Hematopoietic Stem- and Progenitor-Cell Gene Therapy for Hurler Syndrome

BACKGROUND

Allogeneic hematopoietic stem-cell transplantation is the standard of care for Hurler syndrome (mucopolysaccharidosis type I, Hurler variant [MPSIH]). However, this treatment is only partially curative and is associated with complications.

METHODS

We are conducting an ongoing study involving eight children with MPSIH. At enrollment, the children lacked a suitable allogeneic donor and had a Developmental Quotient or Intelligence Quotient score above 70 (i.e., none had moderate or severe cognitive impairment). The children received autologous hematopoietic stem and progenitor cells (HSPCs) transduced ex vivo with an α-L-iduronidase (IDUA)-encoding lentiviral vector after myeloablative conditioning. Safety and correction of blood IDUA activity up to supraphysiologic levels were the primary end points. Clearance of lysosomal storage material as well as skeletal and neurophysiological development were assessed as secondary and exploratory end points. The planned duration of the study is 5 years.

RESULTS

We now report interim results. The children's mean (±SD) age at the time of HSPC gene therapy was 1.9±0.5 years. At a median follow-up of 2.10 years, the procedure had a safety profile similar to that known for autologous hematopoietic stem-cell transplantation. All the patients showed prompt and sustained engraftment of gene-corrected cells and had supraphysiologic blood IDUA activity within a month, which was maintained up to the latest follow-up. Urinary glycosaminoglycan (GAG) excretion decreased steeply, reaching normal levels at 12 months in four of five patients who could be evaluated. Previously undetectable levels of IDUA activity in the cerebrospinal fluid became detectable after gene therapy and were associated with local clearance of GAGs. Patients showed stable cognitive performance, stable motor skills corresponding to continued motor development, improved or stable findings on magnetic resonance imaging of the brain and spine, reduced joint stiffness, and normal growth in line with World Health Organization growth charts.

CONCLUSIONS

The delivery of HSPC gene therapy in patients with MPSIH resulted in extensive metabolic correction in peripheral tissues and the central nervous system. (Funded by Fondazione Telethon and others; ClinicalTrials.gov number, NCT03488394; EudraCT number, 2017-002430-23.).

Mucopolysaccharidosis Type I: A Review of the Natural History and Molecular Pathology

Mucopolysaccharidosis type I (MPS I) is a rare autosomal recessive inherited disease, caused by deficiency of the enzyme α-L-iduronidase, resulting in accumulation of the glycosaminoglycans (GAGs) dermatan and heparan sulfate in organs and tissues. If untreated, patients with the severe phenotype die within the first decade of life. Early diagnosis is crucial to prevent the development of fatal disease manifestations, prominently cardiac and respiratory disease, as well as cognitive impairment. However, the initial symptoms are nonspecific and impede early diagnosis. This review discusses common phenotypic manifestations in the order in which they develop. Similarities and differences in the three animal models for MPS I are highlighted. Earliest symptoms, which present during the first 6 months of life, include hernias, coarse facial features, recurrent rhinitis and/or upper airway obstructions in the absence of infection, and thoracolumbar kyphosis. During the next 6 months, loss of hearing, corneal clouding, and further musculoskeletal dysplasias develop. Finally, late manifestations including lower airway obstructions and cognitive decline emerge. Cardiac symptoms are common in MPS I and can develop in infancy. The underlying pathogenesis is in the intra- and extracellular accumulation of partially degraded GAGs and infiltration of cells with enlarged lysosomes causing tissue expansion and bone deformities. These interfere with the proper arrangement of collagen fibrils, disrupt nerve fibers, and cause devastating secondary pathophysiological cascades including inflammation, oxidative stress, and other disruptions to intracellular and extracellular homeostasis. A greater understanding of the natural history of MPS I will allow early diagnosis and timely management of the disease facilitating better treatment outcomes.

Morphologic description of male reproductive accessory glands in a mouse model of mucopolysaccharidosis type I (MPS I)

Mucopolysaccharidosis type I (MPS I) is a genetic disease caused by a deficiency of the lysosomal hydrolase α-L-iduronidase (IDUA). IDUA degrades two types of glycosaminoglycans (GAGs): heparan and dermatan sulfates, important components of extracellular matrix, with signaling and structural functions. The accumulation of GAGs results in progressive physiological impairments in a variety of tissues, making MPS I a complex and multisystemic disease. Due the advent of therapeutic strategies which have increased patients' life expectancy, our group have been investigating the effect of IDUA deficiency on the reproductive system. In the present study, we aimed to characterize some of the accessory glands of the male reproductive tract in an MPS I mouse model. We used 6-month-old Idua+/+ and Idua-/- male mice to evaluate the histology of the seminal vesicles and prostate. Interstitial deposits of GAGs and collagen fibers were also observed. Seminal vesicles were smaller in the Idua-/- group, regardless of the normal staining pattern of the epithelial cells, marked with antiandrogen receptor. The prostate of Idua-/- mice presented necrotic acini and increased deposition of collagen fibers in the interstitium. All glands presented evident deposits of GAGs in the extracellular matrix, especially inside vacuolated interstitial cells. We concluded that, at this stage of the disease, the prostate is the most damaged accessory gland and may therefore, be the first to manifest functional impairments during disease progression.

Determination of frequencies of alleles, associated with the pseudodeficiency of lysosomal hydrolases, in population of Ukraine

The pseudodeficiency of lysosomal hydrolases described as a significant reduction in enzyme activi­ty in vitro in clinically healthy individuals, can lead to diagnostic errors in the process of biochemical analysis of lysosomal storage disease in case of its combination with pathology of another origin. Pseudodeficiency is mostly caused by some non-pathogenic changes in the corresponding gene. These changes lead to the in vitro lability of the enzyme molecule, whereas in vivo the enzyme retains its functional activity. To assess the prevalence of the most common lysosomal hydrolases pseudodeficiency alleles in Ukraine, we have determined the frequency of alleles c.1055A>G and c.* 96A>G in the ARSA gene, substitutions c.739C>T (R247W) and c.745C>T (R249W) in the HEXA gene, c.1726G>A (G576S) and c.2065G>A (E689K) in the GAA gene, c.937G>T (D313Y) in the GLA1 gene and c.898G>A (A300T) in the IDUA gene in a group of 117 healthy individuals from different regions of the country and 14 heterozygous carriers of pathogenic mutations in the HEXA gene (parents of children with confirmed diagnosis of Tay-Sachs disease). The total frequency of haplotypes, associated with arylsulfatase A pseudodeficiency, in healthy people in Ukraine (c.1055G/c.*96G and c.1055G/c.*96A haplotypes) was 10.3%. The frequency of c.739C>T (R247W) allele, associated with hexo­saminidase A pseudodeficiency, among Tay-Sachs carriers from Ukraine was 7.1%. The total frequency of α-glucosidase pseudodeficiency haplotypes in healthy individuals in Ukraine (c.1726A/c.2065A and c.1726G/c.2065A haplotypes) was 2.6%. No person among examined individuals with the substitution c.937G>T (D313Y) in the GLA1 gene and c.898G>A (A300T) in the IDUA gene was found. The differential diagnostics of lysosomal storage diseases requires obligatory determination of the presence of the pseudodeficiency alleles, particularly the ones with high incidence in the total population. Ignoring phenomenon of pseudodeficiency may lead to serious diagnostic errors.

