caused by defective activity of biotinidase or holocarboxylase synthetase (HLCS) in the biotin cycle. Clinical symptoms include skin lesions and severe metabolic acidosis. Here, we reported four unrelated Thai patients with MCD, diagnosed by urine organic acid analysis. Unlike Caucasians, which biotinidase deficiency has been found to be more common, all of our four Thai patients were affected by HLCS deficiency. Instead of the generally recommended high dose of biotin, our patients were given biotin at 1.2 mg/day. This low‐dose biotin significantly improved their clinical symptoms and stabilized the metabolic state on long‐term follow‐up. Mutation analysis by polymerase chain reaction‐sequencing of the entire coding region of the HLCS gene revealed the c.1522C>T (p.R508W) mutation in six of the eight mutant alleles. This suggests it as the most common mutation in the Thai population, which paves the way for a rapid and unsophisticated diagnostic method for the ethnic Thai. Haplotype analysis revealed that the c.1522C>T was on three different haplotypes suggesting that it was recurrent, not caused by a founder effect. In addition, a novel mutation, c.1513G>C (p.G505R), was identified, expanding the mutational spectrum of this gene.     

Partial response to biotin therapy in a patient with holocarboxylase synthetase deficiency: clinical,biochemical, and molecular genetic aspects

We report the clinical course and biochemical findings of a 10-year-old, mentally retarded girl with late-onset holocarboxylase synthetase (HCS, gene symbol HLCS) deficiency and only partial response to biotin. On treatment, even with an unusually high dose of 200mg/day, activities of the biotin-dependent mitochondrial carboxylases in lymphocytes remained below 50% of the mean control values. Not only urinary 3-hydroxyisovaleric acid excretion has been persistently elevated, but also plasma and, with even higher concentrations, cerebrospinal fluid 3-hydroxyisovaleric acid have not normalized. The unusual and insufficient response of this patient to biotin treatment can be explained by the effect of the combination of the common HLCS allele IVS10 +5 g>a on one chromosome and a truncating mutation on the other. This case illustrates mechanisms involved in the genotype-phenotype correlation that unequivocally exists in HCS deficiency.     

12例多种羧化酶缺乏症的基因突变分析

目的 旨在从基因水平证实多种羧化酶缺乏症(multiple carboxylase deficiency,MCD)的诊断,探讨我国MCD患儿的基因突变情况.方法 12例MCD患儿接受基因诊断.采用PCR及直接测序法分别对4例生物素酶(biotinidase,BT)缺乏症和8例全羧化酶合成酶(holocarboxylase synthetas,HLCS)缺乏症进行BT基因和HLCS基因突变分析,对基因新突变通过限制性片段长度多态性分析及患儿父母和50名正常对照者基因检测以证实.结果 12例患儿基因突变检出率100%.4例BT缺乏症中发现BT基因突变6种:c.98-104del7ins3,c.1369G>A(V457M),c.1157G>A(W386X),c.1284C>A(Y428X),c.1384delA,c.1493_1494insT,后4种为新突变.8例HLCS缺乏症中发现HLCS基因突变4种:c.126G>T(E42D),c.1994G>C(R665P),c.1088T>A(V363D),c.1522C>T(R508W),后两种为热点突变[75%(12/16)],c.1994G>C为新突变.结论 本研究从基因水平上证实了12例MCD的诊断.共发现了6种BT基因突变,4种HLCS基因突变,其中5种为新突变;得出2种HLCS基因的热点突变.     

Plasmapheresis-induced clinical improvement in a patient with steroid-resistant nephrotic syndrome due to podocin (NPHS2) gene mutation

Podocin mutations (NPHS2 gene) are mostly responsible for steroid-resistant nephrotic syndrome (SRNS) of childhood onset. Patients with NPHS2 gene mutations do not respond to corticoids and other immunosuppressive agents; partial remission can be rarely induced by cyclosporin A. We present a boy, where SRNS was diagnosed within first year of life. By the age of 15 years, proteinuria reached 9000 mg/24 h, cholesterolemia 15 mmol/L, albuminemia 19.6 g/L, in spite of combined therapy with cyclosporine A, methylprednisolone, enalapril and losartan. At that time a combined heterozygous form of two NPHS2 gene mutations (p.R138Q and p.V290M) was diagnosed, methylprednisolone was discontinued and patient underwent ten plasmapheresis procedures. This resulted in clinical improvement (proteinuria 3000 mg/24 h, S-cholesterol 6 mmol/L, albumin 30g/L) lasting for three years. In conclusion, plasmapheresis can result in clinical improvement and stabilization of SRNS caused by podocine mutation, before renal replacement therapy is initiated.     

