Does administration of hydroxychloroquine/amiodarone affect the efficacy of enzyme replacement therapy for Fabry mice?

As a standard therapy for Fabry disease, enzyme replacement therapy (ERT) with recombinant human α-galactosidase A (α-Gal) has been successfully used, and the instructions for this drug state that "it should not be co-administrated with cationic amphiphilic drugs such as hydroxychloroquine (HCQ) and amiodarone (AMI), since these drugs have the potential to inhibit intracellular α-Gal activity". However, there would be cases in which HCQ or AMI is required for patients with Fabry disease, considering their medical efficacy and application. Thus, we examined the impact of HCQ/AMI on recombinant human α-Gal by in vitro, cellular, and animal experiments. The results revealed that HCQ/AMI affected the enzyme activity of α-Gal incorporated into cultured fibroblasts from a Fabry mouse when the cells were cultured in medium containing these drugs and the enzyme, although their direct inhibitory effect on the enzyme is not strong. These lysosomotropic drugs may be trapped and concentrated in lysosomes, followed by inhibition of α-Gal. On the other hand, no reduction of α-Gal activity incorporated into the organs and tissues, or acceleration of glycoshingolipid accumulation was observed in Fabry mice co-administered with HCQ/AMI and the enzyme, compared with in the case of usual ERT. As HCQ/AMI administered are catabolized in the liver, these drugs possibly do not affect ERT for Fabry mice, different from in the case of cultured cells in an environment isolated from the surroundings.

Effects of switching from agalsidase-α to agalsidase-β on biomarkers, renal and cardiac parameters, and disease severity in fabry disease forming neutralizing antidrug antibodies: a case report

Fabry disease is an X-linked hereditary disorder caused by deficient α-galactosidase A (GLA) activity. Patients with Fabry disease are often treated with enzyme replacement therapy (ERT). However, ERT often induces the formation of neutralizing antidrug antibodies (ADAs), which may impair the therapeutic efficacy. Here, we report the case of a 32-year-old man with Fabry disease and resultant neutralizing ADAs who was treated by switching from agalsidase-α to agalsidase-β. We monitored biomarkers, such as plasma globotriaosylsphingosine (lyso-Gb3), urinary globotriaosylceramide (Gb3), urinary mulberry bodies, renal and cardiac parameters, and disease severity during the treatment period. Although plasma lyso-Gb3 and urinary Gb3 levels quickly decreased within two months after the initiation of ERT with agalsidase-α, they gradually increased thereafter. The urinary mulberry bodies continued to appear. Both the ADA titer and serum mediated GLA inhibition rates started to increase after two months. Moreover, 3.5 years after ERT, the vacuolated podocyte area in the renal biopsy decreased slightly from 23.1 to 18.9%. However, plasma lyso-Gb3 levels increased, and urinary Gb3, mulberry body levels, and ADA titers remained high. Therefore, we switched to agalsidase-β which reduced, but did not normalize, plasma lyso-Gb3 levels and stabilized renal and cardiac parameters. Disease severity was attenuated. However, urinary Gb3 and mulberry body levels did not decrease noticeably in the presence of high ADA titers. The kidneys take up a small amount of the administered recombinant enzyme, and the clearance of Gb3 that has accumulated in the kidney may be limited despite the switching from agalsidase-α to agalsidase-β.

Profiles of Globotriaosylsphingosine Analogs and Globotriaosylceramide Isoforms Accumulated in Body Fluids from Various Phenotypic Fabry Patients

Objectives Fabry disease is characterized by the systemic accumulation of globotriaosylceramide (Gb3) and globotriaosylsphingosine (Lyso-Gb3), which are widely used as biomarkers of the disease. However, few reports have described the relationship of Lyso-Gb3 analogs and Gb3 isoforms with the disease. The present study determined the profiles of Lyso-Gb3 analogs and Gb3 isoforms accumulated in body fluids from various phenotypic Fabry patients to elucidate the basis of the disease. Methods Plasma Lyso-Gb3 and related analogs were measured in 15 classic Fabry men, 6 later-onset Fabry men, 11 Fabry women, and 36 controls, while urinary Gb3 isoforms were measured in 5 classic Fabry men, 5 later-onset Fabry men, 17 Fabry women, and 11 controls, using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Furthermore, these values were monitored for a classic Fabry man, in whom neutralizing anti-drug antibodies had developed following enzyme replacement therapy (ERT). Results The levels of plasma Lyso-Gb3 analogs/urinary Gb3 isoforms were higher in Fabry patients than in controls, especially in classic Fabry men. However, minor differences in the ratio of each Lyso-Gb3 analog and Gb3 isoform with respect to the total Lyso-Gb3 analogs and Gb3 isoforms, respectively, were observed among individual classic Fabry men. Their time courses were well associated with the development and attenuation of anti-drug antibodies in a patient with classic Fabry disease during ERT. Conclusion Quantification of Lyso-Gb3 analogs and Gb3 isoforms provides us with more detailed information about the substrates that accumulated in the body fluids of Fabry patients than does quantification of Lyso-Gb3 and Gb3 alone, so this approach may be useful for elucidating the basis of Fabry disease.