Neonatal tolerance induction enables accurate evaluation of gene therapy for MPS I in a canine model

High fidelity animal models of human disease are essential for preclinical evaluation of novel gene and protein therapeutics. However, these studies can be complicated by exaggerated immune responses against the human transgene. Here we demonstrate that dogs with a genetic deficiency of the enzyme α-l-iduronidase (IDUA), a model of the lysosomal storage disease mucopolysaccharidosis type I (MPS I), can be rendered immunologically tolerant to human IDUA through neonatal exposure to the enzyme. Using MPS I dogs tolerized to human IDUA as neonates, we evaluated intrathecal delivery of an adeno-associated virus serotype 9 vector expressing human IDUA as a therapy for the central nervous system manifestations of MPS I. These studies established the efficacy of the human vector in the canine model, and allowed for estimation of the minimum effective dose, providing key information for the design of first-in-human trials. This approach can facilitate evaluation of human therapeutics in relevant animal models, and may also have clinical applications for the prevention of immune responses to gene and protein replacement therapies.

Shotgun proteomics reveals possible mechanisms for cognitive impairment in Mucopolysaccharidosis I mice

Mucopolysaccharidosis type I (MPS I) is due to deficient alpha-L-iduronidase (IDUA) which leads to storage of undegraded glycosaminoglycans (GAG). The severe form of the disease is characterized by mental retardation of unknown etiology. Trying to unveil the mechanisms that lead to cognitive impairment in MPS I, we studied alterations in the proteome from MPS I mouse hippocampus. Eight-month old mice presented increased LAMP-1 expression, GAG storage in neurons and glial cells, and impaired aversive and non-aversive memory. Shotgun proteomics was performed and 297 proteins were identified. Of those, 32 were differentially expressed. We found elevation in proteins such as cathepsins B and D; however their increase did not lead to cell death in MPS I brains. Glial fibrillary acid protein (GFAP) was markedly elevated, and immunohistochemistry confirmed a neuroinflammatory process that could be responsible for neuronal dysfunction. We didn't observe any differences in ubiquitin expression, as well as in other proteins related to protein folding, suggesting that the ubiquitin system is working properly. Finally, we observed alterations in several proteins involved in synaptic plasticity, including overexpression of post synaptic density-95 (PSD95) and reduction of microtubule-associated proteins 1A and 1B. These results together suggest that the cognitive impairment in MPS I mice is not due to massive cell death, but rather to neuronal dysfunction caused by multiple processes, including neuroinflammation and alterations in synaptic plasticity.

Effect of recombinant human growth hormone on changes in height, bone mineral density, and body composition over 1-2 years in children with Hurler or Hunter syndrome

Patients with Hurler or Hunter syndrome typically have moderate to severe growth deficiencies despite therapy with allogeneic hematopoietic stem cell transplantation and/or enzyme replacement therapy. It is unknown whether treatment with recombinant human growth hormone (hGH) can improve growth in these children. The objectives of this study were to determine the effects of hGH on growth, bone mineral density (BMD), and body composition in children with Hurler or Hunter syndrome enrolled in a longitudinal observational study. The difference in annual change in outcomes between hGH treated and untreated subjects was estimated by longitudinal regression models that adjusted for age, Tanner stage, and sex where appropriate. We report on 23 participants who completed at least 2 annual study visits (10 [43%] treated with hGH): Hurler syndrome (n=13) average age of 9.8 ± 3.1 years (range 5.3-13.6 years; 54% female) and Hunter syndrome (n=10) average age of 12.0 ± 2.7 years (range 7.0-17.0 years; 0% female). As a group, children with Hurler or Hunter syndrome treated with hGH had no difference in annual change in height (growth velocity) compared to those untreated with hGH. Growth velocity in hGH treated individuals ranged from -0.4 to 8.1cm/year and from 0.3 to 6.6 cm/year in the untreated individuals. Among children with Hunter syndrome, 100% (N=4) of those treated but only 50% of those untreated with hGH had an annual increase in height standard deviation score (SDS). Of the individuals treated with hGH, those with GHD had a trend towards higher annualized growth velocity compared to those without GHD (6.5 ± 1.9 cm/year vs. 3.5 ± 2.1cm/year; p=.050). Children treated with hGH had greater annual gains in BMD and lean body mass. In conclusion, although as a group we found no significant difference in growth between individuals treated versus not treated with hGH, individual response was highly variable and we are unable to predict who will respond to treatment. Thus, a trial of hGH may be appropriate in children with Hurler or Hunter syndrome, severe short stature, and growth failure. However, efficacy of hGH therapy should be evaluated after 1 year and discontinued if there is no increase in growth velocity or height SDS. Finally, the long-term benefits of changes in body composition with hGH treatment in this population are unknown.

High-dose enzyme replacement therapy in murine Hurler syndrome

Mucopolysaccharidosis type I (MPS I) is an autosomal recessive disease that is systemic, including progressive neurodegeneration, mental retardation and death before the age of 10 years. MPS I results from deficiency of α-L-iduronidase (IDUA) in lysosomes and subsequent accumulation of glycosaminoglycans (GAG). Clinical enzyme replacement therapy (ERT) with intravenous laronidase reverses some aspects of MPS I disease (e.g., hepatomegaly, splenomegaly, glycosaminoglycanuria) and ameliorates others (e.g., pulmonary function, cardiac disease, arthropathy, exercise tolerance). However, neurologic benefits are thought to be negligible because the blood-brain barrier (BBB) blocks enzyme from reaching the central nervous system (CNS). We considered the possibility that a very high dose of intravenous laronidase might be able to traverse the BBB in small quantities, and provide some metabolic correction in the brain. To address this question, high-dose laronidase was administered (11.6 mg/kg, once per week, 4 weeks) to adult MPS I mice. IDUA enzyme activity in the cortex of treated mice increased to 97% of that in wild type mice (p<0.01). GAG levels in cortex were reduced by 63% of that from untreated MPS I mice (p<0.05). Further, immunohistochemical analysis showed that treatment reduced secondary GM3-ganglioside accumulation in treated MPS I mice. Water T-maze tests showed that the learning abnormality in MPS I mice was reduced (p<0.0001). In summary, repeated, high-dose ERT facilitated laronidase transit across the BBB, reduced GAG accumulation within the CNS, and rescued cognitive impairment.

