Different diseases, different needs: Patient preferences for gene therapy in lysosomal storage disorders, a probabilistic threshold technique survey.

BACKGROUND: Gene therapy is currently in development for several monogenetic diseases including lysosomal storage disorders. Limited evidence is available on patient preferences for gene therapy in this population. In this study, we compare gene therapy-related risk tolerance between people affected by three lysosomal storage diseases currently faced with different therapeutic options and prognoses. METHODS: A survey including the probabilistic threshold technique was developed in which respondents were asked to choose between gene therapy and the current standard of care. The attributes included to establish participants' risk tolerance were previously identified in focus groups of affected people or their representatives, namely: risk of mild side effects, severe side effects, the need for additional medication, and the likelihood of long-term effectiveness. The survey was distributed among people receiving outpatient care for type 1 Gaucher disease (good prognosis with current treatment options), Fabry disease (varying prognosis with current treatment options, XY-genotype on average more severely affected than XX), and parents representing people with severe forms of mucopolysaccharidosis type III A/B (poor prognosis, no disease-specific therapy available). RESULTS: A total of 85 surveys were completed (15 Gaucher disease respondents, 62 Fabry disease respondents (17 self-identifying male), eight parents of ten people with mucopolysaccharidosis type III). Disease groups with higher disease severity trended towards higher risk tolerance: Gaucher disease respondents were most cautious and predominantly preferred the current standard of care as opposed to MPS III representatives who were more risk tolerant. Respondents with Fabry disease were most heterogeneous in their risk tolerance, with male participants being more risk tolerant than female participants. Long-term effectiveness was the attribute in which respondents tolerated the least risk. CONCLUSIONS: People affected by a lysosomal storage disease associated with a poorer prognosis and less effective current treatment options trended towards more risk tolerance when choosing between gene therapy and the current standard of care. This study shows the importance of involvement of patient preferences before and during the development process of new treatment modalities such as gene therapy for rare diseases, to ensure that innovative therapies align with the wishes and needs of people affected by these diseases.

Clinical and preclinical insights into high-dose ambroxol therapy for Gaucher disease type 2 and 3: A comprehensive systematic review.

RATIONALE: Gaucher disease (GD), an autosomal recessive lysosomal storage disease, results from GBA1 variants causing glucocerebrosidase (GCase) deficiency. While enzyme replacement therapy (ERT) helps with systemic symptoms, neurological complications in GD2 and GD3 persist due to the blood-brain-barrier (BBB) limiting ERT efficacy. Ambroxol, a BBB-permeable chaperone, enhances GCase activity. Our review explores high-dose ambroxol's therapeutic potential, both preclinical and clinical, in GD2 and GD3. METHODS: PubMed was searched for studies published before March 2023, including clinical, animal, and in vitro studies focusing on the effect of high-dose ambroxol in GD2 and GD3. A narrative synthesis was performed. RESULTS: Nine in vitro, three animal, and eight clinical studies were included, demonstrating varied responses to ambroxol across diverse outcome measures. In vitro and animal studies demonstrated reduced endoplasmatic reticulum stress due to the relocation of GCase from the ER to the lysosomes. In vitro cell lines exhibited varying degrees of increased GCase activity. Clinical trials observed reduced lyso-GL1 levels in plasma (41-89%) and cerebrospinal fluid (CSF) (26-97%), alongside increased GCase activity in GD3 patients. Ambroxol exhibited varying effects on neurological outcomes and development. No severe adverse events were reported. CONCLUSION: High-dose ambroxol shows promise in managing neurological manifestations in GD3, albeit with uncertainties resulting from genetic heterogeneity and variable response. Further clinical trials, are essential for elucidating dosage-response relationships and refining treatment outcomes and strategies for neuronopathic GD.

Natural disease course of chronic visceral acid sphingomyelinase deficiency in adults: A first step toward treatment criteria.