Monitoring of anti-drug antibodies and disease-specific biomarkers in three patients from a Japanese Fabry family treated with enzyme replacement therapy

We monitored anti-drug antibodies and disease-specific biomarkers in three patients with a nonsense mutation from a Japanese Fabry family treated with enzyme replacement therapy (ERT). In two male patients from the family, neutralizing anti-drug antibodies were induced at an early stage of ERT, the antibody titer peak being found at an earlier stage of ERT in the patient treated with 1.0 mg/kg agalsidase beta than in that treated with 0.2 mg/kg agalsidase alfa. Then, the antibody titers decreased with continuation of ERT. The formation of neutralizing anti-drug antibodies adversely affected the plasma globotriaosylsphingosine (Lyso-Gb3) level and urinary globotriaosylceramide (Gb3) excretion in both patients, the impact being greater in the patient treated with 0.2 mg/kg agalsidase alfa than in that treated with 1.0 mg/kg agalsidase beta. The difference might be explained by the different doses of the infused enzymes based on supersaturation of the antibodies. In a heterozygous Fabry female from the family, no sign of antibody formation was found, and both the plasma Lyso-Gb3 level and urinary Gb3 excretion, which were moderately increased at the baseline, decreased gradually. No deterioration of the manifestations or laboratory findings was observed during ERT in either of the patients. Thus, monitoring of anti-drug antibodies and biomarkers in these Fabry patients provided us with important information on their pathological condition during ERT.

In Vivo Delivery of Therapeutic Molecules by Transplantation of Genome-Edited Induced Pluripotent Stem Cells

Human induced pluripotent stem cells (iPSCs) have already been used in transplantation therapies. Currently, cells from healthy people are transplanted into patients with diseases. With the rapid evolution of genome editing technology, genetic modification could be applied to enhance the therapeutic effects of iPSCs, such as the introduction of secreted molecules to make the cells a drug delivery system. Here, we addressed this possibility by utilizing a Fabry disease mouse model, as a proof of concept. Fabry disease is caused by the lack of α-galactosidase A (GLA). We previously developed an immunotolerant therapeutic molecule, modified α-N-acetylgalactosaminidase (mNAGA). We confirmed that secreted mNAGA from genome-edited iPSCs compensated for the GLA activity in GLA-deficient cells using an in vitro co-culture system. Moreover, iPSCs transplanted into Fabry model mice secreted mNAGA and supplied GLA activity to the liver. This study demonstrates the great potential of genome-edited iPSCs secreting therapeutic molecules.

Screening of Fabry disease in patients with chronic kidney disease in Japan

BACKGROUND

Fabry disease (FD), an X-linked lysosomal storage disorder caused by a deficiency in alfa-galactosidase A (α-Gal A) activity due to mutations in the GLA gene, has a prevalence of 0-1.69% in patients undergoing haemodialysis; however, its prevalence in patients with chronic kidney disease (CKD) Stages 1-5 is unknown.

METHODS

Serum α-Gal A activity analysis and direct sequencing of GLA were used to screen for FD in 2122 male patients with CKD, including 1703 patients with CKD Stage 5D and 419 with CKD Stages 1-5. The correlation between serum α-Gal A activity and confounding factors in patients with CKD Stages 1-5 was evaluated.

RESULTS

FD prevalence rates in patients with CKD Stage 5D and CKD Stages 1-5 were 0.06% (1/1703) and 0.48% (2/419), respectively. A patient with CKD Stage 5D exhibited a novel GLA mutation, p.Met208Arg, whereas two patients with CKD Stages 1-5 had c.370delG and p.Met296Ile. p. Met208Arg caused moderate structural changes in the molecular surface region near the substituted amino acid residue but did not affect the catalytic residues Asp170 and Asp231 in α-Gal A. Serum α-Gal A activity in patients with CKD Stages 1-5 was inversely correlated with age (P < 0.0001) but directly correlated with estimated glomerular filtration rate (P < 0.0001).

CONCLUSIONS

FD prevalence was much higher in male patients with CKD Stages 1-5 than in those with CKD Stage 5D. FD screening in patients with CKD Stages 1-5 may improve patient survival, decreasing the number of patients with CKD Stage 5D.

Genetically Modified Cell Transplantation Through Macroencapsulated Spheroids with Scaffolds to Treat Fabry Disease

Cell transplantation is expected to be another strategy to treat lysosomal diseases, having several advantages compared to enzyme replacement therapy, such as continuous enzyme secretion and one-time treatment to cure diseases. However, cell transplantation for lysosomal diseases holds issues to be resolved for the clinical field. In this study, we developed a new ex vivo gene therapy platform using a transplant pack, which consists of a porous membrane made of ethylene-vinyl alcohol in the pack-type and spheroids with scaffolds. These membranes have countless pores of less than 0.1 µm² capable of secreting proteins, including alpha-galactosidase enzyme, and segregating the contents from the host immune system. When the packs were subcutaneously transplanted into the backs of green fluorescent protein (GFP) mice, no GFP-positive cells migrated to the transplanted pack in either autogenic or allogenic mice. The transplanted cells in the pack survived for 28 days after transplantation. When cells overexpressing alpha-galactosidase were used as donor cells for the packs and implanted into Fabry disease model mice, the accumulation of the alpha-galactosidase enzyme was also observed in the livers. In this study, we reported a new ex vivo therapeutic strategy combining macroencapsulation and cellular spheroids with scaffolds. This pack, macroencapsulated spheroids with scaffolds, can also be applied to other types of lysosomal diseases by modifying genes of interest.