Characterization of joint disease in mucopolysaccharidosis type I mice

Mucopolysaccharidoses (MPS) are lysosomal storage disorders characterized by mutations in enzymes that degrade glycosaminoglycans (GAGs). Joint disease is present in most forms of MPS, including MPS I. This work aimed to describe the joint disease progression in the murine model of MPS I. Normal (wild-type) and MPS I mice were sacrificed at different time points (from 2 to 12 months). The knee joints were collected, and haematoxylin-eosin staining was used to evaluate the articular architecture. Safranin-O and Sirius Red staining was used to analyse the proteoglycan and collagen content. Additionally, we analysed the expression of the matrix-degrading metalloproteinases (MMPs), MMP-2 and MMP-9, using immunohistochemistry. We observed progressive joint alterations from 6 months, including the presence of synovial inflammatory infiltrate, the destruction and thickening of the cartilage extracellular matrix, as well as proteoglycan and collagen depletion. Furthermore, we observed an increase in the expression of MMP-2 and MMP-9, which could conceivably explain the degenerative changes. Our results suggest that the joint disease in MPS I mice may be caused by a degenerative process due to increase in proteases expression, leading to loss of collagen and proteoglycans. These results may guide the development of ancillary therapies for joint disease in MPS I.

Hurler disease (mucopolysaccharidosis type IH): clinical features and consanguinity in Tunisian population

Mucopolysaccharidosis type I (MPS I) was a group of rare autosomal recessive disorder caused by the deficiency of the lysosomal enzyme, alpha -L -iduronidase, and the resulting accumulation of undergraded dematan sulfate and heparan sulfate. MPS I patients have a wide range of clinical presentations, that makes it difficult to predict patient phenotype which is needed for genetic counseling and also impedes the selection and evaluation of patients undergoing therapy bone marrow transplantation.

AIM OF THE STUDY

consanguinity rates have been determined among 14 families with mucopolysaccharidosis type I, seen in the pediatric departments of different geographic areas of Tunisia (Central and Southern areas) for the period August 2004 - August 2011 in order to investigate the relation between consanguinity and this disorder.

PATIENTS AND METHODS

Clinical and molecular analyses confirmed the diagnosis for MPS type I in the studied families.

RESULTS

Most of the Tunisian MPS I patients have been identified at the homozygous status: p.P533R mutation (7 homozygous and one double heterozygous p.L578Q/p.P533R patients; 41.66% of all the investigated MPSI patients), p.F177S (1 homozygous patient; 5.55%), p.L530fs (1 patient; 5.55%), p.Y581X (2 patients; 11.11%), p.F602X (3 patients; 16.66%), p.R628X (1 patient; 5.55%). Another mutation: p.L578Q has been identified at the heterozygous status in the only double heterozygous p.L578Q/p.P533R case. Part of the mutations was the result of a founder effect. These described points are the consequences of the high rate of consanguinity.

CONCLUSION

The high frequency of p.P533R mutation could be explained by the high degree of inbreeding. This is due to the richness of the genetic background of the studied population.A multidisciplinary approach is essential to develop adequate preventive program adapted to the social, cultural, and economic context.

[Mutation analysis of 11 Chinese patients with attenuated mucopolysaccharidosis type]

OBJECTIVE

Mucopolysaccharidosis type I (MPS I) is an autosomal recessive disease resulting from the deficiency in the lysosomal enzyme alpha-L-iduronidase (IDUA). The present study was conducted to identify IDUA gene mutations in attenuated (MPS I H/S and MPS I S) patients with MPS I in northern China.

METHODS

Fourteen exons with adjacent intronic sequences of the IDUA gene in 11 MPS I patients were amplified by polymerase chain reaction (PCR), and the PCR products were sequenced directly and origin analysis was conducted.

RESULTS

Seven mutations were detected in the 11 MPS I patients, i.e., c.236 C to T (p. A79V), c.266 G to A (p.R89Q), c.265 C to T (p.R89W), c.532G to A (p.E178K), c.589G to A (p.G197S), c.1037T to G (p.L346R), and c.1877 G to A (p.W626X). All of them were known mutations. Six patients were homozygotes and 1 was heterozygote with nonsense mutation. In addition, 9 reported single nucleotide polymorphism (SNP) were detected, i.e., p.A8, p.A20, p.H33Q, p.R105Q, p.A314, p. A361T, p.T388, p.T410 and p.V454I.

CONCLUSION

The mutation spectrum of the IDUA gene in attenuated MPS I Chinese patients may be different from that in patients from other countries.

Characterization of an MPS I-H knock-in mouse that carries a nonsense mutation analogous to the human IDUA-W402X mutation

Here we report the characterization of a knock-in mouse model for the autosomal recessive disorder mucopolysaccharidosis type I-Hurler (MPS I-H), also known as Hurler syndrome. MPS I-H is the most severe form of alpha-l-iduronidase deficiency. alpha-l-iduronidase (encoded by the IDUA gene) is a lysosomal enzyme that participates in the degradation of dermatan sulfate and heparan sulfate. Using gene replacement methodology, a nucleotide change was introduced into the mouse Idua locus that resulted in a nonsense mutation at codon W392. The Idua-W392X mutation is analogous to the human IDUA-W402X mutation commonly found in MPS I-H patients. We found that the phenotype in homozygous Idua-W392X mice closely correlated with the human MPS I-H disease. Homozygous W392X mice showed no detectable alpha-l-iduronidase activity. We observed a defect in GAG degradation as evidenced by an increase in sulfated GAGs excreted in the urine and stored in multiple tissues. Histology and electron microscopy also revealed evidence of GAG storage in all tissues examined. Additional assessment revealed bone abnormalities and altered metabolism within the Idua-W392X mouse. This new mouse will provide an important tool to investigate therapeutic approaches for MPS I-H that cannot be addressed using current MPS I-H animal models.

Developmental outcome in five children with Hurler syndrome after stem cell transplantation: a pilot study

Hurler syndrome (mucopolysaccharidosis type 1H; MPS1H) is a lysosomal storage disease caused by a deficiency of alpha-L-iduronidase activity. The natural course of this neurodegenerative disease inevitably leads to premature death within the first 10 years of life. Enzyme replacement therapy is effective in correcting the enzymatic deficiency of organs other than the central nervous system. Hematopoietic stem cell transplantation (SCT) is the only treatment known to prevent psychomotor deterioration. However, the classical transplantation protocols resulted in a high incidence of graft failure and regimen-related toxicity. Recently, we published a well-tolerated, fludarabine-based, radiation-free conditioning regimen for SCT in patients with Hurler syndrome. Here we report the developmental outcome (assessed by the Denver Developmental Screening Test before and yearly after SCT) of four females and one male with MPS1H (mean age at last follow-up 71mo, range 42-87mo) treated in accordance with this strategy. Mean age at SCT was 25 months (range 10-36mo). All children were engrafted and in ambulatory care. They all showed psychomotor development without neurodegeneration. In all patients, after SCT a regression of intracranial lesions could be seen that paralleled the psychomotor improvements. SCT led to a relative reduction of head circumference in all cases.

