Mutations among Italian mucopolysaccharidosis type I patients

Lysosomal Dysfunction: Connecting the Dots in the Landscape of Human Diseases

Lysosomes are the main organelles responsible for the degradation of macromolecules in eukaryotic cells. Beyond their fundamental role in degradation, lysosomes are involved in different physiological processes such as autophagy, nutrient sensing, and intracellular signaling. In some circumstances, lysosomal abnormalities underlie several human pathologies with different etiologies known as known as lysosomal storage disorders (LSDs). These disorders can result from deficiencies in primary lysosomal enzymes, dysfunction of lysosomal enzyme activators, alterations in modifiers that impact lysosomal function, or changes in membrane-associated proteins, among other factors. The clinical phenotype observed in affected patients hinges on the type and location of the accumulating substrate, influenced by genetic mutations and residual enzyme activity. In this context, the scientific community is dedicated to exploring potential therapeutic approaches, striving not only to extend lifespan but also to enhance the overall quality of life for individuals afflicted with LSDs. This review provides insights into lysosomal dysfunction from a molecular perspective, particularly in the context of human diseases, and highlights recent advancements and breakthroughs in this field.

Mucopolysaccharidosis type I - Clinical and genetic characteristics of Romanian patients

Background: Mucopolysaccharidosis type I (MPS I) is an autosomal recessive lysosomal storage disorder caused by a deficiency of α-L-iduronidase (IDUA), which leads to the accumulation of partially digested glycosaminoglycans (dermatan sulfate and heparan sulfate) in the lysosomes and induces multisystemic alteration. Hurler (severe), Scheie (mild), and Hurler/Scheie (intermediate) syndromes are clinical subtypes of MPS-I. To date, more than 290 IDUA mutations have been reported. The purpose of this study was to present the clinical and genetic characteristics of Romanian MPS I syndrome patients and their genotype-phenotype correlation.

Patients and methods: Seven patients (5 girls and 2 boys) with MPS type I, belonging to 4 unrelated families, aged 0,75-17.9 years, were enrolled. The study methods consisted in: clinical and standard auxological assessment, bone radiographs, joint ultrasonography, goniometry, neurological and psychological evaluation, hepatic and splenic ultrasonography, cardiological evaluation, otorhinolaryngology examination, ophthalmological examination, spirometry, α-L-iduronidase enzyme activity assay and molecular analysis.

Results: The seven patients originated from 4 unrelated families, three patients with severe, two patients with intermediate and two with attenuated clinical phenotype. Each patient presented the classical picture of MPS type I picture, represented by: variable coarse facial features, arthropathy, hepatosplenomegaly, cardiac involvement, respiratory dysfunction and neurological impairment. Five patological variants, three point mutations (p.Q70 *, p.I238Q and p.K324R), two deletion c.1045_1047delGAC, c.46_57delTCGCTCCTG) and an insertion (c.1389 insC) were identified in both alleles of the ADUA gene in homozygous or heterozygous form. Two novel mutations (p.K324R and c.1389 insC) were reported. The p.Q70*(c.208C>T) variant was identified in 2 families with severe form of disease (Hurler syndrome) in homozygous status in one family and in compound heterozygous status in the other family.

Conclusion: The p.Q70* missense variant was the most frequent, correlated in all the cases who presented it with severe form, Hurler syndrome, the other mutations being usually isolated and particular for each patient, associated in our patients with less severe MPS I phenotype, as Hurler-Scheie or Scheie syndrome. The results of this study indicated the mutational heterogeneity of the IDUA gene and the difficulty to indicate some correlation between the genotype and phenotype in MPS I patients.

