Community consensus for Heparan sulfate as a biomarker to support accelerated approval in Neuronopathic Mucopolysaccharidoses.

Mucopolysaccharidoses (MPS) disorders are a group of ultra-rare, inherited, lysosomal storage diseases caused by enzyme deficiencies that result in accumulation of glycosaminoglycans (GAGs) in cells throughout the body including the brain, typically leading to early death. Current treatments do not address the progressive cognitive impairment observed in patients with neuronopathic MPS disease. The rarity and clinical heterogeneity of these disorders as well as pre-existing brain disease in clinically diagnosed patients make the development of new therapeutics utilizing a traditional regulatory framework extremely challenging. Children with neuronopathic MPS disorders will likely sustain irreversible brain damage if randomized to a placebo or standard-of-care treatment arm that does not address brain disease. The United States Food and Drug Administration (FDA) recognized these challenges, and, in 2020, issued final guidance for industry on slowly progressive, low-prevalence, rare diseases with substrate deposition that result from single enzyme defects, outlining a path for generating evidence of effectiveness to support accelerated approval based on reduction of substrate accumulation [1]. Neuronopathic MPS disorders, which are characterized by the accumulation of the GAG heparan sulfate (HS) in the brain, fit the intended disease characteristics for which this guidance was written, but to date, this guidance has not yet been applied to any therapeutic candidate for MPS. In February 2024, the Reagan-Udall Foundation for the FDA convened a public workshop for representatives from the FDA, patient advocacy groups, clinical and basic science research, and industry to explore a case study of using cerebrospinal fluid (CSF) HS as a relevant biomarker to support accelerated approval of new therapeutics for neuronopathic MPS disorders. This review provides a summary of the MPS presentations at the workshop and perspective on the path forward for neuronopathic MPS disorders.

First-in-human in vivo genome editing via AAV-zinc-finger nucleases for mucopolysaccharidosis I/II and hemophilia B.

Zinc-finger nuclease (ZFN)-based in vivo genome editing is a novel treatment that can potentially provide lifelong protein replacement with single intravenous administration. Three first-in-human open-label ascending single-dose phase 1/2 studies were performed in parallel (starting November 2017) primarily to assess safety and tolerability of ZFN in vivo editing therapy in mucopolysaccharidosis I (MPS I) (n = 3), MPS II (n = 9), and hemophilia B (n = 1). Treatment was well tolerated with no serious treatment-related adverse events. At the 1e13 vg/kg dose, evidence of genome editing was detected through albumin-transgene fusion transcripts in liver for MPS II (n = 2) and MPS I (n = 1) subjects. The MPS I subject also had a transient increase in leukocyte iduronidase activity to the lower normal range. At the 5e13 vg/kg dose, one MPS II subject had a transient increase in plasma iduronate-2-sulfatase approaching normal levels and one MPS I subject approached mid-normal levels of leukocyte iduronidase activity with no evidence of genome editing. The hemophilia B subject was not able to decrease use of factor IX concentrate; genome editing could not be assessed. Overall, ZFN in vivo editing therapy had a favorable safety profile with evidence of targeted genome editing in liver, but no long-term enzyme expression in blood.

Long-term open-label phase I/II extension study of intrathecal idursulfase-IT in the treatment of neuronopathic mucopolysaccharidosis II.

PURPOSE: Intrathecal (IT) idursulfase-IT for the treatment of cognitive impairment is being investigated in pediatric patients with neuronopathic mucopolysaccharidosis II (MPS II) in addition to intravenous idursulfase. In this article, we report the findings for 54 months of idursulfase-IT treatment in an ongoing phase I/II extension trial (NCT01506141). METHODS: A total of 15 male participants with neuronopathic MPS II (aged 3-11 years at enrollment) who were previously treated with intravenous idursulfase entered the extension study. Idursulfase-IT 10 mg or 30 mg was administered monthly via an IT drug delivery device or lumbar puncture, if indicated. The primary endpoint was safety and tolerability; secondary endpoints included pharmacokinetics, cerebrospinal fluid glycosaminoglycan levels, and cognitive function. RESULTS: In total, 15 participants received a median (range) of 50 (18-55) idursulfase-IT doses. Idursulfase-IT was generally well tolerated; there were no life-threatening adverse events (AEs) or deaths. Most serious AEs were related to the IT drug delivery device; only 2 serious AEs were related solely to idursulfase-IT. After treatment with idursulfase-IT, cerebrospinal fluid glycosaminoglycans were decreased in all participants; these decreases were maintained. Cognitive function was stabilized in 3 of 4 testable participants at month 55. CONCLUSION: These long-term results support the clinical development of idursulfase-IT for patients with MPS II with cognitive impairment.

