The long-awaited structure of human fucosidase FucA1 opens novel avenues for the treatment of fucosidosis.

In this issue of Structure, Armstrong and colleagues probe the structure of human fucosidase FucA1. Their work resolves an ongoing debate around the enzyme's catalytic mechanism and provides a valid structural template to guide the design of drugs alleviating the rare, yet severe, lysosomal storage disease fucosidosis.

Fucosidosis: clinical and molecular findings of Turkish patients.

BACKGROUND: Fucosidosis is a rare, autosomal recessive lysosomal storage disease caused by alpha L- fucosidase enzyme deficiency in all tissues. Here, we identify a patient with a novel homozygous pathogenic variant and atypical clinical findings and summarized the clinical and molecular features of Turkish patients reported in the literature and present. CASE: The patient was born to consangineous parents at the 28th week of gestation. He had developmental delay that was attributed to prematurity. At he age of 2.5 years, brain magnetic resonans imaging revealed hyperintensities of symmetrical periventricular, subcortical, centrum semiovale and corona radiata regions on T2 and FLAIR weighted images. He developed seizures and showed developmental regression at he age of 3,5 years. Beside, coarse facial features and hepatomegaly were detected on phsyical examination. Lysosomal enzyme analysis revelaed alfa fucosidase deficiency and molecular genetic analysis identified a novel homozygous pathogenic p. Lys431 fs variant in FUCA1 gene. CONCLUSIONS: In Turkish patients no distinguishable clinical and radiologic finding could be established. Molecular analysis was performed in few patients. Increasing of molecular and biochemical facilities might enable to make diagnosis and increase the prevalence of the disease in countries with high rate of consanguineous marriages. Moreover, it will provide genetic counseling, and enlighten the therapeutic effects of hematopoietic stem cell transplantation.

An unusual presentation of fucosidosis in a Chinese boy: a case report and literature review (childhood fucosidosis).

BACKGROUND: Fucosidosis is one of the rare autosomal recessive lysosomal storage diseases (LSDs) attributed to FUCA1 variants causing the deficiency of α-L-fucosidase in vivo. Α-L-fucosidase deficiency will cause excessive accumulation of fucosylated glycoproteins and glycolipids, which eventually leads to dysfunction in all tissue systems and presents with multiple symptoms. Fucosidosis is a rare disease which is approximately 120 cases have been reported worldwide (Wang, L. et al., J Int Med Res 48, 1-6, 2020). The number of reported cases in China is no more than 10 (Zhang, X. et al., J Int Med Res 49:3000605211005975, 2021). CASE PRESENTATION: The patient was an 8-year-old Chinese boy who presented with postnatal motor retardation, intellectual disability, short stature, language development retardation, coarse facial features, hepatomegaly, and diffuse angiokeratoma of both palms. His genetic testing showed the presence of a homozygous pathogenic variant (c.671delC) in the FUCA1 gene. In addition, the enzymatic activity of α-L-fucosidase was low. Ultimately, the patient was diagnosed with fucosidosis. CONCLUSIONS: Fucosidosis is a rare lysosomal storage disease because of FUCA1 variants that cause the deficiency of α-L-fucosidase in vivo. An explicit diagnosis requires a combination of clinical manifestations, imaging examination, genetic testing and enzyme activity analysis. Early diagnosis plays an important role in fucosidosis.

Glycan degradation promotes macroautophagy.

Macroautophagy promotes cellular homeostasis by delivering cytoplasmic constituents to lysosomes for degradation [Mizushima, Nat. Cell Biol. 20, 521-527 (2018)]. However, while most studies have focused on the mechanisms of protein degradation during this process, we report here that macroautophagy also depends on glycan degradation via the glycosidase, α-l-fucosidase 1 (FUCA1), which removes fucose from glycans. We show that cells lacking FUCA1 accumulate lysosomal glycans, which is associated with impaired autophagic flux. Moreover, in a mouse model of fucosidosis-a disease characterized by inactivating mutations in FUCA1 [Stepien et al., Genes (Basel) 11, E1383 (2020)]-glycan and autophagosome/autolysosome accumulation accompanies tissue destruction. Mechanistically, using lectin capture and mass spectrometry, we identified several lysosomal enzymes with altered fucosylation in FUCA1-null cells. Moreover, we show that the activity of some of these enzymes in the absence of FUCA1 can no longer be induced upon autophagy stimulation, causing retardation of autophagic flux, which involves impaired autophagosome-lysosome fusion. These findings therefore show that dysregulated glycan degradation leads to defective autophagy, which is likely a contributing factor in the etiology of fucosidosis.