Mutation Analysis of the IDUA Gene in Iranian Patients with Mucopolysaccharidosis Type 1: Identification of Four Novel Mutations

Background and Purpose: Mucopolysaccharidosis 1 (MPS1) is an autosomal recessive disorder of a lysosomal enzyme called alpha-l-iduronidase caused by mutations in the IDUA gene. This enzyme is responsible for the degradation of the mucopolysaccharides, heparan sulfate, and dermatan sulfate. Based on clinical features and enzyme deficiency, MPS1 is divided into three subtypes, including a severe subtype (Hurler syndrome), an intermediate subtype (Hurler-Scheie syndrome), and an attenuated subtype (Scheie syndrome). The objective of this study was to characterize the mutation profiles of 17 Iranian patients with MPS1 and characterize the clinical features associated with their genotypes. Materials and Methods: Polymerase chain reaction-based sequencing of the IDUA gene was carried out for 10 patients with clinical diagnoses of MPS1 and 50 healthy controls. To estimate the impact of newly identified variants on the structure and function of the encoded alpha-l-iduronidase, in silico analyses was performed. Results: Eight genetic variations were detected, including five missense mutations (p.M1L, p.G51D, p.G134V, p.S157P, p.D301E), two nonsense mutations (p.W402* and p.Y343*), and one deletion (p.GFLNYY197-202), among which p.G134V, p.S157P, p.D301E, and p.GFLNYY197-202 were novel variations that had not been previously reported. Conclusion: After combining the results of the two previous IDUA gene studies performed on Iranian MPS1 patients and the results obtained from the current study, it is inferred that despite the presence of a number of previously known mutations, about half of the detected variations were unique in Iranian patients.

Epidemiology of mucopolysaccharidoses

The aim of this study was to obtain data about the epidemiology of the different types of mucopolysaccharidoses in Japan and Switzerland and to compare with similar data from other countries. Data for Japan was collected between 1982 and 2009, and 467 cases with MPS were identified. The combined birth prevalence was 1.53 per 100,000 live births. The highest birth prevalence was 0.84 for MPS II, accounting for 55% of all MPS. MPS I, III, and IV accounted for 15, 16, and 10%, respectively. MPS VI and VII were more rare and accounted for 1.7 and 1.3%, respectively. A retrospective epidemiological data collection was performed in Switzerland between 1975 and 2008 (34years), and 41 living MPS patients were identified. The combined birth prevalence was 1.56 per 100,000 live births. The highest birth prevalence was 0.46 for MPS II, accounting for 29% of all MPS. MPS I, III, and IV accounted for 12, 24, and 24%, respectively. As seen in the Japanese population, MPS VI and VII were more rare and accounted for 7.3 and 2.4%, respectively. The high birth prevalence of MPS II in Japan was comparable to that seen in other East Asian countries where this MPS accounted for approximately 50% of all forms of MPS. Birth prevalence was also similar in some European countries (Germany, Northern Ireland, Portugal and the Netherlands) although the prevalence of other forms of MPS is also reported to be higher in these countries. Birth prevalence of MPS II in Switzerland and other European countries is comparatively lower. The birth prevalence of MPS III and IV in Switzerland is higher than in Japan but comparable to that in most other European countries. Moreover, the birth prevalence of MPS VI and VII was very low in both, Switzerland and Japan. Overall, the frequency of MPS varies for each population due to differences in ethnic backgrounds and/or founder effects that affect the birth prevalence of each type of MPS, as seen for other rare genetic diseases. Methods for identification of MPS patients are not uniform across all countries, and consequently, if patients are not identified, recorded prevalence rates will be aberrantly low.

Report of 5 novel mutations of the α-L-iduronidase gene and comparison of Korean mutations in relation with those of Japan or China in patients with mucopolysaccharidosis I

BACKGROUND

Mucopolysaccharidosis I (MPS I) is an autosomal recessive lysosomal storage disorder caused by a lack of the lysosomal enzyme α-L-iduronidase (IDUA). To date, more than 200 IDUA mutations have been reported. However, only a few types of mutations are recurrent and the frequencies of mutations differ from country to country.

METHODS

We performed the IDUA mutation analysis in seven patients who were biochemically diagnosed with MPS I in the Department of Pediatrics, Samsung Medical Center, from 2009 to 2014. Here, we describe the results of the IDUA mutation analysis in seven patients with MPS I and the IDUA mutational spectrum in Korean patients with MPS I, including previous data.

