Newborn Screening for Mucopolysaccharidosis Type II in Illinois: An Update

Current Status of Newborn Bloodspot Screening Worldwide 2024: A Comprehensive Review of Recent Activities (2020-2023)

Newborn bloodspot screening (NBS) began in the early 1960s based on the work of Dr. Robert "Bob" Guthrie in Buffalo, NY, USA. His development of a screening test for phenylketonuria on blood absorbed onto a special filter paper and transported to a remote testing laboratory began it all. Expansion of NBS to large numbers of asymptomatic congenital conditions flourishes in many settings while it has not yet been realized in others. The need for NBS as an efficient and effective public health prevention strategy that contributes to lowered morbidity and mortality wherever it is sustained is well known in the medical field but not necessarily by political policy makers. Acknowledging the value of national NBS reports published in 2007, the authors collaborated to create a worldwide NBS update in 2015. In a continuing attempt to review the progress of NBS globally, and to move towards a more harmonized and equitable screening system, we have updated our 2015 report with information available at the beginning of 2024. Reports on sub-Saharan Africa and the Caribbean, missing in 2015, have been included. Tables popular in the previous report have been updated with an eye towards harmonized comparisons. To emphasize areas needing attention globally, we have used regional tables containing similar listings of conditions screened, numbers of screening laboratories, and time at which specimen collection is recommended. Discussions are limited to bloodspot screening.

Frequency of iduronate-2-sulfatase gene variants detected in newborn screening for mucopolysaccharidosis type II in Japan

Mucopolysaccharidosis II (MPS II) is an X-linked, recessive, inborn metabolic disorder caused by defects in iduronate-2-sulfatase (IDS). The age at onset, disease severity, and rate of progression vary significantly among patients. This disease is classified into severe or mild forms depending on neurological symptom involvement. The severe form is associated with progressive cognitive decline while the mild form is predominantly associated with somatic features. Newborn screening (NBS) for MPS II has been performed since December 2016, mainly in Kyushu, Japan, where 197,700 newborns were screened using a fluorescence enzyme activity assay of dried blood spots. We diagnosed one newborn with MPS II with lower IDS activity, elevated urinary glycosaminoglycans, and a novel variant of the IDS gene. In the future, NBS for MPS II is expected to be performed in many regions of Japan and will contribute to the detection of more patients with MPS II, which is crucial to the early treatment of the disorder.

Cognitive and adaptive behaviors associated with disease severity and genotype in patients with mucopolysaccharidosis II

BACKGROUND

Mucopolysaccharidosis II (MPS II) is a rare, X-linked lysosomal storage disease caused by pathogenic variants of the iduronate-2-sulfatase gene (IDS) and is characterized by a highly variable disease spectrum. MPS II severity is difficult to predict based on IDS variants alone; while some genotypes are associated with specific phenotypes, the disease course of most genotypes remains unknown. This study aims to refine the genotype-phenotype categorization by combining information from the scientific literature with data from two clinical studies in MPS II.

METHODS

Genotype, cognitive, and behavioral data from 88 patients in two clinical studies (NCT01822184, NCT02055118) in MPS II were analyzed post hoc in combination with published information on IDS variants from the biomedical literature through a semi-automated multi-stage review process. The Differential Ability Scales, second edition (DAS-II) and the Vineland Adaptive Behavior Scales™, second edition (VABS-II) were used to measure cognitive function and adaptive behavior.

RESULTS

The most common category of IDS variant was missense (47/88, 53.4% of total variants). The mean (standard deviation [SD]) baseline DAS-II General Conceptual Ability (GCA) and VABS-II Adaptive Behavior Composite (ABC) scores were 74.0 (16.4) and 82.6 (14.7), respectively. All identified IDS complete deletions/large rearrangements (n = 7) and large deletions (n = 1) were associated with a published 'severe' or 'predicted severe' progressive neuronopathic phenotype, characterized by central nervous system involvement. In categories comprising more than one participant, mean baseline DAS-II GCA scores (SD) were lowest among individuals with complete deletions/large rearrangements 64.0 (9.1, n = 4) and highest among those with splice site variants 83.8 (14.2, n = 4). Mean baseline VABS-II ABC scores (SD) were lowest among patients with unclassifiable variants 79.3 (4.9, n = 3) and highest among those with a splice site variant 87.2 (16.1, n = 5), in variant categories with more than one participant.