Identification of a novel homozygous loss-of-function mutation in FUCA1 gene causing severe fucosidosis: A case report.

Fucosidosis is a rare lysosomal storage disorder characterized by deficiency of α-L-fucosidase with an autosomal recessive mode of inheritance. Here, we describe a 4-year-old Chinese boy with signs and symptoms of fucosidosis but his parents were phenotypically normal. Whole exome sequencing (WES) identified a novel homozygous single nucleotide deletion (c.82delG) in the exon 1 of the FUCA1 gene. This mutation will lead to a frameshift which will result in the formation of a truncated FUCA1 protein (p.Val28Cysfs*105) of 132 amino acids approximately one-third the size of the wild type FUCA1 protein (466 amino acids). Both parents were carrying the mutation in a heterozygous state. This study expands the mutational spectrum of the FUCA1 gene associated with fucosidosis and emphasises the benefits of WES for accurate and timely clinical diagnosis of this rare disease.

A new UHPLC-MS/MS method for the screening of urinary oligosaccharides expands the detection of storage disorders.

BACKGROUND: Oligosaccharidoses are storage disorders due to enzymatic defects involved in the breakdown of the oligosaccharidic component of glycosylated proteins. The defect cause the accumulation of oligosaccharides (OS) and, depending on the lacking enzyme, results in characteristic profiles which are helpful for the diagnosis. We developed a new tandem mass spectrometry method for the screening of urinary OS which was applied to identify a large panel of storage disorders. METHODS: The method was set-up in urine and dried urine spots (DUS). Samples were analysed, without derivatization and using maltoheptaose as internal standard, by UHPLC-MS/MS with MRM acquisition of target OS transitions, including Glc4, the biomarker of Pompe disease. The chromatographic run was < 30 min. Samples from patients with known storage disorders were used for clinical validation. RESULTS: The method allowed to confirm the diagnosis of oligosaccharidoses (sialidosis, α-/ß-mannosidosis, fucosidosis, aspartylglucosaminuria) and of GM1 and GM2 (Sandhoff type) gangliosidosis, by detecting specific OS profiles. In other storage disorders (mucolipidosis II and III, mucopolysaccharidosis type IVB) the analyisis revealed abnormal OS excretion with non-specific profiles. Besides Pompe disease, the tetrasaccharide Glc4 was increased also in disorders of autophagy (Vici syndrome, Yunis-Varon syndrome, and Danon disease) presenting cardiomuscular involvement with glycogen storage. Overall, results showed a clear separation between patients and controls, both in urine and in DUS. CONCLUSION: This new UHPLC/MS-MS method, which is suitable for rapid and easy screening of OS in urine and DUS, expands the detection of storage disorders from oligosaccharidoses to other diseases, including the novel category of inherited disorders of autophagy.

The Identification of a Novel Fucosidosis-Associated FUCA1 Mutation: A Case of a 5-Year-Old Polish Girl with Two Additional Rare Chromosomal Aberrations and Affected DNA Methylation Patterns.

Fucosidosis is a rare neurodegenerative autosomal recessive disorder, which manifests as progressive neurological and psychomotor deterioration, growth retardation, skin and skeletal abnormalities, intellectual disability and coarsening of facial features. It is caused by biallelic mutations in FUCA1 encoding the α-L-fucosidase enzyme, which in turn is responsible for degradation of fucose-containing glycoproteins and glycolipids. FUCA1 mutations lead to severe reduction or even loss of α-L-fucosidase enzyme activity. This results in incomplete breakdown of fucose-containing compounds leading to their deposition in different tissues and, consequently, disease progression. To date, 36 pathogenic variants in FUCA1 associated with fucosidosis have been documented. Among these are three splice site variants. Here, we report a novel fucosidosis-related 9-base-pair deletion (NG_013346.1:g.10233_10241delACAGGTAAG) affecting the exon 3/intron 3 junction within a FUCA1 sequence. This novel pathogenic variant was identified in a five-year-old Polish girl with a well-defined pattern of fucosidosis symptoms. Since it is postulated that other genetic, nongenetic or environmental factors can also contribute to fucosidosis pathogenesis, we performed further analysis and found two rare de novo chromosomal aberrations in the girl's genome involving a 15q11.1-11.2 microdeletion and an Xq22.2 gain. These abnormalities were associated with genome-wide changes in DNA methylation status in the epigenome of blood cells.

Fucosidosis-Clinical Manifestation, Long-Term Outcomes, and Genetic Profile-Review and Case Series.

