The deleterious variants of N-acetylgalactosamine-6-sulfatase (GalN6S) enzyme trigger Morquio a syndrome by disrupting protein foldings.

Lysosomal enzymes degrade cellular macromolecules, while their inactivation causes human hereditary metabolic disorders. Mucopolysaccharidosis IVA (MPS IVA; Moquio A syndrome) is one of the lysosomal storage disorders caused by a defective Galactosamine-6-sulfatase (GalN6S) enzyme. In several populations, disease incidence is elevated due to missense mutations brought on by non-synonymous allelic variation in the GalN6S enzyme. Here, we studied the effect of non-synonymous single nucleotide polymorphism (nsSNPs) on the structural dynamics of the GalN6S enzyme and its binding with N-acetylgalactosamine (GalNAc) using all-atom molecular dynamics simulation and an essential dynamics approach. Consequently, in this study, we have identified three functionally disruptive mutations in domain-I and domain-II, that is, S80L, R90W, and S162F, which presumably contribute to post-translational modifications. The study delineated that both domains work cooperatively, and alteration in domain II (S80L, R90W) leads to conformational changes in the catalytic site in domain-I, while mutation S162F mainly provokes higher residual flexibility of domain II. These results show that these mutations impair the hydrophobic core, implying that Morquio A syndrome is caused by misfolding of the GalN6S enzyme. The results also show the instability of the GalN6S-GalNAc complex upon substitution. Overall, the structural dynamics resulting from point mutations give the molecular rationale for Moquio A syndrome and, more importantly, the Mucopolysaccharidoses (MPS) family of diseases, re-establishing MPS IVA as a protein-folding disease.Communicated by Ramaswamy H. Sarma.

Clinical and treatment of 2 children with severe mucopolysaccharidosis type ⅣA from 2 pedigrees and prenatal diagnosis for their sibling / 中华实用儿科临床杂志

Objective:To explore the treatment of the patients with severe phenotype of mucopolysaccharidosis (MPS) type ⅣA by analysing the clinical feature and diagnosis.Methods:Two pediatric patients diagnosed as MPS ⅣA in severe form were enrolled in Children′s Hospital Affiliated to Zhengzhou University from August 2021 to April 2022.Two children from 2 pedigrees with the main manifestations of short stature and bone deformities were retrospectively included.The clinical manifestations, biochemical indexes, and bone imaging findings were retrospectively analyzed.Peripheral blood leukocytes were collected and subjected to the N-acetylgalactosamine-6-sulfatase (GALNS) assay and genetic sequencing.Gene analysis of amniotic fluid cells at the 18 th week of the second pregnancy of the mother of case 2 was performed for prenatal diagnosis.Allogeneic hematopoietic stem cell transplantation (allo-HSCT) was performed in both patients and to explore the treatment of patients with MPS ⅣA. Results:Both cases presented clinical manifestations of short stature, joint laxity, pectus carinatum, and genu valgus.X-ray examination revealed the decreased bone mineral density, ulnar deviation of the radial epiphysis, kyphosis and scoliosis.The respiratory and skeletal systems were affected in both patients, and the optic nerve was suspiciously affected. GALNS gene analysis showed that there were 2 missense mutations of c. 1019G>A (p.G340D) and c. 706C>G (p.H236D) in case 1, and 2 missense mutations of c. 425A>G (p.H142R) and c. 463G>A (p.G155R) were detected in case 2.Mutations in both cases were inherited from their fathers and mothers, which were all newly discovered that have not been reported.Only the c. 463G>A mutation was detected in the amniotic fluid cells of the mother of case 2.It is confirmed that case 2 was the carrier of MPS ⅣA, whose gene mutation was from the mother, and case 2 did not suffer the same disease as the proband.Both cases were treated with allo-HSCT with full donor chimerism and no severe transplant complications were reported.Their GALNS activity was within the normal range, and the scores of activities of daily living were higher than those before transplantation. Conclusions:The MPS ⅣA patients with severe phenotype is a rare autosomal recessive disease caused by GALNS mutations that is difficult to diagnose and poor prognosis.Early detection, diagnosis, and effective treatment contribute to improve the long-term quality of life.The allo-HSCT is an effective therapeutic strategy for MPS ⅣA.

