[Show abstract][Hide abstract] ABSTRACT: Background
Mutations affecting RNA splicing represent more than 20% of the mutant alleles in Sanfilippo syndrome type C, a rare lysosomal storage disorder that causes severe neurodegeneration. Many of these mutations are localized in the conserved donor or acceptor splice sites, while few are found in the nearby nucleotides.Methods
In this study we tested several therapeutic approaches specifically designed for different splicing mutations depending on how the mutations affect mRNA processing. For three mutations that affect the donor site (c.234¿+¿1G¿>¿A, c.633¿+¿1G¿>¿A and c.1542¿+¿4dupA), different modified U1 snRNAs recognizing the mutated donor sites, have been developed in an attempt to rescue the normal splicing process. For another mutation that affects an acceptor splice site (c.372-2A¿>¿G) and gives rise to a protein lacking four amino acids, a competitive inhibitor of the HGSNAT protein, glucosamine, was tested as a pharmacological chaperone to correct the aberrant folding and to restore the normal trafficking of the protein to the lysosome.ResultsPartial correction of c.234¿+¿1G¿>¿A mutation was achieved with a modified U1 snRNA that completely matches the splice donor site suggesting that these molecules may have a therapeutic potential for some splicing mutations. Furthermore, the importance of the splice site sequence context is highlighted as a key factor in the success of this type of therapy. Additionally, glucosamine treatment resulted in an increase in the enzymatic activity, indicating a partial recovery of the correct folding.Conclusions
We have assayed two therapeutic strategies for different splicing mutations with promising results for the future applications.
[Show abstract][Hide abstract] ABSTRACT: Methylmalonic aciduria cblB type is caused by mutations in the MMAB gene, which codes for the enzyme ATP: cobalamin adenosyltransferase (ATR). This study reports differences in the metabolic and disease outcomes of two pairs of siblings with methylmalonic aciduria cblB type, respectively harbouring the novel changes p.His183Leu/p.Arg190dup (P1 and P2) and the previously described mutations p.Ile96Thr/p.Ser174fs (P3 and P4). Expression analysis showed p.His183Leu and p.Arg190dup to be destabilising mutations. Both were associated with reduced ATR stability and a shorter half-life than wild-type ATR. Analysis of several parameters related to oxidative stress and mitochondrial function showed an increase in ROS content, a decrease in mitochondrial respiration and changes in mitochondria morphology and structure in patient-derived fibroblasts compared to control cells. The impairment in energy production and the presence of oxidative stress and fission of the mitochondrial reticulum suggested mitochondrial dysfunction in cblB patients´ fibroblasts. The recovery of mitochondrial function should be a goal in efforts to improve the clinical outcome of methylmalonic aciduria cblB type.
[Show abstract][Hide abstract] ABSTRACT: Deficiencies in glycosyltransferases, glycosidases or nucleotide-sugar transporters involved in protein glycosylation lead to Congenital Disorders of Glycosylation (CDG), a group of genetic diseases mostly showing multisystem phenotype. Despite recent advances in the biochemical and molecular knowledge of these diseases, no effective therapy exists for most. Efforts are now being directed towards therapies based on identifying new targets, which would allow to treat specific patients in a personalized way. This work presents proof-of concept for the antisense RNA rescue of the Golgi-resident protein TMEM165, a gene involved in a new type of CDG with a characteristic skeletal phenotype. Using a functional in vitro splicing assay based on minigenes, it was found that the deep intronic change c.792+182G>A is responsible for the insertion of an aberrant exon, corresponding to an intronic sequence. Antisense morpholino oligonucleotide therapy targeted towards TMEM165 mRNA recovered normal protein levels in the Golgi apparatus of patient-derived fibroblasts. This work expands the application of antisense oligonucleotide-mediated pseudoexon skipping to the treatment of a Golgi-resident protein, and opens up a promising treatment option for this specific TMEM165-CDG.
