Background: Mucopolysaccharidosis type IIIC (MPS IIIC) is a rare lysosomal storage disorder caused by pathogenic variants in the HGSNAT gene. Data from large patient cohorts remain scarce, particularly in Latin America. Methods: We retrospectively analyzed clinical, biochemical, and genetic data from patients diagnosed with MPS IIIC through the MPS Brazil Network. Diagnosis was based on reduced activity of acetyl-CoA:α-glucosaminide N-acetyltransferase (HGSNAT), elevated urinary glycosaminoglycans (uGAGs), and/or molecular genetics tests. Results: A total of 101 patients were confirmed with MPS IIIC, representing one of the largest cohorts worldwide. Females accounted for 60% of cases. The mean age at symptom onset was 5.4 ± 3.9 years, while the mean age at diagnosis was 11.7 ± 6.9 years, reflecting a 6-year diagnostic delay. Most patients initially presented with developmental delay (82%) and facial dysmorphism (80%), whereas behavioral manifestations were less frequently identified (25%), suggesting a milder phenotype than previously reported. Genetic information was available for 28% of patients, showing recurrent alleles (c.372-2A>G, c.252dupT) and several novel mutations, which expand the mutational spectrum of the disease. Genotype–phenotype similarities with Portuguese, Italian, and Chinese cases suggest shared ancestry contributions. Regional differences included earlier diagnoses in the North of Brazil and high consanguinity rates in the Northeast region. Conclusions: This study describes the largest Brazilian cohort of MPS IIIC, documenting novel variants and regional heterogeneity. Findings highlight diagnostic delays, ancestry influences, and the urgent need for disease-modifying therapies.

Hunter syndrome, also known as mucopolysaccharidosis type II, is an X-linked lysosomal storage disease caused by the deficiency of functional iduronate-2-sulfatase (I2S) enzyme, leading to the accumulation of lysosomal glycosaminoglycans (GAGs) affecting multiple organs. Two-thirds of patients have central nervous system (CNS) manifestations. The current standard of care, enzyme replacement therapy (ERT) via weekly intravenous delivery of recombinant human I2S (rhI2S), does not address the neuropathy in the CNS due to its inability to cross the blood-brain barrier (BBB). Next-generation ERTs consisting of systemically administered rhI2S linked to antibodies that target the transferrin receptor (TfR) have shown clinical efficacy in addressing CNS and peripheral manifestations of disease. We demonstrate here that systemic administration of recombinant AAV9 gene therapy vectors encoding human I2S fusion protein with a TfR1-targeted Variable Heavy chain domain of Heavy chain (VHH) nanobody at the N-terminus normalized brain and cerebrospinal fluid GAGs in symptomatic Ids knockout (Ids KO) mice. This ability to correct toxic substrate accumulation in the CNS was superior to gene therapy vectors expressing I2S with a C-terminal VHH tag or untagged I2S control. The VHH-I2S transgene product demonstrated a broader distribution in the brain parenchyma, coincident with a significant reduction of lysosomal-associated membrane protein 1 immunoreactivity, unlike untagged I2S and I2S-VHH transgene products. These data illuminate strategies to enhance AAV gene therapy vector design and leverage receptor-mediated transcytosis to strategize BBB-penetrating gene therapy for addressing the unmet medical needs of neuronopathic Hunter syndrome.

