Gene therapy for mucopolysaccharidosis

Usefulness of urinary glycosaminoglycans assay for a mucopolysaccharidosis-specific screening

BACKGROUND

Mucopolysaccharidoses (MPS), a group of inherited metabolic disorders characterized by the accumulation of glycosaminoglycans, can be diagnosed early through newborn screening programs. Establishing newborn screening in Morocco is a challenging task for multiple economic and social reasons. Screening in a Moroccan population using 1,9-dimethylmethylene blue urinary glycosaminoglycan (GAG) assays may allow for an earlier diagnosis of MPS. We studied the feasibility of implementing screening in Moroccan children as an alternative to national newborn screening. We determined the reference ranges for GAGs in the Moroccan population, their stability during transport, the effectiveness of this test as a screening procedure for MPS in patients, and its use as a screening test for MPS in the Imssouane region, where the rate of consanguineous marriage is 38%.

METHODS

Using dimethylmethylene blue assays, urine samples of 47 MPS patients were analyzed, together with urine samples from healthy controls (n = 368, age ranging from 1 month to 25 years), and from Imssouane region children (n = 350, age ranging from 6 months to 24 month). Precision, linearity, recovery, limits, and stability were tested.

RESULTS

Urinary GAGs reference values are age and ethnicity dependent. The validation parameters established displayed great precision and accuracy leading to recoveries according to internationally accepted values for bioanalytical methods. Urinary GAGs were stable for a maximum of 7 weeks at 40 °C. Screening of Imssouane children resulted in the detection of a 6-month-old child, diagnosed with MPS I.

CONCLUSIONS

Our results demonstrate the usefulness of quantifying glycosaminoglycans for early screening of MPS.

Abnormalities in the hair morphology of patients with some but not all types of mucopolysaccharidoses

Mucopolysaccharidoses (MPS) are a group of inherited, progressive, metabolic diseases, caused by the deficiency of one of the enzymes involved in the degradation of glycosaminoglycans (GAGs). The disease is usually fatal, with the life span of most untreated MPS patients being between one and two decades. In this report, on the basis of scanning electron microscopy (SEM) studies, we demonstrate that, besides the many other symptoms of MPS, there are characteristic abnormalities in the hair morphology of patients suffering from some types of this disease (MPS I, MPS II, MPS IIIA, MPS IIIB), but not from other types (MPS IVA, MPS IVB, MPS VI), where the changes are minor, if any. Different GAGs accumulate in the tissues of patients suffering from the various MPS types, and analysis of the disease types in which severe hair abnormalities occur or not could suggest that the accumulation of heparan sulfate, rather than dermatan sulfate or keratan sufate, may be responsible for the major changes in hair morphology. Considerable abnormalities in hair morphology occur in patients suffering from MPS I, MPS II, MPS IIIA, and MPS IIIB, but not in patients suffering from MPS IVA, MPS IVB, and MPS VI; this feature might potentially be used as an additional test for the assessment of the efficacy of treatments for MPS patients (types I, II, IIIA, and IIIB).

alpha-L-Iduronidase transport in neurites

Effective therapeutic strategies for mucopolysaccharidosis type I (MPSI) rely on mannose-6-phosphate receptor-mediated uptake of extracellular alpha-l-iduronidase (IDUA), the missing lysosomal enzyme in this disease, by deficient cells. Intravenously infused recombinant human IDUA does not reach the central nervous system, whereas neuropathology and neurological manifestations are prominent in Hurler syndrome, the most severe and most frequent form of MPSI. The creation of a single intracerebral source of IDUA by gene therapy was proved efficient to deliver enzyme throughout the brain of MPSI mice. IDUA spreading far beyond areas where the enzyme was synthesized suggested transport along neuronal processes. To examine the mechanisms of IDUA spreading in the brain, we constructed a chimeric protein in which GFP is fused at the C-terminus of IDUA. The fusion protein was expressed in rat primary neurons using lentivirus vectors. Fluorescent IDUA retained full catalytic activity including on natural substrates, interacted with mannose-6-phosphate receptors and was appropriately addressed to lysosomes. Fluorescent vesicles were broadly distributed over neuronal soma and processes. Time-lapse fluorescent video-microscopy showed that 54% of fluorescent vesicles exhibited either retrograde or anterograde displacements along neurites. Most moving organelles showed complex movements with frequent direction changes and arrests. Motility depended on microtubule integrity. Efficient axono-dendritic transport of IDUA provides a rationale for gene therapy based on the release of therapeutic enzyme at discrete locations within the central nervous system of patients with severe form of MPSI.