Comparative urinary globotriaosylceramide analysis by thin-layer chromatography-immunostaining and liquid chromatography-tandem mass spectrometry in patients with Fabry disease

In Fabry disease, accumulation of glycolipids, predominantly globotriaosylceramide (Gb3), affects the kidneys, and nephropathy is one of the important disorders that influence the disease severity and prognosis of patients. Urinary Gb3 has been analyzed for diagnosis and monitoring of Fabry disease. In this study, we analyzed urinary Gb3 by thin-layer chromatography (TLC)-immunostaining and liquid chromatography (LC)-tandem mass spectrometry (MS/MS). An improved qualitative method, TLC-immunostaining, revealed excessive urinary Gb3 excretion in 100 (8/8), 88 (14/16), and 74% (45/61) of the classic Fabry males, later-onset Fabry males, and Fabry females examined, respectively. This authentic method is robust, easy, economic, and hardly affected by abundant urinary sediment, and this is useful for diagnosing individual Fabry patients. LC-MS/MS can determine the level of Gb3 in urine with high sensitivity, and it revealed that the Gb3 excretion level was higher in the order of classic Fabry males, later-onset Fabry males, Fabry females, and controls, respectively, and this is expected to be a useful quantitative method not only for diagnosis but also for predicting the progression of Fabry nephropathy. As to the relation of the urinary Gb3 level and renal events, our study revealed that the urinary Gb3 level in Fabry patients experiencing renal events tended to be higher than that in ones who did not have any renal events in each phenotypic group of the disease.

Fabry disease associated with multiple myeloma: a case report

Fabry disease (FD) is an X-linked genetic lysosomal disorder caused by alpha-galactosidase A (GLA) deficiency. Multiple myeloma (MM) predominately affects older adults, which ranks as the second commonest hematological malignancy. Their overlap has rarely been reported. We present a case of the coexistence of FD and MM in a patient. We report the case of a 68-year-old woman who was referred to our hospital for the evaluation of thoracic spine tumor with bone destruction. On admission, her serum creatinine (Cr) level was elevated to 12.70 mg/dL from the baseline value of 0.91 mg/dL. Bone marrow aspiration revealed MM. Renal biopsy showed myeloma cast nephropathy, which was the primary cause of acute kidney injury. Renal pathology also showed podocyte swelling and tubule myeloid bodies in a mosaic pattern compatible with female FD. Consequently, the patient was diagnosed as FD based on the germ line mutation in GLA. The patient was treated with bortezomib and dexamethasone therapy, which significantly improved the renal function. This is the second case demonstrating a potential pathogenic relationship between FD and MM. Since FD is one of the few genetic diseases for which there are therapeutic agents with fewer side effects, diagnostic value of FD is high. If an MM patient has multiple organ abnormalities or any familial history, the physician should suspect FD.

Cell Transplantation Combined with Recombinant Collagen Peptides for the Treatment of Fabry Disease

Fabry disease is caused by a decrease in or loss of the activity of alpha-galactosidase, which causes its substrates globotriaosylceramide (Gb3) and globotriaosylsphingosine (lyso-Gb3) to accumulate in cells throughout the body. This accumulation results in progressive kidney injury due to glomerulosclerosis and in heart failure due to hypertrophy. Enzyme replacement therapy (ERT) has been used as the standard therapy for Fabry disease, but it causes a significant financial burden, and regular administration is inconvenient for patients. Because of the short half-life of alpha-galactosidase in vivo, therapeutic methods that can supplement or replace ERT are expected to involve continuous release of alpha-galactosidase, even at low doses. Cell transplantation therapy is one of these methods; however, its use has been hindered by the short-term survival of transplanted cells. CellSaic technology, which utilizes cell spheroids that form after cells are seeded simultaneously with a recombinant collagen peptide scaffold called a μ-piece, has been used to improve cell survival upon implantation. In this study, syngeneic murine embryonic fibroblasts were used to generate CellSaic that were transplanted into Fabry mice. These spheroids survived for 28 days in the renal subcapsular space with forming blood vessels. These results indicate CellSaic technology could be a platform to promote cellular graft survival and may facilitate the development of cell transplantation methods for lysosomal diseases.

[Glial cells and pharmacological targets in Sandhoff disease]

Sandhoff disease (SD) is a genetic disorder caused by a mutation in the β-hexosaminidase B (HexB) gene in humans. This results in the massive accumulation of GM2 gangliosides in the nervous system, causing progressive neurodegeneration. The symptoms of SD include muscle weakness, seizures, and mental illness;along with loss of muscle coordination, vision, and hearing. In the most severe form, the onset begins during early infancy, and death usually occurs within 3-5 years of age. The established animal model, Hexb-deficient (Hexb^-/-) mouse, shows abnormalities that resemble the severe phenotype found in human infants. We have previously reported that activated microglia causes astrogliosis in Hexb^-/- mouse at the early stage of development that can be ameliorated via immunosuppression. Moreover, within the cerebral cortices of Hexb^-/- mouse, reactive astrocytes were found to express adenosine A_2A receptors in later inflammatory phases. Inhibiting this receptor with istradefylline decreases the number of activated microglial cells and inflammatory cytokines/chemokines. Thus, we underline the importance of the astrocytic A_2A receptor as a sensor, in regulating microglial activation in the late phase of inflammation.

Does administration of hydroxychloroquine/amiodarone accelerate accumulation of globotriaosylceramide and globotriaosylsphingosine in Fabry mice?

