Newborn screening for Pompe disease: synthesis of the evidence and development of screening recommendations

The Importance of Early Treatment of Inherited Neuromuscular Conditions

There has been tremendous progress in treatment of neuromuscular diseases over the last 20 years, which has transformed the natural history of these severely debilitating conditions. Although the factors that determine the response to therapy are many and in some instance remain to be fully elucidated, early treatment clearly has a major impact on patient outcomes across a number of inherited neuromuscular conditions. To improve patient care and outcomes, clinicians should be aware of neuromuscular conditions that require prompt treatment initiation. This review describes data that underscore the importance of early treatment of children with inherited neuromuscular conditions with an emphasis on data resulting from newborn screening efforts.

The Progress and Future of US Newborn Screening

Progress in newborn screening (NBS) has been driven for 60 years by developments in science and technology, growing consumer advocacy, the actions of providers involved in the care of rare disease patients, and by federal and State government funding and policies. With the current explosion of clinical trials of treatments for rare diseases, the pressure for expansion has grown, and concerns about the capacity for improvement and growth are being expressed. Genome and exome sequencing (GS/ES) have now opened more opportunities for early identification and disease prevention at all points in the lifespan. The greatest challenge facing NBS stems from the conditions most amenable to screening, and new treatment development is that we are screening for rare genetic diseases. In addition, understanding the spectrum of severity requires vast amounts of population and genomic data. We propose recommendations on improving the NBS system and addressing specific demands to grow its capacity by: better defining the criteria by which screening targets are established; financing the NBS system's responsiveness to opportunities for expansion, including engagement and funding from stakeholders; creating a national quality assurance, data, IT, and communications infrastructure; and improving intra-governmental communications. While our recommendations may be specific to the United States, the underlying issues should be considered when working to improve NBS programs globally.

Current and emerging pharmacotherapy for Gaucher disease in pediatric populations

INTRODUCTION

The past decades have witnessed a remarkable improvement in the health of patients with Gaucher disease, the inherited deficiency of the lysosomal enzyme glucocerebrosidase, resulting from the availability of enzyme replacement and substrate reduction therapies. Especially in pediatric populations, early diagnosis and initiation of treatment is essential to achieving optimal outcomes.

AREAS COVERED

The authors review the literature pertaining to the effectiveness of currently available therapies and describe new pharmacotherapies under development, especially for young patients.

EXPERT OPINION

For pediatric patients with non-neuronopathic Gaucher disease, there may be new therapeutic options on the horizon in the form of gene therapy or small molecule glucocerebrosidase chaperones. These have the potential to result in a cure for systemic disease manifestations and/or to reduce the cost and convenience of treatment. For children with neuronopathic Gaucher disease, the challenge of targeting therapy to the central nervous system is being explored through new modalities including brain-targeted gene therapy, in-utero therapy, brain-penetrant small molecule chaperones, and other methods that convey enzyme across the blood-brain barrier. Indeed, these are exciting times for both pediatric patients with Gaucher disease and those with other lysosomal storage disorders.

Health and economic outcomes of newborn screening for infantile-onset Pompe disease

PURPOSE

To estimate health and economic outcomes associated with newborn screening (NBS) for infantile-onset Pompe disease in the United States.

METHODS

A decision analytic microsimulation model simulated health and economic outcomes of a birth cohort of 4 million children in the United States. Universal NBS and treatment was compared with clinical identification and treatment of infantile-onset Pompe disease. Main outcomes were projected cases identified, costs, quality-adjusted life-years (QALYs), and incremental cost-effectiveness ratios (ICERs) over the life course.

RESULTS

Universal NBS for Pompe disease and confirmatory testing was estimated to cost an additional $26 million annually. Additional medication costs associated with earlier treatment initiation were $181 million; however, $8 million in medical care costs for other services were averted due to delayed disease progression. Infants with screened and treated infantile-onset Pompe disease experienced an average lifetime increase of 11.66 QALYs compared with clinical detection. The ICER was $379,000/QALY from a societal perspective and $408,000/QALY from the health-care perspective. Results were sensitive to the cost of enzyme replacement therapy.

CONCLUSION

Newborn screening for Pompe disease results in substantial health gains for individuals with infantile-onset Pompe disease, but with additional costs.

Targeted Therapies for Metabolic Myopathies Related to Glycogen Storage and Lipid Metabolism: a Systematic Review and Steps Towards a 'Treatabolome'

BACKGROUND

Metabolic myopathies are a heterogenous group of muscle diseases typically characterized by exercise intolerance, myalgia and progressive muscle weakness. Effective treatments for some of these diseases are available, but while our understanding of the pathogenesis of metabolic myopathies related to glycogen storage, lipid metabolism and β-oxidation is well established, evidence linking treatments with the precise causative genetic defect is lacking.

OBJECTIVE

The objective of this study was to collate all published evidence on pharmacological therapies for the aforementioned metabolic myopathies and link this to the genetic mutation in a format amenable to databasing for further computational use in line with the principles of the "treatabolome" project.

METHODS

A systematic literature review was conducted to retrieve all levels of evidence examining the therapeutic efficacy of pharmacological treatments on metabolic myopathies related to glycogen storage and lipid metabolism. A key inclusion criterion was the availability of the genetic variant of the treated patients in order to link treatment outcome with the genetic defect.