Acid sphingomyelinase deficiency (ASMD) is an ultra-rare lysosomal storage disease with a broad spectrum of manifestations ranging from severe neuropathic forms to attenuated, chronic visceral forms. Manifestations of the chronic visceral subtype are variable and encompass different degrees of hepatosplenomegaly, pulmonary disease and dyslipidemia. The aim of this study was to provide insights into the natural course of adult patients with the chronic visceral subtype. Based on these insights, we proposed tentative criteria for initiation and follow-up of enzyme replacement therapy (ERT). The data of 23 adult patients were collected in a prospective study. Clinical, genetic and demographic data, plasma measurements, abdominal imaging, pulmonary imaging, pulmonary function tests and quality of life questionnaires were collected. Stability of disease based on several clinical, biochemical and radiological markers (i.e., spleen volume, platelet levels, liver volume, alanine aminotransferase [ALT] levels, diffusion capacity of the lungs for carbon monoxide [DLCO] chitotriosidase activity and lysosphingomyelin [LSM]) was assessed. Cardiovascular risk was estimated based on sex, age, smoking, systolic blood pressure and lipid profile. Quality of life was evaluated with the 36-Item Short Form Health Survey and the Health Assessment Questionnaire. Median follow-up was 6.1 years (range 1.3-19.5 years). The most common manifestations were splenomegaly (100%), decreased high-density lipoprotein cholesterol (HDL-C) plasma levels (83%), (signs of) steatosis measured with transient elastography (82%), thrombocytopenia (64%), hepatomegaly (52%) and decreased diffusion capacity (45%). The majority of markers remained stable during follow-up. Twelve patients showed progression of disease: four for spleen volume, two for liver volume, three for DLCO, seven for chitotriosidase activity and three for LSM. One patient showed progression of disease based on four markers, although this patient did not report any problems at the last visit. Cardiovascular risk was estimated and was increased in half of the patients older than 40 years. Patient-reported quality of life did not differ from the general population, but differences in median 36-Item Short Form Health Survey (SF-36) scores of patients with severe pulmonary involvement and those of patients without pulmonary involvement were observed. Tentative criteria for initiation and effect of therapy were proposed. In conclusion, the chronic visceral subtype of ASMD showed a predominantly stable disease course in this cohort. We propose that ERT should be initiated on an individual basis and only in case of progression or symptomatic disease. Collection and analysis of real world data are necessary to refine start, stop and follow-up criteria in the future.

Extending diagnostic practices in gyrate atrophy: Enzymatic characterization and the development of an in vitro pyridoxine responsiveness assay.

Gyrate atrophy of the choroid and retina (GACR) is caused by pathogenic biallelic variants in the gene encoding ornithine-δ-aminotransferase (OAT), and is characterized by progressive vision loss leading to blindness. OAT is a pyridoxal-5'-phosphate (PLP) dependent enzyme that is mainly involved in ornithine catabolism, and patients with a deficiency develop profound hyperornithinemia. Therapy is aimed at lowering ornithine levels through dietary arginine restriction and, in some cases, through enhancement of OAT activity via supraphysiological dosages of pyridoxine. In this study, we aimed to extend diagnostic practices in GACR by extensively characterizing the consequences of pathogenic variants on the enzymatic function of OAT, both at the level of the enzyme itself as well as the flux through the ornithine degradative pathway. In addition, we developed an in vitro pyridoxine responsiveness assay. We identified 14 different pathogenic variants, of which one variant was present in all patients of Dutch ancestry (p.(Gly353Asp)). In most patients the enzymatic activity of OAT as well as the rate of [14C]-ornithine flux was below the limit of quantification (LOQ). Apart from our positive control, only one patient cell line showed responsiveness to pyridoxine in vitro, which is in line with the reported in vivo pyridoxine responsiveness in this patient. None of the patients harboring the p.(Gly353Asp) substitution were responsive to pyridoxine in vivo or in vitro. In silico analysis and small-scale expression experiments showed that this variant causes a folding defect, leading to increased aggregation properties that could not be rescued by PLP. Using these results, we developed a diagnostic pipeline for new patients suspected of having GACR. Adding OAT enzymatic analyses and in vitro pyridoxine responsiveness to diagnostic practices will not only increase knowledge on the consequences of pathogenic variants in OAT, but will also enable expectation management for therapeutic modalities, thus eventually improving clinical care.

A cohort study of 19 patients with gyrate atrophy of the choroid and retina (GACR).