Drug-induced lysosomal storage disease (DILSD) caused by cationic amphiphilic drugs (CADs), which exhibits toxic manifestations and pathological findings mimicking Fabry disease (α-galactosidase A deficiency), has attracted the interests of clinicians and pathologists. Although the affected region is lysosomes in both the diseases, DILSD is characterized by intralysosomal accumulation of phospholipids and Fabry disease that of globotriaosylceramide (Gb3) and globotriaosylsphingosine (Lyso-Gb3). However, it is unknown whether administration of CADs affects the catabolism of Gb3 and Lyso-Gb3 in Fabry disease. In this study, we independently administered hydroxychloroquine/amiodarone to wild-type and Fabry mice and examined the effects of the drugs on the enzyme activity and substrates accumulated in organs and tissues. The results revealed that the administration of the drugs induced accumulation of phosphatidylcholine in both the wild-type and Fabry mice. However, reduction of α-galactosidase A activity in the organs and tissues of the wild-type mice was not found, and the storage of Gb3 and Lyso-Gb3 was not accelerated by these drugs in the Fabry mice. This suggests that hydroxychloroquine/amiodarone do not have any significant impact on the catabolism of Gb3 and Lyso-Gb3 in organs and tissues of both wild-type and Fabry mice.

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Effects of cationic amphiphilic drugs on the catabolism of Gb3/Lyso-Gb3 were examined.

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The drugs induced phospholipidosis in the wild-type and Fabry mice.

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The drugs did not induce reduction of α-galactosidase A activity in the wild-type mice.

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The drugs did not accelerate accumulation of Gb3/Lyso-gb3 in the Fabry mice.

Anti-drug antibody formation in Japanese Fabry patients following enzyme replacement therapy

Enzyme replacement therapy (ERT) for Fabry disease (deficiency of α-galactosidase A, α-Gal) with recombinant α-Gals (agalsidase alfa and agalsidase beta) is widely available and improves some of the clinical manifestations and biochemical findings. However, recent reports suggest that recurrent administration of recombinant enzymes often induces the formation of anti-drug antibodies, which may have a negative impact on the outcome of the therapy. We examined the formation of anti-drug antibodies using blood samples from 97 Japanese Fabry patients following ERT and tried to characterize them by means of enzyme-linked immunosorbent assay (ELISA), serum-mediated α-Gal inhibition, and immunochromatographic (IC) assay, followed by GLA gene analysis and measurement of plasma globotriaosylsphingosine (lyso-Gb3). ELISA revealed that 20/35 (57%) classic Fabry males were antibody (Immunoglobulin G, IgG) -positive (Ab+) at 6 months after the initiation of ERT, although only two of the seventeen (12%) later-onset Fabry males and none of the 45 Fabry females were. The Ab+ state was maintained at least until 24 months after the initiation of ERT in most of the cases, the exceptions being two patients who acquired immune tolerance during ERT. As many Ab+ patients have nonsense mutations, attention should be paid to the formation of anti-drug antibodies in Fabry patients harboring such gene mutations, who hardly produce α-Gal protein. Serum-mediated α-Gal inhibition was seen in most of the Ab+ patients and the antibodies affected the reduction of the plasma lyso-Gb3 level following ERT, suggesting that the antibodies inhibit the enzyme activity. There was a correlation between the results of the IC test and those of the ELISA. As the former is easy and rapid, it should be useful as a bed-side test.

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The anti-drug antibodies formed in Fabry patients during ERT were characterized.

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Serum-mediated α-Gal inhibition was seen in most of the antibody-positive patients.

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The immunochromatographic test is easy, rapid, and useful as a bed-side test.

Surface plasmon resonance analysis of complex formation of therapeutic recombinant lysosomal enzymes with domain 9 of human cation-independent mannose 6-phosphate receptor

The efficacy of enzyme replacement therapy (ERT) for lysosomal storage diseases (LSDs) possibly depends on the cellular uptake of recombinant lysosomal enzymes (LEs), and it is known that cation-independent mannose 6-phosphate receptor (CI-M6PR) on the cell membrane is predominantly involved in the endocytosis of many LEs. To examine the biomolecular interaction between therapeutic LEs and CI-M6PR, we biophysically analyzed the complex formation of four LEs available with domain 9 of human CI-M6PR, a binding site of the receptor, by means of surface plasmon resonance (SPR) biosensor assays. The results revealed that the affinity of the LEs for domain 9 of the receptor increased in the following order: laronidase, agalsidase beta, idursulfase, and alglucosidase alfa; and the high affinity of laronidase for domain 9 of CI-M6PR was due to fast complex formation rather than slow dissociation of the complex. The affinity of the enzymes for domain 9 of CI-M6PR almost coincided with their cellular uptake. The SPR biosensor assay is sensitive and provides important information for the development of effective therapeutic LEs for LSDs.

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The biomolecular interaction between LEs and domain 9 of human CI-M6PR was examined by means of SPR biosensor assays.

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The binding of LEs with the receptor increased in the order: laronidase, agalsidase beta, idursulfase, and agalsidase alfa.

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The strong binding of laronidase with the receptor was due to fast complex formation rather than slow dissociation of the complex.

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The affinity of the LEs for domain 9 of CI-M6PR almost coincided with the cellular uptake of the enzymes.