Mucopolysaccharidoses: A biochemical study under limited resources

Glycosaminoglycans (GAGs), also named 'mucopolysaccharides', are nodal constituents of the connective tissue matrix which go through synthesis, demolition, and reconstruction within several cellular structures: an abnormal GAG catabolism is the basis of progressive intra-lysosomal accumulation of non-metabolized GAGs, defining all mucopolysaccharidoses (MPS), protean disorders characterized by physical abnormalities and multi-organ failure depending on the specific site of non-renewable GAGs stored. A severe cognitive decline is typically observed in the Sanfilippo syndrome, which corresponds to MPS type III, a group of four inherited neurodegenerative diseases resulting from the lack of specific enzymes involved in heparan sulfate (HS) metabolism. As a consequence, the storage of partially degraded HS fragments within lysosomes of the central nervous system elicits chain inflammatory reactions involving the NLRP3-inflammasome in microglia and astrocytes, which cease their homeostatic and immune functions and finally compromise neuron survival. This article provides an overview of the neuroinflammatory picture observed in children with MPS type III, postulating a role of HS accumulation to prime innate immunity responses which culminate with pro-inflammatory cytokine release in the brain and highlighting the relevance of interleukin-1 as a main contributor to neuroinflammation.

IntroductionSanfilippo syndrome is a rare disease and fatal genetic disorder with no FDA-approved treatment in the United States (US), and no comprehensive assessment of economic disease burden is available.ObjectivesTo develop a model to project the economic burden associated with Sanfilippo syndrome in the US using direct costs, indirect costs and valued intangibles (disability-adjusted life years, or DALYs) from 2023 onward.Design and settingA multistage comorbidity model was generated based on Sanfilippo syndrome symptoms, and disability weights from the 2010 Global Burden of Disease Study. Attributable increase in caregiver mental health burden was estimated using data from the CDC National Comorbidity Survey and retrospective studies on caregiver burden. Direct costs were approximated from the 2019 EveryLife Foundation survey, and indirect costs were estimated from Federal income data. Monetary valuations were adjusted to USD 2023 and given a 3% discount rate from 2023 onward.Main outcome measuresIncidence of Sanfilippo syndrome was calculated for each age group in each year, and year-over-year DALYs due to patient years lived with disability (YLDs) and years life lost (YLLs) were calculated by comparing to the health-adjusted life expectancy (HALE) in the US.ResultsFrom 2023 to 2043, overall economic burden in the US attributable to Sanfilippo syndrome was estimated to be $2.19 billion USD present value (2023) with current standard of care. The burden to individual families exceeded millions of dollars in present value from time of birth per child born with Sanfilippo syndrome.ConclusionSanfilippo syndrome is a rare lysosomal storage disease, however the severe burden associated with the disease for individual families suggests a possible cumulative impact. Our model represents the first disease burden value estimate associated with Sanfilippo syndrome, and underscores the substantial morbidity and mortality burden of Sanfilippo syndrome.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13690-025-01733-x.

Limited or absent genetic counseling and testing resources in low- and medium-income countries lead to missed or late diagnoses for treatable metabolic conditions with irreversible complications. In some communities, misunderstanding about the etiology of a genetic condition may lead women whose children are affected to be viewed as a bad omen and become stigmatized or ostracized from their community. Mucopolysaccharidosis type II (MPS II), or Hunter syndrome, is a lysosomal storage disorder in which deficiency or inactivity of the enzyme iduronate-2-sulfatase leads to accumulation of glycosaminoglycans throughout the body. The diagnosis can be made through clinical assessment, enzyme activity analysis, or DNA sequencing. Treatment requires a multidisciplinary approach combining supportive care with disease-modifying therapies, including enzyme replacement therapy where available. To understand the incidence and impact of MPS II in Kenya, we sought to provide counseling and genetic testing to individuals and families with suspected MPS II. After pretest counseling, we collected blood from 25 individuals to determine iduronate-2-sulfatase levels and sequence the IDS gene. We identified a pathogenic or likely pathogenic variant in 17 of 25 individuals and subsequently identified 18 female carriers in these families. We catalog the genotype of males with MPS II and correlate this with the phenotypic profile of these individuals, the female carrier rate, and mortality within the families. This study provides the first summary of genotype-phenotype correlations for MPS II in individuals from Kenya. These findings will allow the development of guidelines to identify individuals who may benefit from early evaluation, especially in those families where there is a risk of MPS II.

