[Natural history of mucopolysaccharidosis type III in a series of Colombian patients]. / Historia natural de la mucopolisacaridosis III en una serie de pacientes colombianos.

INTRODUCTION: Mucopolysaccharidosis type III (MPS III), also known as Sanfilippo syndrome, is a lysosomal storage disease with progressive neurodegenerative features, predominantly affecting the central nervous system. Diagnosis is based on clinical features, with neurodevelopmental and neuropsychiatric alterations taking precedence, including over phenotype alterations. The disease is confirmed by biochemical analysis to identify the type of glycosaminoglycans present, enzyme assay and molecular genetic studies. CASE REPORTS: A clinical description was performed for eight patients diagnosed with MPS III in Colombia. Their initial symptoms were related to developmental delay and behavioural disorders presenting between 3 and 8 years of age, associated in all cases with coarse facial features, thick eyebrows, hepatomegaly and progressive hearing loss. One of the patients presented cardiac anomalies; two presented focal epilepsy; and one presented optic atrophy. They all presented neuroimaging alterations, with evidence of parenchymal volume loss, corpus callosum atrophy and cortical thinning; the diagnosis was performed by biochemical glycosaminoglycan chromatography studies, and all patients have a confirmatory genetic study. CONCLUSIONS: MPS III is a challenge for diagnosis, particularly in its early stages and in patients in which the course of the disease is attenuated. This is due to its variable course, non-specific early neuropsychiatric symptoms, and the absence of obvious somatic features compared to other types of MPS. After a definitive diagnosis has been made, interdisciplinary care must be provided for the patient and their family, and support given for the treatment of physical symptoms, ensuring the best possible care and quality of life for the patient and their family, as the condition is neurodegenerative.

TITLE: Historia natural de la mucopolisacaridosis III en una serie de pacientes colombianos.Introducción. La mucopolisacaridosis de tipo III (MPS III), o síndrome de Sanfilippo, es un trastorno de almacenamiento lisosómico con características neurodegenerativas progresivas, predominante del sistema nervioso central. Su diagnóstico se basa en el cuadro clínico, y priman alteraciones en el neurodesarrollo y neuropsiquiátricas, incluso antes de la presencia de alteraciones fenotípicas. El análisis bioquímico para identificar el tipo de glucosaminoglucanos presente, la determinación enzimática y el estudio de genética molecular confirman la enfermedad. Casos clínicos. Se realiza la descripción clínica de ocho pacientes con diagnóstico de MPS III en Colombia, con síntomas iniciales en relación con retraso del desarrollo y trastornos comportamentales evidenciados entre los 3 y 8 años, asociado a facies toscas, cejas pobladas, hepatomegalia y pérdida auditiva progresiva en todos los casos. Uno de los pacientes presentó anomalías cardíacas; dos de ellos, epilepsia focal; y en uno se evidenció atrofia óptica. Todos presentaron alteraciones en las neuroimágenes con evidencia de pérdida del volumen parenquimatoso, atrofia del cuerpo calloso y adelgazamiento cortical; el diagnostico se realizó a través de estudios bioquímicos de cromatografía de glucosaminoglucanos y todos cuentan con un estudio genético confirmatorio. Conclusiones. La MPS III es un desafío diagnóstico, particularmente en pacientes con un curso atenuado de la enfermedad, debido al curso variable, síntomas neuropsiquiátricos tempranos inespecíficos y falta de características somáticas evidentes en comparación con otros tipos de MPS. Cuando se tiene el diagnóstico definitivo, es fundamental brindar atención interdisciplinaria para el paciente y la familia, y apoyar el tratamiento de los síntomas físicos, garantizando ofrecer el mejor cuidado posible y la mejor calidad de vida para el paciente y su familia, al tratarse de una condición neurodegenerativa.

Sanfilippo syndrome type B: Analysis of patients diagnosed by the MPS Brazil Network.