Chemically modified recombinant human sulfamidase (SOBI003) in mucopolysaccharidosis IIIA patients: Results from an open, non-controlled, multicenter study.

PURPOSE: Mucopolysaccharidosis IIIA (MPS IIIA) is an inherited lysosomal storage disorder caused by mutations in the N-sulfoglucosamine sulfohydrolase gene that result in deficient enzymatic degradation of heparan sulfate (HS), resulting in progressive neurodegeneration in early childhood and premature death. A chemically modified variant of recombinant human sulfamidase, SOBI003, has shown to cross the blood-brain barrier (BBB) in mice and achieve pharmacologically relevant levels in cerebrospinal fluid (CSF). We report on a phase 1/2, open-label, first-in-human (FIH) study (NCT03423186) and its extension study (NCT03811028) to evaluate the long-term safety, tolerability, pharmacokinetics/pharmacodynamics (PK/PD) and clinical efficacy of SOBI003 in patients with MPS IIIA for up to 104 weeks. METHODS: Six patients aged 1-6 years with confirmed MPS IIIA with developmental age ≥ 12 months received weekly intravenous injections of SOBI003 at 3 mg/kg (Cohort 1, n = 3) or 10 mg/kg (Cohort 2, n = 3). During the extension study, the individual dose of SOBI003 could be adjusted up to 20 mg/kg at the discretion of the investigator. RESULTS: SOBI003 was generally well tolerated. Serum concentrations of SOBI003 increased in proportion to dose, and presence in CSF confirmed that SOBI003 crosses the BBB. Anti-drug antibodies (ADA) were detected in serum and CSF in all patients, with subsequent reductions in serum SOBI003 exposure at high ADA titers. SOBI003 exerted a clear PD effect: a mean reduction in HS levels in CSF of 79% was recorded at the last assessment, together with reductions in HS levels in serum and urine. Neurocognitive development age-equivalent scores showed a stabilization of cognition for all patients, whereas no clear overall clinical effect was observed on adaptive behavior, sleep pattern or quality of life. CONCLUSION: SOBI003 was well tolerated when administered as weekly intravenous infusions at doses of up to 20 mg/kg for up to 104 weeks. ADA development was common and likely affected both PK and PD parameters. SOBI003 crossed the BBB and showed pharmacological activity on HS in CSF.

Intrathecal idursulfase-IT in patients with neuronopathic mucopolysaccharidosis II: Results from a phase 2/3 randomized study.