RESULTS

Of the 1,085 articles initially identified, 268 full-text articles were assessed for eligibility, of which 87 were carried over into the final data extraction. The most studied metabolic myopathies were Pompe disease (45 articles), multiple acyl-CoA dehydrogenase deficiency related to mutations in the ETFDH gene (15 articles) and systemic primary carnitine deficiency (8 articles). The most studied therapeutic management strategies for these diseases were enzyme replacement therapy, riboflavin, and carnitine supplementation, respectively.

CONCLUSIONS

This systematic review provides evidence for treatments of metabolic myopathies linked with the genetic defect in a computationally accessible format suitable for databasing in the treatabolome system, which will enable clinicians to acquire evidence on appropriate therapeutic options for their patient at the time of diagnosis.

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.

The decision-making levels of urine tetrasaccharide for the diagnosis of Pompe disease in the Turkish population

Background Recently, urinary excretion of the tetrasaccharide 6-α-D-glucopyranosyl-maltotriose (Glc4) has been proposed as a marker for the diagnosis and monitoring of Pompe disease (PD). We aimed to determine the reference intervals and reliable decision-making levels of urine tetrasaccharide concentrations for the diagnosis of infantile- and late-onset Pompe patients in the Turkish population. Methods In this study, nine patients with PD (five of them with late-onset PD [LOPD]) and 226 healthy individuals (aged 0-64 years) were included. Urine Glc4 concentrations were determined using the ultra-high-performance liquid chromatography (UHPLC) tandem mass spectrometry (MS/MS) method. Results Our data showed that the urine tetrasaccharide levels decreased with age in healthy individuals (p < 0.001, r = -0.256). It was higher especially during the first year of life compared to that in the elder subjects. The tetrasaccharide level of Pompe patients was higher compared to that of healthy controls of the same age: 99 ± 68 mmol/mol creatinine for infantile onset vs. 4.0 ± 3.0 mmol/mol creatinine for healthy controls of the same age group and 12.1 ± 17.4 mmol/mol creatinine for late onset vs. 1.7±1.2 mmol/mol creatinine for healthy controls of the same age group. Conclusions The results of this study showed that the reference intervals of tetrasaccharide in urine changed over time; therefore, it is critically important to define age-based decision levels for the diagnosis of LOPD.

Development of Newborn Screening for Pompe Disease

Pompe disease is an inborn error of lysosomal degradation of glycogen [...]

Incidence of infantile Pompe disease in the Maroon population of French Guiana

OBJECTIVES

The aim of this study was to describe the epidemiology of infantile Pompe disease (IPD) in French Guiana, a French overseas territory, by combining a retrospective case records study and a prospective anonymous genotyping in a sample of mothers followed in the two major maternity units of French Guiana.

METHODS

We identified 19 newborns with IPD born within a 13-year-period in French Guiana, corresponding to 1/4528 births. All children were born within the African-American Maroon (Bushinengue) community originating from slaves who settled along the Maroni river in the 19th century. We also performed an anonymised screening for all women in postpartum, in the two main maternity units of French Guiana.

RESULTS

Genetic investigations revealed that all patients with IPD were homozygotes or compound heterozygotes for two known pathogenic variations: c.2560C>T p.(Arg854*) that has already been reported in African-Americans and c.1942G>A p.(Gly648Ser), a rare previously considered to be variant. We identified no heterozygotes among 453 mothers of various ethnicities in Cayenne, but 15 heterozygotes among 425 mothers (1/27) in Saint-Laurent-du-Maroni (95% CI 1/45 to 1/17), all from the Maroon community, which corresponds to an expected IPD incidence in Maroons of 1/1727 (95% CI 1/1156 to 1/8100).

CONCLUSION

The incidence of IPD in the Maroon community is roughly 50 times higher than elsewhere in the world. The presence of only two different variants in all affected patients is compatible with a double founder effect in a relatively small population that has seldom mixed with other regional populations in the past and therefore has a reduced pool of genotypes.

Identification of GAA variants through whole exome sequencing targeted to a cohort of 606 patients with unexplained limb-girdle muscle weakness

Background

Late-onset Pompe disease is a rare genetic neuromuscular disorder caused by a primary deficiency of α-glucosidase and the associated accumulation of glycogen in lysosomal vacuoles. The deficiency of α-glucosidase can often be detected using an inexpensive and readily accessible dried blood spot test when Pompe disease is suspected. Like several neuromuscular disorders, Pompe disease typically presents with progressive weakness of limb-girdle muscles and respiratory insufficiency. Due to the phenotypic heterogeneity of these disorders, however, it is often difficult for clinicians to reach a diagnosis for patients with Pompe disease. Six hundred and six patients from a European population were recruited onto our study. Inclusion criteria stipulated that index cases must present with limb-girdle weakness or elevated serum creatine kinase activity. Whole exome sequencing with at least 250 ng DNA was completed using an Illumina exome capture and a 38 Mb baited target. A panel of 169 candidate genes for limb-girdle weakness was analysed for disease-causing variants.