Mucopolysaccharidosis type IIIB is a rare autosomal recessive disorder characterized by deficiency of the enzyme N-acetyl-alpha-d-glucosaminidase (NAGLU), caused by biallelic pathogenic variants in the NAGLU gene, which leads to storage of heparan sulfate and a series of clinical consequences which hallmark is neurodegeneration. In this study clinical, epidemiological, and biochemical data were obtained from MPS IIIB patients diagnosed from 2004-2019 by the MPS Brazil Network ("Rede MPS Brasil"), which was created with the goal to provide an easily accessible and comprehensive investigation of all MPS types. One hundred and ten MPS IIIB patients were diagnosed during this period. Mean age at diagnosis was 10.9 years. Patients were from all over Brazil, with a few from abroad, with a possible cluster of MPS IIIB identified in Ecuador. All patients had increased urinary levels of glycosaminoglycans and low NAGLU activity in blood. Main clinical symptoms reported at diagnosis were coarse facies and neurocognitive regression. The most common variant was p.Leu496Pro (30% of alleles). MPS IIIB seems to be relatively frequent in Brazil, but patients are diagnosed later than in other countries, and reasons for that probably include the limited awareness about the disease by health professionals and the difficulties to access diagnostic tests, factors that the MPS Brazil Network is trying to mitigate.

Mutación novel en el Síndrome Sanfilippo B. Presentación de un caso / A novel mutation in Sanfilippo Syndrome type B. Case report

Introducción: El Síndrome Sanfilippo B es un error innato en el metabolismo lisosomal, con herencia autosómica recesiva. Se caracteriza por facie ligeramente tosca, deterioro neurológico progresivo y poca repercusión somática, provocado por mutaciones en el gen NAGLU, cuyo locus es 17q21.2. La incidencia internacionalmente es muy baja y en Cuba solo se han diagnosticado siete pacientes desde 1985. Objetivo: Describir las manifestaciones clínicas, bioquímicas y moleculares de un paciente cubano diagnosticado con Síndrome Sanfilippo B. Presentación de Caso: Se describió un paciente de 13 años, cuyas principales manifestaciones clínicas fueron: facie ligeramente tosca, sinofris, alteraciones de conducta y deterioro neurológico progresivo. El trastorno del sueño fue ocasional y frecuente las infecciones respiratorias. Se demostró la presencia de colitis ulcerativa y pólipo intestinal. Se confirmó excreción aumentada de heparán sulfato y disminución de la actividad enzimática N-acetil αD-glucosaminidasa. Se identificó la mutación c.640dupC en el gen NAGLU en homocigosis en el paciente y ambos padres resultaron ser portadores. Conclusiones: Predominaron las alteraciones de conducta, deterioro neurológico progresivo e infecciones respiratorias en el caso reportado; siendo la colitis ulcerativa y el pólipo intestinal un hallazgo no descrito anteriormente para esta enfermedad. Los estudios cromatográficos y enzimáticos resultaron positivos para Sanfilippo B. El genotipo de este paciente resultó ser homocigótico para una nueva variante alélica patogénica en el gen NAGLU. Se demostró la segregación mendeliana de la mutación en la familia(AU)

Introduction: Sanfilippo syndrome type B is an autosomal recessive lysosomal storage disease. The frequent clinical manifestations include slightly coarse facial features, progressive neurodegeneration and mild somatic repercussion caused by mutations in the NAGLU gene, whose locus is 17q21.2. The worldwide incidence is very low and only seven patients have been diagnosed in Cuba since 1985. Objective: To describe clinical, biochemical and molecular characteristics of a Cuban patient with the diagnosis of Sanfilippo Syndrome type B. Case presentation: A 13 years old patient was described. The main clinical manifestations included mild coarse facie, synophrys, behavior disturbances, and progressive neurologic deterioration. Intermittent sleep disturbance and frequent upper respiratory infections were identified. Ulcerative colitis and intestinal polyp were demonstrated. Increased excretion of heparan sulfate and very low N-acetyl α-Dglucosaminidase activity were confirmed. In addition, the presence of mutation c.640dupC in NAGLU gene was identified. The patient had homozygous genotype and both parents were heterozygous. Conclusions: Behavioral alterations, progressive neurological deterioration and respiratory infections predominated in the reported case. Other findings such as ulcerative colitis and intestinal polyps were not previously described in this disease. The chromatographic and enzymatic studies were positive for Sanfilippo type B. This patient's genotype was found to be homozygous for a novel pathogenic allelic variant in the NAGLU gene. Mendelian segregation of the mutation in the family was demonstrated(AU)

Estimated birth prevalence of mucopolysaccharidoses in Brazil.