CONCLUSIONS

Most patients in the studies had an MPS II phenotype categorized as 'severe' or 'predicted severe' according to classifications, as reported in the literature. Patients with IDS complete deletion/large rearrangement variants had lower mean DAS-II GCA scores than those with other variants, as well as low VABS-II ABC, confirming an association with the early progressive 'severe' (neuronopathic) disease. These data provide a starting point to improve the classification of MPS II phenotypes and the characterization of the genotype-phenotype relationship.

Endogenous, non-reducing end glycosaminoglycan biomarkers for the mucopolysaccharidoses: Accurate diagnosis and elimination of false positive newborn screening results

The mucopolysaccharidoses (MPS) are a family of inborn errors of metabolism resulting from a deficiency in a lysosomal hydrolase responsible for the degradation of glycosaminoglycans (GAG). From a biochemical standpoint, excessive urinary excretion of GAG has afforded first-tier laboratory investigations for diagnosis whereas newborn screening programs employ lysosomal hydrolase measurements. Given false positives are not uncommon, second-tier diagnostic testing relies on lysosomal hydrolase measurements following elevated urinary GAG, and newborn screening results are often corroborated with GAG determinations. Molecular genetics requires acknowledgement, as identifying pathogenic variants in the hydrolase genes confirms the diagnosis and allows cascade testing for families, but genetic variants of uncertain significance complicate this paradigm. Initiating cellular, tissue and organ damage that leads to an MPS phenotype is undoubtedly the accumulation of partially degraded GAG, and with mass spectrometry technologies now readily available in the biochemical genetics' laboratory, the ability to properly measure these GAG fragments has been realized. The most common approach involves bacterial lyase/hydrolase digestion of the long chain GAG polymers into their disaccharide units that can be measured by mass spectrometry. Another, less well-known method, the endogenous, non-reducing end method, does not require depolymerization of GAG but rather relies on the mass spectrometric measurement of the naturally produced oligosaccharides that arise from the enzyme deficiency. All MPS can be identified by this one method, and evidence to date shows it to be the only GAG analysis method that gives no false positives when employed as a first-tier laboratory diagnostic test and second-tier newborn screening test.

Newborn screening for mucopolysaccharidosis type II: Lessons learned

We describe our experience with population-based newborn screening for mucopolysaccharidosis type II (MPS II) in 586,323 infants by measurement of iduronate-2-sulfatase activity in dried blood spots between December 12, 2017 and April 30, 2022. A total of 76 infants were referred for diagnostic testing, 0.01% of the screened population. Of these, eight cases of MPS II were diagnosed for an incidence of 1 in 73,290. At least four of the eight cases detected had an attenuated phenotype. In addition, cascade testing revealed a diagnosis in four extended family members. Fifty-three cases of pseudodeficiency were also identified, for an incidence of 1 in 11,062. Our data suggest that MPS II may be more common than previously recognized with a higher prevalence of attenuated cases.

Evidence and recommendation for mucopolysaccharidosis type II newborn screening in the United States

Mucopolysaccharidosis type II (MPS II), also known as Hunter syndrome, is an X-linked condition caused by pathogenic variants in the iduronate-2-sulfatase gene. The resulting reduced activity of the enzyme iduronate-2-sulfatase leads to accumulation of glycosaminoglycans that can progressively affect multiple organ systems and impair neurologic development. In 2006, the US Food and Drug Administration approved idursulfase for intravenous enzyme replacement therapy for MPS II. After the data suggesting that early treatment is beneficial became available, 2 states, Illinois and Missouri, implemented MPS II newborn screening. Following a recommendation of the Advisory Committee on Heritable Disorders in Newborns and Children in February 2022, in August 2022, the US Secretary of Health and Human Services added MPS II to the Recommended Uniform Screening Panel, a list of conditions recommended for newborn screening. MPS II was added to the Recommended Uniform Screening Panel after a systematic evidence review reported the accuracy of screening, the benefit of presymptomatic treatment compared with usual case detection, and the feasibility of implementing MPS II newborn screening. This manuscript summarizes the findings of the evidence review that informed the Advisory Committee's decision.