RESULTS

The IDUA mutations were found in all 14 alleles of 7 patients, and 11 kinds of IDUA mutations were identified. The detected mutations were five missense mutations (p.A79V, p.L346R, p.T388K, p.P496R, and p.C577Y), two nonsense mutations (p.Y618* and p.R628*), two deletions (c.683delC and c.1591delC), one splice site mutation (c.972+1G>A), and one duplication (c.613_617dup). Among these, p.T388K, p.C577Y, c.683delC, c.1591delC, and c.972+1G>A were novel mutations that have not previously been reported. After taking everything into consideration, including IDUA mutation analysis of the previously reported 10 unrelated Korean patients with MPS I, p.L346R and c.704ins5 were most commonly found in Korean patients with MPS I. However, p.W402* and p.Q70*, which have mainly been found in Caucasian patients, were not found.

CONCLUSION

As a result, p.L346R and c.704ins5, which were the most common in Korea, which is geographically situated midway between China and Japan, were some of the most common mutations in China and Japan, respectively. These results are especially worthy of notice.

[Genetic aspects of mucopolysaccharidoses]

Mucopolysaccharidoses (MPS) are inherited metabolic diseases caused by mutations in the genes coding for one of the eleven enzymes involved in lysosomal catabolism of different glycosaminoglycans (or mucopolysaccharides). The different enzyme deficiencies result in a total of seven distinct mucopolysaccharidoses (I to IV, VI, VII and IX). This review considers the genetic and molecular aspects of the seven types of MPS.

4-Phenylbutyrate attenuates the ER stress response and cyclic AMP accumulation in DYT1 dystonia cell models

Dystonia is a neurological disorder in which sustained muscle contractions induce twisting and repetitive movements or abnormal posturing. DYT1 early-onset primary dystonia is the most common form of hereditary dystonia and is caused by deletion of a glutamic acid residue (302/303) near the carboxyl-terminus of encoded torsinA. TorsinA is localized primarily within the contiguous lumen of the endoplasmic reticulum (ER) and nuclear envelope (NE), and is hypothesized to function as a molecular chaperone and an important regulator of the ER stress-signaling pathway, but how the mutation in torsinA causes disease remains unclear. Multiple lines of evidence suggest that the clinical symptoms of dystonia result from abnormalities in dopamine (DA) signaling, and possibly involving its down-stream effector adenylate cyclase that produces the second messenger cyclic adenosine-3', 5'-monophosphate (cAMP). Here we find that mutation in torsinA induces ER stress, and inhibits the cyclic adenosine-3', 5'-monophosphate (cAMP) response to the adenylate cyclase agonist forskolin. Both defective mechanins are corrected by the small molecule 4-phenylbutyrate (4-PBA) that alleviates ER stress. Our results link torsinA, the ER-stress-response, and cAMP-dependent signaling, and suggest 4-PBA could also be used in dystonia treatment. Other pharmacological agents known to modulate the cAMP cascade, and ER stress may also be therapeutic in dystonia patients and can be tested in the models described here, thus supplementing current efforts centered on the dopamine pathway.

Whole exome sequencing unravels disease-causing genes in consanguineous families in Qatar

Whole exome sequencing (WES) has greatly facilitated the identification of causal mutations for diverse human genetic disorders. We applied WES as a molecular diagnostic tool to identify disease-causing genes in consanguineous families in Qatar. Seventeen consanguineous families with diverse disorders were recruited. Initial mutation screening of known genes related to the clinical diagnoses did not reveal the causative mutations. Using WES approach, we identified the definitive disease-causing mutations in four families: (i) a novel nonsense homozygous (c.1034C>G) in PHKG2 causing glycogen storage disease type 9C (GSD9C) in a male with initial diagnosis of GSD3; (ii) a novel homozygous 1-bp deletion (c.915del) in NSUN2 in a male proband with Noonan-like syndrome; (iii) a homozygous SNV (c.1598C>G) in exon 11 of IDUA causing Hurler syndrome in a female proband with unknown clinical diagnosis; (iv) a de novo known splicing mutation (c.1645+1G>A) in PHEX in a female proband with initial diagnosis of autosomal recessive hypophosphatemic rickets. Applying WES as a diagnostic tool led to the unambiguous identification of disease-causing mutations in phenotypically complex disorders or correction of the initial clinical diagnosis in ˜25% of our cases.