PURPOSE: Gyrate atrophy of the choroid and retina (GACR) is an autosomal recessive inherited metabolic disorder (IMD) characterised by progressive retinal degeneration, leading to severe visual impairment. The rapid developments in ophthalmic genetic therapies warrant knowledge on clinical phenotype of eligible diseases such as GACR to define future therapeutic parameters in clinical trials. METHODS: Retrospective chart analysis was performed in nineteen patients. Data were analysed using IBM SPSS Statistics version 28.0.1.1. RESULTS: Nineteen patients were included with a mean age of 32.6 years (range 8-58). Mean age at onset of ophthalmic symptoms was 7.9 years (range 3-16). Median logMAR of visual acuity at inclusion was 0.26 (range -0.18-3.00). Mean age at cataract surgery was 28.8 years (n = 11 patients). Mean spherical equivalent of the refractive error was -8.96 (range -20.87 to -2.25). Cystoid maculopathy was present in 68% of patients, with a loss of integrity of the foveal ellipsoid zone (EZ) in 24/38 eyes. Of the 14 patients treated with dietary protein restriction, the four patients who started the diet before age 10 showed most benefit. CONCLUSION: This study demonstrates the severe ophthalmic disease course associated with GACR, as well as possible benefit of early dietary treatment. In addition to visual loss, patients experience severe myopia, early-onset cataract, and CME. There is a loss of foveal EZ integrity at a young age, emphasising the need for early diagnosis enabling current and future therapeutic interventions.

Navigating the outcome maze: a scoping review of outcomes and instruments in clinical trials in genetic neurodevelopmental disorders and intellectual disability.

Background: Individuals with genetic neurodevelopmental disorders (GNDs) or intellectual disability (ID) are often affected by complex neuropsychiatric comorbidities. Targeted treatments are increasingly available, but due to the heterogeneity of these patient populations, choosing a key outcome and corresponding outcome measurement instrument remains challenging. Objectives: The aim of this scoping review was to describe the research on outcomes and instruments used in clinical trials in GNDs and ID. Eligibility criteria: Clinical trials in individuals with GNDs and ID for any intervention over the past 10 years were included in the review. Sources of evidence: MEDLINE, PsycINFO, and Cochrane CENTRAL were searched. Titles and abstracts were independently screened for eligibility with a subsample of 10% double-screening for interrater reliability. Data from full texts were independently reviewed. Discrepancies were discussed until consensus was reached. Charting methods: Information was recorded on patient populations, interventions, designs, outcomes, measurement instruments, and type of reporter when applicable. Qualitative and descriptive analyses were performed. Results: We included 312 studies reporting 91 different outcomes, with cognitive function most frequently measured (28%). Various outcome measurement instruments (n = 457) were used, with 288 in only a single clinical trial. There were 18 genetic condition-specific instruments and 16 measures were designed ad-hoc for one particular trial. Types of report included proxy-report (39%), self-report (22%), clinician-report (16%), observer-report (6%), self-assisted report (1%), or unknown (16%). Conclusion: This scoping review of current practice reveals a myriad of outcomes and outcome measurement instruments for clinical trials in GNDs and ID. This complicates generalization, evidence synthesis, and evaluation. It underlines the need for consensus on suitability, validity, and relevancy of instruments, ultimately resulting in a core outcome set. A series of steps is proposed to move from the myriad of measures to a more unified approach.

Navigating the maze of outcome measures in rare disorders Treatments for genetic neurodevelopmental disorders and intellectual disability are increasingly available. However, it is hard to find appropriate instruments to measure whether these treatments are working. This hampers research and means some patients might not get the treatment they need. This scoping review provides an overview of investigated outcomes in this group, and with which instruments these are measured. It reveals that many different and overlapping outcomes are measured, complicating gathering, combining, and comparing of evidence. This scoping review underlines the need for harmonization and consensus on suitability, validity, and relevancy. Steps are proposed to move from the maze of outcome measures to a unified approach. Also, we provided recommendations for researchers to measure what matters to affected individuals and patient-centered care.

Platelet proteomic profiling in sitosterolemia suggests thrombocytopenia is driven by lipid disorder and not platelet aberrations.