Several studies have been published on the frequency of the mucopolysaccharidoses (MPS) in different countries. The objective of the present study was to estimate the birth prevalence (BP) of MPS in Brazil. MPS diagnosis registered at MPS-Brazil Network and in Instituto Vidas Raras were reviewed. BP was estimated by (a) the number of registered patients born between 1994 and 2015 was divided by the number of live births (LBs), and (b) a sample of 1,000 healthy individuals was tested for the most frequent variant in IDUA gene in MPS I (p.Trp402Ter) to estimate the frequency of heterozygosity and homozygosity. (a) The BP based on total number of LBs was (cases per 100,000 LBs): MPS overall: 1.25; MPS I: 0.24; MPS II: 0.37; MPS III: 0.21; MPS IV: 0.14; MPS VI: 0.28; MPS VII: 0.02. (b) The overall frequency of p.Trp402Ter was 0.002. Considering the frequency of heterozygotes for the p.Trp402Ter IDUA variant in the RS state, the frequency of this variant among MPS I patients and the relative frequency of the different MPSs, we estimated the birth prevalence of MPS in total and of each MPS type, as follows: MPS overall: 4.62; MPS I: 0.95; MPS II: 1.32; MPS III: 0.56; MPS IV: 0.57; MPS VI: 1.02; MPS VII: 0.05. This study provided original data about BP and relative frequency of the MPS types, in Brazil, based on the frequency of the commonest IDUA pathogenic variant and in the records of two large patient databases.

Molecular characterization of a large group of Mucopolysaccharidosis type IIIC patients reveals the evolutionary history of the disease.

Mucopolysaccharidosis type IIIC (MPSIIIC) is a severe, rare autosomal recessive disorder caused by variants in the heparan-α-glucosaminide N-acetyltransferase (HGSNAT) gene which result in lysosomal accumulation of heparan sulfate. We analyzed clinical presentation, molecular defects and their haplotype context in 78 (27 novel) MPSIIIC cases from 22 countries, the largest group studied so far. We describe for the first time disease-causing variants in the patients from Brazil, Algeria, Azerbaijan, and Iran, and extend their spectrum within Canada, Colombia, Turkey, and the USA. Six variants are novel: two missense, c.773A>T/p.N258I and c.1267G>T/p.G423W, a nonsense c.164T>A/p.L55*, a splice-site mutation c.494-1G>A/p.[P165_L187delinsQSCYVTQAGVRWHHLGSLQALPPGFTPFSYLSLLSSWNC,P165fs], a deletion c.1348delG/p.(D450fs) and an insertion c.1479dupA/p.(Leu494fs). The missense HGSNAT variants lacked lysosomal targeting, enzymatic activity, and likely the correct folding. The haplotype analysis identified founder mutations, p.N258I, c.525dupT, and p.L55* in the Brazilian state of Paraiba, c.493+1G>A in Eastern Canada/Quebec, p.A489E in the USA, p.R384* in Poland, p.R344C and p.S518F in the Netherlands and suggested that variants c.525dupT, c.372-2G>A, and c.234+1G>A present in cis with c.564-98T>C and c.710C>A rare single-nucleotide polymorphisms, have been introduced by Portuguese settlers in Brazil. Altogether, our results provide insights into the origin, migration roots and founder effects of HGSNAT disease-causing variants, and reveal the evolutionary history of MPSIIIC.

Polymorphic variants (p.Ser141Ser and p.Arg737Gly) at the NAGLU gene are really indicative of pseudodeficiency alleles?