Mucopolysaccharidoses in northern Brazil: Targeted mutation screening and urinary glycosaminoglycan excretion in patients undergoing enzyme replacement therapy

Mucopolysaccharidoses (MPS) are rare lysosomal disorders caused by the deficiency of specific lysosomal enzymes responsible for glycosaminoglycan (GAG) degradation. Enzyme Replacement Therapy (ERT) has been shown to reduce accumulation and urinary excretion of GAG, and to improve some of the patients’ clinical signs. We studied biochemical and molecular characteristics of nine MPS patients (two MPS I, four MPS II and three MPS VI) undergoing ERT in northern Brazil. The responsiveness of ERT was evaluated through urinary GAG excretion measurements. Patients were screened for eight common MPS mutations, using PCR, restriction enzyme tests and direct sequencing. Two MPS I patients had the previously reported mutation p.P533R. In the MPS II patients, mutation analysis identified the mutation p.R468W, and in the MPS VI patients, polymorphisms p.V358M and p.V376M were also found. After 48 weeks of ERT, biochemical analysis showed a significantly decreased total urinary GAG excretion in patients with MPS I (p < 0.01) and MPS VI (p < 0.01). Our findings demonstrate the effect of ERT on urinary GAG excretion and suggest the adoption of a screening strategy for genotyping MPS patients living far from the main reference centers.

Mucopolysaccharidosis type I: molecular characteristics of two novel alpha-L-iduronidase mutations in Tunisian patients

BACKGROUND

Mucopolysaccharidosis type I (MPS I) is an autosomal storage disease resulting from defective activity of the enzyme α-L-iduronidase (IDUA). This glycosidase is involved in the degradation of heparan sulfate and dermatan sulfate. MPS I has severe and milder phenotypic subtypes.

AIM OF STUDY

This study was carried out on six newly collected MPS I patients recruited from many regions of Tunisia.

PATIENTS AND METHODS

Mutational analysis of the IDUA gene in unrelated MPS I families was performed by sequencing the exons and intron-exon junctions of IDUA gene.

RESULTS

Two novel IDUA mutations, p.L530fs (1587_1588 insGC) in exon 11 and p.F177S in exon 5 and two previously reported mutations p.P533R and p.Y581X were detected. The patient in family 1 who has the Hurler phenotype was homozygous for the previously described nonsense mutation p.Y581X.The patient in family 2 who also has the Hurler phenotype was homozygous for the novel missense mutation p.F177S. The three patients in families 3, 5 and 6 were homozygous for the p.P533R mutation. The patient in family 4 was homozygous for the novel small insertion 1587_1588 insGC. In addition, eighteen known and one unknown IDUA polymorphisms were identified.

CONCLUSION

The identification of these mutations should facilitate prenatal diagnosis and counseling for MPS I in Tunisia.

Molecular analysis of mucopolysaccharidosis type I in Tunisia: identification of novel mutation and eight Novel polymorphisms

Mucopolysaccharidosis type I (MPS I) is an autosomal recessive lysosomal storage disorder caused by a genetic defect in alpha-L-iduronidase (IDUA) which is involved in the degradation of dermatan and heparan sulfates. The disease has severe and milder phenotypic subtypes. The aim of this study was the detection of mutations in the IDUA gene from 12 additional MPS I patients with various clinical phenotypes (severe, 8 cases; intermediate, 3 cases; mild, 1 case).

PATIENTS AND METHODS

In this study, the IDUA mutations in eight unrelated Tunisian families were performed by amplifying and sequencing the IDUA exons and intron-exon jonctions.

RESULTS

Five IDUA mutations were detected: one is the L578Q, a novel mutation found, in milder patient. The others were the previously described: P533R, Y581X, F602X and R628X that produce a severe and intermediate phenotype. In addition, eighteen variants, including eight previously unreported polymorphisms (IVS6+21c>a, IVS7+79c>t, IVS7-45 g>c, IVS9+36t>c, IVS10+140c>a, IVS11+33c>t, IVS12+13c>t and IVS12-31c>g), were detected.

CONCLUSION

This paper, showed a heterogeneous pattern of mutations and polymorphisms among Tunisian patients.