Mucopolysaccharidosis type II or Hunter's syndrome is a rare, X-linked genetic lysosomal storage disorder, which results in multiorgan dysfunction and accumulation of glycosaminoglycans in various tissues, including the airway. Because of this, airway management in these patients has been a challenge among anaesthesiologists. In this report, we describe an awake tracheal intubation of a preadolescent-aged child with Hunter's syndrome scheduled for ventriculoperitoneal shunt insertion. The preservation of ventilatory drive and airway tone, combined with continuous passive oxygen supplementation during airway manipulation, allowed for safe use of advanced airway techniques in an anticipated difficult paediatric airway. Moreover, understanding of the full range of issues surrounding the condition helped mitigate complications and successfully deliver anaesthesia for the patient.

Bow Hunter's Syndrome (BHS) is a rare cause of vertebrobasilar insufficiency that results from dynamic mechanical compression of the vertebral artery, typically at the V2 segment as it traverses the cervical transverse foramina. While classically unilateral, bilateral BHS is exceedingly rare and may present as posterior circulation ischemia due to compounded hemodynamic compromise or thromboembolism. We present the case of a 71‐year‐old man with a history of rheumatoid arthritis (RA) on chronic prednisone, and recent presumed diagnosis of cerebral vasculitis because of bilateral vertebral artery occlusions noted on CT angiography (CTA), for which he was started on Rituximab, who presented with acute‐onset dizziness. Neurological examination revealed binocular diplopia, left‐beating nystagmus on leftward gaze, and torsional nystagmus on upward gaze.Non‐contrast head CT was unremarkable, and CTA of the head and neck demonstrated bilateral V1 vertebral artery occlusions of undetermined age with distal reconstitution at the mid V2 segments. MRI of the brain revealed acute infarctions involving the left cerebellum and thalamus. Given the patient's presumed diagnosis of vasculitis, lumbar puncture was performed and showed elevated protein levels without evidence of pleocytosis. Digital subtraction angiography (DSA) revealed preserved anterograde flow with the head straight and bilateral dynamic occlusion of the V2 vertebral artery segments with head turning at the C6 spinal level associated with severe cervical spondylosis ‐ consistent with a diagnosis of bilateral BHS. Robust collateral flow via bilateral posterior communicating arteries (PComs) was noted with head turning, presuming reversal of direction of blood flow in the basilar artery. Cervical spine MRI confirmed multilevel spondylitic changes with the most severe stenosis at C5‐C6 and C6‐C7 levels, related to his RA diagnosis.The stroke mechanism was thromboembolic, either from transient stagnation caused by retrograde basilar artery filling via PComs during head turning or embolism from the proximal vertebral artery stump, resulting in infarction of the posterior inferior cerebellar artery (PICA) and left thalamo‐geniculate artery territories. Robust collateralization argues against vertebrobasilar hypoperfusion as a possible mechanism. The patient was switched from aspirin to apixaban for secondary prevention, and he has since been managed conservatively under neurosurgical observation and has had no recurrent vascular events over a four‐month follow‐up.Our case illustrates the diagnostic value of dynamic DSA in capturing position‐dependent vertebral artery occlusion. The presence of robust collaterals may mask symptoms until collateral flow becomes insufficient to maintain adequate perfusion, or thromboembolism occurs, as seen in this patient. Conservative management with antithrombotic or anticoagulants and avoidance of provocative neck movements may be sufficient in select cases, though surgicaldecompression or endovascular vessel sacrifice is considered in refractory or high‐risk patients. Given the bilateral nature and embolic stroke in this case, long‐term follow‐up is warranted to monitor for recurrence or need for surgical intervention.

