A Comparative Effectiveness Study of Newborn Screening Methods for Four Lysosomal Storage Disorders.

Newborn screening for one or more lysosomal disorders has been implemented in several US states, Japan and Taiwan by multiplexed enzyme assays using either tandem mass spectrometry or digital microfluidics. Another multiplex assay making use of immunocapture technology has also been proposed. To investigate the potential variability in performance of these analytical approaches, we implemented three high-throughput screening assays for the simultaneous screening for four lysosomal disorders: Fabry disease, Gaucher disease, mucopolysaccharidosis type I, and Pompe disease. These assays were tested in a prospective comparative effectiveness study using nearly 100,000 residual newborn dried blood spot specimens. In addition, 2nd tier enzyme assays and confirmatory molecular genetic testing were employed. Post-analytical interpretive tools were created using the software Collaborative Laboratory Integrated Reports (CLIR) to determine its ability to improve the performance of each assay vs. the traditional result interpretation based on analyte-specific reference ranges and cutoffs. This study showed that all three platforms have high sensitivity, and the application of CLIR tools markedly improves the performance of each platform while reducing the need for 2nd tier testing by 66% to 95%. Moreover, the addition of disease-specific biochemical 2nd tier tests ensures the lowest false positive rates and the highest positive predictive values for any platform.

Slow, continuous enzyme replacement via spinal CSF in dogs with the paediatric-onset neurodegenerative disease, MPS IIIA.

Intra-cerebrospinal fluid (CSF) injection of recombinant human lysosomal enzyme is a potential treatment strategy for several neurodegenerative lysosomal storage disorders including Sanfilippo syndrome (Mucopolysaccharidosis type IIIA; MPS IIIA). Here we have utilised the MPS IIIA Huntaway dog model to compare the effectiveness of the repeated intermittent bolus injection strategy being used in the trials with an alternate approach; slow, continual infusion of replacement enzyme (recombinant human sulphamidase; rhSGSH) into the spinal CSF using a SynchroMed II® pump attached to a spinal infusion cannula. The ability of each enzyme delivery strategy to ameliorate lesions in MPS IIIA brain was determined in animals treated from ∼three- to six-months of age. Controls received buffer or no treatment. Significant reductions in heparan sulphate (primary substrate) were observed in brain samples from dogs treated via either cisternal or lumbar spinal CSF bolus injection methods and also in slow intra-spinal CSF infusion-treated dogs. The extent of the reduction differed regionally. Pump-delivered rhSGSH was less effective in reducing secondary substrate (GM3 ganglioside) in deeper aspects of cerebral cortex, and although near-amelioration of microglial activation was seen in superficial (but not deep) layers of cerebral cortex in both bolus enzyme-treated groups, pump-infusion of rhSGSH had little impact on microgliosis. While continual low-dose infusion of rhSGSH into MPS IIIA dog CSF reduces disease-based lesions in brain, it was not as efficacious as repeated cisternal or spinal CSF bolus infusion of rhSGSH over the time-frame of these experiments.

Low-dose, continual enzyme delivery ameliorates some aspects of established brain disease in a mouse model of a childhood-onset neurodegenerative disorder.

AIM: To determine the capacity of continual low-dose lysosomal enzyme infusion into the cerebrospinal fluid of mucopolysaccharidosis type IIIA (MPS IIIA) mice to reverse established neurodegenerative disease. The rationale behind the study is that there is only limited animal model-derived evidence supporting treatment of symptomatic patients, principally because few studies have been designed to examine disease reversibility. METHODS: Twelve-week old MPS IIIA mice were implanted with indwelling unilateral intra-ventricular cannulae. These were connected to subcutaneous mini-osmotic pumps infusing recombinant human sulphamidase. Pump replacement was carried out in some mice at 16-weeks of age, enabling treatment to continue for a further month. Control affected/unaffected mice received vehicle via the same method. Behavioural, neuropathological and biochemical parameters of disease were assessed. RESULTS: Improvement in some, but not all, behavioural parameters occurred. Sulphamidase infusion mediated a statistically significant reduction in primary (heparan sulphate) and secondary (gangliosides GM2, GM3) substrate accumulation in the brain, with small reductions in micro- but not astro-gliosis. There was no change in axonal spheroid number. All mice developed a humoural response, however the antibodies were non-neutralising and no adverse clinical effects were observed. CONCLUSIONS: Continual infusion of replacement enzyme partially ameliorates clinical, histological and biochemical aspects of MPS IIIA mice, when treatment begins at an early symptomatic stage.

Screening patients referred to a metabolic clinic for lysosomal storage disorders.

BACKGROUND: Lysosomal protein profiling is being developed as a high throughput method to screen populations for lysosomal storage disorders (LSD). DESIGN: 1415 blood spots from patients referred to a metabolic clinic for LSD were screened using a single multiplex assay for 14 proteins in a dried blood spot. RESULTS: All patients with Pompe disease, metachromatic leukodystrophy, and mucopolysaccharidosis (MPS) type I, IIIA, IIIB and VI were identified by reduced lysosomal protein. Five samples were identified as possible pseudo-arylsulfatase A deficiency; four were confirmed. One multiple sulfatase deficiency patient was identified with multiple reduced sulfatase proteins. There were 10 MPS II patients identified with reduced iduronate 2-sulfatase, and one MPS II patient with iduronate 2-sulfatase in the unaffected range. For Fabry disease, 10 male patients were identified with reduced α-galactosidase and 2/6 female Fabry heterozygotes returned α-galactosidase concentrations in the male Fabry range. All 10 mucolipidosis II/III patients were identified with multiple raised proteins. For 79 blood spots with chitotriosidase >3.4mg/l, a follow-up one-plex chitotriosidase assay enabled identification of all nine Gaucher patients. CONCLUSION: This study demonstrates the sensitivity and specificity of this technology to accurately identify 99% of LSD patients, with the exception of one MPS II false negative.