Three novel α-L-iduronidase mutations in 10 unrelated Chinese mucopolysaccharidosis type I families

Mucopolysaccharidosis type I (MPS I) arises from a deficiency in the α-L-iduronidase (IDUA) enzyme. Although the clinical spectrum in MPS I patients is continuous, it was possible to recognize 3 phenotypes reflecting the severity of symptoms, viz., the Hurler, Scheie and Hurler/Scheie syndromes. In this study, 10 unrelated Chinese MPS I families (nine Hurler and one Hurler/Scheie) were investigated, and 16 mutant alleles were identified. Three novel mutations in IDUA genes, one missense p.R363H (c.1088G > A) and two splice-site mutations (c.1190-1G > A and c.792+1G > T), were found. Notably, 45% (nine out of 20) and 30% (six out of 20) of the mutant alleles in the 10 families studied were c.1190-1G > A and c.792+1G > T, respectively. The novel missense mutation p.R363H was transiently expressed in CHO cells, and showed retention of 2.3% IDUA activity. Neither p.W402X nor p.Q70X associated with the Hurler phenotype, or even p.R89Q associated with the Scheie phenotype, was found in this group. Finally, it was noted that the Chinese MPS I patients proved to be characterized with a unique set of IDUA gene mutations, not only entirely different from those encountered among Europeans and Americans, but also apparently not even the same as those found in other Asian countries.

Cervical pachymeningeal hypertrophy as the initial and cardinal manifestation of mucopolysaccharidosis type I in monozygotic twins with a novel mutation in the alpha-L-iduronidase gene

We describe a pair of monozygotic twins with an attenuated form of mucopolysaccharidosis type I (MPS-I). At age 24, they both developed cervical myelopathy as a cardinal manifestation. They each also had mild valve abnormalities and both inguinal and umbilical hernia, however, other characteristic features of MPS-I were absent or very mild. Magnetic resonance imaging revealed the cervical cord compressed by pachymeningeal hypertrophy. Surgery with dural plasty and laminoplasty resulted in decompression of the cervical cord with clinical improvement, revealing marked thickening of the dura mater. Both patients showed a marked decrease of alpha-L-iduronidase (IDUA) activity with c.252insC (p.P55fsX62; known) and c.1209C>A (p.T374N; novel) mutations of the IDUA gene (IDUA). Patients with MPS-I have been reported to present with various clinical phenotypes and severities even if they have identical mutations of IDUA. The quite similar, unique phenotype in monozygotic twins suggests that not only IDUA mutation but also other genetic factors than IDUA markedly influence the clinical manifestations of MPS-I.

Mutational Analysis of the alpha-L-iduronidase gene in three Egyptian families: identification of three novel mutations and five novel polymorphisms

Mucopolysaccharidosis type I (MPS I) is an autosomal recessive disorder that results from a deficiency in alpha-L-iduronidase (IDUA), which is involved in the degradation of dermatan and heparan sulfates. MPS I has three clinical phenotypes, ranging from the severe Hurler form to the milder Scheie phenotype. In this study, mutational analysis of the IDUA gene in three unrelated Egyptian families with Hurler phenotype was performed by sequencing the IDUA exons and exon-intron boundaries. Three novel mutations (c.854delC in exon 6, T141S in exon 4, and IVS2+6c>t) and the previously reported G51D in exon 1 were detected. In addition, nine sequence variants, including five previously unreported polymorphisms (N73H, N297N, R363S, IVS10 (3025) g>t, and IVS11 (3318) c>a), were identified. This is the first report of IDUA mutations in Egyptian patients with MPS I. Our study showed a heterogeneous pattern of mutations and polymorphisms among Egyptian patients.