Introduction Rotational occlusion of the vertebral artery, known as Bow Hunter's Syndrome, is a rare but recognized cause of transient neurological symptoms due to dynamic vascular compression during head rotation. While typically associated with positional vertigo or dizziness, it can occasionally lead to vertebrobasilar ischemia and infarction. We present 2 unique cases of recurrent posterior circulation strokes due to compression of the same vertebral artery segment, highlighting the diagnostic importance of dynamic vascular imaging. Case Description: Case 1 A female in her 50s with ADHD, chronic migraines, and cervical spine pathology (status post C3‐T2 posterior fusion and C4‐C7 anterior discectomy) presented with sudden‐onset headache, blurry vision, and dizziness. CTA showed occlusion of the right vertebral artery at C3‐C4 with distal reconstitution, initially interpreted as chronic. MRI revealed bilateral cerebellar infarcts, right > left. RCVS was considered given Vyvanse use, but DSA showed no vasospasm, and the artery had spontaneously recanalized. Further workup revealed a PFO and positive JAK2 mutation. She underwent PFO closure and was discharged on aspirin. Six months later, she re‐presented with left facial droop, left‐sided weakness, and right gaze preference. She received TNK and was admitted. MRI showed multifocal infarcts in the right > left cerebellum, right thalamus, and midbrain. MRA showed recanalization of the right vertebral artery with features suggestive of intramural hematoma consistent with dissection. Repeat DSA with head maneuvers demonstrated dynamic, flow‐limiting stenosis of the right V3 segment, worsened with leftward and upward head positioning. Imaging identified a chronic odontoid fracture with posterior displacement. Neurosurgery deferred intervention, opting for follow‐up after healing of the dissection. The patient was managed conservatively with dual antiplatelet therapy, neck bracing, and avoidance of provocative neck movements. Case 2 A female in her 70s with hyperlipidemia, hypothyroidism, and diabetes mellitus established care in 2023. She reported episodic dizziness since a presumed TIA in 2021. In 2022, she had an acute left cerebellar and occipital infarct, plus chronic infarcts in the left PICA territory and anterior circulation. Imaging revealed a hypoplastic left vertebral artery with compression at the V2 segment. A loop recorder remained unremarkable. In July 2024, she developed new subacute bilateral occipital infarcts. CTA showed persistent occlusion of the left V3 segment. Given recurrent strokes without cardioembolic source, antiplatelet therapy was switched to anticoagulation. Follow‐up CTA after two months showed spontaneous recanalization, raising concern for intermittent compression. DSA with head positioning revealed positional occlusion of the left vertebral artery at C3 transverse foramen when the head was neutral or turned left, and reconstitution with the head turned right. She underwent C2‐C5 laminectomy and posterior cervical fusion. Discussion In patients with recurrent posterior strokes and spontaneous vertebral artery recanalization, dissection should be suspected. DSA with provocative maneuvers is critical to identify dynamic compression and delineate the injury mechanism. No consensus on optimal management. Both DAPT and anticoagulation are used, often guided by protocols, patient‐specific factors, and recurrence risk. These cases underscore the importance of recognizing cervical pathology as a precipitant of dynamic vascular injury.

Evaluation and follow-up of newborns screening positive for mucopolysaccharidosis II: Results from an international modified Delphi consensus.

Lysosomal storage disorders (LSDs) such as Sanfilippo syndrome (Mucopolysaccharidosis type III) are characterized by impaired lysosomal degradation due to inherited in lysosomal proteins. This dysfunction leads to the accumulation of undegraded substrates, such as heparan sulfate, ultimately leading to progressive neuroinflammation and neurodegeneration. Despite well-defined genetic causes, no disease-modifying therapies exist for Sanfilippo syndrome. While microglia, the brain's resident immune cells, can play both protective and pathogenic roles, the contribution of neuroinflammation to LSD pathology remains underexplored. This review examines the contribution of neuroinflammation to Sanfilippo syndrome, emphasizing emerging mechanisms involving TLR4 signaling, inflammasome activation, the cGAS-STING pathway, and lysosomal biogenesis regulators such as TFE family transcription factors. We also discuss the potential of cellular therapies to modulate neuroimmune responses and offer new therapeutic avenues. By integrating insights from neuroimmunology and lysosomal biology, we aim to identify shared mechanisms and therapeutic targets across Sanfilippo syndrome and related LSDs.