Two-thirds of patients with mucopolysaccharidosis II (MPS II; Hunter syndrome) have cognitive impairment. This phase 2/3, randomized, controlled, open-label, multicenter study (NCT02055118) investigated the effects of intrathecally administered idursulfase-IT on cognitive function in patients with MPS II. Children older than 3 years with MPS II and mild-to-moderate cognitive impairment (assessed by Differential Ability Scales-II [DAS-II], General Conceptual Ability [GCA] score) who had tolerated intravenous idursulfase for at least 4 months were randomly assigned (2:1) to monthly idursulfase-IT 10 mg (n = 34) via an intrathecal drug delivery device (IDDD; or by lumbar puncture) or no idursulfase-IT treatment (n = 15) for 52 weeks. All patients continued to receive weekly intravenous idursulfase 0.5 mg/kg as standard of care. Of 49 randomized patients, 47 completed the study (two patients receiving idursulfase-IT discontinued). The primary endpoint (change from baseline in DAS-II GCA score at week 52 in a linear mixed-effects model for repeated measures analysis) was not met: although there was a smaller decrease in DAS-II GCA scores with idursulfase-IT than with no idursulfase-IT at week 52, this was not significant (least-squares mean treatment difference [95% confidence interval], 3.0 [-7.3, 13.3]; p = 0.5669). Changes from baseline in Vineland Adaptive Behavioral Scales-II Adaptive Behavior Composite scores at week 52 (key secondary endpoint) were similar in the idursulfase-IT (n = 31) and no idursulfase-IT (n = 14) groups. There were trends towards a potential positive effect of idursulfase-IT across DAS-II composite, cluster, and subtest scores, notably in patients younger than 6 years at baseline. In a post hoc analysis, there was a significant (p = 0.0174), clinically meaningful difference in change from baseline in DAS-II GCA scores at week 52 with idursulfase-IT (n = 13) versus no idursulfase-IT (n = 6) among those younger than 6 years with missense iduronate-2-sulfatase gene variants. Overall, idursulfase-IT reduced cerebrospinal glycosaminoglycan levels from baseline by 72.0% at week 52. Idursulfase-IT was generally well tolerated. These data suggest potential benefits of idursulfase-IT in the treatment of cognitive impairment in some patients with neuronopathic MPS II. After many years of extensive review and regulatory discussions, the data were found to be insufficient to meet the evidentiary standard to support regulatory filings.

Long-term open-label extension study of the safety and efficacy of intrathecal idursulfase-IT in patients with neuronopathic mucopolysaccharidosis II.

Enzyme replacement therapy with weekly infused intravenous (IV) idursulfase is effective in treating somatic symptoms of mucopolysaccharidosis II (MPS II; Hunter syndrome). A formulation of idursulfase for intrathecal administration (idursulfase-IT) is under investigation for the treatment of neuronopathic MPS II. Here, we report 36-month data from the open-label extension (NCT02412787) of a phase 2/3, randomized, controlled study (HGT-HIT-094; NCT02055118) that assessed the safety and efficacy of monthly idursulfase-IT 10 mg in addition to weekly IV idursulfase on cognitive function in children older than 3 years with MPS II and mild-to-moderate cognitive impairment. Participants were also enrolled in this extension from a linked non-randomized sub-study of children younger than 3 years at the start of idursulfase-IT therapy. The extension safety population comprised 56 patients who received idursulfase-IT 10 mg once a month (or age-adjusted dose for sub-study patients) plus IV idursulfase (0.5 mg/kg) once a week. Idursulfase-IT was generally well tolerated over the cumulative treatment period of up to 36 months. Overall, 25.0% of patients had at least one adverse event (AE) related to idursulfase-IT; most treatment-emergent AEs were mild in severity. Of serious AEs (reported by 76.8% patients), none were considered related to idursulfase-IT treatment. There were no deaths or discontinuations owing to AEs. Secondary efficacy analyses (in patients younger than 6 years at phase 2/3 study baseline; n = 40) indicated a trend for improved Differential Ability Scale-II (DAS-II) General Conceptual Ability (GCA) scores in the early idursulfase-IT versus delayed idursulfase-IT group (treatment difference over 36 months from phase 2/3 study baseline: least-squares mean, 6.8 [90% confidence interval: -2.1, 15.8; p = 0.2064]). Post hoc analyses of DAS-II GCA scores by genotype revealed a clinically meaningful treatment effect in patients younger than 6 years with missense variants of the iduronate-2-sulfatase gene (IDS) (least-squares mean [standard error] treatment difference over 36 months, 12.3 [7.24]). These long-term data further suggest the benefits of idursulfase-IT in the treatment of neurocognitive dysfunction in some patients with MPS II. After many years of extensive review and regulatory discussions, the data were found to be insufficient to meet the evidentiary standard to support regulatory filings.

Growth in individuals with attenuated mucopolysaccharidosis type I during untreated and treated periods: Data from the MPS I registry.