[Show abstract][Hide abstract] ABSTRACT: Purine and pyrimidine disorders represent a heterogeneous group with variable clinical symptoms and low prevalence rate. In the last thirteen years, we have studied urine/plasma specimens from about 1600 patients and we have identified 35 patients: eight patients with adenylosuccinate lyase deficiency, eight patients with hypoxanthine-guanine phosphoribosyltransferase deficiency, one patient with purine nucleoside phosphorylase deficiency, ten patients with xanthine dehydrogenase deficiency, six patients with molybdenum cofactor deficiency and two patients with dihydropyrimidine dehydrogenase deficiency. Despite low incidence of these diseases, our findings highlight the importance of including the purine and pyrimidine analysis in the selective screening for inborn errors of metabolism in specialized laboratories, where amino acid and organic acid disorders are simultaneously investigated.
[Show abstract][Hide abstract] ABSTRACT: In the past few years, research in targeted mutation therapies has experienced significant advances, especially in the field of rare diseases. In particular, the efficacy of antisense therapy for suppression of normal, pathogenic, or cryptic splice sites has been demonstrated in cellular and animal models and has already reached the clinical trials phase for Duchenne muscular dystrophy. In different inherited metabolic diseases, splice switching oligonucleotides (SSOs) have been used with success in patients' cells to force pseudoexon skipping or to block cryptic splice sites, in both cases recovering normal transcript and protein and correcting the enzyme deficiency. However, future in vivo studies require individual approaches for delivery depending on the gene defect involved, given the different patterns of tissue and organ expression. Herein we review the state of the art of antisense therapy targeting RNA splicing in metabolic diseases, grouped according to their expression patterns-multisystemic, hepatic, or in central nervous system (CNS)-and summarize the recent progress achieved in the field of in vivo delivery of oligonucleotides to each organ or system. Successful body-wide distribution of SSOs and preferential distribution in the liver after systemic administration have been reported in murine models for different diseases, while for CNS limited data are available, although promising results with intratechal injections have been achieved.
[Show abstract][Hide abstract] ABSTRACT: Pyruvate carboxylase deficiency is a rare metabolic disorder, with three different phenotypes. We aim to report the case of a newborn presenting the severe neonatal form of this deficiency (the B or "French" phenotype, hypokinesia and rigidity being the main features) and the results of the study of classic neurotransmitters involved in movement control. Hyperdopaminergic transmission (both in the cerebrospinal fluid and in the substantia nigra) and hypogabaergic transmission (in the substantia nigra) was found. Both gamma-aminobutyric acid and dopamine markers were found coexisting in individual neurons of the substantia nigra. This is the first time this phenomenon has been reported in the literature. We discuss the possible role of gabaergic deficiency, its interaction with other neurotransmitters and its implication in neurotransmitter homeostasis. A better comprehension of that field would increase understanding of the pathophysiology of neurological symptoms and neurotransmitter plasticity.
[Show abstract][Hide abstract] ABSTRACT: Presently pregnancy is no more exceptional in women with metabolic diseases. However, it still poses significant medical problems both before and after childbirth. The challenge is even greater if the mother has undergone organ transplantation, because of her metabolic disease. We report on a case of pregnancy in a patient 29-year-old with methylmalonic acidemia cblA type (OMIM 251100) who received a renal transplantation at the age of 17 for end-stage renal disease (ESRD) caused by her primary disease. During pregnancy neither metabolic crises nor renal function changes were observed in the mother, with the only exception of a mild increase of her systemic blood pressure. To the fetus pregnancy was uneventful and during the first 30 months after birth the baby's neuropsychomotor development was normal and there were no episodes of metabolic derangement. This is evidence that methylmalonicacidemia cblA, even when treated with renal transplantation for inherent ESRD, is no contraindication to pregnancy. It is even possible that a functioning transplanted kidney contributes to improve metabolic parameters.