ABSTRACT: Sitosterolemia is a rare autosomal recessive genetic disorder in which patients develop hypercholesterolemia and may exhibit abnormal hematologic and/or liver test results. In this disease, dysfunction of either ABCG5 or ABCG8 results in the intestinal hyperabsorption of all sterols, including cholesterol and, more specifically, plant sterols or xenosterols, as well as in the impaired ability to excrete xenosterols into the bile. It remains unknown how and why some patients develop hematologic abnormalities. Only a few unrelated patients with hematologic abnormalities at the time of diagnosis have been reported. Here, we report on 2 unrelated pedigrees who were believed to have chronic immune thrombocytopenia as their most prominent feature. Both consanguineous families showed recessive gene variants in ABCG5, which were associated with the disease by in silico protein structure analysis and clinical segregation. Hepatosplenomegaly was absent. Thrombopoietin levels and megakaryocyte numbers in the bone marrow were normal. Metabolic analysis confirmed the presence of strongly elevated plasma levels of xenosterols. Potential platelet proteomic aberrations were longitudinally assessed following dietary restrictions combined with administration of the sterol absorption inhibitor ezetimibe. No significant effects on platelet protein content before and after the onset of treatment were demonstrated. Although we cannot exclude that lipotoxicity has a direct and platelet-specific impact in patients with sitosterolemia, our data suggest that thrombocytopenia is neither caused by a lack of megakaryocytes nor driven by proteomic aberrations in the platelets themselves.

Corrigendum to "Effectiveness of L-serine supplementation in children with a GRIN2B loss-of-function mutation: Rationale and protocol for single patient (n-of-1) multiple cross-over trials" [Contemp. Clin. Trials Commun. 36 (2023)/ DOI: 10.1016/j.conctc.2023.101233].

[This corrects the article DOI: 10.1016/j.conctc.2023.101233.].

Breaking the chains of lipoprotein lipase deficiency: A pediatric perspective on the efficacy and safety of Volanesorsen.

RATIONALE: Lipoprotein lipase (LPL) deficiency, a rare inherited metabolic disorder, is characterized by high triglyceride (TG) levels and life-threatening acute pancreatitis. Current treatment for pediatric patients involves a lifelong severely fat-restricted diet, posing adherence challenges. Volanesorsen, an EMA-approved RNA therapy for adults, effectively reduces TG levels by decreasing the production of apolipoprotein C-III. This 96-week observational open-label study explores Volanesorsen's safety and efficacy in a 13-year-old female with LPL deficiency. METHODS: The patient, with a history of severe TG elevations, 53 hospital admissions, and life-threatening recurrent pancreatitis despite dietary restrictions, received weekly subcutaneous Volanesorsen injections. We designed a protocol for this investigator-initiated study, primarily focusing on changes in fasting TG levels and hospital admissions. RESULTS: While the injections caused occasional pain and swelling, no other adverse events were observed. TG levels decreased during treatment, with more measurements below the pancreatitis risk threshold compared to pre-treatment. No hospital admissions occurred in the initial 14 months of treatment, contrasting with 21 admissions in the 96 weeks before. In the past 10 months, two pancreatitis episodes may have been linked to dietary noncompliance. Dietary restrictions were relaxed, increasing fat intake by 65% compared to baseline. While not fully reflected in the PedsQL, both parents and the patient narratively reported an improved quality of life. CONCLUSION: This study demonstrates, for the first time, that Volanesorsen is tolerated in a pediatric patient with severe LPL deficiency and effectively lowers TG levels, preventing life-threatening complications. This warrants consideration for expanded access in this population.

Vision on gyrate atrophy: why treat the eye?

In the April issue of this Journal, Boffa and coworkers put forward a new therapeutic approach for Gyrate Atrophy of the Choroid and Retina (GACR; OMIM 258870) (Boffa et al, 2023). The authors propose to apply gene therapy to the liver for GACR, a metabolic disease primarily affecting eyesight due to retinal degeneration. Their vision is enthusiastically supported by a News and Views comment in the same issue (Seker Yilmaz and Gissen, 2023). However, based on disease pathology, patient's needs, ethical considerations, therapeutic developmental time lines, and current state of the art of gene therapy for liver and eye, we have a different view on this issue: We argue below that local treatment of the eye is the preferred option for GACR.

Effectiveness of L-serine supplementation in children with a GRIN2B loss-of-function mutation: Rationale and protocol for single patient (n-of-1) multiple cross-over trials.