Correction of clinical manifestations of canine mucopolysaccharidosis I with neonatal retroviral vector gene therapy

Mucopolysaccharidosis I (MPS I) (Hurler syndrome) is due to deficient alpha-L-iduronidase (IDUA) activity and is the most common of the MPS disorders. Neonatal MPS I dogs were injected intravenously (IV) with a gamma retroviral vector containing a complete long-terminal repeat (LTR) and an internal human alpha(1)-antitrypsin (hAAT) promoter upstream of the canine IDUA complementary DNA (cDNA). This resulted in stable serum IDUA activity of 366 +/- 344 units (U)/ml (28-fold normal) for up to 1.8 years, which likely derived primarily from secretion of IDUA by transduced liver cells. Retroviral vector (RV)-treated dogs had >18% of normal IDUA activity in organs and had decreased severity and/or incidence of hernias, chest deformities, joint disease, facial dysmorphia, corneal clouding, valvular heart disease, and aortic dilatation as compared with untreated MPS I dogs. The marked reduction that was observed in lysosomal storage in the brain of RV-treated dogs may have been due in part to expression from the LTR of the vector in cells in the brain. This possibility will be explored in future studies, because the potential for insertional mutagenesis has raised concerns about using vectors with an intact LTR. If proven safe, this gene therapy technique may be utilized in treating children with Hurler syndrome.

Legg-Perthes disease-like joint involvement and diagnosis delay in Scheie syndrome: a case report

Mucopolysaccharidosis (MPS) type I is an inherited disease caused by the absence or malfunctioning of lysosomal enzymes. Three subtypes, based on severity of symptoms, were described, and Scheie syndrome (also called MPS I S) is the mildest form. Although there may be some typical extra-articular manifestations, musculoskeletal involvement may be the only presenting sign in the absence of other symptoms in the patients with less severe forms. The patients with MPS I S, especially in attenuated phenotypes, may be sometimes difficult to recognize for physicians not familiar with the disease. With this case presentation, it is aimed to draw attention to this disease, which could be delayed for the correct diagnosis. An increased awareness of the disease may contribute to more accurate diagnosis, and patients may benefit from early intervention.

Mucopolysaccharidosis I cats mount a cytotoxic T lymphocyte response after neonatal gene therapy that can be blocked with CTLA4-Ig

Although gene therapy has reduced manifestations of genetic diseases, immune responses can abrogate the effect. One approach to inducing tolerance is to perform gene transfer in newborns when the immune system is immature. We demonstrate here that the dose of retroviral vector (RV) is important in mice, as mucopolysaccharidosis I (MPS I) mice that received neonatal intravenous gene therapy with a high dose of a canine alpha-L-iduronidase (cIDUA)-expressing RV had stable expression, while those that received a low dose did not. It was unclear, however, if neonatal transfer with any dose could induce tolerance in large animals. Therefore, newborn MPS I cats were injected intravenously with the RV expressing cIDUA. Although this resulted in high serum IDUA activity due to secretion by transduced cells, expression fell due to a CTL response. Cats that transiently received the immunosuppressive agent CTLA4-Ig did not develop a CTL response. In contrast, MPS I dogs, which can respond immunologically to canine IDUA, had stable serum IDUA activity after neonatal gene therapy. We conclude that cats, but not dogs, mount a potent CTL response to canine IDUA after neonatal gene therapy, which can be prevented with transient CTLA4-Ig.

Neonatal gene therapy of MPS I mice by intravenous injection of a lentiviral vector

Mucopolysaccharidosis type I (MPS I) is a lysosomal glycosaminoglycan (GAG) storage disorder caused by deficiency of alpha-l-iduronidase (IDUA). In this study, we evaluated the potential to perform gene therapy for MPS I by direct in vivo injection of a lentiviral vector, using an IDUA gene knockout murine model. We compared the efficacy in newborn versus young adult MPS I mice of a single intravenous injection of the lentiviral vector. The extent of transduction was dose-dependent, with the liver receiving the highest level of vector, but other somatic organs reaching almost the same level. The phenotypic manifestations of disease were partially improved in the mice treated as young adults, but were nearly normalized at every end-point measured in the mice treated as neonates. In the neonatally treated mice, the expressed IDUA activity resulted in decreased GAG storage, prevention of skeletal abnormalities, a more normal gross appearance, and improved survival. Most strikingly, significant levels of IDUA enzyme were produced in the brain of mice treated as neonates, with transduction of neurons at high levels. The sustained expression of enzymatically active IDUA in multiple organs had a significant beneficial effect on the phenotypic abnormalities of MPS I, which may be translated to clinical gene therapy of patients with Hurler disease.

Liver-directed neonatal gene therapy prevents cardiac, bone, ear, and eye disease in mucopolysaccharidosis I mice

Mucopolysaccharidosis I (MPS I) due to deficient alpha-L-iduronidase (IDUA) activity results in accumulation of glycosaminoglycans in many cells. Gene therapy could program liver to secrete enzyme with mannose 6-phosphate (M6P), and enzyme in blood could be taken up by other cells via the M6P receptor. Newborn MPS I mice were injected with 10(9) (high dose) or 10(8) (low dose) transducing units/kg of a retroviral vector (RV) expressing canine IDUA. Most animals achieved stable expression of IDUA in serum at 1240 +/- 147 and 110 +/- 31 units/ml, respectively. At 8 months, untreated MPS I mice had aortic insufficiency, increased bone mineral density (BMD), and reduced responses to sound and light. In contrast, MPS I mice that received high-dose RV had normal echocardiograms, BMD, auditory-evoked brain-stem responses, and electroretinograms. This is the first report of complete correction of these clinical manifestations in any model of mucopolysaccharidosis. Biochemical and pathologic evaluation confirmed that storage was reduced in these organs. Mice that received low-dose RV and achieved 30 units/ml of serum IDUA activity had no or only partial improvement. We conclude that high-dose neonatal gene therapy with an RV reduces some major clinical manifestations of MPS I in mice, but low dose is less effective.