Results

A total of 35 variants within GAA were detected. Ten distinct variants in eight unrelated index cases (and four siblings not sequenced in our study) were considered disease-causing, with the patients presenting with heterogeneous phenotypes. The eight unrelated individuals were compound heterozygotes for two variants. Six patients carried the intronic splice site c.-13 T > G transversion and two of the six patients also carried the exonic p.Glu176ArgfsTer45 frameshift. Four of the ten variants were novel in their association with Pompe disease.

Conclusions

Here, we highlight the advantage of using whole exome sequencing as a tool for detecting, diagnosing and treating patients with rare, clinically variable genetic disorders.

Muscle ultrasound: A useful tool in newborn screening for infantile onset pompe disease

Our study aimed to evaluate the utility of muscle ultrasound in newborn screening of infantile-onset Pompe disease (IOPD) and to establish a system of severity grading. We retrospectively selected 35 patients with initial low acid alpha-glucosidase (GAA) activity and collected data including muscle ultrasound features, GAA gene mutation, activity/performance, and pathological and laboratory findings. The echogenicity of 6 muscles (the bilateral vastus intermedius, rectus femoris, and sartorius muscles) was compared to that of epimysium on ultrasound and rated either 1 (normal), 2 (mildly increased), or 3 (obviously increased). These grades were used to divide patients into 3 groups. IOPD was present in none of the grade-1 patients, 5 of 9 grade-2 patients, and 5 of 5 grade-3 patients (P < .001). Comparing grade-2 plus grade-3 patients to grade-1 patients, muscle ultrasound detected IOPD with a sensitivity and specificity of 100.0% (95% confidence interval [CI]: 69.2%-100%) and 84.0% (95% CI: 63.9%-95.5%), respectively. The mean number of affected muscles was larger in grade-3 patients than in grade-2 patients (4.2 vs. 2.0, P = .005). Mean alanine transaminase (ALT), aspartate transaminase (AST), creatine kinase (CK), and lactate dehydrogenase (LDH) levels were differed significantly different between grade-3 and grade-1 patients (P < .001). Because it permits direct visualization of injured muscles, muscle ultrasound can be used to screen for IOPD. Our echogenicity grades of muscle injury also correlate well with serum levels of muscle-injury biochemical markers.

Enzyme activities of α-glucosidase in Japanese neonates with pseudodeficiency alleles

Lysosomal storage disorders (LSDs) are caused by defective enzyme activities in lysosomes, characterized by the accumulation of sphingolipids, glycolipids, oligosaccharides, mucopolysaccharides, the oxidation products of cholesterol, and other biological substances. A growing number of clinical studies have suggested the enhanced efficacy of existing therapies, including enzyme replacement therapy, which is effective when it is initiated during the presymptomatic period. Thus, the identification of disease-affected individuals by newborn screening has been considered an effective platform. Previous studies have suggested that the discrimination of infantile-onset Pompe disease (IOPD) requires multi-step examination of GAA enzyme activity using the fluorometric technique. In sharp contrast, the MS/MS-based technique can identify the population of IOPD and the pseudodeficiency alleles of the GAA enzyme [Liao HC et al. Clin Chem (2017) in press; doi: http://dx.doi.org/10.1373/clinchem.2016.269027]. To determine whether MS/MS-based assay can identify these two populations in Japanese neonates, we first performed a validation study of this assay using flow-injection analysis (FIA)-MS/MS and liquid chromatography (LC)-MS/MS followed by examination of GAA enzyme activity in our population. By minimizing the effect of substrate-derived in-source decomposition products, the activities of 6 LSD enzymes were quantified in FIA-MS/MS and LC-MS/MS. The mean value of GAA activity with IOPD, pseudodeficiency alleles, and healthy controls by FIA-MS/MS were 1.0 ± 0.3 μmol/h/L (max, 1.3; min, 0.7; median, 1.2; n = 3), 2.7 ± 0.7 μmol/h/L (max, 4.5; min, 1.5; median, 2.5; n = 19), and 12.9 ± 5.4 μmol/h/L (max, 29.6; min, 2.5; median, 11.0; n = 83), respectively. These results suggest that the population of GAA with pseudodeficiency alleles has approximately 20% of GAA enzyme activity compared to controls, providing the preliminary evidence to estimate the cut-off values in the Japanese population using this technique.

Divergent clinical outcomes of alpha-glucosidase enzyme replacement therapy in two siblings with infantile-onset Pompe disease treated in the symptomatic or pre-symptomatic state

Pompe disease is an autosomal recessive, lysosomal glycogen storage disease caused by acid α-glucosidase deficiency. Infantile-onset Pompe disease (IOPD) is the most severe form and is characterized by cardiomyopathy, respiratory distress, hepatomegaly, and skeletal muscle weakness. Untreated, IOPD generally results in death within the first year of life. Enzyme replacement therapy (ERT) with recombinant human acid alpha glucosidase (rhGAA) has been shown to markedly improve the life expectancy of patients with IOPD. However, the efficacy of ERT in patients with IOPD is affected by the presence of symptoms and cross-reactive immunologic material (CRIM) status.