American Journal of Transplantation 05/2013; · 6.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: CblD disorder is an autosomal recessive, rare, heterogeneous disease with variable clinical presentations, depending on the nature and location of the MMADHC gene mutations. Mutations in MMADHC lead to three distinct phenotypes: cblD-MMA, cblD-HC, and cblD-MMA/HC. To date, 18 cblD patients have been reported. Six of them were affected by cblD-MMA, but only three had a known clinical history. One of these patients presented with a metabolic decompensation at 11 months; the second one, born prematurely, was diagnosed with cblD after being treated for intracranial hemorrhage, respiratory distress syndrome, necrotizing enterocolitis, and convulsions at birth; the third one was diagnosed at 5 years of age.Here we present a case of a cblD-MMA patient who had an acute neonatal onset with severe hyperammonemia requiring hemodiafiltration. To the best of our knowledge, this is the first cblD-MMA patient who presented acutely in the newborn period. He has developed well upon treatment with B12, carnitine, and hypoproteic diet. At present time, at the age of 7, he shows normal growth and cognitive development. Thus, it is likely that the aggressive treatment of this child with hemodiafiltration might have prevented him from long-term neurological sequelae. Overall, this case shows that even severe, neonatal-onset patients may display a vitamin B12-responsive MMA. Furthermore, it suggests that an early treatment with vitamins might be beneficial for patients presenting with neonatal-onset hyperammonemia regardless of the suspected disease and before receiving the biochemical diagnosis.
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to identify the most common genotypes in the phenylketonuria (PKU) population of Andalusia, assessing the correlation with the phenotype and the usefulness in predicting the response to treatment with tetrahydrobiopterin. We conducted a retrospective observational study between January 1980 and January 2010 in 147 Andalusian PKU patients assessing phenotype, genotype and response to a 24-h BH4 loading test. Our cohort of patients exhibited 65 different mutations, 69.2% corresponding to the missense type, in a total of 123 different genotypes. IVS10nt-11g>a was the most common mutation (10.9%). Four novel missense mutations were identified: p.L258P; p.E66K, p.R155C and p.P122S. Although generally there is a good genotype-phenotype correlation, for eight of the repeated genotypes a slightly different phenotype was observed. In 96 PKU subjects BH4 challenge was carried out. Patients with previously reported unresponsive mutations on both alleles showed a negative response, while 95.5% (28/29) of the responsive patients carry at least one missense mutation previously associated to the BH4. Our data reveal a great genetic heterogeneity in the Andalusian population. Genotype is quite a good predictor of the phenotype and of the responsiveness to tetrahydrobiopterin, which is relevant for patient management and follow-up.Journal of Human Genetics advance online publication, 21 March 2013; doi:10.1038/jhg.2013.16.
Journal of Human Genetics 03/2013; · 2.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Knowledge of hyperphenylalaninaemia (HPA) mutational spectrum in a population allows in many cases an accurate prediction of the phenotype and tetrahydrobiopterin (BH4) responsiveness, thus selecting an adequate treatment. In this work, we have performed the molecular characterization of 105 HPA patients from Galicia, northwest region of Spain, evaluating their phenotype and BH4 response. The mutational spectrum analysis showed 47 distinct mutations in 89 families, 37 of them (78.7%) corresponding to missense mutations. Six mutations account for 47.2% of all the investigated alleles, each one with a frequency ≥5% (IVS10-11G>A, p.R261Q, p.V388M, p.R176L, p.E280K, p.A300S). The most prevalent HPA mutations in Galicia are the common Mediterranean mutation IVS10-11G>A and p.R261Q, with frequencies of 13.8% and 10.5%, respectively. One novel mutation (p.K361Q; c.1081A>C) was also reported. Although a good genotype-phenotype correlation is observed, there is no exact correlation for some genotypes involving mutations p.R261Q, p.I65T or IVS10-11G>A. Forty seven patients were monitored for post-challenge BH4, establishing genotype-based predictions of BH4-responsiveness in all of them. All phenylketonuric patients with 2 non responsive mutations all were unresponsive to BH4 and all patients with mutations previously associated with BH4 responsiveness in the two alleles had a clear positive response to the test, with the exception of 5 patients with mutations p.R261Q, p.I65T and p.R68S. Our study supports similar degree of heterogeneity of HPA mutation spectrum in Galicia compared to reported data from Southern Europe. Patients carrying null mutations in both alleles showed the highest degree of concordance with the most severe phenotypes. Genotype is a good predictor of BH4 response.