Enzyme replacement therapy in mucopolysaccharidosis type I

Mucopolysaccharidosis (MPS) type I is a lysosomal storage disorder caused by deficiency of the enzyme alpha-L-iduronidase (IDUA), which presents with a wide spectrum of phenotypes. Recently, enzyme replacement therapy (ERT) became available for patients with MPS I and has been demonstrated to be safe and effective in patients with the milder Hurler-Scheie and Scheie phenotypes. Treatment for 26 weeks with recombinant human IDUA (laronidase) has been shown to significantly increase the percentage of predicted normal forced vital capacity and the distance walked in the 6-minute walk test. There was also a clear reduction in the volume of the liver and the levels of urinary glycosaminoglycan excretion. The drug was generally well tolerated. There were no drug-related severe adverse events, and although the majority of patients developed IgG antibodies, these declined by the end of the study.

CONCLUSION

ERT seems to be a very promising new therapeutic regimen for patients with MPS I, especially for those with the less severe variants. However, as laronidase does not cross the blood-brain barrier it will probably not influence the central nervous manifestations in the most severely affected patients with the Hurler phenotype, although it may improve general lung and heart function, making bone marrow transplantation easier to tolerate.

Mucopolysaccharidosis I under enzyme replacement therapy with laronidase--a mortality case with autopsy report

There is little information about MPS I-related complications during laronidase therapy. We describe the first autopsy report of a young male MPS I patient who died of infection-induced cardiopulmonary failure following 2 years of weekly treatment with laronidase.

Identification and molecular characterization of α-L-iduronidase mutations present in mucopolysaccharidosis type I patients undergoing enzyme replacement therapy

Mucopolysaccharidosis type I (MPS I) is an autosomal recessive lysosomal storage disorder caused by a deficiency of alpha-L-iduronidase (IDUA). Mutations in the gene are responsible for the enzyme deficiency, which leads to the intralysosomal storage of the partially degraded glycosaminoglycans dermatan sulfate and heparan sulfate. Molecular characterization of MPS I patients has resulted in the identification of over 70 distinct mutations in the IDUA gene. The high degree of molecular heterogeneity reflects the wide clinical variability observed in MPS I patients. Six novel mutations, c.1087C>T (p.R363C), c.1804T>A (p.F602I), c.793G>C, c.712T>A (p.L238Q), c.1727+2T>A, and c.1269C>G (p.S423R), in a total of 14 different mutations, and 13 different polymorphic changes, including the novel c.246C>G (p.H82Q), were identified in a cohort of 10 MPS I patients enrolled in a clinical trial of enzyme-replacement therapy. Five novel amino acid substitutions and c.236C>T (p.A79V) were engineered into the wild-type IDUA cDNA and expressed. A p.G265R read-through mutation, arising from the c.793G>C splice mutation, was also expressed. Each mutation reduced IDUA protein and activity levels to varying degrees with the processing of many of the mutant forms also affected by IDUA. The varied properties of the expressed mutant forms of IDUA reflect the broad range of biochemical and clinical phenotypes of the 10 patients in this study. IDUA kinetic data derived from each patient's cultured fibroblasts, in combination with genotype data, was used to predict disease severity. Finally, residual IDUA protein concentration in cultured fibroblasts showed a weak correlation to the degree of immune response to enzyme-replacement therapy in each patient.

In vivo microstructural analysis of the cornea in Scheie's syndrome

PURPOSE

To analyze clinical and in vivo microstructural characteristics of both corneas of a 13-year-old male subject with Scheie's syndrome and compare the observations with the pathologic reports in the literature.

METHODS

Standard clinical examination and real-time, slit-scanning in vivo confocal microscopy were performed and repeated after 1 year.

RESULTS

In vivo confocal microscopy images at all cellular layers demonstrated brighter intercellular spaces than those of normal corneas. Cicatrization of the anterior stroma was identified, and the keratocytes of the middle and posterior stroma exhibited markedly altered morphology, often round or elliptical in shape, and with clearly demarcated, hyporeflective centers. The nerve fibers of the subbasal plexus were somewhat more irregular and difficult to distinguish, possibly due to underlying fibrosis.

CONCLUSIONS

The potential of in vivo confocal microscopy to highlight microstructural alterations of the intact human cornea and evaluate such changes over time might reduce reliance on histopathologic investigations in such conditions and contribute to the ophthalmic management of the mucopolysaccharidoses in the future.

In utero injection of alpha-L-iduronidase-carrying retrovirus in canine mucopolysaccharidosis type I: infection of multiple tissues and neonatal gene expression

Canine alpha-L-iduronidase (alpha-ID) deficiency is caused by a single base pair mutation in the alpha-ID gene, resulting in no enzyme activity in homozygous affected pups. The disease clinically resembles human mucopolysaccharidosis type I (MPSI). We used the canine MPSI model system to address the efficacy of a new retroviral vector, MND-MFG, containing the human alpha-ID cDNA (MND-MFG-alpha-ID) for direct in utero gene delivery to MPSI cells. In vitro, the MND-MFG-alpha-ID vector showed high-level, long-term expression of the transgene in both canine and human alpha-ID-deficient fibroblasts. The effectiveness of this vector for in utero gene transfer and expression in multiple tissues was assessed by injecting viral supernatants into MPSI fetuses and evaluating transduction efficiency and enzyme expression at various times after birth. Transduction of a spectrum of cell types and tissues was observed in all seven live-born pups and in one stillborn pup. Although enzyme activity was not detected in adult tissues from the seven surviving pups, significant alpha-ID enzyme activity was detected in both the liver and kidney of the deceased pup. Our combined gene delivery vector and in utero transfer approach, while encouraging in terms of overall gene transfer efficiency to multiple tissues and successful short-term gene expression, was unable to meet the important requirement of sustained in vivo gene expression.

[Ocular Manifestation of Mucopolysaccharidosis I-S (Scheie's Syndrome)]

BACKGROUND

Bilateral stromal corneal opacifications are a differential diagnostical challenge to identify associated systemic diseases.

CASE-REPORT

A 47-year old civil engineer (height 167 cm) with bilateral stromal corneal clouding presented with visual loss for the last 27 years: VA 20/100 OD and 20/50 OS (following penetrating keratoplasty OS). The cornea showed milky-whitish, cloudy, diffuse stromal deposits without a separate lipoid arc. The posterior segment showed tapetoretinal degeneration. Scotopic ERG was decreased. A suspicious stiffness of interphalangeal joints on both hands was observed. There was an aortic and mitral insufficiency grade I. Serum levels of LDL, HDL and triglycerides were normal. The biomicroscopical diagnosis of Scheie's syndrome (mucopolysaccharidosis I-S) was confirmed by a deficiency of alpha-L-iduronidase in leukocytes (0.02 nmol/min/mg protein, normal range: 0.3 - 1.5).

CONCLUSION

The differential diagnosis of bilateral corneal stromal opacification includes in addition to the mucopolysaccharidoses HDL-deficiency diseases (LCAT deficiency, Tangier disease, Fish eye disease), Schnyder's crystalline stromal dystrophy, cystinosis, gout and mucolipidoses. MPS I-S may easily be detected by alpha-L-iduronidase deficiency in leukocytes and increased mucopolysaccharides in the urine. Furthermore, patients with MPS I-S need general medical care because of cardiovascular abnormalities, joint stiffness and myopathies.