Natural history, clinical symptoms, and cognitive development of Japanese patients with mucopolysaccharidosis III

Lysosomal storage diseases (LSDs) are a group of genetically heterogeneous inherited metabolic disorders that affect the functions of the lysosomes in different human tissues. Mucopolysaccharidosis IIIB (MPS IIIB), Sanfilippo B syndrome, is an autosomal recessive LSD characterized by a deficiency of the lysosomal enzyme α-N-acetylglucosaminidase. This study aims to investigate the molecular genetic spectrum of α-N-acetyl-glucosaminidase (NAGLU) variants, as well as their biochemical and clinical characteristics, in a cohort of MPS IIIB Egyptian patients. This study aims to expand the characterization of biochemical and molecular spectrum profiles of MPSIIIB in Egyptian patients since this monogenic disease seems commonly encountered in our population. A cohort of eleven children from unrelated Egyptian families, clinically and biochemically diagnosed with MPS IIIB based on heparan sulphate accumulation, were enrolled in the present study. Patients variably presented with early-onset, progressive neurological and mental deterioration, aggressive and hyperactive behaviors, sleep disturbances, and hepatosplenomegaly. Bayesian Gaussian Mixture machine learning (ML) model, an in-silico prediction tool, protein modelling, and thermodynamic stability predictions were applied to assess the functional consequences, and the potential clinical impact of two missense variants, recently reported . RESULTS: Sanger sequencing of the NAGLU coding and exon-intron boundaries revealed seven different homozygous disease-causing variants [p.(Leu348Arg), p.(Val117Leu), p.(Trp268Arg), p.(Glu452Lys), p.(Arg482Trp), p.(Arg482Gln), and p.(Leu550Pro)] The most frequently encountered variant was the p.(Arg482Trp) (12/22; 37%) located in exon 6, followed by the missense variant p.(Trp268Arg) (4/22; 18%) in exon 5, while the other three missense variants, p.(Glu452Lys), p.(Arg482Gln), and p.(Leu550Pro)] each appeared in only one patient, representing 9% of the disease-causing variants. Sixteen mutant alleles (16/22; 72%) were identified in NAGLU exon 6, indicating that exon 6 is a hotspot in Egyptian Sanfilippo B patients. In silico analysis using multiple computational tools and the Bayesian Gaussian Mixture ML model for assessment of missense variants predicted the p.(Leu348Arg) missense variant to be deleterious and destabilizing the protein structure. In contrast, the p.(Val117Leu) missense variant was consistently predicted to have a stabilizing effect on the protein. This study expands the molecular genetic spectrum of the NAGLU mutations associated with MPS IIIB in Egyptian patients. The study results highlight exon 6 as a hot-spot for the first screening of NAGLU gene in Egyptian families with MPS IIIB. This will promote the early diagnosis and genetic counselling for patients and their families in Egypt. The application of a machine learning (ML) model to assess missense variants identified in our Egyptian patients provided significant insights into their clinical impact and the observed variable clinical severity. The use of AMCMG criteria and in silico tools to predict the pathogenicity and protein stability changes of these variants proved valuable and demonstrated the utility of computational methods in assessing the clinical relevance of genetic variants.

