The ultrastructure of skin from a patient with mucopolysaccharidosis IIID

Enzyme Replacement Therapy for Mucopolysaccharidosis IIID using Recombinant Human α-N-Acetylglucosamine-6-Sulfatase in Neonatal Mice

There is currently no cure or effective treatment available for mucopolysaccharidosis type IIID (MPS IIID, Sanfilippo syndrome type D), a lysosomal storage disorder (LSD) caused by the deficiency of α-N-acetylglucosamine-6-sulfatase (GNS). The clinical symptoms of MPS IIID, like other subtypes of Sanfilippo syndrome, are largely localized to the central nervous system (CNS), and any treatments aiming to ameliorate or reverse the catastrophic and fatal neurologic decline caused by this disease need to be delivered across the blood-brain barrier. Here, we report a proof-of-concept enzyme replacement therapy (ERT) for MPS IIID using recombinant human α-N-acetylglucosamine-6-sulfatase (rhGNS) via intracerebroventricular (ICV) delivery in a neonatal MPS IIID mouse model. We overexpressed and purified rhGNS from CHO cells with a specific activity of 3.9 × 10⁴ units/mg protein and a maximal enzymatic activity at lysosomal pH (pH 5.6), which was stable for over one month at 4 °C in artificial cerebrospinal fluid (CSF). We demonstrated that rhGNS was taken up by MPS IIID patient fibroblasts via the mannose 6-phosphate (M6P) receptor and reduced intracellular glycosaminoglycans to normal levels. The delivery of 5 μg of rhGNS into the lateral cerebral ventricle of neonatal MPS IIID mice resulted in normalization of the enzymatic activity in brain tissues; rhGNS was found to be enriched in lysosomes in MPS IIID-treated mice relative to the control. Furthermore, a single dose of rhGNS was able to reduce the accumulated heparan sulfate and β-hexosaminidase. Our results demonstrate that rhGNS delivered into CSF is a potential therapeutic option for MPS IIID that is worthy of further development.

A histological and ultrastructural study of the iliac crest apophysis in Legg-Calve-Perthes disease

BACKGROUND

Legg-Calve-Perthes disease (LCPD) is a common hip disorder in children characterized by avascular necrosis of the proximal capital femoral epiphysis. The underlying etiology of the vascular disturbance is still unknown, but it is suggested that LCPD may be a part of a generalized constitutional disorder associated with growth disturbance of bone and cartilage tissue. In this study, the biopsy specimens of the iliac crest apophysis from LCPD patients were examined histologically and ultrastructurally to determine preexisting generalized abnormalities of endochondral ossification.

METHODS

Iliac crest apophysis cartilage was taken during Salter innominate osteotomy from 11 children (8 boys and 3 girls) with LCPD at an average age of 7.8 years. As controls, the samples were also obtained from 10 children (2 boys and 8 girls) at an average age of 6.3 years undergoing Salter osteotomy due to residual acetabular dysplasia after reduction of developmental dysplasia of the hip. Each iliac crest apophysis specimen was examined histologically (Toluidine blue staining and Sudan III staining) and ultrastructurally.

RESULTS

Although there were no obvious differences in Toluidine blue-stained sections of the iliac crest cartilage between LCPD and control patients, the Sudan III-positive chondrocytes in the resting cartilage were more prominent in the LCPD specimens than in the control specimens. These sudanophilic granules were confirmed to be lipid droplets by electron microscopic examinations. Ultrastructural examinations of the resting chondrocytes from 3 LCPD patients demonstrated numerous cytoplasmic inclusion bodies with electron dense materials, which were similar to those seen in some of the mucopolysaccharidoses.

CONCLUSIONS

Increased lipid droplets and numerous cytoplasmic inclusions filled with fibrillar materials were suggestive of the initial metabolic changes of the chondrocytes, which may have a pivotal role in degenerating matrix and lead to vulnerability of the cartilage tissue. Our results indicated that generalized insufficiency in growth cartilage metabolism may be related to the onset of the disease in some LCPD patients.

Defective glycosylation of decorin and biglycan, altered collagen structure, and abnormal phenotype of the skin fibroblasts of an Ehlers–Danlos syndrome patient carrying the novel Arg270Cys substitution in galactosyltransferase I (β4GalT-7)

The Ehlers-Danlos syndrome (EDS) is a heterogeneous group of connective tissue disorders affecting skin and joint function. Molecular defects in extracellular matrix proteins, including collagen (type I, III, and V) and tenascin X are associated with different forms of EDS. Compound heterozygous mutations in the B4GALT7 gene, resulting in aberrant glycosylation of the dermatan sulfate proteoglycan decorin, had been described in a single patient affected with the progeroid form of EDS. We have studied the molecular phenotype of decorin, biglycan, and collagen type I containing fibrils in skin fibroblasts of a patient carrying the novel homozygous C808T point mutation in the B4GALT7 gene, which causes an Arg270Cys substitution in beta4GalT-7. Compared to control fibroblasts, galactosyltransferase activity in beta4GalT-7(Arg270Cys) cells was approximately three times reduced over a temperature range of 25-41 degrees C. Pulse-chase experiments and confocal microscopy demonstrated that synthesis and secretion of decorin were normal in beta4GalT-7(Arg270Cys) cells. However, about 50% of decorin were synthesized as a protein core in addition to its proteoglycan form. Biglycan was found in a monoglycanated form in addition to its mature form. Glycosaminoglycan chains were of the dermatan/chondroitin sulfate type both in beta4GalT-7(Arg270Cys) and control cells, and epimerization was reduced for decorin and biglycan. Compared to control cells, beta4GalT-7(Arg270Cys) cells showed altered, highly spread or stretched phenotypes and decreased proliferation rates. At the ultrastructural level, an intracellular accumulation of multiple secondary lysosomes and degenerative vacuoles was seen in beta4GalT-7(Arg270Cys) cells. Furthermore, the collagen suprastructures were altered in the beta4GalT-7(Arg270Cys) cells. The reduced beta4GalT-7 activity resulting in defective glycosylation of decorin and biglycan may be responsible for the complex molecular pathology in beta4GalT-7 deficient EDS patients, given the role of these proteoglycans in bone formation, collagen fibrillogenesis, and skeletal muscle development.

Genomic basis of mucopolysaccharidosis type IIID (MIM 252940) revealed by sequencing of GNS encoding N-acetylglucosamine-6-sulfatase

Mucopolysaccharidosis type IIID (MPS IIID; Sanfilippo syndrome type D; MIM 252940) is caused by deficiency of the activity of N-acetylglucosamine-6-sulfatase (GNS), which is normally required for degradation of heparan sulfate. The clinical features of MPS IIID include progressive neurodegeneration, with relatively mild somatic symptoms. Biochemical features include accumulation of heparan sulfate and N-acetylglucosamine-6-sulfate in the brain and viscera. To date, diagnosis required a specific lysosomal enzyme assay for GNS activity. From genomic DNA of a subject with MPS IIID, we amplified and sequenced the promoter and 14 exons of GNS. We found a homozygous nonsense mutation in exon 9 (1063C --> T), which predicted premature termination of translation (R355X). We also identified two common synonymous coding single-nucleotide polymorphisms and genotyped these in samples from four ethnic groups. This first report of a mutation in GNS resulting in MPS IIID indicates the potential utility of molecular diagnosis for this rare condition.