Mucopolysaccharidosis Type I (MPS I) is caused by deficiency of α-L-iduronidase. Short stature and growth deceleration are common in individuals with the attenuated MPS I phenotype. Study objectives were to assess growth in individuals with attenuated MPS I enrolled in The MPS I Registry while untreated and after initiation of enzyme replacement therapy (ERT) with laronidase (recombinant human iduronidase). Individuals in the MPS I Registry with at least one observation for height and assigned attenuated MPS I phenotype as of September 2020 were included. The cohort included 142 males and 153 females 2-18 years of age. Age and sex adjusted standardized height-for-age z-scores during the natural history and ERT-treatment periods were assessed using linear mixed model repeated measures analyses. Growth curves were estimated during both periods and compared to standard growth charts from the Center for Disease Control (CDC). There was a significantly slower decline in height z-scores with age during the ERT-treated period compared to the natural history period. Estimated average height z-scores in the ERT-treatment versus the natural history period at age 10 were -2.4 versus -3.3 in females and -1.4 versus -2.9 in males (females first treated 3 year; males <4.1 year). While median height remained below CDC standards during both the natural history and ERT-treated periods for individuals with attenuated MPS I, laronidase ERT was associated with slower declines in height z-scores.

A multicenter open-label extension study of intrathecal heparan-N-sulfatase in patients with Sanfilippo syndrome type A.

Sanfilippo syndrome type A (mucopolysaccharidosis type IIIA) is a rare autosomal recessive lysosomal disorder characterized by deficient heparan-N-sulfatase (HNS) activity, and subsequent accumulation of heparan sulfate, especially in the central nervous system. The disease is associated with progressive neurodegeneration in early childhood. For this open-label extension study of a phase 2b clinical trial, we report on safety and cognitive decline in patients receiving intrathecal (IT) administration of recombinant human HNS (rhHNS). Of 21 patients who completed the phase 2b study, 17 continued in the open-label extension. Patients receiving rhHNS IT 45 mg continued to receive the same treatment regimen (i.e., every 2 weeks or every 4 weeks) throughout the extension. Patients receiving no treatment in the phase 2b study were re-randomized to the treatment groups. Neurocognition was assessed using the Bayley Scales of Infant and Toddler Development®, Third Edition (BSID-III). Adverse events were recorded over the duration of the treatment period. Cognitive decline was observed in most patients in both treatment groups; however, improvements in BSID-III development quotient score were observed for two patients, in receptive and expressive communication scores for three patients each, in fine motor skills for one patient, and in gross motor skills for six patients. Treatment-emergent adverse events that occurred with rhHNS IT were mostly mild, none led to study discontinuation, and there were no deaths. The extension study was terminated early as the primary endpoints of the phase 2b study were not met, and no statistical analyses were carried out. Although cognitive decline was apparent in most patients, improvements were observed in a small group of patients. Greater declines were observed in patients at the higher end of the age range, suggesting earlier intervention may increase the possibility of a response to treatment. rhHNS IT treatment remained generally well tolerated up to 96 weeks.

Therapy development for the mucopolysaccharidoses: Updated consensus recommendations for neuropsychological endpoints.

Neurological dysfunction represents a significant clinical component of many of the mucopolysaccharidoses (also known as MPS disorders). The accurate and consistent assessment of neuropsychological function is essential to gain a greater understanding of the precise natural history of these conditions and to design effective clinical trials to evaluate the impact of therapies on the brain. In 2017, an International MPS Consensus Panel published recommendations for best practice in the design and conduct of clinical studies investigating the effects of therapies on cognitive function and adaptive behavior in patients with neuronopathic mucopolysaccharidoses. Based on an International MPS Consensus Conference held in February 2020, this article provides updated consensus recommendations and expands the objectives to include approaches for assessing behavioral and social-emotional state, caregiver burden and quality of life in patients with all mucopolysaccharidoses.

Intrathecal heparan-N-sulfatase in patients with Sanfilippo syndrome type A: A phase IIb randomized trial.