Hunter syndrome, also known as Mucopolysaccharidosis type II (MPS II), is a rare X-linked lysosomal storage disorder caused by mutations in the IDS, which encodes the iduronate-2-sulfatase enzyme. The main aim of the current genetic study was to investigate a non-consanguineous Pakistani family segregating Hunter's syndrome.Clinical evaluation, biochemical assays, radiological imaging, and genetic sequencing were performed on the affected individuals.The Family was recruited from Khyber Pakhtunkhwa (KP) province of Pakistan and has two affected male individuals. Routine blood investigations showed low blood sugar (1/2), elevated SGPT (1/2), and increased RDW-CV levels (2/2). Both patients (2/2) presented with a severe phenotype, including cognitive impairment (2/2), coarse facial features (2/2), skeletal abnormalities (2/2), growth delay (2/2), hepatomegaly (2/2), hydrocephalus (2/2), macrocephaly (2/2), visual impairment (2/2), and restricted joint mobility (2/2). A previously reported hemizygous c.1122C>T mutation in exon 8 of the IDS. The identified mutation presumably creates an aberrant splicing and leads to the deletion of 20 amino acids in the open reading frame, which would distort the local folding of the polypeptide chain and lead to loss of its interacting sites. MRI analysis demonstrated typical MPS-II-related abnormalities, including enlarged perivascular spaces, ventriculomegaly, posterior fossa and sella turcica deformities, and spinal cord compression due to periodontoid thickening and spinal stenosis.Although the c.1122C>T (IDS) mutation is not novel, its identification in a Pakistani Pashtun family is reported here for the first time, contributing to the ethnic and geographic mapping of MPS II. This study underscores the importance of population-specific mutation data for effective genetic counseling, early diagnosis, and carrier screening.

Abstract Bow hunter’s syndrome (BHS) is a rare condition causing dynamic vertebral artery compression, which can result in recurrent strokes, posing unique challenges in patients with cardiovascular comorbidities like atrial fibrillation (AF). This case study describes the presentation, management and outcomes of a 75-year-old female with BHS and AF, who experienced recurrent posterior circulation strokes despite anticoagulation and antiplatelet therapy. A comprehensive stroke work-up, including advanced imaging, identified BHS as the primary cause. Despite adding aspirin to apixaban (Eliquis) and later switching to prasugrel (Efficient), the patient had another stroke, prompting vertebral artery embolisation. No further events occurred prior to the nine-month follow-up. Nurses play a crucial role throughout the patient’s journey and were instrumental in recognising BHS symptoms early, advocating for timely advanced imaging, and educating the patient on avoiding head rotation to minimise vertebral artery compression. They also monitored for complications, provided ongoing support during recovery, and contributed to improved patient outcomes through vigilant care and coordination with the multidisciplinary team. This case underscores the complexity of managing BHS in AF patients, highlighting the need for nuanced, multidisciplinary approaches and further research into the management of BHS in the context of other stroke risk factors.

We present the SWAP design, a novel, structurally cohesive IGF2-based tag for modular receptor targeting during gene therapy for lysosomal storage disorders (LSDs). We found that IGF2’s central loop is critical for high-affinity binding to the insulin receptor (IR) and IGF1 receptor (IGF1R)—both involved in glucose homeostasis—but is not required for interaction with the cation independent mannose 6-phosphate/IGF2 receptor (CI-M6P/IGF2R)—a key target for lysosomal delivery. This formed the basis for designing the Substitution of the central-loop With Augmenting Peptides (SWAP) tag. By replacing the central loop with alternative epitopes, SWAP ensures high-affinity multimodal receptor targeting while maintaining structural integrity. In vivo, lentiviral gene therapy employing IDS fused to SWAP variants containing ApoE and RAP12x2 inserts corrected Hunter disease pathology across multiple tissues, including liver, spleen, heart, bone, and brain, matching the efficacy of the traditional IGF2 tag. These findings position SWAP as a novel and effective tag design for IGF2-based therapeutics with a more favourable ligand–receptor interaction.