Rationale: Loss-of-function (LoF) mutations in GRIN2B result in neurologic abnormalities due to N-methyl-D-aspartate receptor (NMDAR) dysfunction. Affected persons present with various symptoms, including intellectual developmental disability (IDD), hypotonia, communication deficits, motor impairment, complex behavior, seizures, sleep disorders and gastrointestinal disturbance. Recently, in vitro experiments showed that D-serine mitigates function to GluN2B (mutation)-containing NMDARs. 11 previous case reports are published on (experimental) L-serine treatment of patients between 1.5 and 12 years old with GRIN2B missense or null mutations, some of whom showed notable improvement in motor and cognitive performance, communication, behavior and abnormalities on electro encephalography (EEG). Our objective is to further evaluate the effectiveness of L-serine for GRIN2B-related neurodevelopmental disorder (GRIN2B-NDD), using an n-of-1 trial design, increasing the level of evidence. Methods/design: These n-of-1 trials, consisting of 2 cycles of 6 months, will be performed to evaluate the effect of L-serine compared to placebo in 4 patients with a GRIN2B LoF mutation. The aggregation of multiple n-of-1 trials will provide an estimate of the average treatment effects.The primary outcome is the Perceive-Recall-Plan-Perform of Task Analysis, assessing developmental skills. Secondary outcomes include Goal Attainment Scaling, seizure log books, EEGs, sleep log books, the irritability subscale of the Aberrant Behavior Checklist, the Bristol Stool Scale and the Pediatric Quality of Life Inventory. Conclusion: This study employs an innovative methodological approach to evaluate the effectiveness of L-serine for patients with a GRIN2B LoF mutation. The results will establish a foundation for implementing L-serine as a disease-modifying treatment in GRIN2B-NDD.

A Delphi Survey Study to Formulate Statements on the Treatability of Inherited Metabolic Disorders to Decide on Eligibility for Newborn Screening.

The Wilson and Jungner (W&J) and Andermann criteria are meant to help select diseases eligible for population-based screening. With the introduction of next-generation sequencing (NGS) methods for newborn screening (NBS), more inherited metabolic diseases (IMDs) can technically be included, and a revision of the criteria was attempted. This study aimed to formulate statements and investigate whether those statements could elaborate on the criterion of treatability for IMDs to decide on eligibility for NBS. An online Delphi study was started among a panel of Dutch IMD experts (EPs). EPs evaluated, amended, and approved statements on treatability that were subsequently applied to 10 IMDs. After two rounds of Delphi, consensus was reached on 10 statements. Application of these statements selected 5 out of 10 IMDs proposed for this study as eligible for NBS, including 3 IMDs in the current Dutch NBS. The statement: 'The expected benefit/burden ratio of early treatment is positive and results in a significant health outcome' contributed most to decision-making. Our Delphi study resulted in 10 statements that can help to decide on eligibility for inclusion in NBS based on treatability, also showing that other criteria could be handled in a comparable way. Validation of the statements is required before these can be applied as guidance to authorities.

Early Risk Stratification for Natural Disease Course in Fabry Patients Using Plasma Globotriaosylsphingosine Levels.

BACKGROUND: Fabry disease is a very heterogeneous X-linked lysosomal storage disease. Disease manifestations in the kidneys, heart, and brain vary greatly, even between patients of the same sex and with the same disease classification (classical or nonclassical). A biomarker with a strong association with the development of disease manifestations is needed to determine the need for Fabry-specific treatment and appropriate frequency of follow-up because clinical manifestations of the disorder may take decennia to develop. METHODS: We investigated the levels of plasma lysoGb3 levels over time and its association with disease manifestations and disease course in 237 untreated patients with Fabry disease (median age 42 years, 38% male) using linear mixed-effect models. RESULTS: LysoGb3 levels are stable over time in plasma of untreated patients with Fabry disease. Higher levels of lysoGb3 were associated with steeper decline in eGFR ( P = 0.05) and a faster increase in albuminuria (measured as the urinary albumin-to-creatinine ratio, P < 0.001), left ventricular mass (measured on echocardiography, P < 0.001), left atrial volume index ( P = 0.003), and Fazekas score ( P = 0.003). In addition, regardless of age, higher lysoGb3 levels were associated with higher relative wall thickness ( P < 0.001) and unfavorable functional markers on echocardiography, including septal mitral annular early diastolic velocity (e', P < 0.001) and the ratio of early transmitral velocity (E) to e' (E/e', P = 0.001). CONCLUSIONS: In an individual patient with Fabry disease, the plasma lysoGb3 level reached a specific level in early childhood which, in the absence of Fabry-specific treatment, remained stable throughout life. The level of lysoGb3 in untreated patients was associated with nearly all Fabry-specific disease manifestations, regardless of the sex of the patient.