Gene therapy for a mucopolysaccharidosis type I murine model with lentiviral-IDUA vector

Mucopolysaccharidosis type I is a lysosomal disease due to mutations in the IDUA gene, resulting in deficiency of alpha-L-iduronidase and accumulation of glycosaminoglycans (GAGs). Bone marrow transplantation and enzyme replacement are two therapies considered only moderately successful for affected patients, making the development of novel treatments necessary. We have previously shown the efficacy of lentivirus-mediated gene transfer to correct patient fibroblasts in vitro. Here we tested lentiviral-IDUA vector gene therapy in vivo on a murine MPS I model. Eight- to 10 week-old mice were injected with increasing lentiviral doses via the tail vein and analyzed 1 month after treatment. A single injection of lentiviral-IDUA vector resulted in transgene expression in several murine tissues, with the highest level reached in liver and spleen. Expression of 1% normal activity was sufficient in treated animals to normalize the GAG level in urine, liver, and spleen and was able to reduce the GAG level in kidney, heart, and lung. Polymerase chain reaction assays showed integration of the viral genome only in liver and spleen of treated animals, suggesting that the correction of the pathology in other tissues was due to secretion into the plasma by liver and spleen and uptake of corrective enzyme by distant tissues. Long-term (6 months) analysis showed the presence of enzyme-specific antibodies and the loss of enzyme activity and vector sequence in the target tissue, suggesting that the transgene-specific immune response interfered with long-term therapeutic correction and led to clearance of transduced cells. In conclusion, our results show the promising potential and the limitations of lentiviral-IDUA vector-mediated gene therapy in an in vivo model.

A homology model for human alpha-l-iduronidase: insights into human disease

Genotype-phenotype correlations in genetic diseases for which missense mutations lead to disease remain a challenge. This is particularly true for diseases caused by alterations of proteins for which no three-dimensional structure is available. One such disease is Mucopolysaccharidosis type I, a disorder arising from a lack of activity of the lysosomal enzyme alpha-l-iduronidase (IDUA, EC 3.2.1.76). This deficiency compromises the degradation pathway of glycosaminoglycans such as heparan sulfate and dermatan sulfate, leading to substrate accumulation, which ultimately results in a multisystem disorder. Patients with IDUA deficiency have a wide spectrum of disease ranging from an early onset, rapidly progressive form leading to death in the first decade of life, to an attenuated disease which manifests in adolescence and leads to progressive joint and cardiac disease but is associated with a normal life span. Many patients fit into a disease phenotype intermediate to these extremes. While a number of point mutations have been described as leading to varying degrees of disease severity, a structural basis for these genotype-phenotype correlations has not been available owing to the lack of a three-dimensional structure for IDUA. A homology model for the IDUA enzyme was constructed based on the recently solved crystal structure of the beta-xylosidase from Thermoanaerobacterium saccharolyticum (XyTS, EC 3.2.1.37), both of which belong to the same sequence-related family (CAZY family 39). This model provides insights into why certain point mutations produce severely misfolded proteins and thus lead to severe disease, and why other mutations produce proteins with only minor structural perturbations and therefore the attenuated form of the disease.

Mucopolysaccharidosis I: Alpha-L-Iduronidase mutations in three Tunisian families

Mucopolysaccharidosis type I (MPS I) is a lysosomal storage disease resulting from the defective activity of the enzyme alpha-L-iduronidase (IDUA). The disease has severe and milder phenotypic subtypes. The IDUA mutations in five MPS I patients from three unrelated families from central and southern Tunisia were determined by amplifying and sequencing each of the IDUA exons and intron-exon junctions. Two novel IDUA mutations, c.1805delTinsGAACA in exon 13 and I270S in exon 7, and two previously reported mutations, P533R and R628X, were detected. The two patients in family 1 who had the Hurler phenotype were homoallelic for the novel deletion-insertion mutation. The patient in family 2 who also had the Hurler phenotype was heteroallelic for the novel missense mutation I270S and the previously reported nonsense mutation R628X. The two patients in family 3 who had the Hurler-Scheie phenotype were homoallelic for P533R. In addition, six known IDUA polymorphisms were identified. These are the first Tunisian MPS I patients to be genotyped. The identification of these mutations and their genotype-phenotype correlations should facilitate prenatal diagnosis and counselling for MPS I in Tunisia, where a very high rate of consanguinity exists.