Mutation spectrum and pivotal features for differential diagnosis of Mucopolysaccharidosis IVA patients with severe and attenuated phenotype.

Mucopolysaccharidosis IVA (MPS IVA) is a lysosomal storage disease caused by biallelic mutations in GALNS gene and characterized by progressive skeletal deformities with short stature. The aim of this study was to evaluate the genotype, longitudinal height measurement and clinical features of MPS IVA patients. Thirty-two patients from 22 families were enrolled. The ages of patients at diagnosis ranged from two months to 18 years of age, and followed up for three to twenty years. They were classified as severe and attenuated form (intermediate and mild) according to their height measurements. The mean height standard deviation scores (SDS) for Turkish standards at 0-3, 5 and 10 years of ages were found to be -1.1, -4.2 and -7.3 respectively in patients with severe phenotype, while they were +0.4, -1.5 and -3 for intermediate phenotype. Patients with severe form reached a mean final height of -8.5 SDS, and mild phenotype -3.6 SDS. The most common initial and current symptoms in the patients with the severe phenotype were pectus carinatus and/or kyphosis deformities which occurred between 5 months and 3 years of age, and genu valgum deformity which developed after 3 years of age. However, kyphoscoliosis was the most common initial and current findings in the attenuated phenotype. Although, initial symptoms appeared in early childhood in the intermediate phenotype, similar to the severe phenotype, the clinical findings progressed slowly and genu valgum deformity did not develop. In patients with mild phenotype, the onset of symptoms was after 5 years of age. In conclusion, this study provides significant insights into the initial and follow-up clinical features and height values that contribute to the differential diagnosis of the severe and intermediate phenotypes in early childhood. Eleven mutations in GALNS gene in which one of them is novel (c.416G>A) were associated with the severe phenotype and three mutations (c.1038C>A, c.850T>G, c.752G>A) lead to the attenuated phenotype.

Mutation analysis and pathogenicity identification of Mucopolysaccharidosis type IVA in 8 south China families.

BACKGROUND: Mucopolysaccharidosis type IVA (MPS IVA) is a rare autosomal recessive lysosomal storage disorder caused by GALNS gene mutation. The aim of our study is to detect pathogenic variants for patients suspected of MPS IVA and set the base for subsequent prenatal diagnosis and preimplantation genetic diagnosis. METHODS: In our study, 9 MPS IVA patients from south China families were investigated. Urine glycosaminoglycans (GAGS) screening was used as an initial method. For patients with abnormal result, all 14 exons and intron-exon junctions of the GALNS gene were sequenced after amplification from genomic DNA. The pathogenicity of novel mutations were analyzed with molecular genetics, bioinformatics and structure modeling in light of clinical manifestations and biochemical results. RESULTS: Among 12 mutations detected, direct sequencing found 3 novel mutations (c.686A>C, p.Y229S; c.1498G>T, p.G500C; c.278T>C, p.I93T). The pathogenicity of these novel mutations was illustrated by correlating clinical symptoms with pedigree analysis and bioinformatics analysis. CONCLUSION: The detection and variant analysis are essential for accurate diagnosis of MPS IVA patients. Our results enrich GALNS gene mutation spectrum of Chinese population. This information has important clinical value for molecular diagnosis and genetic counseling of patients with this disease.

Muscle Weakness: A Misleading Presentation in Children With Distinctive Syndromic Entities (Clinical Case Reports).

Marked ligamentous hyperlaxity and muscle weakness/wasting associated with awkward gait are the main deficits confused with the diagnosis of myopathy. Seven children (6 boys and 1 girl with an average age of 8 years) were referred to our department because of diverse forms of skeletal abnormalities. No definitive diagnosis was made, and all underwent a series of sophisticated investigations in other institutes in favor of myopathy. We applied our methodology through the clinical and radiographic phenotypes followed by targeted genotypic confirmation. Three children (2 boys and 1 girl) were compatible with the diagnosis of progressive pseudorheumatoid chondrodysplasia. The genetic mutation was correlated with the WISP 3 gene actively expressed by articular chondrocytes and located on chromosome 6. Klinefelter syndrome was the diagnosis in 2 boys. Karyotyping confirmed 47,XXY (aneuploidy of Klinefelter syndrome). And 2 boys were finally diagnosed with Morquio syndrome (MPS type IV A) as both showed missense mutations in the N-acetylgalactosamine-sulfate sulfatase gene. Misdiagnosis can lead to the initiation of a long list of sophisticated investigations.

