Fayuvi (rebisufligene etisparvovec-hopf/UX111) for MPS IIIA: AAV9 SGSH Gene Therapy, Cognition, and Safety

　　1.Disease and Unmet Need

　　Mucopolysaccharidosis IIIA(MPS IIIA,Sanfilippo syndrome type A)is an autosomal-recessive lysosomal storage disorder caused by SGSH mutations and sulfamidase deficiency.Heparan sulfate accumulates in brain and somatic tissues,producing language delay,hyperactivity,sleep disturbance,cognitive and language regression,motor decline,and sometimes seizures.Skeletal changes are usually milder than in other MPS types,but neurodegenerative burden is severe.Before Fayuvi,care was supportive—seizure control,behavior,rehabilitation,nutrition;no disease-modifying drug was approved in the United States for this indication.

　　2.Drug and Mechanism

　　Fayuvi(generic name rebisufligene etisparvovec-hopf;code UX111)is developed by Ultragenyx.It uses a modified,non-pathogenic AAV9 vector for a single intravenous infusion of functional human SGSH.Transduced cells express sulfamidase,restore lysosomal degradation of heparan sulfate,and reduce central and peripheral substrate accumulation.It is gene replacement,not enzyme infusion:one administration seeks durable expression,while AAV mostly remains episisomal but carries potential genomic-integration and long-term risks requiring follow-up.

　　3.Indication and Center Criteria

　　The FDA granted standard full approval on 17 September 2026 for pediatric MPS IIIA patients with preserved neurodevelopment.Practical selection:

　　Confirm biallelic SGSH pathogenic variants and sulfamidase deficiency or abnormal heparan sulfate metabolism;

　　Prefer early disease and retained cognition;the key Transpher A efficacy group used 3.0×10¹³vg/kg in patients≤2 years or>2 years with cognitive developmental quotient≥60;

　　Treat only at centers experienced in AAV infusion reactions,steroid prophylaxis,laboratory monitoring,and long-term follow-up;

　　Do not use as reversal therapy for advanced irreversible neurodegenereneration;do not replace antiepileptic,rehabilitative,behavioral,or nutritional care.

　　Baseline anti-AAV9 neutralizing antibodies can reduce transduction;the treatment center should interpret titers against the current prescribing information rather than a single home test.

　　4.Dosing and Follow-up

　　Dose:3.0×10¹³viral genomes/kg by single intravenous infusion over about 1 hour.

　　Steroids:start one day before infusion and continue at least 8 weeks after,then taper by liver tests,inflammatory markers,and clinical response to reduce vector-related hepatitis and immune reactions.

　　Setting:hospital or gene-therapy center with capacity for infusion reactions,anaphylaxis,hepatotoxicity,cytopenias,and TMA.

　　Monitoring:baseline LFTs,CBC with differential and platelets,amylase/lipase,renal function,electrolytes,coagulation,urinalysis/proteinuria,anti-AAV9 antibodies,SGSH/heparan-sulfate biomarkers;frequent LFTs and blood counts early after infusion,then extended intervals;long-term cognition,development,seizures,growth/nutrition,and oncology/integration surveillance.

　　Symptomatic care continues:antiepileptic drugs,sleep/behavior programs,physical/occupational/speech therapy;gene therapy does not mean stopping all supportive treatment.

　　5.Key Clinical Data

　　The core evidence is Transpher A(NCT02716246),an open-label,single-arm,multicenter study,plus long-term follow-up(NCT04360265).Efficacy used preserved-neurodevelopment patients at the recommended dose,comparing Bayley-III cognitive raw scores with untreated natural-history external controls:

　　Early/2–5-year groups showed slower cognitive decline and,in parts of the population,maintained or improved scores;published summaries report treatment effects around 22.7–23.5 points versus natural history,with differences by cohort matching;

　　CSF heparan sulfate fell substantially,with reported median reduction about 66%in some analyses and≥50%in most patients during long-term follow-up,correlating with cognitive preservation;

　　Median follow-up about 4.2 years and最长near 8 years support durable biomarker response;

　　Natural history shows stagnation/regression in the same age band;Fayuvi may improve milestones but does not guarantee normal language,motor function,or life span.

　　6.Safety

　　Common adverse events(>5%):AST increase,nausea/vomiting,fever,decreased appetite,leukopenia,thrombocytopenia,amylase increase.Management:

　　Hepatotoxicity/vector hepatitis:monitor ALT,AST,total bilirubin,INR;significant transaminase rise with bilirubin abnormality warrants drug-induced liver injury workup and steroid/immunosuppression adjustment.

　　Cytopenias:serial CBC;clinically important leukocyte/neutrophil or platelet drops require infection/bleeding evaluation.

　　Fever,vomiting,anorexia:rule out infection and dehydration;treat as infusion reaction and metabolic disturbance.

　　Pancreatitis signal:amylase/lipase rise with abdominal pain or persistent vomiting needs pancreatitis evaluation.

　　Thrombotic microangiopathy(TMA):labeled risk—anemia,thrombocytopenia,schistocytes,elevated LDH,falling hemoglobin/platelets,renal dysfunction,proteinuria/hematuria;suspend relevant immune loading and manage with nephrology,hematology,and gene-therapy team.

　　Long-term risk:potential AAV genomic integration and late tumor risk;follow the center’s multi-year surveillance plan even if short-term labs normalize.

　　7.Concise Parent FAQ

　　Q1 Best age?Earlier and with preserved cognition gives more benefit;advanced regression limits expected gain and needs multidisciplinary review.

　　Q2 One infusion forever?It is one-time dosing,not guaranteed cure;continue biomarker,cognitive,seizure,and organ follow-up.

　　Q3 Steroids after infusion?Start one day before and at least 8 weeks after per protocol;taper only under the gene-therapy team.

　　Q4 Epilepsy and gene therapy?Allowed,but antiepileptics continue;fever,hyponatremia,or metabolic shifts around infusion can trigger seizures.

　　Q5 Most serious safety issues?Marked transaminase rise,significant cytopenia,TMA,persistent vomiting with high amylase;return to the treatment center immediately for any of these.