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.

White matter changes mimicking a leukodystrophy in a patient with Mucopolysaccharidosis: characterization by MRI

Mucopolysaccharidosis (MPS) type I (alpha-iduronidase deficiency) is characterized by storage and massive urinary excretion of dermatan sulfate and heparan sulfate; it may be distinguished into three different subtypes based on age at onset and severity of the clinical symptoms. We report on progressive white matter involvement documented by serial MR imaging in a patient with the MPS type I, severe skeletal involvement and preserved mental capabilities (intermediate phenotype or Hurler/Scheie syndrome).The natural history of white matter abnormalities in patients with MPS is still unclear; based on the present study, it appears that degenerative changes of the white matter mimicking a leukodystrophy may mark the course of MPS type I. We also suggest that the degree of MR changes in patients with MPS does not always reflect their neurological impairment.

Outcome of second hematopoietic cell transplantation in Hurler syndrome

Hurler syndrome (HS) is an autosomal recessive, inherited metabolic storage disorder due to deficiency of lysosomal alpha-L-iduronidase (IDU) enzyme activity. Untreated patients develop progressive mental retardation and multisystem morbidity with a median life expectancy of 5 years. Allogeneic hematopoietic cell transplantation (HCT) can achieve stabilization and even improvement of intellect, with long-term survival. However, children with HS have an increased incidence of graft failure, usually with concomitant autologous marrow reconstitution. Between 1983 and 2000, 71 Hurler children underwent HCT at the University of Minnesota. Of these 71, 19 (27%) experienced graft failure. We report HCT outcomes in all 11 Hurler patients receiving a second HCT at the University of Minnesota. Median age at second HCT was 25 months (range, 16 to 45 months); median time from first HCT was 8 months (range, 4 to 18.5 months). The conditioning regimen consisted of cyclophosphamide/TBI/ATG (n = 8) or busulfan/cyclophosphamide/ATG (n = 3). The source of bone marrow was an unrelated donor in six, matched sibling in four, and mismatched related in one. Five of the 11 grafts were T cell depleted prior to infusion. Overall, 10 of 11 patients showed donor-derived engraftment, of whom three developed grade 3 to 4 acute GVHD. Five of 11 patients are surviving a median of 25 months (range, 2 months to 12 years) with an overall actuarial survival of 50% (95% CI, 27% to 93%) at 4 years. All five show sustained donor engraftment with normalization of IDU activity levels. Three of five evaluable patients demonstrated stabilization of neuropsychological function after second HCT. Currently, allogeneic donor-derived hematopoiesis provides the only chance for long-term survival and improved quality of life in Hurler patients. While graft failure in Hurler patients requires further investigation, a timely second HCT can be well-tolerated and beneficial.

Hurler's syndrome, West's syndrome, and vitamin D-dependent rickets

Mucopolysaccharidosis I is a metabolic disease of autosomal recessive inheritance caused by deficient activity of alpha-L-iduronidase. The clinical phenotype presents a wide spectrum of signs in the first year of life. We report a child with clinical features and laboratory data consistent with mucopolysaccharidosis I who precociously developed hydrocephalus and flexion spasms with hypsarrythmia in the electroencephalographic registration characteristic of West's syndrome. His radiologic and biochemical data suggested vitamin D-dependent rickets. To our knowledge, this is the first report of a patient demonstrating an association among mucopolysaccharidosis 1, West's syndrome, and vitamin D-dependent rickets.

Mucopolysaccharidosis type I: clinical and biochemical study

Of 1240 outpatients referred to the Human Genetics Clinic between 1997 and 1998, 248 (20%) had inborn errors of metabolism, 36 (14%) of which were diagnosed as mucopolysaccharidoses. Parental consanguinity was present in 82% of these patients. Deficiency of alpha-L-iduronidase (IDUA) enzyme in leukocytes and increased urinary mucopolysaccharides excretion were detected in 17 patients. The urinary spot test for glucosaminoglycans was inconclusive in 4 of the 17 cases. Results showed a correlation between the biochemical enzyme activity in leukocytes, the amount of excreted mucopolysaccharides and the subtype and course of mucopolysaccharidosis type I. We conclude that estimation of IDUA enzyme activity in leukocytes can differentiate between clinically overlapping cases of MPS I and MPS II and given the clinical manifestations of MPS I is a definitive and unequivocal method of diagnosis while the urinary spot test is inconclusive.

Gene therapy for canine alpha-L-iduronidase deficiency: in utero adoptive transfer of genetically corrected hematopoietic progenitors results in engraftment but not amelioration of disease

Canine alpha-L-iduronidase (iduronidase) deficiency is a model of the human lysosomal storage disorder mucopolysaccharidosis type I (MPS I). We used this canine model to evaluate the therapeutic potential of hematopoietic stem cell (HSC) gene therapy for enzyme deficiencies. In previous studies, iduronidase-deficient dogs infused with autologous marrow cells genetically modified to express iduronidase had long-term engraftment with provirally marked cells, but there was no evidence of proviral iduronidase expression or clinical improvement. The presence of humoral and cellular immune responses against iduronidase apparently abrogated the therapeutic potential of HSC gene therapy in these experiments. To evaluate HSC gene therapy for canine MPS I in the absence of a confounding immune response, we have now performed in utero adoptive transfer of iduronidase-transduced MPS I marrow cells into preimmune fetal pups. In three separate experiments, 17 midgestation fetal pups were injected with 0.5-1.5 x 10(7) normal or MPS I allogeneic long-term marrow culture (LTMC) cells transduced with neo(r)- or iduronidase-containing retroviral vectors. Nine normal and three MPS I pups survived the neonatal period and demonstrated engraftment of provirally marked progenitors at levels of up to 12% for up to 12 months. However, the proportion of provirally marked circulating leukocytes was approximately 1%. Neither iduronidase enzyme nor proviral-specific transcripts were detected in blood or marrow leukocytes of any MPS I dog. Humoral immune responses to iduronidase were not detected in neonates, even after "boosting" with autologous iduronidase-transduced LTMC cells. All MPS I dogs died at 8-11 months of age from complications of MPS I disease with no evidence of amelioration of MPS I disease. Our results suggest that iduronidase-transduced primitive hematopoietic progenitors can engraft in fetal recipients, contribute to hematopoiesis, and induce immunologic nonresponsiveness to iduronidase in MPS I dogs. However, the therapeutic potential of HSC gene transfer in this model of iduronidase deficiency appears to be limited by poor maintenance of proviral iduronidase gene expression and relatively low levels of genetically corrected circulating leukocytes.