We have treated two siblings with IOPD with ERT at different ages: the first was symptomatic and the second was asymptomatic. The female proband (Patient 1) was diagnosed with IOPD and initiated ERT at 4 months of age. Her younger sister (Patient 2) was diagnosed with IOPD at 10 days of age and initiated ERT at Day 12. Patient 1, now 6 years old, is alive but bedridden, and requires 24-hour invasive ventilation due to gradually progressive muscle weakness. In Patient 2, typical symptoms of IOPD, including cardiac failure, respiratory distress, progressive muscle weakness, hepatomegaly and myopathic facial features were largely absent during the first 12 months of ERT. Her cardiac function and mobility were well-maintained for the first 3 years, and she had normal motor development. However, she developed progressive hearing impairment and muscle weakness after 3 years of ERT. Both siblings have had low anti-rhGAA immunoglobulin G (IgG) antibody titers during ERT and have tolerated the treatment well.

These results suggest that initiation of ERT during the pre-symptomatic period can prevent and/or attenuate the progression of IOPD, including cardiomyopathy, respiratory distress, and muscle weakness for first several years of ERT. However, to improve the long-term efficacy of ERT for IOPD, new strategies for ERT for IOPD, e.g. modifying the enzyme to enhance uptake into skeletal muscle and/or to cross the blood brain barrier (BBB), will be required.

Very Early Treatment for Infantile-Onset Pompe Disease Contributes to Better Outcomes

OBJECTIVE

To evaluate whether very early treatment in our patients would result in better clinical outcomes and to compare these data with other infantile-onset Pompe disease (IOPD) cohort studies.

METHODS

In this nationwide program, 669,797 newborns were screened for Pompe disease. We diagnosed IOPD in 14 of these newborns, and all were treated and followed in our hospital.

RESULTS

After 2010, the mean age at first enzyme-replacement therapy (ERT) was 11.92 days. Our patients had better biological, physical, and developmental outcomes and lower anti-rh acid α-glucosidase antibodies after 2 years of treatment, even compared with one group that began ERT just 10 days later than our cohort. No patient had a hearing disorder or abnormal vision. The mean age for independent walking was 11.6 ± 1.3 months, the same age as normal children.

CONCLUSIONS

ERT for patients with IOPD should be initiated as early as possible before irreversible damage occurs. Our results indicate that early identification of patients with IOPD allows for the very early initiation of ERT. Starting ERT even a few days earlier may lead to better patient outcomes.

Diagnosis of late-onset Pompe disease and other muscle disorders by next-generation sequencing

Background

Late-onset Pompe disease (LOPD) is a rare treatable lysosomal storage disorder characterized by progressive lysosomal glycogen accumulation and muscle weakness, with often a limb-girdle pattern. Despite published guidelines, testing for LOPD is often overlooked or delayed in adults, owing to its low frequency compared to other muscle disorders with similar muscle patterns. Next-generation sequencing has the capability to test concurrently for several muscle disorders. This could potentially lead to increased diagnosis of LOPD, disorders with non-specific muscle weakness or atypical patients.

Methods

We developed a gene panel to further study its clinical utility in a cohort of patients with suspected muscle disorders. We designed a gene panel to analyze the coding sequences and splice site junctions of GAA causing LOPD, along with 77 other genes causing muscle disorders with overlapping phenotypes.

Results

At a median coverage of ~200X (sequences per base), all GAA exons were successfully covered with >20X and only 0.3 % of exons across all genes were <20X. The panel showed an excellent sensitivity (100 %) and specificity (98 %) across all selected genes, using known variations in Pompe patients and controls. We determined its clinical utility by analyzing 34 patients with suspected muscle disorders of undetermined etiology and various muscle patterns, who were referred or followed in neuromuscular and genetics clinics. A putative diagnosis was found in up to 32 % of patients. The gene panel was instrumental in reaching a diagnosis in atypical patients, including one LOPD case. Acid alpha-glucosidase activity was used to confirm the molecular results in all patients.

Conclusion

This work highlights the high clinical utility of gene panels in patients with suspected muscle disorders and its potential to facilitate the diagnosis of patients showing non-specific muscle weakness or atypical phenotypes. We propose that gene panels should be used as a first-tier test in patients with suspected muscle disorders of undetermined etiology, which could further increase overall diagnosis of muscle conditions, and potentially reduce diagnostic delay. Further studies are necessary to determine the impact of first-tier gene panels on diagnostic delay and on treatment outcome for LOPD.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-016-0390-6) contains supplementary material, which is available to authorized users.

Enzyme enhancers for the treatment of Fabry and Pompe disease

Lysosomal storage disorders (LSD) are a group of heterogeneous diseases caused by compromised enzyme function leading to multiple organ failure. Therapeutic approaches involve enzyme replacement (ERT), which is effective for a substantial fraction of patients. However, there are still concerns about a number of issues including tissue penetrance, generation of host antibodies against the therapeutic enzyme, and financial aspects, which render this therapy suboptimal for many cases. Treatment with pharmacological chaperones (PC) was recognized as a possible alternative to ERT, because a great number of mutations do not completely abolish enzyme function, but rather trigger degradation in the endoplasmic reticulum. The theory behind PC is that they can stabilize enzymes with remaining function, avoid degradation and thereby ameliorate disease symptoms. We tested several compounds in order to identify novel small molecules that prevent premature degradation of the mutant lysosomal enzymes α-galactosidase A (for Fabry disease (FD)) and acid α-glucosidase (GAA) (for Pompe disease (PD)). We discovered that the expectorant Ambroxol when used in conjunction with known PC resulted in a significant enhancement of mutant α-galactosidase A and GAA activities. Rosiglitazone was effective on α-galactosidase A either as a monotherapy or when administered in combination with the PC 1-deoxygalactonojirimycin. We therefore propose both drugs as potential enhancers of pharmacological chaperones in FD and PD to improve current treatment strategies.