Liquid Chromatography-Tandem Mass Spectrometry in Newborn Screening Laboratories

Tandem mass spectrometry (MS/MS) is the most universal platform currently available for the analysis of enzymatic activities and biomarkers in dried blood spots (DBS) for applications in newborn screening (NBS). Among the MS/MS applications in NBS, the most common is flow-injection analysis (FIA-) MS/MS, where the sample is introduced as a bolus injection into the mass spectrometer without the prior fractionation of analytes. Liquid chromatography combined with MS/MS (LC-MS/MS) has been employed for second-tier tests to reduce the false-positive rate associated with several nonspecific screening markers, beginning two decades ago. More recently, LC-MS/MS has been applied to primary screening for new conditions for which FIA-MS/MS or other methods, including genomic screening, are not yet adequate. In addition to providing a list of the currently used LC-MS/MS-based assays for NBS, the authors share their experience regarding the maintenance requirements of LC-MS/MS vs. FIA-MS/MS systems. The consensus is that the maintenance of LC-MS/MS and FIA-MS/MS instrumentation is similar, and LC-MS/MS has the advantage of allowing for a larger number of diseases to be screened for in a multiplex, cost-effective fashion with a high throughput and an adequate turnaround time.

Addition of MPS-II to the Recommended Uniform Screening Panel in the United States

It has recently been announced that the Secretary of the U.S. Department of Health and Human Services has approved the recommendation by the Advisory Committee on Heritable Disorders in Newborns and Children (ACHDNC) to add mucopolysaccharidosis type II (MPS-II, Hunter Syndrome) to the recommended uniform screening panel (RUSP) in the United States [...].

Newborn Screening Program for Mucopolysaccharidosis Type II and Long-Term Follow-Up of the Screen-Positive Subjects in Taiwan

Background: Mucopolysaccharidosis II (MPS II) is an X-linked disorder resulting from a deficiency in lysosomal enzyme iduronate-2-sulfatase (IDS), which causes the accumulation of glycosaminoglycans (GAGs) in the lysosomes of many tissues and organs, leading to progressive cellular dysfunction. An MPS II newborn screening program has been available in Taiwan since 2015. The aim of the current study was to collect and analyze the long-term follow-up data of the screen-positive subjects in this program. Methods: From August 2015 to April 2022, 548,624 newborns were screened for MPS II by dried blood spots using tandem mass spectrometry, of which 202 suspected infants were referred to our hospital for confirmation. The diagnosis of MPS II was confirmed by IDS enzyme activity assay in leukocytes, quantitative determination of urinary GAGs by mass spectrometry, and identification of the IDS gene variant. Results: Among the 202 referred infants, 10 (5%) with seven IDS gene variants were diagnosed with confirmed MPS II (Group 1), 151 (75%) with nine IDS gene variants were classified as having suspected MPS II or pseudodeficiency (Group 2), and 41 (20%) with five IDS gene variants were classified as not having MPS II (Group 3). Long-term follow-up every 6 months was arranged for the infants in Group 1 and Group 2. Intravenous enzyme replacement therapy (ERT) was started in four patients at 1, 0.5, 0.4, and 0.5 years of age, respectively. Three patients also received hematopoietic stem cell transplantation (HSCT) at 1.5, 0.9, and 0.6 years of age, respectively. After ERT and/or HSCT, IDS enzyme activity and the quantity of urinary GAGs significantly improved in all of these patients compared with the baseline data. Conclusions: Because of the progressive nature of MPS II, early diagnosis via a newborn screening program and timely initiation of ERT and/or HSCT before the occurrence of irreversible organ damage may lead to better clinical outcomes. The findings of the current study could serve as baseline data for the analysis of the long-term effects of ERT and HSCT in these patients.