Genetically corrected autologous stem cells engraft, but host immune responses limit their utility in canine alpha-L-iduronidase deficiency

Canine alpha-L-iduronidase (alpha-ID) deficiency, a model of the human storage disorder mucopolysaccharidosis type I (MPS I), is an ideal system in which to evaluate the clinical benefit of genetically corrected hematopoietic stem cells. We performed adoptive transfer of genetically corrected autologous hematopoietic cells in dogs with alpha-ID deficiency. Large volume marrow collections were performed on five alpha-ID-deficient dogs. Marrow mononuclear cells in long-term marrow cultures (LTMCs) were exposed on three occasions during 3 weeks of culture to retroviral vectors bearing the normal canine alpha-ID cDNA. Transduced LTMC cells from deficient dogs expressed enzymatically active alpha-ID at 10 to 200 times the levels seen in normal dogs. An average of 32% of LTMC-derived clonogenic hematopoietic cells were provirus positive by polymerase chain reaction and about half of these expressed alpha-ID. Approximately 10(7) autologous gene-modified LTMC cells/kg were infused into nonmyeloablated recipients. Proviral DNA was detected in up to 10% of individual marrow-derived hematopoietic colonies and in 0.01% to 1% of blood and marrow leukocytes at up to 2 to 3 years postinfusion. Despite good evidence for engraftment of provirally marked cells, neither alpha-ID enzyme nor alpha-ID transcripts were detected in any dog. We evaluated immune responses against alpha-ID and transduced cells. Humoral responses to alpha-ID and serum components of the culture media (fetal bovine and horse sera and bovine serum albumin) were identified by enzyme-linked immunosorbent assay. Cellular immune responses to autologous alpha-ID but not neo(r) transduced cells were demonstrated by lymphocyte proliferation assays. To abrogate potential immune phenomena, four affected dogs received posttransplant cyclosporine A. Whereas immune responses were dampened in these dogs, alpha-ID activity remained undetectable. In none of the dogs engrafted with genetically corrected cells was there evidence for clinical improvement. Our data suggest that, whereas the alpha-ID cDNA may be transferred and maintained in approximately 5% of hematopoietic progenitors, the potential of this approach appears limited by the levels of provirally derived enzyme that are expressed in vivo and by the host's response to cultured and transduced hematopoietic cells expressing foreign proteins.

Mucopolysaccharidosis type I: characterization of a common mutation that causes Hurler syndrome in Moroccan subjects

A group of 13 Moroccan patients with MPS I and their families, including three siblings and twin siblings, was screened for mutations of the alpha-L-iduronidase gene using fluorescence-assisted mismatch analysis (FAMA) and cycle sequencing of PCR products. The P533R mutation, which is rare in Europeans, was identified in 92% of mutant alleles (24/26). This is the highest frequency of this mutation detected in patients with Hurler syndrome. None of the patients carried the W402X or Q70X alleles, the most common MPS I mutations in Europeans. These results suggest that the P533R mutation constitutes the genetic lesion which results in MPS I in people of Moroccan descent and provides yet more evidence for the uneven geographical distribution of mutations in MPS I.

Molecular genetics of mucopolysaccharidosis type I: mutation analysis among the patients of the former Soviet Union

Mucopolysaccharidosis type I (MPS-I) is an autosomal recessive lysosomal storage disorder resulting from a deficiency of the lysosomal protein alpha-l-iduronidase (IDUA). Patients present within a broad spectrum of phenotypes from severe (Hurler syndrome) to clinically less severe (Scheie syndrome). Since 1982 a special program for the diagnosis and prevention of lysosomal storage diseases has operated in the former Soviet Union (FSU). We report the genotypes of 25 MPS-I patients with different clinical severities from the FSU. All the patients were screened for two common mutations (W402X and Q70X) and four other mutations (P533R, R89Q, A327P, 474 2a-->g). W402X and Q70X alleles accounted for 4 and 44%, respectively. Using SSCP analysis and subsequent direct sequencing we also detected four novel mutations (P533L, Q63X, Y343X, and A75P) in the IDUA gene, together with two mutations (974ins12bp, 134del12bp) described elsewhere. All were found in the heterozygous form in MPS-I patients with different clinical severities. A total of 32 mutant alleles leading to MPS-I was identified with nine patients fully genotyped. Four patients were homozygous for Q70X while five others were genetic compounds. Besides the eight identified mutations, six known polymorphisms were found. The spectrum of mutant alleles discovered is highly specific and proves the peculiarity of genetic loads in the FSU. Our data suggest a closer relationship between the FSU and Scandinavian populations than with Western and Central European populations.

Murine mucopolysaccharidosis type I: targeted disruption of the murine alpha-L-iduronidase gene

Mucopolysaccharidosis type I (MPS I) is considered to represent the prototypical mucopolysaccharide storage disorder. Although a spectrum of severity is seen within the MPS I subgroup, Hurler syndrome represents the most severe and frequent manifestation of MPS I. We describe here the generation of a murine model for Hurler syndrome by targeted disruption of the murine Idua gene. Homozygous Idua -/- mice have no detectable alpha-L-iduronidase enzyme activity and show increased urinary glycosaminoglycan levels. Although normal appearing at birth, Idua -/- mice develop a flattened facial profile and thickening of the digits discernible by 3 weeks of age. No obvious growth deficiency nor mortality is seen within the first 20 weeks of life. Radiographs reveal anterior flaring of the ribs and thickening of the facial bones as early as 4 weeks of age with more extensive dysostosis detectable by 15 weeks of age. At 4 weeks of age, lysosomal storage is noted primarily within reticuloendothelial cells with abundant lysosomes noted in Kupffer cells, splenic sinusoidal lining cells, and glial cells. More widespread lysosomal storage is noted by 8 weeks of age in hepatocytes, chondrocytes, neurons, as well as renal tubular cells. Thus, targeted disruption of the murine Idua locus has produced a murine strain representative of the severe form of MPS I. This model should permit detailed evaluation of the pathophysiology of lysosomal storage disorders and provide a small animal model for the testing and development of enzyme replacement and gene therapy regimes.