BACKGROUND: Sanfilippo syndrome type A (mucopolysaccharidosis type IIIA) is a lysosomal disorder wherein deficient heparan-N-sulfatase (HNS) activity results in the accumulation of heparan sulfate in the central nervous system and is associated with progressive neurodegeneration in early childhood. We report on the efficacy, pharmacokinetics, safety, and tolerability of intrathecal (IT) administration of recombinant human HNS (rhHNS) from a phase IIb randomized open-label trial. METHODS: Twenty-one patients, randomized 1:1:1 to rhHNS IT 45 mg administered every 2 weeks (Q2W), every 4 weeks (Q4W), or no treatment, were assessed for amelioration in neurocognitive decline as determined by the Bayley Scales of Infant and Toddler Development®, Third Edition. The primary efficacy goal was defined as ≤10-point decline (responder) in at least three patients in a dosing cohort after 48 weeks. Other efficacy assessments included adaptive behavioral function, assessments of cortical gray matter volume, and glycosaminoglycan (GAG) levels in urine. RESULTS: A clinical response to rhHNS IT was observed in three treated patients (two in the Q2W group, one in the Q4W group). Cerebrospinal fluid heparan sulfate and urine GAG levels were reduced in all treated patients. However, most secondary efficacy assessments were similar between treated patients (n = 14; age, 17.8-47.8 months) and untreated controls (n = 7; age, 12.6-45.0 months). Treatment-emergent adverse events that occurred with rhHNS IT were mostly mild, none led to study discontinuation, and there were no deaths. CONCLUSION: rhHNS IT treatment reduced heparan sulfate and GAG levels in treated patients. Though the primary neurocognitive endpoint was not met, important lessons in the design and endpoints for evaluation of cognitive and behavioral diseases resulted. TRIAL REGISTRATION: ClinicalTrials.govNCT02060526; EudraCT 2013-003450-24.

The North Carolina Experience with Mucopolysaccharidosis Type I Newborn Screening.

OBJECTIVE: To evaluate the performance of a 2-tiered newborn screening method for mucopolysaccharidosis type I (MPS I) in North Carolina. STUDY DESIGN: The screening algorithm included a flow injection analysis-tandem mass spectrometry assay as a first-tier screening method to measure α-L-iduronidase (IDUA) enzyme activity and Sanger sequencing of the IDUA gene on dried blood spots as a second-tier assay. The screening algorithm was revised to incorporate the Collaborative Laboratory Integrated Reports, an analytical interpretive tool, to reduce the false-positive rate. A medical history, physical examination, IDUA activity, and urinary glycosaminoglycan (GAG) analysis were obtained on all screen-positive infants. RESULTS: A total of 62 734 specimens were screened with 54 screen-positive samples using a cut-off of 15% of daily mean IDUA activity. The implementation of Collaborative Laboratory Integrated Reports reduced the number of specimens that screened positive to 19 infants. Of the infants identified as screen-positive, 1 had elevated urinary GAGs and a homozygous pathogenic variant associated with the severe form of MPS I. All other screen-positive infants had normal urinary GAG analysis; 13 newborns had pseudodeficiency alleles, 3 newborns had variants of unknown significance, and 2 had heterozygous pathogenic variants. CONCLUSIONS: An infant with severe MPS I was identified and referred for a hematopoietic stem cell transplant. Newborn IDUA enzyme deficiency is common in North Carolina, but most are due to pseudodeficiency alleles in infants with normal urinary GAG analysis and no evidence of disease. The pilot study confirmed the need for second-tier testing to reduce the follow-up burden.

Genotype-phenotype relationships in mucopolysaccharidosis type I (MPS I): Insights from the International MPS I Registry.

Mucopolysaccharidosis type I (MPS I) is a rare autosomal recessive disorder resulting from pathogenic variants in the α-L-iduronidase (IDUA) gene. Clinical phenotypes range from severe (Hurler syndrome) to attenuated (Hurler-Scheie and Scheie syndromes) and vary in age of onset, severity, and rate of progression. Defining the phenotype at diagnosis is essential for disease management. To date, no systematic analysis of genotype-phenotype correlation in large MPS I cohorts have been performed. Understanding genotype-phenotype is critical now that newborn screening for MPS I is being implemented. Data from 538 patients from the MPS I Registry (380 severe, 158 attenuated) who had 2 IDUA alleles identified were examined. In the 1076 alleles identified, 148 pathogenic variants were reported; of those, 75 were unique. Of the 538 genotypes, 147 (27%) were unique; 40% of patients with attenuated and 22% of patients with severe MPS I had unique genotypes. About 67.6% of severe patients had genotypes where both variants identified are predicted to severely disrupt protein/gene function and 96.1% of attenuated patients had at least one missense or intronic variant. This dataset illustrates a close genotype/phenotype correlation in MPS I but the presence of unique IDUA missense variants remains a challenge for disease prediction.