Glycoprotein non-metastatic protein B (GPNMB) plasma values in patients with chronic visceral acid sphingomyelinase deficiency.

Acid sphingomyelinase deficiency (ASMD) is a rare LSD characterized by lysosomal accumulation of sphingomyelin, primarily in macrophages. With the recent availability of enzyme replacement therapy, the need for biomarkers to assess severity of disease has increased. Glycoprotein non-metastatic protein B (GPNMB) plasma levels were demonstrated to be elevated in Gaucher disease. Given the similarities between Gaucher disease and ASMD, the hypothesis was that GPNMB might be a potential biochemical marker for ASMD as well. Plasma samples of ASMD patients were analyzed and GPNMB plasma levels were compared to those of healthy volunteers. Visceral disease severity was classified as severe when splenic, hepatic and pulmonary manifestations were all present and as mild to moderate if this was not the case. Median GPNMB levels in 67 samples of 19 ASMD patients were 185 ng/ml (range 70-811 ng/ml) and were increased compared to 10 healthy controls (median 36 ng/ml, range 9-175 ng/ml, p < 0.001). Median plasma GPNMB levels of ASMD patients with mild to moderate visceral disease compared to patients with severe visceral disease differed significantly and did not overlap (respectively 109 ng/ml, range 70-304 ng/ml and 325 ng/ml, range 165-811 ng/ml, p < 0.001). Correlations with other biochemical markers of ASMD (i.e. chitotriosidase activity, CCL18 and lysosphingomyelin, respectively R = 0.28, p = 0.270; R = 0.34, p = 0.180; R = 0.39, p = 0.100) and clinical parameters (i.e. spleen volume, liver volume, diffusion capacity and forced vital capacity, respectively R = 0.59, p = 0.061, R = 0.5, p = 0.100, R = 0.065, p = 0.810, R = -0.38, p = 0.160) could not be established within this study. The results of this study suggest that GPNMB might be suitable as a biomarker of visceral disease severity in ASMD. Correlations between GPNMB and biochemical or clinical markers of ASMD and response to therapy have to be studied in a larger cohort.

Oral sialic acid supplementation in NANS-CDG: Results of a single center, open-label, observational pilot study.

NANS-CDG is a congenital disorder of glycosylation (CDG) caused by biallelic variants in NANS, encoding an essential enzyme in de novo sialic acid synthesis. It presents with intellectual developmental disorder (IDD), skeletal dysplasia, neurologic impairment, and gastrointestinal dysfunction. Some patients suffer progressive intellectual neurologic deterioration (PIND), emphasizing the need for a therapy. In a previous study, sialic acid supplementation in knockout nansa zebrafish partially rescued skeletal abnormalities. Here, we performed the first in-human pre- and postnatal sialic-acid study in NANS-CDG. In this open-label observational study, 5 patients with NANS-CDG (range 0-28 years) were treated with oral sialic acid for 15 months. The primary outcome was safety. Secondary outcomes were psychomotor/cognitive testing, height and weight, seizure control, bone health, gastrointestinal symptoms, and biochemical and hematological parameters. Sialic acid was well tolerated. In postnatally treated patients, there was no significant improvement. For the prenatally treated patient, psychomotor and neurologic development was better than two other genotypically identical patients (one treated postnatally, one untreated). The effect of sialic acid treatment may depend on the timing, with prenatal treatment potentially benefiting neurodevelopmental outcomes. Evidence is limited, however, and longer-term follow-up in a larger number of prenatally treated patients is required.

Patients' view on gene therapy development for lysosomal storage disorders: a qualitative study.