Effectiveness of immunosuppressive therapy for nephrotic syndrome in a patient with late-onset Fabry disease: a case report and literature review

BACKGROUND

Fabry disease (FD) is an X-linked lysosomal storage disorder caused by mutations of the GLA gene, followed by deficiency in α-galactosidase A (α-gal) activity. Nephrotic syndrome, as the renal phenotype of FD, is unusual. Here, we report the rare case of a patient with FD with nephrotic syndrome whose proteinuria disappeared by immunotherapy.

CASE PRESENTATION

A 67-year-old Japanese man was admitted to our hospital because of emesis, abdominal pain, and facial edema due to nephrotic syndrome. The patient was diagnosed with focal segmental glomerulosclerosis (FSGS) by renal biopsy before being diagnosed with FD, and immunotherapy was initiated. After treatment, the kidney biopsy results showed typical glycosphingolipid accumulation in the podocytes of this patient. The white blood cell α-gal activity was very low, and genetic analysis revealed a GLA gene variant (M296I), which is known as a late-onset genetic mutation of FD. Immunotherapy (steroids and cyclosporine A) dramatically improved the massive proteinuria. Currently, he has been undergoing enzyme replacement therapy, and his proteinuria has further decreased. There is the possibility that other nephrotic syndromes, such as minimal change nephrotic syndrome or FSGS, may co-exist in this patient.

CONCLUSIONS

We experienced the rare case of a FD patient whose nephrotic syndrome disappeared by immunotherapy. These findings suggest that immunosuppressive treatment may be considered if nephrotic syndrome develops, even in patients with FD.

Abnormal organization during neurodevelopment in a mouse model of Sandhoff disease

Sandhoff disease (SD) is a genetic disorder caused by a mutation of HEXB, which is the β-subunit gene of β-hexosaminidase A and B (HexA and HexB) in humans. HEXB mutation reduces HexA and HexB enzymatic activities, and results in the massive accumulation of ganglioside GM2 in the nervous system. Severe phenotypes of SD show progressive neurodegeneration in human infants, and lysosomal dysfunction that may affect the early development of the nervous system. In a previous study, neural stem cells (NSCs) and induced pluripotent stem cells derived from SD model mice, which are Hexb-deficient (Hexb^-/-), demonstrated impaired neuronal differentiation. This study investigated early neurodevelopment in vivo using Hexb^-/- mice. The structure of adult cerebral cortices of Hexb^-/- mice was normal. However, the expression of Sox2, an NSC-related gene, was reduced in the embryonic cerebral cortices of Hexb^-/- mice. Moreover, a reduction of early neuronal migration and differentiation was observed in the embryonic cerebral cortices of Hexb^-/- mice. In addition, we showed that the production of layer-specific neurons was delayed in somatosensory cerebral cortices of Hexb^-/- mice. These findings suggest that the alterations observed in embryonic Hexb^-/- mice may contribute to deficits in neurodevelopment of SD.

Fabry disease in a Japanese population-molecular and biochemical characteristics

We had experienced 117 Japanese Fabry patients (72 males and 45 females) from 1977 to 2006, and then we generated an improved Fabry analysis system in 2007 and have found 196 ones (95 males and 101 females) since then. In this study, we summarized the data of the patients and tried to elucidate the molecular and biochemical characteristics of Japanese Fabry patients. Gene analysis revealed various GLA mutations, including missense mutations (56.5%, 48 types); nonsense mutations (15.9%, 13 types); deletions (12.6%, 13 types); splicing defects (10.1%, 6 types); insertions (1.0%, 2 types), and insertions/deletions (0.5%, 1 type), in the patients that were tested. Amino acid substitutions resulting from the missense mutations found in the classic form patients tended to be localized in the core of the GLA protein, and those in the later-onset ones in the peripheral region. The most commonly identified pathogenic mutations are c.888G > A (p.M296I), c.936 + 919G > A, c.679C > T (p.R227X), c.335G > A (p.R112H), c.334C > T (p.R112C), and c.902G > A (p.R301Q). Among them, c.888G > A (p.M296I) is unique to Japanese Fabry patients. On the other hand, c.936 + 919G > A is a variant that has been frequently detected in Taiwan Chinese Fabry patients, and c.335G > A (p.R112H) in various countries. These are found in later-onset patients, and c.679C > T (p.R227X) and c.334C > T (p.R112C) classic ones. c.902G > A (p.R301Q) is found in both classic and later-onset form patients. A possible functional polymorphism, c.196G > C (p.E66Q), was identified in 0.4% of the subjects who underwent high-risk screening. The biochemical findings including leukocyte α-galactosidase A activity, plasma globotriaosylsphingosine level and urinary globotriaosylceramide in the individual phenotypic groups well reflected the phenotypic differences in this disease. The results will be useful for understanding the basis of Fabry disease in Japan.

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The characteristics of Japanese Fabry patients were elucidated.

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p.M296I unique to Japanese Fabry patients was commonly identified.

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The biochemical findings well reflected the phenotypic differences.