Outcome of unrelated donor bone marrow transplantation in 40 children with Hurler syndrome

Long-term survival and improved neuropsychological function have occurred in selected children with Hurler syndrome (MPS I H) after successful engraftment with genotypically matched sibling bone marrow transplantation (BMT). However, because few children have HLA-identical siblings, the feasibility of unrelated donor (URD) BMT as a vehicle for adoptive enzyme therapy was evaluated in this retrospective study. Forty consecutive children (median, 1.7 years; range, 0.9 to 3.2 years) with MPS I H received high-dose chemotherapy with or without radiation followed by BMT between January 27, 1989 and May 13, 1994. Twenty-five of the 40 patients initially engrafted. An estimated 49% of patients are alive at 2 years, 63% alloengrafted and 37% autoengrafted. The probability of grade II to IV acute graft-versus-host disease (GVHD) was 30%, and the probability of extensive chronic GVHD was 18%. Eleven patients received a second URD BMT because of graft rejection or failure. Of the 20 survivors, 13 children have complete donor engraftment, two children have mixed chimeric grafts, and five children have autologous marrow recovery. The BM cell dose was correlated with both donor engraftment and survival. Thirteen of 27 evaluable patients were engrafted at 1 year following URD BMT. Neither T-lymphocyte depletion (TLD) of the bone marrow nor irradiation appeared to influence the likelihood of engraftment. Ten of 16 patients alive at 1 year who received a BM cell dose greater than or equal to 3.5 x 10(8) cells/kg engrafted, and 62% are estimated to be alive at 3 years. In contrast, only 3 of 11 patients receiving less than 3.5 x 10(8) cells/kg engrafted, and 24% are estimated to be alive at 3 years (P = .05). The mental developmental index (MDI) was assessed before BMT. Both baseline and post-BMT neuropsychological data were available for 11 engrafted survivors. Eight children with a baseline MDI greater than 70 have undergone URD BMT (median age, 1.5 years; range, 1.0 to 2.4 years). Of these, two children have had BMT too recently for developmental follow-up. Of the remaining six, none has shown any decline in age equivalent scores. Four children are acquiring skills at a pace equal to or slightly below their same age peers; two children have shown a plateau in learning or extreme slowing in their learning process. For children with a baseline MDI less than 70 (median age, 2.5 years; range, 0.9 to 2.9 years), post-BMT follow-up indicated that two children have shown deterioration in their developmental skills. The remaining three children are maintaining their skills and are adding to them at a highly variable rate. We conclude that MPS I H patients with a baseline MDI greater than 70 who are engrafted survivors following URD BMT can achieve a favorable long-term outcome and improved cognitive function. Future protocols must address the high risk of graft rejection or failure and the impact of GVHD in this patient population.

Molecular genetic defect underlying alpha-L-iduronidase pseudodeficiency

Mucopolysaccharidosis type I (i.e., Hurler, Hurler-Scheie, and Scheie syndromes) and type II (i.e., Hunter syndrome) are lysosomal storage disorders resulting from alpha-L-iduronidase (IDUA) deficiency and iduronate-2-sulfatase (IDS) deficiency, respectively. The a priori probability that both disorders would occur in a single individual is approximately 1 in 5 billion. Nevertheless, such a proband was referred for whom clinical findings (i.e., a male with characteristic facies, dysostosis multiplex, and mental retardation) and biochemical tests indicated these concomitant diagnoses. In repeated studies, leukocyte 4 methylumbelliferyl-alpha-L-iduronidase activities in this kindred were as follows: <1.0 nmol/mg protein/h in the proband and proband's clinically normal sister; 45.3 in mother; and 45.7 in father (normal range 65.0-140). Leukocyte L-O-(alpha-iduronate-2-sulfate)-(1->4)-D-O-2,5-anhydro[1-3H]mannitol-6- sulfate activities were as follows: 0.0 U/mg protein/h in the proband; 5.7 in his sister; 4.9 in mother; and 15.0 in father (normal range 11.0-18.4). Multiple techniques, including automated sequencing of the entire IDS and IDUA coding regions, were employed to unravel the molecular genetic basis of these intriguing observations. The common IDS mutation R468W was identified in the proband, his mother, and his sister, thus explaining their biochemical phenotypes. Additionally, the proband, his sister, and his father were found to be heterozygous for a common IDUA mutation, W402X. Notably, a new IDUA mutation A300T was also identified in the proband, his sister, and his mother, accounting for reduced IDUA activity in these individuals; the asymptomatic sister, whose cells demonstrated normal glycosaminoglycan metabolism, is thus a compound heterozygote for W402X and the new allele. This A300T mutation is the first IDUA pseudodeficiency gene to be elucidated at the molecular level.

Four novel mutations underlying mild or intermediate forms of alpha-L-iduronidase deficiency (MPS IS and MPS IH/S)

The alpha-L-iduronidase deficiency diseases (Mucopolysaccharidosis I) cover a spectrum of clinical severity ranging from the very severe (Hurler syndrome, MPS IH) through an intermediate (Hurler/Scheie syndrome, MPS IH/S) to a relatively mild form (Scheie syndrome, MPS IS). Numerous mutations of the gene encoding alpha-L-iduronidase (IDUA) are known in Hurler syndrome, but only three in the other disorders. We report on novel mutations of the IDUA gene in one patient with the Scheie syndrome and in three patients with the Hurler/Scheie syndrome. The novel mutations, all single base changes, encoded the substitutions R492P (Scheie), and X654G, P496L, and L490P (Hurler/Scheie). The L490P mutation was apparently homozygous, whereas each of the others was found in compound heterozygosity with a Hurler mutation. The deleterious nature of the mutations was confirmed by absence of enzyme activity upon transfection of the corresponding mutagenized cDNAs into Cos-1 cells. These results provide additional information for genotype-phenotype correlations.

Long-term clinical progress in bone marrow transplanted mucopolysaccharidosis type I patients with a defined genotype

Two mucopolysaccharidosis type I (MPS-I) patients, subjected to bone marrow transplantation (BMT) more than 10 years ago, have recently had their alpha-L-iduronidase genotypes defined. Both patients, homozygous for the relatively common W402X mutation, received BMT when they were 14 and 11 months of age, and are now 12 and 14 years old, respectively. Untreated MPS-I patients, homozygous for W402X, have an extremely severe clinical phenotype with rapid clinical deterioration and death before 6 years of age. The 12-year-old patient, with limited mobility, is coping well at school, while the other patient is wheelchair-bound with severe disability in his lower limbs, and attends a school for the physically handicapped. Both patients have less than normal intelligence with slowly continuing losses. A third MPS-I patients, diagnosed at the age of 6 months, was felt, prior to BMT at 14 months, to have a severe phenotype. Twelve years post-BMT, he is ambulatory, albeit with restricted movement, and has normal intelligence. This patient did not have a defined MPS-I genotype and had alpha-L-iduronidase protein and activity consistent with a less severe outcome than the first two patients. We conclude that BMT has significantly slowed down the clinical regression of the W402X phenotype. We propose that if further gains are to be made, BMT should be performed within the first few months of life. Early diagnosis is therefore essential.

Cerebral MRI in two brothers with mucopolysaccharidosis type I and different clinical phenotypes

We describe a cerebral MRI study of two brothers with mucopolysaccharidosis type I. They are of similar physical appearance, but the younger is severely mentally retarded while the elder is of normal intelligence. MRI shows characteristic abnormalities in the CNS, but it is not yet possible to establish a correlation between them and the mental retardation.