[Show abstract][Hide abstract] ABSTRACT: This study describes a cblE type of homocystinuria associated with haemolytic-uremic syndrome (HUS) features. We report on a male infant aged 43 days presenting with failure to thrive, hypotonia, pancytopaenia, HUS symptoms (microangiopathic haemolytic anaemia and thrombocytopaenia with signs of renal involvement) and fatal evolution. An underlying cobalamin disorder was diagnosed after a bone marrow examination revealed megaloblastic changes associated with hyperhomocysteinaemia. An urinary organic acid analysis revealed normal methylmalonic acid excretion. The cblE diagnosis was confirmed with a complementation analysis using skin fibroblasts and genetic studies of the MTRR gene. The patient treatment included parenteral hydroxocobalamin, carnitine, betaine and folinic acid, but there was no response. After the autopsy, the histopathological examination of the kidneys showed marked myointimal proliferation and narrowing of the vascular lumen. The central nervous system showed signs of haemorrhage that affected the putamen and the thalamus; diffuse white matter lesions with spongiosis, necrosis and severe astrogliosis were also observed. Microangiopathy was observed with an increase in vessel wall thickness, a reduction of the arterial inner diameter and capillary oedema. The signs of necrosis and haemorrhage were detected in the cerebellum, the cerebellar peduncles, the tegmentum and the bulbar olives.In conclusion, cblE should be considered when diagnosing patients presenting with HUS signs and symptoms during the newborn period. Despite early diagnosis, however, the specific treatment measures were not effective in this patient.
[Show abstract][Hide abstract] ABSTRACT: Inherited metabolic diseases (IMDs) belong to the group of rare diseases due to their low individual prevalence. Most of them are inherited in autosomal recessive fashion and represent good candidates for novel therapeutical strategies aimed at recovering partial enzyme function as they lack an effective treatment, and small levels of enzymatic activity have been shown to be associated with improved outcome and milder phenotypes. Recently, a novel therapeutic approach for genetic diseases has emerged, based on the ability of aminoglycosides and other compounds in allowing translation to proceed through a premature termination codon introduced by a nonsense mutation, which frequently constitute a significant fraction of the mutant alleles in a population. In this review we summarize the essentials of what is known as suppression therapy, the different compounds that have been identified by high-throughput screens or developed using a medicinal chemistry approach and the preclinical and clinical trials that are being conducted in general and in the field of IMDs in particular. Several IMDs have shown to be good models for evaluating readthrough compounds using patients' cells carrying nonsense mutations, monitoring for an increase in functional recovery and/or enzyme activity. Overall, the positive results obtained indicate the feasibility of the approach for different diseases and although the levels of protein function reached are low, they may be enough to alleviate the consequences of the pathology. Nonsense suppression thus represents a potential therapy or supplementary treatment for a number of IMD patients encouraging further clinical trials with readthrough drugs with improved functionality and low toxicity.
