Jerry N. Thompson

Diagnosing mucopolysaccharidosis IVA

Mucopolysaccharidosis IVA (MPS IVA; Morquio A syndrome) is an autosomal recessive lysosomal storage disorder resulting from a deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS) activity. Diagnosis can be challenging and requires agreement of clinical, radiographic, and laboratory findings. A group of biochemical genetics laboratory directors and clinicians involved in the diagnosis of MPS IVA, convened by BioMarin Pharmaceutical Inc., met to develop recommendations for diagnosis. The following conclusions were reached. Due to the wide variation and subtleties of radiographic findings, imaging of multiple body regions is recommended. Urinary glycosaminoglycan analysis is particularly problematic for MPS IVA and it is strongly recommended to proceed to enzyme activity testing even if urine appears normal when there is clinical suspicion of MPS IVA. Enzyme activity testing of GALNS is essential in diagnosing MPS IVA. Additional analyses to confirm sample integrity and rule out MPS IVB, multiple sulfatase deficiency, and mucolipidoses types II/III are critical as part of enzyme activity testing. Leukocytes or cultured dermal fibroblasts are strongly recommended for enzyme activity testing to confirm screening results. Molecular testing may also be used to confirm the diagnosis in many patients. However, two known or probable causative mutations may not be identified in all cases of MPS IVA. A diagnostic testing algorithm is presented which attempts to streamline this complex testing process.

N-acetylglucosamine 6-sulphatase deficiency in a Nubian goat: A model of Sanfilippo syndrome type D (mucopolysaccharidosis IIID)

SummaryA male Nubian goat (SD-1) presented at birth with neurological manifestations consistent with a lysosomal storage disease. Histological studies of tissue obtained at autopsy suggested glycosaminoglycan storage. Total urinary glycosaminoglycan levels, as measured by the uronic acid method, were elevated but overlapped with levels in a younger control goat. However,N-sulphate content was increased 2- to 5-fold, suggestive of heparan sulphate excretion, and this elevation was confirmed by cellulose acetate electrophoresis. Further, urinary levels of freeN-acetylglucosamine 6-sulphate were increased 6-fold over controls, SD-1 cultured skin fibroblasts, labelled with [35S]sulphate, incorporated twice as much radioactivity into macromolecular material as did normal fibroblasts. Forty-eight hours after removal of [35S]sulphate from the medium the SD-1 fibroblasts retained 58% of the label, whereas in control fibroblasts it had declined to 20%, indicative of [35S]proteoglycan storage in SD-1. The assay of fibroblast extracts revealed a profound deficiency ofN-acetylglucosamine 6-sulphatase whereas eight other activities includingβ-mannosidase, arylsulphatase B, iduronate 2-sulphatase,N-acetylgalactosamine 6-sulphatase, and heparin sulphamidase were normal. Mixing of SD-1 sonicates with normal sonicates showed no evidence of an inhibitor, and mixing of SD-1 sonicates with Sanfilippo D cell sonicates yielded no activity. These data ruled out multiple sulphatase deficiency and suggested the first example of the human Sanfilippo syndrome, type D (N-acetylglucosamine 6-sulphatase deficiency) in goats.

A model of mucopolysaccharidosis IIIB (Sanfilippo syndrome type IIIB): N-acetyl-α-D-glucosaminidase deficiency in Schipperke dogs