The alpha-L-iduronidase mutations R89Q and R89W result in an attenuated mucopolysaccharidosis type I clinical presentation

Mucopolysaccharidosis type I (MPS I; McKusick 25280; Hurler syndrome, Hurler-Scheie syndrome and Scheie syndrome) is caused by a deficiency in the lysosomal hydrolase, alpha-L-iduronidase (EC 3.2.1.76). MPS I patients present within a clinical spectrum bounded by the extremes of Hurler and Scheie syndromes. The alpha-L-iduronidase missense mutations R89Q and R89W were investigated and altered an important arginine residue proposed to be a nucleophile activator in the catalytic mechanism of alpha-L-iduronidase. The R89Q alpha-L-iduronidase mutation was shown to result in a reduced level of alpha-L-iduronidase protein (< or =10% of normal control) compared to a normal control level of alpha-L-iduronidase protein that was detected for the R89W alpha-L-iduronidase mutation. When taking into account alpha-L-iduronidase specific activity, the R89W mutation had a greater effect on alpha-L-iduronidase activity than the R89Q mutation. However, overall the R89W mutation produced more residual alpha-L-iduronidase activity than the R89Q mutation. This was consistent with MPS I patients, with an R89W allele, having a less severe clinical presentation compared to MPS I patients with either a double or single allelic R89Q mutation. The effects of the R89Q and R89W mutations on enzyme activity supported the proposed role of R89 as a nucleophile activator in the catalytic mechanism of alpha-L-iduronidase.

Can mucopolysaccharidosis type I disease severity be predicted based on a patient's genotype? A comprehensive review of the literature

Mucopolysaccharidosis type I (MPS I) is an autosomal recessive genetic disorder that results in a wide range of clinical symptoms from mild somatic complications and a normal lifespan to severe central nervous system involvement and a significantly shortened lifespan. An extensive review of the literature was performed to pool data from studies that have identified mutations in patients with mucopolysaccharidosis type I (MPS I) and have reported clinical information about disease severity in an attempt to make correlations between a patient's genotype and phenotype. To date, all patients with a nonsense mutation identified on both alleles have developed the severe form of MPS I. The phenotypes of patients with missense, insertion, deletion, or splice site mutations are much more variable. Missense mutations are the most likely to allow for some residual enzyme activity, and in particular, the R89Q mutation has been identified in several mild patients even when in combination with a nonsense mutation. Conversely, most splice site and insertion/deletion mutations result in the severe phenotype unless in combination with a less severe missense mutation. Currently, genotype-phenotype correlations cannot be confidently made unless the patient has 2 nonsense mutations. Although most families have private mutations, some insight into phenotypic expression may be obtained by observing the clinical severity of other patients with the same genotype. This review also confirms that MPS I allele frequencies vary between different ethnic populations, and that W402X and Q70X are the most common mutations and are present in over 50% of Caucasian alleles.

Identification and characterization of 13 new mutations in mucopolysaccharidosis type I patients

In this study we have investigated a group of 29 Brazilian patients, who had been diagnosed with the lysosomal storage disorder, Mucopolysaccharidosis type I (MPS-I). MPS I is caused by a deficiency in the lysosomal hydrolase, alpha-L-iduronidase. Ninety percent of the MPS I patients in this study were genotyped and revealed 10 recurrent and thirteen novel IDUA gene mutations. Eight of these new mutations and three common mutations W402X, P533R, and R383H were individually expressed in CHO-K1 cells and analyzed for alpha-L-iduronidase protein and enzyme activity. A correlation was observed between the MPS I patient clinical phenotype and the associated mutant alpha-L-iduronidase protein/enzyme activity expressed in CHO-K1 cells. This was the first time that Brazilian MPS I patients had been thoroughly analyzed and highlighted the difficulties of mutation screening and clinical phenotype assessment in populations with high numbers of unique mutations.