Mucopolysaccharidosis type VI (MPS VI) and molecular analysis: Review and classification of published variants in the ARSB gene

Maroteaux–Lamy syndrome (MPS VI) is an autosomal recessive lysosomal storage disorder caused by pathogenic ARSB gene variants, commonly diagnosed through clinical findings and deficiency of the arylsulfatase B (ASB) enzyme. Detection of ARSB pathogenic variants can independently confirm diagnosis and render genetic counseling possible. In this review, we collect and summarize 908 alleles (201 distinct variants, including 3 polymorphisms previously considered as disease‐causing variants) from 478 individuals diagnosed with MPS VI, identified from literature and public databases. Each variant is further analyzed for clinical classification according to American College of Medical Genetics and Genomics (ACMG) guidelines. Results highlight the heterogeneity of ARSB alleles, with most unique variants (59.5%) identified as missense and 31.7% of unique alleles appearing once. Only 18% of distinct variants were previously recorded in public databases with supporting evidence and clinical significance. ACMG recommends publishing clinical and biochemical data that accurately characterize pathogenicity of new variants in association with reporting specific alleles. Variants analyzed were sent to ClinVar (https://www.ncbi.nlm.nih.gov/clinvar/), and MPS VI locus‐specific database (http://mps6-database.org) where they will be available. High clinical suspicion coupled with diagnostic testing for deficient ASB activity and timely submission and classification of ARSB variants with biochemical and clinical data in public databases is essential for timely diagnosis of MPS VI.

Plasma lyso-Gb3: a biomarker for monitoring fabry patients during enzyme replacement therapy

BACKGROUND

Recently, globotriaosylsphingosine (lyso-Gb3) has attracted interest as a biomarker of Fabry disease. However, little is known regarding its utility for the evaluation of the therapeutic efficacy.

METHOD

We measured plasma lyso-Gb3 concentration in Japanese healthy subjects and Fabry patients by means of liquid chromatography-tandem mass spectrometry (LC-MS/MS). We determined the reference interval in Japanese (UMIN000016854), and examined the effect of enzyme replacement therapy (ERT) with recombinant α-galactosidase A (GLA) and the influence of antibodies against the enzyme on the plasma lyso-Gb3 level in Fabry patients (UMIN000017152).

RESULTS

The reference interval was determined to be 0.35-0.71 nmol/L, this being almost the same as the normal range in a non-Japanese population previously reported. The analysis revealed that the plasma lyso-Gb3 level was strikingly increased in classic Fabry males, and to a lesser extent in later-onset Fabry males and Fabry females. The elevation of the plasma lyso-Gb3 level was related to renal involvement in the Fabry females. ERT gave a rapid reduction in the elevated plasma lyso-Gb3 level in the classic Fabry males, and a gradual one or stabilization in most of the later-onset Fabry males and Fabry females. However, formation of antibodies against the recombinant GLA had a negative effect on the reduction of plasma lyso-Gb3.

CONCLUSIONS

Regular observation of plasma lyso-Gb3 and antibodies is useful for monitoring of Fabry patients during ERT.

In Vitro Study of Encapsulation Therapy for Fabry Disease Using Genetically Engineered CHO Cell Line

Fabry disease is an X-linked recessive disorder caused by a deficiency of the lysosomal hydrolase α-galac-tosidase A (α-gal). The deficiency of this enzyme leads to the systemic deposition of ceramide trihexoside (CTH) in various tissues and organs. Enzyme replacement using IV doses of recombinant human α-gal produced in CHO cells or in human fibroblasts is currently being evaluated in clinical trials as a potential therapy for this disease. However, it requires lifelong therapy involving a large amount of purified α-gal. As a novel approach for treatment of Fabry disease we used polymer encapsulated Chinese hamster ovary (CHO) cells genetically modified to express α-gal. The secreted high levels of α-gal passed through the semipermeable polymeric membrane. Using coculture system with Fabry fibroblasts, the secreted enzyme was taken up in cells, resulting in reduced accumulation of CTH in Fabry fibroblasts. This in vitro study demonstrated that an encapsulated α-gal-secreting cell line can be used to treat Fabry mice by transplantation in vivo. Judging from the protection against immune rejection by a semipermeable synthetic membrane, this novel approach may be applied to treat patients with Fabry disease and other lysosomal storage diseases.

Abnormal differentiation of Sandhoff disease model mouse-derived multipotent stem cells toward a neural lineage

In Sandhoff disease (SD), the activity of the lysosomal hydrolytic enzyme, β-hexosaminidase (Hex), is lost due to a Hexb gene defect, which results in the abnormal accumulation of the substrate, GM2 ganglioside (GM2), in neuronal cells, causing neuronal loss, microglial activation, and astrogliosis. We established induced pluripotent stem cells from the cells of SD mice (SD-iPSCs). In the present study, we investigated the occurrence of abnormal differentiation and development of a neural lineage in the asymptomatic phase of SD in vitro using SD mouse fetus-derived neural stem cells (NSCs) and SD-iPSCs. It was assumed that the number of SD mouse fetal brain-derived NSCs was reduced and differentiation was promoted, resulting in the inhibition of differentiation into neurons and enhancement of differentiation into astrocytes. The number of SD-iPSC-derived NSCs was also reduced, suggesting that the differentiation of NSCs was promoted, resulting in the inhibition of differentiation into neurons and enhancement of that into astrocytes. This abnormal differentiation of SD-iPSCs toward a neural lineage was reduced by the glucosylceramide synthase inhibitor, miglustat. Furthermore, abnormal differentiation toward a neural lineage was reduced in SD-iPSCs with Hexb gene transfection. Therefore, differentiation ability along the time axis appears to be altered in SD mice in which the differentiation ability of NSCs is promoted and differentiation into neurons is completed earlier, while the timing of differentiation into astrocytes is accelerated. These results clarified that the abnormal differentiation of SD-iPSCs toward a neural lineage in vitro was shown to reflect the pathology of SD.