Clinical and genetic analysis of three Korean children with pyridoxine-dependent epilepsy

Pyridoxine-dependent epilepsy (PDE) is a rare autosomal recessive disorder that causes intractable seizures, especially in neonates and infants. Patients are typically resistant to typical antiepileptic drugs (AEDs) but respond dramatically to pyridoxine. Mutations in the ALDH7A1 gene are associated with the pathogenesis of PDE. Herein, we report the clinical phenotypes and disease-causative mutations in the ALDH7A1 gene in three Korean patients with PDE. We reviewed the medical records, electroencephalography (EEG), brain magnetic resonance imaging (MRI) findings, and the results of molecular genetic tests for the patients who were diagnosed with PDE in our institution between Jan. 1996 and Dec. 2010. In all patients, the first seizures began during the first week of life. The seizures were not fully controlled with multiple AEDs, but disappeared immediately after administration of pyridoxine and returned after it was transiently discontinued. Before the use of pyridoxine, interictal EEGs showed multifocal epileptiform discharges, which became normalized with pyridoxine. Direct sequencing analyses revealed two mutant alleles in all three patients. Patient 1 was compound heterozygous with two different missense mutations, c.1061A>G (p.Y354C) and c.1232C>T (p.P411L). Patient 2 was homozygous for a missense mutation, c.1279G>C (p.E427Q). Patient 3 was compound heterozygous for two different missense mutations, c.1061A>G (p.Y354C) and c.1279G>C (p.E427Q), and her parents and younger brother were heterozygous carriers of each one of the mutations. All three mutations had not previously been reported. Herein, we report three Korean patients with three novel mutations who presented with PDE.     

Novel mutations in 3‐phosphoglycerate dehydrogenase (PHGDH) are distributed throughout the protein and result in altered enzyme kinetics

Three‐phosphoglycerate dehydrogenase (3‐PGDH) deficiency is a rare recessive inborn error in the biosynthesis of the amino acid L‐serine characterized clinically by congenital microcephaly, psychomotor retardation, and intractable seizures. The biochemical abnormalities associated with this disorder are low concentrations of L‐serine, D‐serine, and glycine in cerebrospinal fluid (CSF). Only two missense mutations (p.V425M and p.V490M) have been identified in PHGDH, the gene encoding 3‐PGDH, but it is currently unclear how these mutations in the carboxy‐terminal regulatory domain of the protein affect enzyme function. We now describe five novel mutations in five patients with 3‐PGDH deficiency; one frameshift mutation (p.G238fsX), and four missense mutations (p.R135W, p.V261M, p.A373T, and p.G377S). The missense mutations were located in the nucleotide binding and regulatory domains of 3‐PGDH and did not affect steady‐state expression, protein stability, and protein degradation rates. Patients' fibroblasts displayed a significant, but incomplete, reduction in maximal enzyme activities associated with all missense mutations. In transient overexpression studies in HEK293T cells, the p.A373T, p.V425M, and p.V490M mutations resulted in almost undetectable enzyme activities. Molecular modeling of the p.R135W and p.V261M mutations onto the partial crystal structure of 3‐PGDH predicted that these mutations affect substrate and cofactor binding. This prediction was confirmed by the results of kinetic measurements in fibroblasts and transiently transfected HEK293T cells, which revealed a markedly decreased V_max and an increase in K_m values, respectively. Taken together, these data suggest that missense mutations associated with 3‐PGDH deficiency either primarily affect substrate binding or result in very low residual enzymatic activity. Hum Mutat 0, 1–8, 2009. © 2009 Wiley‐Liss, Inc.     

p53 nuclear protein accumulation correlates with mutations in the p53 gene, tumor grade, and stage in bladder cancer.