Mucopolysaccharidosis type III, also referred to as Sanfilippo disease, is a rare hereditary lysosomal storage illness and one of the more common variants. The illness can affect all tissues and organs of the body, with the central nervous system being the most profoundly impacted. Autoimmune hemolytic anemia (AIHA) is a rare, diverse, antibody-mediated disorder characterized by the production of antibodies that target and destroy red blood cells, leading to their rapid destruction. AIHA is a prevalent and notable complication in recipients following umbilical cord blood stem cell transplantation. Immunosuppressive treatments, including intravenous immunoglobulin and rituximab, have been the primary therapeutic modalities. There is no consensus on the appropriate treatment for post-transplant severe AIHA. This article details a 5-year-old male diagnosed with mucopolysaccharidosis type III. He developed AIHA + 144 days after umbilical cord blood stem cell transplantation. Genetic testing, cranial CT, blood cell analysis, direct/indirect antihuman globulin test. Treatment encompasses red blood cell transfusion to rectify anemia, intravenous administration of methylprednisolone, calcium gluconate, alkaline solutions, plasma exchange, rituximab, gamma globulin, and more symptomatic therapies. The symptoms of hemolysis were inadequately managed throughout the disease progression and were alleviated upon therapy with daratumumab. The treatment was conducted without adverse effects, and the problem was well managed. A telephonic follow-up with the patient was conducted by our department 546 days post-discharge. The child's cognitive ability, linguistic skills, and other neurological processes remained stable without further decline. This report discusses a child with MPS III, a rare disorder characterized by complex and varied phenotypes, including distinctive facial features, short stature, cognitive regression, varying degrees of skeletal deformities, and hepatosplenomegaly. The patient has autoimmune hemolysis after umbilical cord blood transplantation. For patients who do not respond to rituximab and gamma globulin, daratumumab may be considered.

Mutation Analysis of the Iduronate-2-Sulfatase Gene among Egyptian Patients with Hunter Syndrome

A case of mucopolysaccharidosis type ⅢA with ventricular hypertrophy as the first clinical presentation

Background/Objectives: Sanfilippo Syndrome type B or Mucopolysaccharidosis type IIIB (MPS IIIB, OMIM 252920) is a lysosomal storage disease caused by deficiency of alpha-N-acetylglucosaminidase (NAGLU, E.C. 3.2.1.50) due to pathogenic variants in the NAGLU gene (17q21.2). The disease is characterized by progressive neurological manifestations, marked by cognitive decline, with relatively mild somatic involvement. We aim to present relevant information on a cluster of MPS IIIB identified in Ecuador, particularly regarding their clinical, biochemical, genetic, demographic, and ancestry characteristics. Methods: We present a characterization of a clinical, biochemical, genetic and demographic cluster of MPS IIIB patients in Ecuador, located in four main regions: Manabí, Guayas, Los Ríos, and Santo Domingo de los Tsáchilas. The patients included were diagnosed due to increased levels of urinary glycosaminoglycans (uGAG), plus deficient activity of NAGLU, and/or identification of biallelic pathogenic mutations in the NAGLU gene. Patients’ charts were reviewed for biochemical findings, medical history, clinical manifestations and assessments. Results: We present the results of clinical, biochemical, genetic and demographic characterization of a cluster in Ecuador with 24 patients identified with Sanfilippo syndrome type IIIB, resulting in an estimated incidence of 1.5/100,000. The mean age at diagnosis was 8.8 years, with symptom onset at 4.5 years on average. All patients exhibited elevated levels of uGAG and undetectable NAGLU activity, and all of them presented the c.1487T>C (p.Leu496Pro) variant in the NAGLU gene in homozygosis, indicating a possible founder effect, with the exception of one heterozygous one (p.Leu496Pro/p.Arg482Gln). A positive correlation between age of diagnosis and the concentration of one isoform of heparan sulfate (HS-OS) was found (p < 0.05). Clinical findings included neuropsychomotor developmental delay (75%), neurological regression (65%), hepatomegaly (55%), growth deficiency (50%), coarse facies (45%) and hernia (40%). Male patients presented earlier onset of symptoms. Maternal ancestry was successfully determined for 21 of the 24 patients. The majority were of Native American ancestry (71.4%), followed by European (19%), African (4.8%), and Asian (4.8%) lineages. Haplogroup A was the most prevalent (42.9%), followed by haplogroups D (19%), C, U, and H (each 9.5%), and R and L2 (each 4.8%). Conclusions: Ancestry can indicate a possible mechanism to explain the heterogeneous symptomatic presentation. These findings highlight the need for further research on genetic and environmental influences on disease severity in this population.