Novel missense mutation in the GALNS gene in an affected patient with severe form of mucopolysaccharidosis type IVA.

Mucopolysaccharidosis type IVA (MPS IVA), also known as Morquio A, is an autosomal recessive disorder characterized by a deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS), which causes major skeletal and connective tissue abnormalities and affects multiple organ systems. In this study, one MPS IVA patient with a severe form from consanguine large Iranian family has been investigated. To find a mutation, all of the 14 exons and intron-exon junctions of GALNS gene were sequenced. Sequencing results were analyzed using bioinformatic analysis in order to predict probable pathogenic effect of the variant. One novel homozygous missense mutation in exon 5, c.542A>G (p.Y181C), was found in the proband. That was predicted as being probably pathogenic by bioinformatics analysis. Segregation and familial study confirmed this pathogenic mutation. In conclusion, we have identified the novel mutation responsible for MPS IVA in an Iranian patient to assist in the diagnosis, genetic counseling and prenatal diagnosis of the affected families.

GALNS mutations in Indian patients with mucopolysaccharidosis IVA.

Mucopolysaccharidosis IV A (Morquio syndrome A, MPS IVA) is a lysosomal storage disease caused by the deficiency of N-acetylgalactosamine-6-sulfatase (GALNS). The mutation spectrum in this condition is yet to be determined in Indians. We aimed to analyze the mutations in the GALNS gene in Asian Indians with MPS IVA. All the exons and the adjacent intronic regions of the gene were amplified and sequenced in sixty-eight unrelated Indian families. We identified 136 mutant alleles comprising of 40 different mutations. We report twenty-two novel mutations that comprise of seventeen missense (p.Asn32Thr, p.Leu36Arg, p.Pro52Leu, p.Pro77Ser, p.Cys79Arg, p.His142Pro, p.Tyr191Asp, p.Asn204Thr, p.Gly188Ser, p.Phe216Ser, p.Trp230Cys, p.Ala291Ser, p.Gly317Arg, p.His329Pro, p.Arg386Ser, p.Glu450Gly, p.Cys501Ser), three splice-site variants (c.120+1G>C, c.1003-3C>G, c.1139+1G>A), one nonsense mutation (p.Gln414*) and one frameshift mutation (p.Pro420Leufs*440). Eighteen mutations have been reported earlier. Among these p.Ser287Leu (8.82%), p.Phe216Ser (7.35%), p.Asn32Thr (6.61%) and p.Ala291Ser (5.88%) were the most frequent mutations in Indian patients but were rare in the mutational profiles reported in other populations. These results indicate that the Indian patients may have a distinct mutation spectrum compared to those of other populations. Mutant alleles in exon 1, 7 and 8 accounted for 44.8% of the mutations, and sequencing of these exons initially may be a cost-effective approach in Asian Indian patients. This is the largest study on molecular analysis of patients with MPS IVA reported in the literature, and the first report from India.

Molecular genetic assay of mucopolysaccharidosis IVA in South China.

Mucopolysaccharidosis IVA (MPS IVA) is an autosomal recessive lysosomal storage disorder caused by the deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS). Molecular mutational analysis was performed by PCR product sequencing for fourteen exons and exon-intron boundaries of GALNS gene in 21 patients from 19 unrelated families with severe MPS IVA in South China. We identified fifteen different mutations, including 10 reported mutations (p.P125L, p.G290S, p.M318R, p.G340D, p.L366P, p.R386C, p.A392V, c.1243-1G>C, p.L440RfsX54 and p.X523E) and five novel mutations (p.N177S, p.G290R, p.F306S, p.W403_T404delinsCS, p.W520X). All five novel mutations were inherited from parents of the patients and not found in 100 normal control alleles. Three mutations, p.M318R, p.L366P and p.R386C were common, accounting for 36.8% of mutant alleles investigated. One patient homozygous of p.A392V and the other two unrelated patients homozygous of p.L366P presented classical disease course. The results show that the GALNS gene has a different mutational spectrum in South China as compared to other regions. The p.A392V and p.L366P mutations were associated with severe phenotype of MPS IVA.