Seventy-three transitional cell carcinomas of the bladder were analyzed by immunohistochemistry for p53 nuclear accumulation, and the results were compared to mutations detected in the p53 gene by single strand conformational polymorphism analysis (SSCP) and DNA sequence analysis. Immunohistochemical studies were performed on formalin-fixed, paraffin-embedded tissue sections. A highly significant association between the presence of p53 mutations and p53 nuclear reactivity as detected by immunohistochemistry was found (P = 0.0001). Of 32 tumors that demonstrated p53 mutations by SSCP, 27 (84%) showed p53 nuclear reactivity. Of the five cases that did not demonstrate p53 nuclear reactivity, four had mutations in exon 5. However, of 41 tumors with no evidence of p53 mutation by molecular analysis, 12 (29%) showed p53 immunoreactivity. This indicates that immunohistochemical methods may be more sensitive than SSCP in detecting p53 mutations or that discordant cases represent tumors with accumulation of wild type p53 protein, without mutations at the p53 locus. Of the 15 tumors that were found to have mutations at exon 8, 13 demonstrated high-intensity homogeneous p53 nuclear reactivity by immunohistochemistry, and all mutations located at codon 280 demonstrated high-intensity homogeneous immunoreactivity. However, three of three tumors with exon 6 mutations demonstrated low-level p53 immunoreactivity, and four of six tumors with mutations in exon 5 showed no detectable p53 nuclear reactivity. This indicates that the heterogeneity of immunoreactivity observed when analyzing p53 nuclear accumulation may be related to the site of the p53 gene mutation. Information on tumor grade, stage, lymph node status, disease-free interval, and overall survival were available in 54 patients who had undergone cystectomy. A significant association was observed between p53 alterations (detected by immunohistochemistry and SSCP) and histological tumor grade (P = 0.003) and stage (P = 0.01). We conclude that the immunohistochemical detection of p53 nuclear accumulation in formalin-fixed, paraffin-embedded tissue is highly associated with mutations in the p53 gene; this association has now been demonstrated in a large number of tumors. The heterogeneity of p53 nuclear reactivity seems to be related to the site of mutation in the p53 gene. A small proportion of tumors with a p53 gene mutation do not demonstrate immunohistochemically detectable p53 nuclear accumulation. Furthermore, a small but substantial proportion of tumors demonstrate p53 nuclear reactivity but do not show detectable mutations in the p53 gene by SSCP. Finally, both grade and stage of bladder cancer are related to p53 alterations, detected by immunohistochemistry or molecular methods.(ABSTRACT TRUNCATED AT 400 WORDS)     

Mucopolysaccharidosis I mutations in Chinese patients: identification of 27 novel mutations and 6 cases involving prenatal diagnosis

Mucopolysaccharidosis I (MPS I) is a lysosomal storage disease that results from the deficiency of α-l-iduronidase and is transmitted in an autosomally recessive manner. This report describes the first systematic screening for mutations in Chinese MPS I patients from mainland China, wherein we have summarized the phenotype/genotype correlation of the individuals in Chinese MPS I patients. Mutational analyses were performed in 57 unrelated Chinese MPS I patients. Overall, 105 mutant alleles were identified from a set of 41 different mutations. Notably, of these 41 mutations, 27 were novel mutations that consisted of 8 splicing mutations (c.1-2C>G, c.296+4G>A, c.300-1G>C, c.792+1G>C, c.973-4G>A, c.1189+5G>T, c.1402+1G>T and c.1402+2T>G), 1 nonsense mutation (p.W41X), 1 insertion (c.668-670ins GCG), 5 duplications (c.531dupT, c.657dupG, c.883dupC, c.1147dupG and c.1225dupG), 3 deletions (c.349delT, c.1593delG and c.1244-1271del27),1 nucleotide substitution c.2T>C and 8 missense mutations (p.H33P,p.F52L, p.G168V,p.T179R,p. E182D, p.L237R, p.L238R and p.L421P). The missense mutations p.A79V and p.L346R, which accounted for 16.7% (19/114) and 12.3% (14/114) respectively, were the common mutations in Chinese patients but were rare in the mutational profiles reported for other populations. These results indicate that Chinese MPS I patients may have a different mutational spectrum compared to those of other populations. Moreover, for the first time in China, molecular genetic methods were used for prenatal diagnosis of six cases in five families.     

Molecular analysis of Sanfilippo syndrome type C in Spain: seven novel HGSNAT mutations and characterization of the mutant alleles