Differences in cleavage of globotriaosylceramide and its derivatives accumulated in organs of young Fabry mice following enzyme replacement therapy

In Fabry disease, large amounts of globotriaosylceramide (Gb3) and related glycosphingolipids accumulate in organs due to a deficiency of α-galactosidase A (GLA) activity. Enzyme replacement therapy (ERT) with recombinant GLA is now available, and it has been reported that ERT is beneficial for patients with Fabry disease, especially those who start treatment at an early stage of the disease. However, it seems that the efficacy of ERT differs with each organ, and Gb3 accumulated in the kidneys shows resistance to ERT when it is started at a late stage. In this study, we examined the differences in cleavage of Gb3 isoforms, and lyso-Gb3 and its analogues in the kidneys, liver, and heart in young Fabry mice subjected to ERT. The results revealed that recurrent administration of recombinant GLA had prominent effects in terms of degradation of Gb3 and its derivatives accumulated in the organs. However, particular Gb3 isoforms, i.e., Gb3 (C20:0) and Gb3 (C24OH), accumulated in the kidneys largely escaped from degradation. Such Gb3 isoforms may gradually accumulate in the kidneys from a young age, which results in a reduction in the efficacy of ERT for Fabry disease.

Structural Basis of Mucopolysaccharidosis Type II and Construction of a Database of Mutant Iduronate 2-Sulfatases

Mucopolysaccharidosis type II (MPS II, Hunter syndrome) is an X-linked genetic disorder caused by a deficiency of iduronate 2-sulfatase (IDS), and missense mutations comprising about 30% of the mutations responsible for MPS II result in heterogeneous phenotypes ranging from the severe to the attenuated form. To elucidate the basis of MPS II from the structural viewpoint, we built structural models of the wild type and mutant IDS proteins resulting from 131 missense mutations (phenotypes: 67 severe and 64 attenuated), and analyzed the influence of each amino acid substitution on the IDS structure by calculating the accessible surface area, the number of atoms affected and the root-mean-square distance. The results revealed that the amino acid substitutions causing MPS II were widely spread over the enzyme molecule and that the structural changes of the enzyme protein were generally larger in the severe group than in the attenuated one. Coloring of the atoms influenced by different amino acid substitutions at the same residue showed that the structural changes influenced the disease progression. Based on these data, we constructed a database of IDS mutations as to the structures of mutant IDS proteins.

Molecular diagnosis of 65 families with mucopolysaccharidosis type II (Hunter syndrome) characterized by 16 novel mutations in the IDS gene: Genetic, pathological, and structural studies on iduronate-2-sulfatase

Mucopolysaccharidosis type II (MPS II: also called as Hunter syndrome) is an X-linked recessive lysosomal storage disorder characterized by the accumulation of extracellular glycosaminoglycans due to the deficiency of the enzyme iduronate-2-sulfatase (IDS). Previous observations suggested that MPS II can be classified into two distinct disease subtypes: (1) severe type of MPS II involves a decline in the cognitive ability of a patient and (2) attenuated type of MPS II exhibits no such intellectual phenotype. To determine whether such disease subtypes of MPS II could be explained by genetic diagnosis, we analyzed mutations in the IDS gene of 65 patients suffering from MPS II among the Japanese population who were diagnosed with both the accumulation of urinary glycosaminoglycans and a decrease in their IDS enzyme activity between 2004 and 2014. Among the specimens examined, we identified the following mutations: 33 missense, 8 nonsense, 7 frameshift, 4 intronic changes affecting splicing, 8 recombinations involving IDS-IDS2, and 7 other mutations including 4 large deletions. Consistent with the previous data, the results of our study showed that most of the attenuated phenotype was derived from the missense mutations of the IDS gene, whereas mutations associated with a large structural alteration including recombination, splicing, frameshift, and nonsense mutations were linked to the severe phenotype of MPS II. Furthermore, we conducted a homology modeling study of IDS P120R and N534I mutant as representatives of the causative mutation of the severe and attenuated type of MPS II, respectively. We found that the substitution of P120R of the IDS enzyme was predicted to deform the α-helix generated by I119-F123, leading to the major structural alteration of the wild-type IDS enzyme. In sharp contrast, the effect of the structural alteration of N534I was marginal; thus, this mutation was pathogenically predicted to be associated with the attenuated type of MPS II. These results suggest that a combination of the genomic diagnosis of the IDS gene and the structural prediction of the IDS enzyme could enable the prediction of a phenotype more effectively.

Combined replacement effects of human modified β-hexosaminidase B and GM2 activator protein on GM2 gangliosidoses fibroblasts

GM2 gangliosidoses are autosomal recessive lysosomal storage diseases (LSDs) caused by mutations in the HEXA, HEXB and GM2A genes, which encode the human lysosomal β-hexosaminidase (Hex) α- and β-subunits, and GM2 activator protein (GM2A), respectively. These diseases are associated with excessive accumulation of GM2 ganglioside (GM2) in the brains of patients with neurological symptoms. Here we established a CHO cell line overexpressing human GM2A, and purified GM2A from the conditioned medium, which was taken up by fibroblasts derived from a patient with GM2A deficiency, and had the therapeutic effects of reducing the GM2 accumulated in fibroblasts when added to the culture medium. We also demonstrated for the first time that recombinant GM2A could enhance the replacement effect of human modified HexB (modB) with GM2-degrading activity, which is composed of homodimeric altered β-subunits containing a partial amino acid sequence of the α-subunit, including the GSEP loop necessary for binding to GM2A, on reduction of the GM2 accumulated in fibroblasts derived from a patient with Tay-Sachs disease, a HexA (αβ heterodimer) deficiency, caused by HEXA mutations. We predicted the same manner of binding of GM2A to the GSEP loop located in the modified HexB β-subunit to that in the native HexA α-subunit on the basis of the x-ray crystal structures. These findings suggest the effectiveness of combinational replacement therapy involving the human modified HexB and GM2A for GM2 gangliosidoses.