Improved behavior and neuropathology in the mouse model of Sanfilippo type IIIB disease after adeno-associated virus-mediated gene transfer in the striatum

Sanfilippo syndrome is a mucopolysaccharidosis (MPS) caused by a lysosomal enzyme defect interrupting the degradation pathway of heparan sulfates. Affected children develop hyperactivity, aggressiveness, delayed development, and severe neuropathology. We observed relevant behaviors in the mouse model of Sanfilippo syndrome type B (MPSIIIB), in which the gene coding for alpha-N-acetylglucosaminidase (NaGlu) is invalidated. We addressed the feasibility of gene therapy in these animals. Vectors derived from adeno-associated virus serotype 2 (AAV2) or 5 (AAV5) coding for NaGlu were injected at a single site in the putamen of 45 6-week-old MPSIIIB mice. Normal behavior was observed in treated mice. High NaGlu activity, far above physiological levels, was measured in the brain and persisted at 38 weeks of age. NaGlu immunoreactivity was detected in neuron intracellular organelles, including lysosomes. Enzyme activity spread beyond vector diffusion areas. Delivery to the entire brain was reproducibly obtained with both vector types. NaGlu activity was higher and distribution was broader with AAV5-NaGlu than with AAV2-NaGlu vectors. The compensatory increase in the activity of various lysosomal enzymes was improved. The accumulation of gangliosides GM2 and GM3 present before treatment and possibly participating in neuropathology was reversed. Characteristic vacuolations in microglia, perivascular cells, and neurons, which were prominent before the age of treatment, disappeared in areas in which NaGlu was present. However, improvement was only partial in some animals, in contrast to high NaGlu activity. These results indicate that NaGlu delivery from intracerebral sources has the capacity to alleviate most disease manifestations in the MPSIIIB mouse model.

Correction of metabolic, craniofacial, and neurologic abnormalities in MPS I mice treated at birth with adeno-associated virus vector transducing the human alpha-L-iduronidase gene

Murine models of lysosomal storage diseases provide an opportunity to evaluate the potential for gene therapy to prevent systemic manifestations of the disease. To determine the potential for treatment of mucopolysaccharidosis type I using a gene delivery approach, a recombinant adeno-associated virus (AAV) vector, vTRCA1, transducing the human iduronidase (IDUA) gene was constructed and 1 x 10(10) particles were injected intravenously into 1-day-old Idua(-/-) mice. High levels of IDUA activity were present in the plasma of vTRCA1-treated animals that persisted for the 5-month duration of the study, with heart and lung of this group demonstrating the highest tissue levels of gene transfer and enzyme activity overall. vTRCA1-treated Idua(-/-) animals with measurable plasma IDUA activity exhibited histopathological evidence of reduced lysosomal storage in a number of tissues and were normalized with respect to urinary GAG excretion, craniofacial bony parameters, and body weight. In an open field test, vTRCA1-treated Idua(-/-) animals exhibited a significant reduction in total squares covered and a trend toward normalization in rearing events and grooming time compared to control-treated Idua(-/-) animals. We conclude that AAV-mediated transduction of the IDUA gene in newborn Idua(-/-) mice was sufficient to have a major curative impact on several of the most important parameters of the disease.

Prevention of neuropathology in the mouse model of hurler syndrome

A defect of the lysosomal enzyme alpha-L-iduronidase (IDUA) interrupts heparan and dermatan sulfate degradation and causes neuropathology in children with severe forms of mucopolysaccharidosis type I (MPSI, Hurler syndrome). Enzyme substitution therapy is beneficial but ineffective on the central nervous system. We could deliver the missing enzyme to virtually the entire brain of MPSI mice through a single injection of gene transfer vectors derived from adenoassociated virus serotype 2 (AAV2) or 5 (AAV5) coding for human IDUA. This result was reproducibly achieved with both vector types in 46 mice and persisted for at least 26 weeks. Success was more frequent, enzyme activity was higher, and corrected areas were broader with AAV5 than with AAV2 vectors. Treatment presumably reversed and certainly prevented the accumulation of GM2 and GM3 gangliosides, which presumably participates to neuropathology. Lysosomal distension, which already was present at the time of treatment, had disappeared from both brain hemispheres and was minimal in the cerebellum in mice analyzed 26 weeks after injection. This study shows that pathology associated with MPSI can be prevented in the entire mouse brain by a single AAV vector injection, providing a preliminary evaluation of the feasibility of gene therapy to stop neuropathology in Hurler syndrome.