Canals I, Elalaoui SC, Pineda M, Delgadillo V, Szlago M, Jaouad IC, Sefiani A, Chabás A, Coll MJ, Grinberg D, Vilageliu L. Molecular analysis of Sanfilippo syndrome type C in Spain: seven novel HGSNAT mutations and characterization of the mutant alleles. The Sanfilippo syndrome type C [mucopolysaccharidosis IIIC (MPS IIIC)] is caused by mutations in the HGSNAT gene, encoding an enzyme involved in heparan sulphate degradation. We report the first molecular study on several Spanish Sanfilippo syndrome type C patients. Seven Spanish patients, one Argentinean and three Moroccan patients were analysed. All mutant alleles were identified and comprised nine distinct mutant alleles, seven of which were novel, including four missense mutations (p.A54V, p.L113P, p.G424V and p.L445P) and three splicing mutations due to two point mutations (c.633+1G>A and c.1378‐1G>A) and an intronic deletion (c.821‐31_821‐13del). Furthermore, we found a new single nucleotide polymorphism (SNP) (c.564‐98T>C). The two most frequent changes were the previously described c.372‐2A>G and c.234+1G>A mutations. All five splicing mutations were experimentally confirmed by studies at the RNA level, and a minigene experiment was carried out in one case for which no fibroblasts were available. Expression assays allowed us to show the pathogenic effect of the four novel missense mutations and to confirm that the already known c.710C>A (p.P237Q) is a non‐pathogenic SNP. Haplotype analyses suggested that the two mutations (c.234+1G>A and c.372‐2A>G) that were present in more than one patient have a common origin, including one (c.234+1G>A) that was found in Spanish and Moroccan patients.     

Congenital hypogonadotropic hypogonadism with split hand/foot malformation: a clinical entity with a high frequency of FGFR1 mutations

PurposeCongenital hypogonadotropic hypogonadism (CHH) and split hand/foot malformation (SHFM) are two rare genetic conditions. Here we report a clinical entity comprising the two.MethodsWe identified patients with CHH and SHFM through international collaboration. Probands and available family members underwent phenotyping and screening for FGFR1 mutations. The impact of identified mutations was assessed by sequence- and structure-based predictions and/or functional assays.ResultsWe identified eight probands with CHH with (n = 3; Kallmann syndrome) or without anosmia (n = 5) and SHFM, seven of whom (88%) harbor FGFR1 mutations. Of these seven, one individual is homozygous for p.V429E and six individuals are heterozygous for p.G348R, p.G485R, p.Q594*, p.E670A, p.V688L, or p.L712P. All mutations were predicted by in silico analysis to cause loss of function. Probands with FGFR1 mutations have severe gonadotropin-releasing hormone deficiency (absent puberty and/or cryptorchidism and/or micropenis). SHFM in both hands and feet was observed only in the patient with the homozygous p.V429E mutation; V429 maps to the fibroblast growth factor receptor substrate 2α binding domain of FGFR1, and functional studies of the p.V429E mutation demonstrated that it decreased recruitment and phosphorylation of fibroblast growth factor receptor substrate 2α to FGFR1, thereby resulting in reduced mitogen-activated protein kinase signaling.ConclusionFGFR1 should be prioritized for genetic testing in patients with CHH and SHFM because the likelihood of a mutation increases from 10% in the general CHH population to 88% in these patients.Genet Med17 8, 651–659.     

Clinical and Molecular Characterization of X‐linked Hyper‐IgM Syndrome Patients in China

X‐linked Hyper‐IgM syndrome (XHIM) is caused by mutations of CD154 gene also known as CD40 ligand (CD40L). CD40L is expressed in activated T cells and interacts with CD40 receptor expressed on B lymphocytes and dendritic cells. Affected patients present cellular and humoral immune defects, with infections by intracellular, opportunistic and extracellular pathogens. In the present study, we investigate molecular defects involved in the XHIM in five patients and identified five distinct CD40L mutations, three of which had not been previously described. P1 harboured a novel p.L193P mutation, which abolished the expression of CD40L. P2 had a frameshift deletion in exon 3 (p.E108fsX19), which also decreased the protein expression. P3 demonstrated p.E54X change in exon 2. P4 harboured the p.Q186X change in the exon 5. P5 demonstrated p. E142X change in exon 5. Mutations in P3, P4 and P5 all led to the production of premature CD40L protein. Two of the five genetically defined patients received umbilical cord blood stem cell transplantation from unrelated donor and achieved clinical remission, and the expression of CD40L on the peripheral blood mononuclear cells restored. These mutations reflect the heterogeneity of CD40L gene, indicating the need for accurate and reliable molecular testing in patients suspected of XHIM.     

Molecular diagnosis of Wiskott-Aldrich syndrome in Taiwan.