Newborn screening and the recommended uniform screening panel: Optimal submissions and suggested improvements based on an advocacy organization's decade-long experience

The National MPS Society, Inc., founded in 1974, is a rare disease advocacy non-profit with a tripartite mission addressing the needs of the mucopolysaccharidosis and mucolipidosis communities through advocacy, research, and family and patient support. The Recommended Uniform Screening Panel (RUSP) of conditions for newborn screening (NBS), legislatively mandated in 2008, was implemented in 2010 by the Secretary of Health and Human Services (HSS), through the adoption of 29 core conditions. Since its inception the RUSP has grown to 35 core conditions. Each addition followed a defined nomination process that has itself undergone further definition over time. Since the adoption of the RUSP, the Society has nominated two conditions that have been approved by the Advisory Committee on Heritable Disorders in Children and Newborns (ACHDNC) and forwarded to the Secretary of HSS for inclusion on the RUSP. This history places the Society in a position to reflect on the process of successfully nominating conditions. Additionally, the Society is well placed by this experience to provide observations on the RUSP process. We will highlight best practices for pending and future nominations and reflect on potential improvements to the process and infrastructure of NBS, the RUSP, and the ACHDNC.

Timing is everything: Clinical courses of Hunter syndrome associated with age at initiation of therapy in a sibling pair

Hunter syndrome, or mucopolysaccharidosis (MPS) II, is a rare lysosomal disorder characterized by progressive, multi-system disease. As most symptoms cannot be reversed once established, early detection and treatment prior to the onset of clinical symptoms are critical. However, it is difficult to identify affected individuals early in disease, and therefore the long-term outcomes of initiating treatment during this optimal time period are incompletely described. We report long-term clinical outcomes of treatment when initiated prior to obvious clinical signs by comparing the courses of two siblings with neuronopathic Hunter syndrome (c.1504 T > G[p.W502G]), one who was diagnosed due to clinical disease (Sibling-O, age 3.7 years) and the other who was diagnosed before disease was evident (Sibling-Y, age 12 months), due to his older sibling's findings. The brothers began enzyme replacement therapy within a month of diagnosis. Around the age of 5 years, Sibling-O had a cognitive measurement score in the impaired range of <55 (average range 85–115), whereas Sibling-Y at this age received a score of 91. Sibling-O has never achieved toilet training and needs direct assistance with toileting, dressing, and washing, while Sibling-Y is fully toilet-trained and requires less assistance with daily activities. Both siblings have demonstrated sensory-seeking behaviors, hyperactivity, impulsivity, and sleep difficulties; however, Sibling-O demonstrates physical behaviors that his brother does not, namely biting, pushing, and frequent elopement. Since the time of diagnosis, Sibling-O has had significant joint contractures and a steady deterioration in mobility leading to the need for an adaptive stroller at age 11, while Sibling-Y at age 10.5 could hike more than 6 miles without assistance. After nearly a decade of therapy, there were more severe and life-limiting disease manifestations for Sibling-O; data from caregiver interview indicated substantial differences in Quality of Life for the child and the family, dependent on timing of ERT. The findings from this sibling pair provide evidence of superior somatic and neurocognitive outcomes associated with presymptomatic treatment of Hunter syndrome, aligned with current considerations for newborn screening.

Evaluation of Two Methods for Quantification of Glycosaminoglycan Biomarkers in Newborn Dried Blood Spots from Patients with Severe and Attenuated Mucopolysaccharidosis Type II

All newborn screening (NBS) for mucopolysaccharidosis-I and -II (MPS-I and MPS-II) is carried out via the measurement of α-iduronidase (IDUA) and iduronate-2-sulfatase (IDS) enzymatic activity, respectively, in dried blood spots (DBS). The majority of low enzyme results are due to pseudodeficiencies, and data from recent MPS-II population screenings and studies from the Mayo Clinic show that the false positive rate can be dramatically reduced by the inclusion of a second-tier analysis of glycosaminoglycans (GAGs) in DBS as part of NBS. In the present study, which focused on MPS-II, we obtained newborn DBS from 17 patients with severe MPS-II, 1 with attenuated MPS-II, and 6 patients with various IDS pseudodeficiencies. These samples were submitted to two different GAG mass spectrometry analyses in a comparative study: (1) internal disaccharide biomarkers and (2) endogenous biomarkers. For both of these methods, the biomarker levels in six patients with pseudodeficiencies were below the range measured in MPS-II patients. One patient with attenuated MPS-II was not distinguishable from severe disease patients, but all MPS-II patients were distinguishable from the reference range using both methods. The minimal differential factor (lowest GAG marker level in MPS-II samples divided by highest level in the reference range of 60 random newborns) was 3.01-fold for the internal disaccharide method. The endogenous biomarker method demonstrated an improved minimum differential of 5.41-fold. The minimum differential factors between MPS-II patients and patients with pseudodeficiencies for the internal disaccharide and endogenous biomarker methods were 3.77-fold and 2.06-fold, respectively. This study supports use of the second-tier GAG analysis of newborn DBS, especially the endogenous disaccharide method, as part of NBS to reduce the false positive rate.