Inborn errors of metabolism and expanded newborn screening: review and update

Inborn errors of metabolism (IEM) are a phenotypically and genetically heterogeneous group of disorders caused by a defect in a metabolic pathway, leading to malfunctioning metabolism and/or the accumulation of toxic intermediate metabolites. To date, more than 1000 different IEM have been identified. While individually rare, the cumulative incidence has been shown to be upwards of 1 in 800. Clinical presentations are protean, complicating diagnostic pathways. IEM are present in all ethnic groups and across every age. Some IEM are amenable to treatment, with promising outcomes. However, high clinical suspicion alone is not sufficient to reduce morbidities and mortalities. In the last decade, due to the advent of tandem mass spectrometry, expanded newborn screening (NBS) has become a mandatory public health strategy in most developed and developing countries. The technology allows inexpensive simultaneous detection of more than 30 different metabolic disorders in one single blood spot specimen at a cost of about USD 10 per baby, with commendable analytical accuracy and precision. The sensitivity and specificity of this method can be up to 99% and 99.995%, respectively, for most amino acid disorders, organic acidemias, and fatty acid oxidation defects. Cost-effectiveness studies have confirmed that the savings achieved through the use of expanded NBS programs are significantly greater than the costs of implementation. The adverse effects of false positive results are negligible in view of the economic health benefits generated by expanded NBS and these could be minimized through increased education, better communication, and improved technologies. Local screening agencies should be given the autonomy to develop their screening programs in order to keep pace with international advancements. The development of biochemical genetics is closely linked with expanded NBS. With ongoing advancements in nanotechnology and molecular genomics, the field of biochemical genetics is still expanding rapidly. The potential of tandem mass spectrometry is extending to cover more disorders. Indeed, the use of genetic markers in T-cell receptor excision circles for severe combined immunodeficiency is one promising example. NBS represents the highest volume of genetic testing. It is more than a test and it warrants systematic healthcare service delivery across the pre-analytical, analytical, and post-analytical phases. There should be a comprehensive reporting system entailing genetic counselling as well as short-term and long-term follow-up. It is essential to integrate existing clinical IEM services with the expanded NBS program to enable close communication between the laboratory, clinicians, and allied health parties. In this review, we will discuss the history of IEM, its clinical presentations in children and adult patients, and its incidence among different ethnicities; the history and recent expansion of NBS, its cost-effectiveness, associated pros and cons, and the ethical issues that can arise; the analytical aspects of tandem mass spectrometry and post-analytical perspectives regarding result interpretation.

Emerging issues in public health genomics

This review highlights emerging areas of interest in public health genomics. First, we describe recent advances in newborn screening (NBS), with a focus on the practice and policy implications of current and future efforts to expand NBS programs (e.g., via next-generation sequencing). Next, we detail research findings from the rapidly progressing field of epigenetics and epigenomics, highlighting ways in which our emerging understanding in these areas could guide future intervention and research efforts in public health. We close by considering various ethical, legal, and social issues posed by recent developments in public health genomics; these include policies to regulate access to personal genomic information, the need to enhance genetic literacy in both health professionals and the public, and challenges in ensuring that the benefits (and burdens) of genomic discoveries and applications are equitably distributed. We also note needs for future genomic research that integrates across basic and social sciences.

Reference intervals of α-glycosidase, β-glycosidase, and α-galactosidase in dried blood spot in a Turkish newborn population

Inherited lysosomal storage diseases (LSDs) are rare, and diagnosis is often delayed for 7-10 years. Since the therapies have become available for a limited number of LSDs, (Fabry, Gaucher, Pompe, and MPS-1), early diagnosis of treatable LSDs can be lifesaving or ameliorating and allows timely treatment before irreversible damage occurs. Recently, the use of dried blood spot test (DBS) for newborn screening of LSDs has been proposed for newborn screening tests. They are noninvasive, sensitive, and specific assays with the further advantage of a fast turnaround time compared to measurement in leukocyte and/or fibroblast culture. We aimed to determine the reference intervals for lysosomal enzyme activities of newborn babies in our population and to investigate the effect of gestational week on enzyme activity. One hundred thirty healthy newborn babies (70 girls, 60 boys) were included into the study. α-Glycosidase, β-glycosidase, and α-galactosidase activities in DBS samples of newborns were determined fluorometrically. Reference intervals were calculated using Dixon's rule and percentiles of 2.5-97.5. Cutoff limits (5 %) for α-glycosidase, β-glycosidase, and α-galactosidase activities were 0.57, 0.92, and 2.18, respectively. α-Galactosidase activity was higher in girls compared to boys (p < 0.05). Interestingly, α-glycosidase and β-glycosidase activities of newborns who were delivered before 38 weeks were significantly lower than those who were delivered at 39-40 weeks. Conclusion It is of utmost importance to define the reference intervals for lysosomal enzyme activities as well as cutoff limits for newborn babies with regard to gestational age and sex. More studies to clarify the reason for the change in enzyme activity by gestational week will be required.