INTRODUCTION: Several new treatment modalities are being developed for lysosomal storage disorders (LSDs), including gene therapy. As the currently available treatment options and their influence on disease progression differ greatly within the spectrum of LSDs, willingness to undergo gene therapy might vary among patients with LSDs and/or their representatives. The width of the LSD spectrum is illustrated by the differences between type 1 Gaucher disease, Fabry disease and Mucopolysaccharidosis type III (MPS III). For type 1 Gaucher and Fabry disease several therapies are available, resulting in a near normal or improved, but individually varying, prognosis. No treatment options are available for MPS III. AIM: To identify factors influencing patients' and/or their representatives' decisions regarding undergoing gene therapy. METHODS: Focus group discussions and semi-structured interviews were conducted with patients with type 1 Gaucher disease, Fabry disease and MPS III. Parents of MPS III patients were included as patients' representatives. RESULTS: Nine Gaucher patients, 23 Fabry patients, two adult MPS III patients and five parents of MPS III patients participated in the study. The five main themes that arose were: outcome of gene therapy, risks and side effects, burden of gene therapy treatment, current situation and ethical aspects. Participants' views ranged from hesitance to eagerness to undergo gene therapy, which seemed to be mostly related to disease severity and currently available treatment options. Severe disease, limited treatment options and limited effectiveness of current treatment augmented the willingness to choose gene therapy. Gaucher and Fabry patients deemed the burden of treatment important. Fabry and MPS III patients and parents considered outcome important, suggesting hope for improvement. When asked to rank the factors discussed in the focus group discussions, Gaucher patients ranked outcome low, which could indicate a more cautious attitude towards gene therapy. CONCLUSION: This study underlines the importance of exploring patients' needs and expectations before using limited resources in the development of therapies for patient groups of which a significant subset may not be willing to undergo that specific therapy.

A review of treatment modalities in gyrate atrophy of the choroid and retina (GACR).

Gyrate atrophy of the choroid and retina (GACR) is a rare inborn error of amino acid metabolism caused by bi-allelic variations in OAT. GACR is characterised by vision decline in early life eventually leading to complete blindness, and high plasma ornithine levels. There is no curative treatment for GACR, although several therapeutic modalities aim to slow progression of the disease by targeting different steps within the ornithine pathway. No international treatment protocol is available. We systematically collected all international literature on therapeutic interventions in GACR to provide an overview of published treatment effects. METHODS: Following the PRISMA guidelines, we conducted a systematic review of the English literature until December 22nd 2020. PubMed and Embase databases were searched for studies related to therapeutic interventions in patients with GACR. RESULTS: A total of 33 studies (n = 107 patients) met the inclusion criteria. Most studies were designed as case reports (n = 27) or case series (n = 4). No randomised controlled trials or large cohort studies were found. Treatments applied were protein-restricted diets, pyridoxine supplementation, creatine or creatine precursor supplementation, l-lysine supplementation, and proline supplementation. Protein-restricted diets lowered ornithine levels ranging from 16.0-91.2%. Pyridoxine responsiveness was reported in 30% of included mutations. Lysine supplementation decreased ornithine levels with 21-34%. Quality assessment showed low to moderate quality of the articles. CONCLUSIONS: Based primarily on case reports ornithine levels can be reduced by using a protein restricted diet, pyridoxine supplementation (variation-dependent) and/or lysine supplementation. The lack of pre-defined clinical outcome measures and structural follow-up in all included studies impeded conclusions on clinical effectiveness. Future research should be aimed at 1) Unravelling the OAT biochemical pathway to identify other possible pathologic metabolites besides ornithine, 2) Pre-defining GACR specific clinical outcome measures, and 3) Establishing an international historical cohort.

NANS-CDG: Delineation of the Genetic, Biochemical, and Clinical Spectrum.