Filocamo et al. recently published a paper describing the presence of a pseudodeficiency allele, constituted by p.Ser141Ser and p.Arg737Gly polymorphisms at the NAGLU gene, which leads to a reduced level of the alpha-N-acetyl-D-glucosaminidase activity. Based on analysis performed in Brazilian patients, using a customized gene panel containing SGSH, NAGLU, HGSNAT and GNS we observed that p.Ser141Ser (rs659497) and p.Arg737Gly (rs86312) variants were present in homozygosis in all of our MPS IIIB patients and in the majority of MPS IIIA, IIIC and IIID patients, and there was no significant decrease of the alpha-N-acetyl-D-glucosaminidase enzyme activity in this group when compared with those without the "pseudodeficiency allele". Thus, we suggest that these two variants are not producing a pseudodeficiency allele.

Molecular defects identified by whole exome sequencing in a child with atypical mucopolysaccharidosis IIIB.

BACKGROUND: Mucopolysaccharidosis IIIB (MPS IIIB) is a genetic disease characterized by mutations in the NAGLU gene, deficiency of α-N-acetylglucosaminidase, multiple congenital malformations and an increased susceptibility to malignancy. Because of the slow progressive nature of this disease and its atypical symptoms, the misdiagnosis of MPS IIIB is not rare in clinical practice. This misdiagnosis could be avoided by using next-generation sequencing (NGS) techniques, which have been shown to have superior performance for detecting mutations underlying rare inherited disorders in previous studies. CASE PRESENTATION: Whole exome sequencing (WES) was conducted and the putative pathogenic variants were validated by Sanger sequencing. The activity of MPS IIIB related enzyme in the patient's blood serum was assayed. A heterozygous, non-synonymous mutation (c.1562C>T, p.P521L) as well as a novel mutation (c.1705C>A, p.Q569K) were found in the NAGLU gene of the patient. The two mutations were validated by Sanger sequencing. Our data showed that this patient's c.1562C>T, p.P521L mutation in the NAGLU gene was inherited from his father and c.1705C>A, p.Q569K was from his mother. The diagnosis was further confirmed by an enzymatic activity assay after patient recall and follow-up. CONCLUSIONS: Our results describe an atypical form of MPS IIIB and illustrate the diagnostic potential of targeted WES in Mendelian disease with unknown etiology. WES could become a powerful tool for molecular diagnosis of MPS IIIB in clinical setting.

Natural History of Sanfilippo Syndrome Type C in Boyacá, Colombia.

Mucopolysaccharidosis type III, or Sanfilippo syndrome, is an autosomal recessive disorder characterized by impairment in the degradation of Heparan sulfate. Here the authors describe the natural history of 5 related individuals; all associated through a large pedigree which reports a total of 11 affected members, originally from the Boyacá region in Colombia, diagnosed with MPS IIIC who all harbor a novel mutation in HGSNAT. The authors report an unusually high incidence of the disease in this population. The clinical features are similar to previously described patients, although some differences in the degree of severity and end-stage of the disease are seen in this specific group. The authors consider that the high degree of endogamy in this specific population could underlie modifying factors for the severity of presentation in these patients. Future studies might provide more information on the functional effect of this novel mutation, which could define this group as a genetic isolate.

Founder mutation R245H of Sanfilippo syndrome type A in the Cayman Islands.

Sanfilippo A syndrome is an autosomal recessive lysosomal storage disease. This disease was reported in the Cayman Islands population with carrier frequency of 1/7 to 1/10 in the West Bay district of Grand Cayman. The carrier testing of Sanfilippo A disease for families at risk was carried out using the thermal characteristics of sulfamidase activity. In the present study, a search for mutations in the sulfamidase gene in an index family was performed. In addition, 77 individuals, relatives of children with Sanfilippo A syndrome, were also studied by single-strand conformation polymorphism (SSCP), restriction fragment-length polymorphism (RFLP) analyses, and sequencing. A single mutation, G746A (R245H), was found in the family, with the patient being homozygous and both parents and 1 of the 3 siblings being carriers. Among the 77 family members of the patient with Sanfilippo syndrome, the same mutation was found among carriers of the disease. The finding of a single mutation supports the idea of a founder effect, which facilitates accurate carrier identification of Sanfilippo A syndrome in the population of Cayman Islands.