Mucopolysaccharidosis III (MPS III) is characterized by lysosomal accumulation of the glycosaminoglycan (GAG) heparan sulphate (HS). In humans, the disease manifests in early childhood, and is characterized by a progressive central neuropathy leading to death in the second decade. This disease has also been described in mice (MPS IIIA and IIIB), dogs (MPS IIIA), emus (MPS IIIB) and goats (MPS IIID). We now report on dogs with naturally occurring MPS IIIB, detailing the clinical signs, diagnosis, histopathology, tissue enzymology and substrate levels. Two 3-year-old Schipperke dogs were evaluated for tremors and episodes of stumbling. Examination of the animals found signs consistent with cerebellar disease including dysmetria, hind limb ataxia and a wide-based stance with truncal swaying. There were mildly dystrophic corneas and small peripheral foci of retinal degeneration. Magnetic resonance imaging of the brain and skeletal radiographs were normal. Intracytoplasmic granules were found in the white cells of peripheral blood and cerebral spinal fluid, and in myeloid lineages in bone marrow. Electrophoresis of urinary GAGs indicated the presence of HS, while assays of cultured fibroblasts found N-acetyl-α-D-glucosaminidase (Naglu) activity of between 4.3% and 9.2% of normal. Owing to neurological deterioration, both dogs were euthanized, and post-mortem examinations were performed. Biochemical studies of liver and kidney from both animals demonstrated profound deficiency of Naglu activity and abnormally high GAG levels. Pathology of the brain included severe cerebellar atrophy, Purkinje cell loss, and cytoplasmic vacuolation in neurons and perithelial cells throughout the central nervous system. Pedigree analyses and Naglu levels of family members supported an autosomal recessive mode of inheritance. Using an obligate heterozygote, a breeding colony has been established to aid in understanding the pathogenesis of MPS IIIB and testing of potential therapies.

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

Purpose: Mucopolysaccharidosis type I (MPS I) is an autosomal recessive disorder resulting from a deficiency of the lysosomal glycosidase, α-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 IDUA 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 IDUA 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 IDUA gene.

Biochemical and molecular analysis in a patient with the severe form of Hunter syndrome after bone marrow transplantation.

Hunter syndrome (mucopolysaccharidosis type II, or MPS II) results from a deficiency of iduronate-2-sulfatase (IDS) activity due to a primary genetic defect in the X-chromosomal iduronate-2-sulfatase gene. We have studied a 10-year-old male, diagnosed with Hunter syndrome at age 2 years, who underwent bone marrow transplantation (BMT) at age 5 years. To evaluate the metabolic effect of BMT, biochemical and enzymatic studies were performed. Urinary glycosaminoglycans (GAGs) were quantitated, and iduronate-2-sulfatase activity was measured in serum, leukocytes, and liver homogenates. Decreased urinary glycosaminoglycan excretion and increased iduronate-2-sulfatase activity in serum and leukocytes were observed. Furthermore, molecular analysis was performed using reverse transcriptional polymerase chain reaction (RT-PCR) sequencing and restriction enzyme assay. The patient was found to have a novel nonsense mutation, L279X (TTA to TGA) in exon 6 of the IDS gene, inherited from his mother. A comparison of the DNA contents of cultured skin fibroblasts prior to BMT with leukocyte DNA after BMT showed coexisting host mutant and donor normal alleles in post-BMT leukocyte DNA. We postulate that the L279X mutation is a severe disease-causing mutation for Hunter syndrome.

Elevated CSF N-acetylaspartylglutamate in patients with free sialic acid storage diseases

Objective: To investigate body fluids of patients with undiagnosed leukodystrophies using in vitro 1H-NMR spectroscopy (H-NMRS). Methods: We conducted a cross-sectional study using high-resolution in vitro H-NMRS on CSF and urine samples. Results: We found a significant increase of free sialic acid in CSF or urine in 6 of 41 patients presenting with hypomyelination of unknown etiology. Molecular genetic testing revealed pathogenic mutations in the SLC17A5 gene in all 6 patients. H-NMRS revealed an increase of N-acetylaspartylglutamate in the CSF of all patients with SLC17A5 mutation (range 13–114 μmol/L, reference <12 μmol/L). Conclusion: In patients with undiagnosed leukodystrophies, increased free sialic acid in CSF or urine is a marker for free sialic acid storage disorder and facilitates the identification of the underlying genetic defect. Because increase of N-acetylaspartylglutamate in CSF has been observed in other hypomyelinating disorders, it can be viewed as a marker of a subgroup of hypomyelinating disorders.