Alpha-L-iduronidase and enzyme replacement therapy for mucopolysaccharidosis I

Mucopolysaccharidosis I (McKusick 25280, Hurler syndrome, Scheie syndrome) is caused by a deficiency in the lysosomal hydrolase, alpha-L-iduronidase (EC 3.2.1.76) and results in a failure to degrade the glycosaminoglycans, dermatan sulfate and heparan sulfate. Mucopolysaccharidosis I patients present within a spectrum of clinical phenotypes, where Hurler and Scheie syndromes represent the two extremes. In the 80 or more years since the discovery of mucopolysaccharidosis I, the molecular defect has been defined, the alpha-L-iduronidase protein purified and characterised, the alpha-L-iduronidase (IDUA) gene cloned, molecular genetic studies performed and expression systems developed. These advances have allowed the development of alpha-L-iduronidase enzyme replacement therapy as a treatment strategy for mucopolysaccharidosis I patients. Using animal models of mucopolysaccharidosis I, the efficacy of alpha-L-iduronidase replacement therapy has been evaluated and justified the initiation of human clinical trials in mucopolysaccharidosis I patients. Phase I/II and Phase III clinical trials have recently been conducted and demonstrated that this therapy is effective in treating patients with the attenuated forms of mucopolysaccharidosis I (that is, little or no neuronal involvement). Further development of this technology is required to effectively treat the problem sites of neuronal and skeletal pathology, present in severe Hurler syndrome patients.

Diversity of mutations and distribution of single nucleotide polymorphic alleles in the human alpha-L-iduronidase (IDUA) gene

PURPOSE

Mucopolysaccharidosis type I (MPS I) is an autosomal recessive disorder resulting from a deficiency of the lysosomal glycosidase, alpha-L-iduronidase (IDUA). Patients with MPS I present with variable clinical manifestations ranging from severe to mild. To facilitate studies of phenotype-genotype correlation, the authors performed molecular studies to detect mutations in MPS I patients and characterize single nucleotide polymorphism (SNP) in the gene.

METHODS

Twenty-two unrelated MPS I patients were subjects for mutation detection using reverse transcriptional polymerase chain reaction (RT-PCR) and genomic PCR sequencing. Polymorphism analyses were performed on controls by restriction enzyme assays of PCR amplicons flanking nine intragenic single nucleotide polymorphic alleles.

RESULTS

Eleven different mutations including two common mutations (Q70X, W402X), five recurrent mutations (D315Y, P533R, R621X, R628X, S633L), and four novel mutations (R162I, G208D, 1352delG, 1952del25bp) were identified from MPS I patients. Multiple SNP alleles coexisting with the disease-causing mutations were detected. Allelic frequencies for nine SNP alleles including A8, A20, Q33H, L118, N181, A314, A361T, T388, and T410 were determined.

CONCLUSIONS

The results provide further evidence for the mutational heterogeneity among MPS I patients and point out possible common haplotype structures in the gene.

In vitro gene therapy of mucopolysaccharidosis type I by lentiviral vectors

Mucopolysaccharidosis type I (MPS I) results from a deficiency in the enzyme alpha-L-iduronidase (IDUA), and is characterized by skeletal abnormalities, hepatosplenomegaly and neurological dysfunction. In this study, we used a late generation lentiviral vector to evaluate the utility of this vector system for the transfer and expression of the human IDUA cDNA in MPS I fibroblasts. We observed that the level of enzyme expression in transduced cells was 1.5-fold the level found in normal cells; the expression persisted for at least two months. In addition, transduced MPS I fibroblasts were capable of clearing intracellular radiolabeled glycosaminoglycan (GAG). Pulse-chase experiments on transduced fibroblasts showed that the recombinant enzyme was synthesized as a 76-kDa precursor form and processed to a 66-kDa mature form; it was released from transduced cells and was endocytosed into a second population of untreated MPS I fibroblasts via a mannose 6-phosphate receptor. These results suggest that the lentiviral vector may be used for the delivery and expression of the IDUA gene to cells in vivo for treatment of MPS I.

Unique frequency of known mutations in Brazilian MPS I patients

The frequency of 10 known mutations in the IDUA gene-Q70X, A75T, H82P, R89Q, 678-7 g-->a, L218P, A327P, R383H, W402X, and P533R-was estimated in a group of 24 index cases with mucopolysaccharidosis type I. Three affected relatives were also analysed. Six of the 10 mutations screened were present in our patients (Q70X, R89Q, A327P, R383H, W402X, and P533R). These mutations account for 54% of the alleles; 37% of the genotypes were defined. Frequencies of these mutations are markedly different from those in the literature. A novel combination Q70X/A327P is described. This was the first time Brazilian MPS I patients were analysed with molecular techniques. The low frequency of common mutations indicates that a more comprehensive analysis of the IDUA gene should be done to delineate the mutation profile of MPS I better in our population.