Newborn screening for lysosomal storage diseases: an ethical and policy analysis

The traditional focus of newborn screening (NBS) is testing infants for medical conditions like phenylketonuria (PKU) that may cause significant morbidity or mortality unless treatment is initiated early. Although the Wilson and Jungner criteria were not designed specifically for NBS, the public health screening criteria have been used, with some modifications, to justify what conditions are included in a universal NBS panel. These criteria are being challenged by platform technologies like tandem mass spectrometry (MS/MS) that allow for the identification of numerous conditions on a single sample because they identify many conditions and variants simultaneously, some of which meet and others which fail to meet the criteria. In this manuscript, I evaluate three lysosomal storage diseases included in this multiplex screening test-Pompe disease, Fabry disease, and Krabbe disease. I show that they fail to meet some of the critical Wilson and Jungner criteria and thus are not ready for inclusion in universal NBS panels. Rather, screening for these conditions should only be performed in the research context with institutional review board approval and parental permission.

Public support for neonatal screening for Pompe disease, a broad-phenotype condition

Background

Neonatal screening for Pompe disease has been introduced in Taiwan and a few U.S. states, while other jurisdictions including some European countries are piloting or considering this screening. First-tier screening flags both classic infantile and late-onset Pompe disease, which challenges current screening criteria. Previously, advocacy groups have sometimes supported expanded neonatal screening more than professional experts, while neutral citizens' views were unknown. This study aimed to measure support for neonatal screening for Pompe disease in the general public and to compare it to support among (parents of) patients with this condition. The study was done in the Netherlands, where newborns are not currently screened for Pompe disease. Newborn screening is not mandatory in the Netherlands but current uptake is almost universal.

Methods

A consumer panel (neutral group) and (parents of) patients with Pompe disease (Pompe group) were sent information and a questionnaire. Responses were analyzed of 555 neutral and 58 Pompe-experienced informants who had demonstrated sufficient understanding.

Results

87% of the neutral group and 88% of the Pompe group supported the introduction of screening (95% CI of difference -10 to 7%). The groups were similar in their moral reasoning about screening and acceptance of false positives, but the Pompe-experienced group expected greater benefit from neonatal detection of late-onset disease. Multivariate regression analysis controlling for demographics confirmed that approval of the introduction of screening was independent of having (a child with) Pompe disease. Furthermore, respondents with university education, regardless of whether they have (a child with) Pompe disease, were more likely to be reluctant about the introduction of screening than those with less education, OR for approval 0.29 (95% CI 0.18 to 0.49, p < 0.001).

Conclusions

This survey suggests a rather high level of support for newborn screening for Pompe disease, not only among those who have personal experience of the disease but also among the general public in the Netherlands. Optional screening on the basis of informed parental consent is probably unrealistic, underlining the need for new guidelines to help policymakers in their consideration of newborn screening for broad phenotype conditions.

Predicting cross-reactive immunological material (CRIM) status in Pompe disease using GAA mutations: lessons learned from 10 years of clinical laboratory testing experience

Enzyme replacement therapy (ERT) for Pompe disease using recombinant acid alpha-glucosidase (rhGAA) has resulted in increased survival although the clinical response is variable. Cross-reactive immunological material (CRIM)-negative status has been recognized as a poor prognostic factor. CRIM-negative patients make no GAA protein and develop sustained high antibody titers to ERT that render the treatment ineffective. Antibody titers are generally low for the majority of CRIM-positive patients and there is typically a better clinical outcome. Because immunomodulation has been found to be most effective in CRIM-negative patients prior to, or shortly after, initiation of ERT, knowledge of CRIM status is important before ERT is begun. We have analyzed 243 patients with infantile Pompe disease using a Western blot method for determining CRIM status and using cultured skin fibroblasts. Sixty-one out of 243 (25.1%) patients tested from various ethnic backgrounds were found to be CRIM-negative. We then correlated the CRIM results with GAA gene mutations where available (52 CRIM-negative and 88 CRIM-positive patients). We found that, in most cases, CRIM status can be predicted from GAA mutations, potentially circumventing the need for invasive skin biopsy and time wasted in culturing cells in the future. Continued studies in this area will help to increase the power of GAA gene mutations in predicting CRIM status as well as possibly identifying CRIM-positive patients who are at risk for developing high antibody titers.

New insights into therapeutic options for Pompe disease

Glycogen storage disease type II or Pompe disease (GSD II, MIM 232300) is a rare inherited metabolic myopathy caused by a deficiency of lysosomal acid α-glucosidase or acid maltase (GAA; EC 3.2.1.20), resulting in a massive lysosomal glycogen accumulation in cardiac and skeletal muscles. Affected individuals exhibit either severe hypotonia associated with hypertrophic cardiomyopathy (infantile forms) or progressive muscle weakness (late-onset forms). Even if enzyme replacement therapy has recently become a standard treatment, it suffers from several limitations. This review will present the main results of enzyme replacement therapy and the recent findings concerning alternative treatments for Pompe disease, such as gene therapy, enzyme enhancement therapy, and substrate reduction therapy.

Pompe's Disease in Childhood: A Metabolic Myopathy

BACKGROUND

Myopathy of metabolic origin in childhood occurs due to a variety of conditions. Pompe's Disease also known as Glycogen storage disease Type II, is a rare storage disorder with clinical presentation akin to spinal muscular atrophy.