Attempted enzyme replacement using human amnion membane implantations in mucopolysaccharidoses

SummaryAmnion membrane implantation has been proposed as an approach to enzyme replacement in mucopolysaccharidoses. Human amnion membranes have been subcutaneously implanted in the abdominal wall in 19 patients with mucopolysaccharidoses (MPS I, II and III). A protocol was developed for the objective evaluation of experimental treatments of these patients. Systematic evaluation of the clinical status before and 6 months after amnion membrane implantation reveals no change in function except improvement in joint mobility. The sum of all joint movements showed improvement from baseline values to 6 months after implantation by ANOVA followed bypost-hoc analysis (p<0.056). The only specific joint movements to significantly improve after 6 months were shoulder extension (p<0.01) and hip internal rotation (p<0.05). Serial measurements of the deficient lysosomal enzyme activity in serum and white blood cells did not increase in any patient after amnion membrane implantation. Urinary glycosaminoglycan excretion decreased transiently in 2 of 10 patients after implantation, but a second amnion membrane implantation did not result in any change. Biopsy of the implantation site in 10 patients 6 months after amnion membrane implantation revealed a foreign-body reaction with giant cell formation and fibrosis and no recognizable amnion membrane tissue. We conclude that human amnion membrane implantation is not an effective therapy in mucopolysaccharidoses.

Free sialic acid storage disease without sialuria.

We performed high‐resolution in vitro proton nuclear magnetic resonance spectroscopy on cerebrospinal fluid and urine samples of 44 patients with leukodystrophies of unknown cause. Free sialic acid concentration was increased in cerebrospinal fluid of two siblings with mental retardation and mild hypomyelination. By contrast, urinary excretion of free sialic acid in urine was normal on repeated testing by two independent methods. Both patients were homozygous for the K136E mutation in SLC17A5, the gene responsible for the free sialic acid storage diseases. Our findings demonstrate that mutations in the SLC17A5 gene have to be considered in patients with hypomyelination, even in the absence of sialuria. Ann Neurol 2009;65:753–757

Comparison of SSCP analysis and CFLP analysis for mutation detection in the human iduronate 2-sulfatase gene.

Scanning methodologies are used for the identification of DNA fragments that differ from the normal nucleotide sequence. Fragments that produce abnormal band patterns are sequenced for characterization of the exact mutation. Factors considered in choosing a scanning methodology include reproducibility, sensitivity, and time. In the present study, we compared single‐stranded conformational polymorphism (SSCP) and Cleavase fragment length polymorphism (CFLP) methodologies for mutation scanning of exon VIII in the iduronate 2‐sulfatase (IDS) gene. Mutations of the IDS gene result in an X‐linked lysosomal storage disease, Hunter syndrome. These six known mutations analyzed by the two methods included a one base pair deletion, a one base pair insertion, and four point mutations. SSCP analysis detected all of the mutations and CFLP analysis detected three of the six mutations. We concluded that SSCP analysis was preferable to CFLP analysis for scanning exon VIII in the IDS gene for mutations.

Oligosaccharide substrates for heparin sulfamidase

The Sanfilippo A syndrome is characterized by a deficiency in heparin sulfamidase, which removes the N-sulfate groups of heparan sulfate and heparin in the course of normal catabolism of these polysaccharides. [N-35S]Heparin is the most commonly used substrate for the assay of sulfamidase activity but has certain disadvantages which have prompted us to search for alternative substrates. We report here on the use of heparin oligosaccharides for this purpose. The trisaccharide, GlcN-IdoUA-GlcN, and the pentasaccharide, GlcN-GlcUA-GlcN-GlcUA-GlcN, were N-sulfated with [35S]sulfur trioxide-trimethylamine complex; the tetrasaccharide, GlcN-UA-GlcN-UA, and the pentasaccharide, GlcN-IdoUA-GlcN-IdoUA-GlcN, were labeled by reduction with sodium borotritide followed by chemical N-sulfation. When incubated with sonicates of cultured skin fibroblasts from normal individuals, all four oligosaccharides were found to serve as substrates for heparin sulfamidase. Fibroblast sonicates from patients with the Sanfilippo A syndrome had little or no activity toward these substrates. Optimal activity of the enzyme was at pH 4.4-4.5. Comparison of the kinetic parameters showed that heparin had a lower Km than the oligosaccharides, whereas the Vmax values of the latter were higher than for heparin.