[Show abstract][Hide abstract] ABSTRACT: Phosphomannomutase 2 deficiency (PMM2-CDG) patients may present as mild phenotypes, with the cerebellum frequently involved. In those cases, false-negative results in screening may occur when applying conventional biochemical procedures. Our aim was to report two patients with a diagnosis of PMM2-CDG presenting with mild clinical phenotype. Patient 1-at 9 months of age, she presented with just psychomotor delay, tremor, hypotonia, and slight lipodystrophy. Patient 2-she presented at 8 months of age with psychomotor delay, hand stereotypes, hypotonia, convergent bilateral strabismus, and tremor but no lipodystrophy. Routine biochemical parameters including blood count, clotting factors, proteins, and thyroid hormone were normal in both cases. Cranial MRI evidenced mild cerebellar atrophy with moderate vermis hypoplasia. In case 1, sialotransferrin pattern showed very slightly increased disialotransferrin with no asialotransferrin, and in case 2, the transferrin pattern was impaired in the first study but nearly normal in the second. Nevertheless, in all the samples, quantification of the patterns obtained by capillary zone electrophoresis analysis gave results out of the control range. High residual PMM2 activity was observed in both cases and the genetic analysis showed that patient 1 was heterozygous for c.722G>C (p.C241S) and c.368G>A (p.R123Q) mutations, and patient 2 showed the c.722G>C and the c.470T>C (p.F157S) mutations in the PMM2 gene. We would like to stress the importance of the use of sensitive semiquantitative methods of screening for CDG in order to achieve early identification of patients with mild phenotypes. Intentional tremor was an atypical but remarkable clinical feature in both cases, and the global cerebellar atrophy with vermis hypoplasia reinforced the early clinical suspicion of a PMM2-CDG disease.
The Cerebellum 10/2011; 11(2):557-63. · 2.60 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: PMM2-CDG is an autosomal recessive disorder and the most frequent form of congenital disorder of N-glycosylation, with more than 100 mutations identified to date. Sixty-six patients from 58 unrelated families were diagnosed as PMM2-CDG (CDG-Ia) based on clinical signs or because of a previous affected sibling. They all presented a type 1 serum transferrin isoform pattern, and, in most cases, the disease was confirmed by determining PMM2 activity in fibroblasts and/or lymphocytes. Residual PMM2 activity in fibroblasts ranged from not detectable to 60% of the mean controls. DNA and RNA were isolated from fresh blood or fibroblasts from patients to perform molecular studies of the PMM2 gene, resulting in the identification of 30 different mutations, four of them newly reported here (p.Y102C, p.T118S, p.P184T, and p.D209G). From these 30 mutations, 15 have only been identified among Iberian PMM2-CDG patients. As in other Caucasian populations, p.R141H was the most frequent mutation (24 alleles, prevalence 20.6%), but less than in other European series in which this mutation represents 35-43% of the disease alleles. The next frequent mutations were p.D65Y (12 alleles, prevalence 10.3%) and p.T237M (9 alleles, prevalence 7.6%), while p.F119L and p.E139K, the most frequent changes in Scandinavian and French populations, respectively, were not found in our patients. The most common genotype was [p.R141H] + [p.T237M], and four homozygous patients for p.Y64C, p.D65Y, p.P113L, and p.T237M were detected. The broad mutational spectrum and the diversity of phenotypes found in the Iberian populations hamper genotype-phenotype correlation.
[Show abstract][Hide abstract] ABSTRACT: ATP:cob(I)alamin adenosyltransferase (ATR, E.C.184.108.40.206) converts reduced cob(I)alamin to the adenosylcobalamin cofactor. Mutations in the MMAB gene encoding ATR are responsible for the cblB type methylmalonic aciduria. Here we report the functional analysis of five cblB mutations to determine the underlying molecular basis of the dysfunction. The transcriptional profile along with minigenes analysis revealed that c.584G>A, c.349-1G>C, and c.290G>A affect the splicing process. Wild-type ATR and the p.I96T (c.287T>C) and p.R191W (c.571C>T) mutant proteins were expressed in a prokaryote and a eukaryotic expression systems. The p.I96T protein was enzymatically active with a K(M) for ATP and K(D) for cob(I)alamin similar to wild-type enzyme, but exhibited a 40% reduction in specific activity. Both p.I96T and p.R191W mutant proteins are less stable than the wild-type protein, with increased stability when expressed under permissive folding conditions. Analysis of the oligomeric state of both mutants showed a structural defect for p.I96T and also a significant impact on the amount of recovered mutant protein that was more pronounced for p.R191W that, along with the structural analysis, suggest they might be misfolded. These results could serve as a basis for the implementation of pharmacological therapies aimed at increasing the residual activity of this type of mutations.
Human Mutation 09/2010; 31(9):1033-42. · 5.05 Impact Factor