Growth patterns for untreated individuals with MPS I: Report from the international MPS I registry.

Mucopolysaccharidosis Type I (MPS I), caused by deficiency of α-L-iduronidase results in progressive, multisystemic disease with a broad phenotypic spectrum including patients with severe (Hurler syndrome) to attenuated (Hurler-Scheie and Scheie syndromes) disease. Disordered growth is common with either phenotype. The study objectives were to construct sex- and age-specific estimated length/height and head circumference growth curves for untreated individuals with severe and attenuated disease and compare them with clinical reference standards. Untreated individuals in the MPS I Registry with at least one observation for length/height and/or head circumference and assigned phenotype as of May 2017 were included. Median growth for 463 untreated individuals with severe disease deviated from reference growth curves by ~6 months of age and fell below the third percentile by 4 years of age. Median head circumference was above reference curves from 3 to 4 months through 3 years of age. Among 207 individuals with untreated attenuated disease, median height fell below the third percentile by 9 years of age with divergence from reference curves by 2 years of age. MPS I-specific growth curves will be useful in evaluation of long-term outcomes of therapeutics interventions and will provide a foundation for understanding the pathogenesis of skeletal disease in MPS I.

Cognitive endpoints for therapy development for neuronopathic mucopolysaccharidoses: Results of a consensus procedure.

The design and conduct of clinical studies to evaluate the effects of novel therapies on central nervous system manifestations in children with neuronopathic mucopolysaccharidoses is challenging. Owing to the rarity of these disorders, multinational studies are often needed to recruit enough patients to provide meaningful data and statistical power. This can make the consistent collection of reliable data across study sites difficult. To address these challenges, an International MPS Consensus Conference for Cognitive Endpoints was convened to discuss approaches for evaluating cognitive and adaptive function in patients with mucopolysaccharidoses. The goal was to develop a consensus on best practice for the design and conduct of clinical studies investigating novel therapies for these conditions, with particular focus on the most appropriate outcome measures for cognitive function and adaptive behavior. The outcomes from the consensus panel discussion are reported here.

Co-occurring Down syndrome and SUCLA2-related mitochondrial depletion syndrome.

Mitochondrial DNA depletion syndrome 5 (MIM 612073) is a rare autosomal recessive disorder caused by homozygous or compound heterozygous pathogenic variants in the beta subunit of the succinate-CoA ligase gene located within the 13q14 band. We describe two siblings of Hispanic descent with SUCLA2-related mitochondrial depletion syndrome (encephalomyopathic form with methylmalonic aciduria); the older sibling is additionally affected with trisomy 21. SUCLA2 sequencing identified homozygous p.Arg284Cys pathogenic variants in both patients. This mutation has previously been identified in four individuals of Italian and Caucasian descent. The older sibling with concomitant disease has a more severe phenotype than what is typically described in patients with either SUCLA2-related mitochondrial depletion syndrome or Down syndrome alone. The younger sibling, who has a normal female chromosome complement, is significantly less affected compared to her brother. While the clinical and molecular findings have been reported in about 50 patients affected with a deficiency of succinate-CoA ligase caused by pathogenic variants in SUCLA2, this report describes the first known individual affected with both a mitochondrial depletion syndrome and trisomy 21.

Carpal tunnel syndrome in mucopolysaccharidosis I: a registry-based cohort study.