METHODS

A series of patients with suspected metabolic myopathy were reviewed at a tertiary care service hospital over a period of three years. The diagnosis was confirmed by estimation of acid alpha glucosidase activity.

RESULT

At our centre, these cases presented with generalized hypotonia, organomegaly (hepatomegaly, cardiomegaly) and congestive cardiac failure. Infantile onset, the most severe form of Pompe's disease, was the commonest form accounting for 75% of the cases. Four of the babies with infantile onset Pompe's disease expired, three due to refractory heart failure and one to fulminant respiratory infection before 15 months of age.

CONCLUSION

Pompe's Disease is now being increasingly diagnosed, due to definitive enzyme estimation facilities. With the recent availability of enzyme replacement therapy with Myozyme, the prognosis is likely to change for the better.

Newborn screening for neuropathic lysosomal storage disorders

Interest in newborn screening (NBS) for lysosomal storage disorders (LSDs) has increased significantly due to newly developed enzyme replacement therapy (ERT), the need for early diagnosis, and advances in technical developments. Since the central nervous system cannot be treated by ERT, neuronopathic LSDs are generally not the primary target of NBS. An exception is Krabbe disease, in which hematopoietic stem cell transplantation before the onset of symptoms has benefits. However, NBS for LSD relies on measuring enzyme activities, so the most severely affected individuals (usually patients with neuronopathic subtypes) will be detected together with patients with less severe disease. In the near future, NBS is likely to be developed for diseases such as Gaucher, Niemann-Pick A/B, and certain mucopolysaccharidoses. The ability to predict phenotypes (neuronopathic or not) by enzyme activity and genotyping will therefore be critical for adequate patient management. This article reviews the status of LSD screening and issues concerning detection of neuronopathic LSDs by screening.

Systematic evidence review of newborn screening and treatment of severe combined immunodeficiency

CONTEXT

Severe combined immunodeficiency (SCID) is a group of disorders that leads to early childhood death as a result of severe infections. Recent research has addressed potential newborn screening for SCID.

OBJECTIVE

To conduct a systematic review of the evidence for newborn screening for SCID, including test characteristics, treatment efficacy, and cost-effectiveness.

METHODS

We searched Medline and the OVID In-Process & Other Non-Indexed Citations databases. We excluded articles if they were reviews, editorials or other opinion pieces, or case series of fewer than 4 patients or if they contained only adult subjects or nonhuman data. The remaining articles were systematically evaluated, and data were abstracted by 2 independent reviewers using standardized tools. For topics that lacked published evidence, we interviewed experts in the field.

RESULTS

The initial search resulted in 719 articles. Twenty-six met inclusion criteria. The results of several small studies suggested that screening for SCID is possible. Interviews revealed that 2 states have begun pilot screening programs. Evidence from large case series indicates that children receiving early stem-cell transplant for SCID have improved outcomes compared with children who were treated later. There is some inconclusive evidence regarding the need for donor-recipient matching and use of pretransplant chemotherapy. Few data on the cost-effectiveness of a SCID-screening program.

CONCLUSIONS

Evidence indicates the benefits of early treatment of SCID and the possibility of population-based newborn screening. Better information on optimal treatment and the costs of treatment and screening would benefit policy makers deciding among competing health care priorities.

Genetic heterozygosity and pseudodeficiency in the Pompe disease newborn screening pilot program

Pompe disease is an autosomal recessive lysosomal storage disorder (LSD) caused by deficiency of lysosomal acid alpha-glucosidase (GAA) activity. This is the first LSD in which newborn screening has been shown to improve clinical outcomes. Newborn screening also identified multiple rare gene variants in this population. Among 132,538 newborns screened, 107 babies (1 in 1239) who had low dried blood spot GAA activity were genotyped. Sixty-nine (64.5%) babies had a total of 54 mutations and 35 novel predictably pathogenic mutations; 36 babies (33.6%) who had no mutation were homozygous for the c.[1726A; 2065A] pseudodeficiency allele. Because 81% of the chromosomes (14% in the controls) were in haplotype *03, we found a link between the pseudodeficiency allele and other mutated alleles. The newborns with Pompe disease detected by screening had lymphocyte GAA activities 0.45 to 1.65 nmol/mg/h (normal 66.7+/-33.8), while only 2 of the 100 false-positive cases had GAA activity less than 2.00 nmol/mg/h (or 3% of the normal mean). Therefore, newborn screening for Pompe disease could be successfully conducted by including genotyping and lymphocyte GAA assay, even in a population with mutation heterozygosity and pseudodeficiency.

Pompe disease in infants: improving the prognosis by newborn screening and early treatment

OBJECTIVE

Pompe disease causes progressive, debilitating, and often life-threatening musculoskeletal, respiratory, and cardiac symptoms. Favorable outcomes with early intravenous enzyme-replacement therapy and alglucosidase alfa have been reported, but early clinical diagnosis before the development of severe symptoms has rarely been possible in infants.