Fucosidosis is a neurodegenerative disorder which progresses inexorably. Clinical features include coarse facial features, growth retardation, recurrent upper respiratory infections, dysostosis multiplex, and angiokeratoma corporis diffusum. Fucosidosis is caused by mutations in the FUCA1 gene resulting in α-L-fucosidase deficiency. Only 36 pathogenic variants in the FUCA1 gene are related to fucosidosis. Most of them are missense/nonsense substitutions; six missense and 11 nonsense mutations. Among deletions there were eight small and five gross changes. So far, only three splice site variants have been described-one small deletion, one complete deletion and one stop-loss mutation. The disease has a significant clinical variability, the cause of which is not well understood. The genotype-phenotype correlation has not been well defined. This review describes the genetic profile and clinical manifestations of fucosidosis in pediatric and adult cases.

Tandem mass spectrometry-based multiplex assays for α-mannosidosis and fucosidosis.

Multiplex tandem mass spectrometry (MS/MS)-based enzyme activity assays for newborn screening (NBS) and diagnosis of lysosomal storage diseases (LSDs) in newborns, using dried blood spots (DBS) on newborn screening cards, have garnered much attention due to its sensitivity, high precision, and the capability to screen for an unprecedented number of diseases in a single assay. Herein we report the development of MS/MS-based enzyme assays for the diagnosis of α-mannosidosis and fucosidosis. These new protocols are able to distinguish untreated patients from random newborns, carriers and a post-bone marrow transplant patient. We have successfully multiplexed the α-mannosidosis assay with a multiplex MS/MS assay for the screening and diagnosis of other LSDs, namely Fabry, Pompe, MPS I, Gaucher, Niemann-Pick-A/B, and Krabbe diseases. Additionally, we also multiplexed the fucosidosis NBS assay with a 5-plex assay that tests for MPS-II, MPS-IIIB, MPS-IVA, MPS-VI and MPS-VII.

A Novel Homozygous Mutation in the FUCA1 Gene Highlighting Fucosidosis as a Cause of Dystonia: Case Report and Literature Review.

BACKGROUND: Fucosidosis is a rare lysosomal disorder caused by mutations in the FUCA1 gene. We describe here a novel homozygous mutation in FUCA1 in an Indian fucosidosis case. Furthermore, we summarize the clinical and genetic findings in the most recently reported individuals with fucosidosis. CASE: The proband is an 8-year-old boy born to consanguineous parents. He had generalized dystonia and bilateral spasticity as well as coarse facies, dysostosis multiplex, recurrent infections, angiokeratoma corporis diffusum, and visceromegaly. Whole exome sequencing analysis detected a homozygous canonical splice variant in the FUCA1 gene [Chr1(GRCh37):g.24172346C > T; NM_000147.4:c.1261-1G > A], not previously reported as causative of a human phenotype. Low levels of α-fucosidase in patient leukocytes and a positive qualitative urine based thin layer chromatography test for fucosidosis confirmed the diagnosis. Our literature review identified 89 cases of fucosidosis since the last major review. We show that dystonia is a rare manifestation (12%) and that only a small minority of cases receive treatment with transplantation (3.37%). CONCLUSION: We report a novel homozygous mutation in FUCA1 as the cause of severe neurological phenotype including generalized dystonia. Early recognition of fucosidosis may be important for consideration of promising treatment options, such as bone marrow transplantation.

Transcriptomic analysis of FUCA1 knock-down in keratinocytes reveals new insights into the pathogenesis of fucosidosis skin lesions.

Fucosidosis is a rare lysosomal storage disease which has been classified into two subtypes, depending on the severity of clinical signs and symptoms. Fucosidosis patients' skin abnormalities include angiokeratoma corporis diffusum, widespread telangiectasia, thick skin, hyperhidrosis and hypohidrosis, acrocyanosis and distal transverse nail bands. It has been described that >50% of fucosidosis patients have angiokeratoma. At molecular level, fucosidosis is caused by lysosomal alpha-L-fucosidase (FUCA1) gene mutations. Obtaining samples for functional studies has been challenging due to the inherent difficulty in finding affected individuals. The effect of FUCA1 dysfunction on gene expression is unknown. The aim of this study was to analyse, in keratinocytes, the transcriptomic effect of FUCA1 knock-down for a better understanding of skin lesions' pathogenesis affecting fucosidosis patients. FUCA1 knock-down (siRNA) was performed in human HaCaT immortalised keratinocytes. Affymetrix arrays and qPCR were used for analysing gene expression. Bioinformatics was used for functional clustering of modified genes. In total, 387 genes showed differential expression between FUCA1 silenced and non-silenced cells (222 up-regulated and 165 down-regulated). Up-regulated genes belonged to two major groups: keratinocyte differentiation/epidermal development (n = 17) and immune response (n = 61). Several transcription factors were up-regulated in FUCA1-siRNA transfected cells. This effect might partly have been produced by abnormal transcription factor expression, that is FOXN1. We thus propose that fucosidosis-related skin lesions (eg angiokeratoma) and those of other diseases (eg psoriasis) might be caused by dysfunctions in common aetiological overlapping molecular cascades.