Background: NANS-CDG is a recently described congenital disorder of glycosylation caused by biallelic genetic variants in NANS, encoding an essential enzyme in de novo sialic acid synthesis. Sialic acid at the end of glycoconjugates plays a key role in biological processes such as brain and skeletal development. Here, we present an observational cohort study to delineate the genetic, biochemical, and clinical phenotype and assess possible correlations. Methods: Medical and laboratory records were reviewed with retrospective extraction and analysis of genetic, biochemical, and clinical data (2016-2020). Results: Nine NANS-CDG patients (nine families, six countries) referred to the Radboudumc CDG Center of Expertise were included. Phenotyping confirmed the hallmark features including intellectual developmental disorder (IDD) (n = 9/9; 100%), facial dysmorphisms (n = 9/9; 100%), neurologic impairment (n = 9/9; 100%), short stature (n = 8/9; 89%), skeletal dysplasia (n = 8/9; 89%), and short limbs (n = 8/9; 89%). Newly identified features include ophthalmological abnormalities (n = 6/9; 67%), an abnormal septum pellucidum (n = 6/9; 67%), (progressive) cerebral atrophy and ventricular dilatation (n = 5/9; 56%), gastrointestinal dysfunction (n = 5/9; 56%), thrombocytopenia (n = 5/9; 56%), and hypo-low-density lipoprotein cholesterol (n = 4/9; 44%). Biochemically, elevated urinary excretion of N-acetylmannosamine (ManNAc) is pathognomonic, the concentrations of which show a significant correlation with clinical severity. Genotypically, eight novel NANS variants were identified. Three severely affected patients harbored identical compound heterozygous pathogenic variants, one of whom was initiated on experimental prenatal and postnatal treatment with oral sialic acid. This patient showed markedly better psychomotor development than the other two genotypically identical males. Conclusions: ManNAc screening should be considered in all patients with IDD, short stature with short limbs, facial dysmorphisms, neurologic impairment, and an abnormal septum pellucidum +/- congenital and neurodegenerative lesions on brain imaging, to establish a precise diagnosis and contribute to prognostication. Personalized management includes accurate genetic counseling and access to proper supports and tailored care for gastrointestinal symptoms, thrombocytopenia, and epilepsy, as well as rehabilitation services for cognitive and physical impairments. Motivated by the short-term positive effects of experimental treatment with oral sialic, we have initiated this intervention with protocolized follow-up of neurologic, systemic, and growth outcomes in four patients. Research is ongoing to unravel pathophysiology and identify novel therapeutic targets.

Systematic Review of N-of-1 Studies in Rare Genetic Neurodevelopmental Disorders: The Power of 1.

OBJECTIVE: To improve the use of N-of-1 studies in rare genetic neurodevelopmental disorders, we systematically reviewed the literature and formulated recommendations for future studies. METHODS: The systematic review protocol was registered in the PROSPERO International Prospective Register of Systematic Reviews (CRD42020154720). EMBASE and MEDLINE were searched for relevant studies. Information was recorded on types of interventions, outcome measures, validity, strengths, and limitations using standard reporting guidelines and critical appraisal tools. Qualitative and descriptive analyses were performed. RESULTS: Twelve studies met the N-of-1 inclusion criteria, including both single trials and series. Interventions were mainly directed to neuropsychiatric manifestations. Main strengths were the use of personalized and clinically relevant outcomes in most studies. Generalizability was compromised due to limited use of validated and generalizable outcome measures. CONCLUSION: N-of-1 studies are sporadically reported in rare genetic neurodevelopmental disorders. Properly executed N-of-1 studies may provide a powerful alternative to larger randomized controlled trials in rare disorders and a much needed bridge between practice and science. We provide recommendations for future N-of-1 studies in rare genetic neurodevelopmental disorders, ultimately optimizing evidence-based and personalized care.

Long-term cognitive follow-up in children treated for Maroteaux-Lamy syndrome.

BACKGROUND: It remains unclear to what extent the brain is affected by Maroteaux-Lamy syndrome (MPS VI), a progressive lysosomal storage disorder. While enzyme replacement therapy (ERT) elicits positive effects, the drug cannot cross the blood-brain barrier. We therefore studied cognitive development and brain abnormalities in the Dutch MPS VI patient population treated with ERT. METHODS: In a series of 11 children with MPS VI (age 2 to 20 years), we assessed cognitive functioning and brain magnetic resonance imaging prospectively at the start of ERT and at regular times thereafter up to 4.8 years. We also assessed the children's clinical characteristics, their siblings' cognitive development, and their parents' educational levels. RESULTS: The patients' intelligence scores ranged from normal to mentally delayed (range test scores 52-131). In 90%, their scores remained fairly stable during follow-up, generally lying in the same range as their siblings' test scores (median for patients = 104, median for siblings = 88) and comparing well with the parental educational levels. Native-speaking patients had higher intelligence test scores than non-native-speaking patients. Two patients, both with high baseline glycosaminoglycan levels in their urine and severe mutations in the arylsulfatase B gene, scored clearly lower than expected. Patients with pY210C performed best. Brain abnormalities were aspecific, occurring more in patients with severe symptoms. CONCLUSION: Our study shows that cognitive development in MPS VI patients is determined not only by familial and social-background factors, but, in patients with a severe form of the disease, also by the disease itself. Therefore in patients with severe disease presentation cognition should be monitored carefully.