METHODS

We recently conducted a newborn screening pilot program in Taiwan to improve the early detection of Pompe disease. Six of 206088 newborns screened tested positive and were treated for Pompe disease. Five had the rapidly progressive form of Pompe disease, characterized by cardiac and motor involvement, and were treated soon after diagnosis. The sixth patient was started on treatment at 14 months of age because of progressive muscle weakness. Outcomes were compared with treated patients whose disease was diagnosed clinically and with untreated historical control subjects.

RESULTS

At the time of this report, patients had been treated for 14 to 32 months. The 5 infants who had early cardiac involvement demonstrated normalization of cardiac size and muscle pathology with normal physical growth and age-appropriate gains in motor development. The infant without cardiac involvement also achieved normal motor development with treatment. Survival in patients who had newborn screening was significantly improved compared with those in the untreated reference cohort (P = .001). Survival in the treated clinical comparators was reduced but not statistically different from that in the newborn screening group (P = .48).

CONCLUSIONS

Results from this study indicate that early treatment can benefit infants with Pompe disease and highlight the advantages of early diagnosis, which can be achieved by newborn screening.

Multiplex enzyme assay screening of dried blood spots for lysosomal storage disorders by using tandem mass spectrometry

BACKGROUND

Reports of the use of multiplex enzyme assay screening for Pompe disease, Fabry disease, Gaucher disease, Niemann-Pick disease types A and B, and Krabbe disease have engendered interest in the use of this assay in newborn screening. We modified the assay for high-throughput use in screening laboratories.

METHODS

We optimized enzyme reaction conditions and procedures for the assay, including the concentrations of substrate (S) and internal standard (IS), assay cocktail compositions, sample clean-up procedures, and mass spectrometer operation. The S and IS for each enzyme were premixed and bottled at an optimized molar ratio to simplify assay cocktail preparation. Using the new S:IS ratio, we validated the modified assay according to CLSI guidelines. Stability of the S, IS, and assay cocktails were investigated. Dried blood spots from 149 healthy adults, 100 newborns, and 60 patients with a lysosomal storage disorder (LSD) were tested using the modified assay.

RESULTS

In our study, the median enzyme activity measured in adults was generally increased 2-3-fold compared to the original method, results indicating higher precision. In the multiplex format, each of the 5 modified enzyme assays enabled unambiguous differentiation between samples from healthy individuals (adults and newborns) and the corresponding disease-specific samples.

CONCLUSIONS

The modified multiplex enzyme assay with premixed S and IS is appropriate for use in high-throughput screening laboratories.

Survival advantage of neonatal CNS gene transfer for late infantile neuronal ceroid lipofuscinosis

Late infantile neuronal ceroid lipofuscinosis (LINCL), a fatal autosomal recessive neurodegenerative lysosomal storage disorder of childhood, is caused by mutations in the CLN2 gene, resulting in deficiency of the protein tripeptidyl peptidase I (TPP-I). We have previously shown that direct CNS administration of AAVrh.10hCLN2 to adult CLN2 knockout mice, a serotype rh.10 adeno-associated virus expressing the wild-type CLN2 cDNA, will partially improve neurological function and survival. In this study, we explore the hypothesis that administration of AAVrh.10hCLN2 to the neonatal brain will significantly improve the results of AAVrh.10hCLN2 therapy. To assess this concept, AAVrh.10hCLN2 vector was administered directly to the CNS of CLN2 knockout mice at 2 days, 3 wk and 7 wk of age. While all treatment groups show a marked increase in total TPP-I activity over wild-type mice, neonatally treated mice displayed high levels of TPP-I activity in the CNS 1 yr after administration which was spread throughout the brain. Using behavioral markers, 2 day-treated mice demonstrate marked improvement over 3 wk, 7 wk or untreated mice. Finally, neonatal administration of AAVrh.10hCLN2 was associated with markedly enhanced survival, with a median time of death 376 days for neonatal treated mice, 277 days for 3 wk-treated mice, 168 days for 7 wk-treated mice, and 121 days for untreated mice. These data suggest that neonatal treatment offers many unique advantages, and that early detection and treatment may be essential for maximal gene therapy for childhood lysosomal storage disorders affecting the CNS.

Waiving informed consent in newborn screening research: balancing social value and respect

While newborn screening (NBS) programs have historically relied on presumptive benefit in deciding when to implement new tests, experience has demonstrated that this approach can lead to screening tests that lack efficacy or, worse yet, cause harm. Population-based NBS research provides an opportunity to evaluate safety and effectiveness of potential tests prior to widespread implementation. Using the example of Pompe disease, we argue that waiving the requirement for informed consent is appropriate for research evaluating the screening phase of potential NBS tests when data support the potential health benefits of testing and when other research safeguards are present. The regulatory requirement for informed consent can be waived if a research study meets criteria of minimal risk, protecting rights and welfare, and practicability. In population-based NBS research, the main risks are related to false positive results and results with ambiguous implications for treatment-risks that are comparable to those posed by many tests newly added to NBS programs without prior population-based NBS research. Waiving the informed consent requirement facilitates the development of flexible strategies for informing and educating parents about NBS research that reflect the logistics of population-based NBS screening. A strict interpretation of the regulatory requirement of informed consent may create significant logistical and financial barriers to adequate evaluation of NBS tests. Without a broader interpretation of this regulatory requirement in NBS research for which there is evidence of a clinically meaningful benefit from treatment, we may create incentives for the implementation of inadequately evaluated NBS tests.