AIM: To characterize carpal tunnel syndrome (CTS) in patients with mucopolysaccharidosis I (MPS I). METHOD: Data were included for patients with MPS I who had either nerve conduction examination that included a diagnosis of CTS or who had CTS release surgery. Although this represented a subset of patients with CTS in the MPS I Registry, the criteria were considered the most objective for data analysis. RESULTS: As of March 2016, 994 patients were categorized with either severe (Hurler syndrome) or attenuated (Hurler-Scheie or Scheie syndromes) MPS I. Among these, 291 had a CTS diagnosis based on abnormal nerve conduction (n=54) or release surgery (n=237). Median ages (minimum, maximum) at first CTS diagnosis were 5 years 2 months (10mo, 16y 2mo) and 9y 11mo (1y 8mo, 44y 1mo) for patients with severe and attenuated MPS I respectively. Most patients had their first CTS diagnosis after MPS I diagnosis (94%) and treatment (hematopoietic stem cell transplant and/or enzyme replacement therapy) (74%). For 11% of patients with attenuated disease, CTS diagnosis preceded MPS I diagnosis by a mean of 7 years 6 months. INTERPRETATION: CTS is a rare complication in pediatric patients and should alert medical care providers to the potential diagnosis of MPS I. Significant delays exist between diagnosis of CTS and MPS I for patients with attenuated disease. WHAT THIS PAPER ADDS: There are significant delays in diagnosing carpal tunnel syndrome (CTS) in patients with mucopolysaccharidosis I (MPS I). Enzyme replacement therapy or hematopoietic stem cell transplant do not prevent the development of CTS. Testing for CTS in patients with MPS I is recommended to prevent irreparable damage. CTS in pediatric patients should alert physicians to potential diagnosis of MPS I.

Inborn Error of Cobalamin Metabolism Associated with the Intracellular Accumulation of Transcobalamin-Bound Cobalamin and Mutations in ZNF143, Which Codes for a Transcriptional Activator.

Vitamin B12 (cobalamin, Cbl) cofactors adenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl) are required for the activity of the enzymes methylmalonyl-CoA mutase (MCM) and methionine synthase (MS). Inborn errors of Cbl metabolism are rare Mendelian disorders associated with hematological and neurological manifestations, and elevations of methylmalonic acid and/or homocysteine in the blood and urine. We describe a patient whose fibroblasts had decreased functional activity of MCM and MS and decreased synthesis of AdoCbl and MeCbl (3.4% and 1.0% of cellular Cbl, respectively). The defect in cultured patient fibroblasts complemented those from all known complementation groups. Patient cells accumulated transcobalamin-bound-Cbl, a complex which usually dissociates in the lysosome to release free Cbl. Whole-exome sequencing identified putative disease-causing variants c.851T>G (p.L284*) and c.1019C>T (p.T340I) in transcription factor ZNF143. Proximity biotinylation analysis confirmed the interaction between ZNF143 and HCFC1, a protein that regulates expression of the Cbl trafficking enzyme MMACHC. qRT-PCR analysis revealed low MMACHC expression levels both in patient fibroblasts, and in control fibroblasts incubated with ZNF143 siRNA.

A phase I/II study of intrathecal idursulfase-IT in children with severe mucopolysaccharidosis II.

PURPOSE: Approximately two-thirds of patients with the lysosomal storage disease mucopolysaccharidosis II have progressive cognitive impairment. Intravenous (i.v.) enzyme replacement therapy does not affect cognitive impairment because recombinant iduronate-2-sulfatase (idursulfase) does not penetrate the blood-brain barrier at therapeutic concentrations. We examined the safety of idursulfase formulated for intrathecal administration (idursulfase-IT) via intrathecal drug delivery device (IDDD). A secondary endpoint was change in concentration of glycosaminoglycans in cerebrospinal fluid. METHODS: Sixteen cognitively impaired males with mucopolysaccharidosis II who were previously treated with weekly i.v. idursulfase 0.5 mg/kg for ≥6 months were enrolled. Patients were randomized to no treatment or 10-mg, 30-mg, or 1-mg idursulfase-IT monthly for 6 months (four patients per group) while continuing i.v. idursulfase weekly. RESULTS: No serious adverse events related to idursulfase-IT were observed. Surgical revision/removal of the IDDD was required in 6 of 12 patients. Twelve total doses were administrated by lumbar puncture. Mean cerebrospinal fluid glycosaminoglycan concentration was reduced by approximately 90% in the 10-mg and 30-mg groups and approximately 80% in the 1-mg group after 6 months. CONCLUSIONS: These preliminary data support further development of investigational idursulfase-IT in MPS II patients with the severe phenotype who have progressed only to a mild-to-moderate level of cognitive impairment.Genet Med 18 1, 73-81.