Functional assessment of the genetic findings indicating mucopolysaccharidosis type II in the prenatal setting

Mucopolysaccharidosis type II (MPS II) is a multi-systemic disorder arising due to pathogenic variants in the gene located on chromosome Xq28 encoding the lysosomal enzyme, iduronate 2-sulfatase (IDS). The broad clinical heterogeneity of MPS II can be partly ascribed to the high level of molecular diversity in the gene locus with the majority of variants localised within one family. Here, we describe a case of fetal hepatomegaly that was causatively investigated for 151 genes associated with fetal hydrops and lysosomal diseases. Sequence analysis identified a novel hemizygous variant, pAsp532Gly, in exon 9 of the IDS gene. Determination of IDS activity in cultured amniotic fluid cells returned 8% of normal activity and analysis of a second sulfatase was normal, the latter virtually excluding multiple sulfatase deficiency. Together, these data supported a diagnosis of MPS II in the fetus. Additional measurement of a signature disaccharide in the amniotic fluid was normal, conflicting with enzymology indications. The baby was unremarkable at birth and 3 years later shows no clinical suspicion of MPS II, normal urinary disaccharide concentrations, and reduced IDS activity in leukocytes. His 5-year-old brother was subsequently shown to carry the same pAsp532Gly variant, with normal urinary disaccharide concentrations, reduced leukocyte IDS activity and normal phenotype. This case highlights the importance of thorough biochemical investigations, clinical and family correlation in determining the significance of genetic variants in IDS.

The future of newborn screening for lysosomal disorders

The goal of newborn screening is to enhance the outcome of individuals with serious, treatable disorders through early, pre-symptomatic detection. The lysosomal storage disorders (LSDs) comprise a group of more than 50 diseases with a combined frequency of approximately 1:7000. With the availability of existing and new enzyme replacement therapies, small molecule treatments and gene therapies, there is increasing interest in screening newborns for LSDs with the goal of reducing disease-related morbidity and mortality through early detection. Novel screening methods are being developed, including efforts to enhance accuracy of screening using an array of multi-tiered, genomic, statistical, and bioinformatic approaches. While NBS data for Gaucher disease, Fabry disease, Krabbe disease, MPS I, and Pompe disease has demonstrated the feasibility of widespread screening, it has also highlighted some of the complexities of screening for LSDs. These include the identification of infants with later-onset, untreatable, and uncertain phenotypes, raising interesting ethical concerns that should be addressed as part of the NBS implementation process. Taken together, these efforts will provide critical, detailed data to help guide objective, ethically sensitive decision-making about NBS for LSDs.

Neonatal Screening for MPS Disorders in Latin America: A Survey of Pilot Initiatives

Newborn screening enables the diagnosis of treatable disorders at the early stages, and because of its countless benefits, conditions have been continuously added to screening panels, allowing early intervention, aiming for the prevention of irreversible manifestations and even premature death. Mucopolysaccharidoses (MPS) are lysosomal storage disorders than can benefit from an early diagnosis, and thus are being recommended for newborn screening. They are multisystemic progressive disorders, with treatment options already available for several MPS types. MPS I was the first MPS disorder enrolled in the newborn screening (NBS) panel in the USA and a few other countries, and other MPS types are expected to be added. Very few studies about NBS for MPS in Latin America have been published so far. In this review, we report the results of pilot studies performed in Mexico and Brazil using different methodologies: tandem mass spectrometry, molecular analysis, digital microfluidics, and fluorimetry. These experiences are important to report and discuss, as we expect to have several MPS types added to NBS panels shortly. This addition will enable timely diagnosis of MPS, avoiding the long diagnostic odyssey that is part of the current natural history of this group of diseases, and leading to a better outcome for the affected patients.