A novel homozygous frameshift mutation in the FUCA1 gene causes both severe and mild fucosidosis.

AIMS: Fucosidosis is a rare autosomal recessive lysosomal storage disorder caused by α-L-fucosidase deficiency as a result of FUCA1 gene mutations. Here, we studied clinical features and the molecular basis of fucosidosis in a family from Iran, including two probands and nine family members. METHODS: DNA sample of two probands were screened for gene defects using a next generation sequencing technique. The sequencing processes were performed on an Illumina Hiseq 4000 platform. Sequence reads were analysed using BWA-GATK. RESULTS: Next generation sequencing revealed a frameshift mutation caused by 2 bp deletion (c.837_838 delTG; p.Cys279) in the FUCA1 gene. The identified mutation was tested in all participants. Homozygous patients had almost all the complications associated with fucosidosis, while heterozygous carriers were unaffected. CONCLUSIONS: The variant c.837_838 delTG; p.Cys279 has not been reported previously and is predicted to be pathogenic due to a premature stop codon.

Recalcitrant chronic rhinosinusitis in the setting of fucosidosis, a rare lysosomal storage disorder.

Fucosidosis is an autosomal recessive lysosomal storage disorder caused by the deficiency of alpha-L-fucosidase. We present the case of an affected female in the second decade of life with chronic rhinosinusitis (CRS) including recalcitrant polypoid inflammation, which has not been previously reported in the literature. With the advancement of life-prolonging measures, children with lysosomal storage disorders may suffer increasingly from CRS due to the lymphohistiocytic and macrophage infiltrate of the paranasal sinus mucosa that resembles severe polypoid inflammation.

Plasma alpha-L-fucosidase activity in chronic inflammation and autoimmune disorders in a pediatric cohort of hospitalized patients.

Human α-fucosidase (EC 3.2.1.51) is an enzyme (hydrolase) of particular biological and medical interest, as the inherited deficiency in its activity leads to fucosidosis, a pathology belonging to severe glycoprotein lysosomal storage disorders. Although its importance has increased in latest years, data about its plasma level in children with inflammatory disorders are still lacking. In the present study, plasma activity of α-L-fucosidase-1 (FUCA-1) and its potential association with chronic inflammatory pathologies was evaluated in hospitalized individuals, both pediatric and adult ones. A number of 201 Hungarian hospitalized patients, 144 children (1-13 years) and 57 adults (31-88 years), were enrolled in the study and underwent plasma assay of FUCA-1 activity, following the normal routine analytical run in the hospital service. Regression and Pearson tests were evaluated to investigate the relationship between FUCA-1 plasma levels and inflammatory disorders diagnosed with subjects recruited in the study. No correlation of FUCA-1 activity was observed in the pediatric patients with immune (p = 0.9677) or metabolic (p = 0.6974) disorders, but a correlation was reported when comparing clusters of chronic inflammatory and autoimmune disease vs. controls (p < 0.05). Furthermore, a relationship was found between FUCA-1 activity in plasma and inflammatory disorders and autoimmunity both in adults and in the pediatric cohort of patients (Pearson test, p = 0.000148). Alterations in plasma levels of FUCA-1 were significantly associated with chronic inflammatory and autoimmune disorders, both in children and adults. The result of the present study should encourage further research on FUCA-1 as a marker of chronic inflammation and autoimmunity.

Brain abnormalities in fucosidosis: transplantation or supportive therapy?

Fucosidosis is a rare lysosomal storage disease caused by α-fucosidase deficiency, which leads to progressive neurological deterioration and death. Hematopoietic stem cell transplantation is the best curative therapy if performed during the early stages of disease. We report two fucosidosis patients with brain abnormalities and the challenge faced in their management. The first patient received supportive therapy and the second one firstly underwent unrelated donor umbilical cord blood transplantation. After a period of follow-up, we found neurological symptoms were worsening day by day on patient1. By contrast, patient2 who received cord blood transplantation acquired clinical neurologic improvement in response to normalization of deficient enzymatic activity. This report indicates that hematopoietic transplant could reduce the severity and retard the progression of clinical neurological deterioration. Umbilical cord blood transplantation is a novel approach for treating fucosidosis patients who lack suitable bone morrow donors.