The spectrum of Wiskott-Aldrich syndrome (WAS) mutation in Han Chinese residing in Taiwan has not been previously reported. We describe a multidisciplinary approach to the molecular diagnosis of WAS which could be applied to clinical diagnosis, carrier prediction, and prenatal diagnosis. A total of 6 male patients, from 6 independent families, were referred for the molecular diagnosis of WAS. The respective methylation status of the 6 X chromosomes in peripheral blood leukocytes from obligatory female carriers was analyzed initially, followed by analysis of the level of expression of WAS protein (WASP) in peripheral leukocytes from patients, using a Western blotting technique. The analysis of the specific WAS gene mutation was done by direct sequencing. Mutations were identified in the WAS gene of all patients. Mutations identified included p.R13X, p.R41X, p.S82P, IVS1-1 G --> C, p.L342TFsX493, and a large deletion. Four patients had no WASP expression in peripheral leukocytes obtained before bone marrow transplantation. Several female carriers in the families of the 6 patients with such mutations were confirmed. One prenatal diagnosis was made in a fetus and he did not inherit the mutation. The importance of mutations in the first 2 exons of the WAS gene was demonstrated in this study, which represented 5 of the 6 mutations identified in 6 patients. The use of a multidisciplinary approach including DNA and protein analysis is required for molecular diagnosis and genetic counseling of WAS.     

Hepatitis C virus-related resistance mechanisms to interferon alpha-based antiviral therapy.

Only 50-60% of the patients chronically infected with the hepatitis C virus (HCV) achieve a sustained virologic response to the current standard antiviral therapy consisting of pegylated interferon alpha in combination with ribavirin. The definite reasons for virologic response or non-response to interferon alpha-based therapy are unknown. Besides host and treatment efficacy factors, it is presumable that HCV is able to antagonize the antiviral activity of interferon alpha. So far, among the different HCV proteins, the envelope (E)2 protein, the non-structural (NS)3/4A protein, and the NS5A protein have been associated with interferon alpha resistance mechanisms in vitro. The clinical significance of amino acid mutations within these HCV proteins in HCV isolates from patients who did or did not respond to interferon alpha-based therapy was investigated in multiple studies. Within the E2 (HVR2, CD81 binding sites, PePHD) and the NS3/4A proteins no specific mutations in correlation with virologic response to interferon alpha-based therapy were observed. For the NS5A protein, mutations within the interferon sensitivity determining region (ISDR) and the complete NS5A protein may be of importance for response to interferon alpha-based treatment in patients infected with HCV subtype 1a/b.     

Identification of the bruton tyrosine kinase (BTK) gene mutations in 20 Australian families with X-linked agammaglobulinemia (XLA)

X-linked agammaglobulinemia (XLA) is an immunodeficiency caused by mutations in the Bruton tyrosine kinase (BTK) gene. Twenty Australian patients with an XLA phenotype, from 15 unrelated families, were found to have 14 mutations. Five of the mutations were previously described c.83G>A (p.R28H), c.862C>T (p.R288W), c.904G>A (p.R302G), c.1535T>C (p.L512P), c.700C>T (p.Q234X), while nine novel mutations were identified: four missense c.82C>A (p.R28S), c.494G>A (p.C165Y), c.464G>A (p.C155Y), c.1750G>A (p.G584E), one deletion c.142_144delAGAAGA (p.R48_G50del), and four splice site mutations c.241-2A>G, c.839+4A>G, c.1350-2A>G, c.1566+1G>A. Carrier analysis was performed in 10 mothers and 11 female relatives. The results of this study further support the notion that molecular genetic testing represents an important tool for definitive and early diagnosis of XLA and may allow accurate carrier status and prenatal diagnosis.     

Molecular and functional analysis of SUMF1 mutations in multiple sulfatase deficiency

Multiple sulfatase deficiency (MSD) is a rare disorder characterized by impaired activity of all known sulfatases. The gene mutated in this disease is SUMF1, which encodes a protein involved in a post-translational modification at the catalytic site of all sulfatases that is necessary for their function. SUMF1 strongly enhances the activity of sulfatases when coexpressed with sulfatase in Cos-7 cells. We performed a mutational analysis of SUMF1 in 20 MSD patients of different ethnic origin. The clinical presentation of these patients was variable, ranging from severe neonatal forms to mild phenotypes showing mild neurological involvement. A total of 22 SUMF1 mutations were identified, including missense, nonsense, microdeletion, and splicing mutations. We expressed all missense mutations in culture to study their ability to enhance the activity of sulfatases. Of the predicted amino acid changes, 11 (p.R349W, p.R224W, p.L20F, p.A348P, p.S155P, p.C218Y, p.N259I, p.A279V, p.R349Q, p.C336R, p.A177P) resulted in severely impaired sulfatase-enhancing activity. Two (p.R345C and p.P266L) showed a high residual activity on some, but not all, of the nine sulfatases tested, suggesting that some SUMF1 mutations may have variable effects on the activity of each sulfatase. This study compares, for the first time, clinical, biochemical, and molecular data in MSD patients. Our results show lack of a direct correlation between the type of molecular defect and the severity of phenotype.