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Purification of recombinant human GM2A proteins by CHO cell line overexpressing GM2A.

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Reduction of GM2 accumulated in GM2A deficiency fibroblasts by GM2A replacement.

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Combined effects of modified HexB and GM2A for HexA deficiency fibroblasts.

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In silico prediction of molecular interaction between modified HexB and GM2A.

Protease-resistant modified human β-hexosaminidase B ameliorates symptoms in GM2 gangliosidosis model

GM2 gangliosidoses, including Tay-Sachs and Sandhoff diseases, are neurodegenerative lysosomal storage diseases that are caused by deficiency of β-hexosaminidase A, which comprises an αβ heterodimer. There are no effective treatments for these diseases; however, various strategies aimed at restoring β-hexosaminidase A have been explored. Here, we produced a modified human hexosaminidase subunit β (HexB), which we have termed mod2B, composed of homodimeric β subunits that contain amino acid sequences from the α subunit that confer GM2 ganglioside-degrading activity and protease resistance. We also developed fluorescent probes that allow visualization of endocytosis of mod2B via mannose 6-phosphate receptors and delivery of mod2B to lysosomes in GM2 gangliosidosis models. In addition, we applied imaging mass spectrometry to monitor efficacy of this approach in Sandhoff disease model mice. Following i.c.v. administration, mod2B was widely distributed and reduced accumulation of GM2, asialo-GM2, and bis(monoacylglycero)phosphate in brain regions including the hypothalamus, hippocampus, and cerebellum. Moreover, mod2B administration markedly improved motor dysfunction and a prolonged lifespan in Sandhoff disease mice. Together, the results of our study indicate that mod2B has potential for intracerebrospinal fluid enzyme replacement therapy and should be further explored as a gene therapy for GM2 gangliosidoses.

Distributions of Globotriaosylceramide Isoforms, and Globotriaosylsphingosine and Its Analogues in an α-Galactosidase A Knockout Mouse, a Model of Fabry Disease

Fabry disease is caused by deficient activity of α-galactosidase A (GLA) and characterized by systemic accumulation of glycosphingolipids, substrates of the enzyme. To gain insight into the pathogenesis of Fabry disease based on accumulated substrates, we examined the tissue and plasma distributions of globotriaosylceramide (Gb3) isoforms, and globotriaosylsphingosine (lyso-Gb3) and its analogues in a GLA knockout mouse, a model of Fabry disease, by means of liquid chromatography-mass spectrometry and nano-liquid chromatography-tandem mass spectrometry, respectively. The results revealed that the contents of these substrates in the liver, kidneys, heart, and plasma of GLA knockout mice were apparently higher than in those of wild-type ones, and organ specificity in the accumulation of Gb3 isoforms was found. Especially in the kidneys, accumulation of a large amount of Gb3 isoforms including hydroxylated residues was found. In the GLA knockout mice, the proportion of hydrophobic Gb3 isoforms was apparently higher than that in the wild-type mice. On the other hand, hydrophilic residues were abundant in plasma. Unlike that of Gb3, the concentration of lyso-Gb3 was high in the liver, and the lyso-Gb3/Gb3 ratio in plasma was significantly higher than those in the organs. The concentration of lyso-Gb3 was apparently higher than those of its analogues in the organs and plasma from both the GLA knockout and wild-type mice. This information will be useful for elucidating the basis of Fabry disease.

Clinical and biochemical investigation of male patients exhibiting membranous cytoplasmic bodies in biopsied kidney tissues; a pitfall in diagnosis of Fabry disease

Background: The existence of membranous cytoplasmic bodies in biopsied kidney tissues is one of the important findings when considering Fabry disease as the first choice diagnosis. However, there are possible acquired lysosomal diseases associated with pharmacological toxicity, although less attention has been paid to them.

Case Presentation: We experienced 3 male patients presenting with proteinuria and specific pathological changes strongly suggesting Fabry disease. We sought detailed clinical and biochemical information to avoid a wrong diagnosis. The patients were examined clinically and pathologically, and plasma α-galactosidase A (GLA) activity and the globotriaosylsphingosine (lyso-Gb3) concentrations were measured. Electron microscopic examination revealed numerous membranous inclusion bodies in podocytes, and biochemical analysis revealed normal GLA activity and a normal lyso-Gb3 level in plasma, showing that they did not have Fabry disease. They suffered from hyperlipidemia, myeloma, or lupus nephritis. They had received pitavastatin calcium, clarithromycin, loxoprofen and/or prednisolone, and there was no medication history of cationic amphiphilic drugs.

Conclusions: In this case series, the etiology of the inclusions was not clarified. However, these cases indicate that careful attention should be paid on diagnosis of patients exhibiting inclusion bodies in kidney cells, and it is important to confirm their past and present illnesses, and medication history as well as to measure the GLA activity and lyso-Gb3 level.

Chaperone therapy for Krabbe disease: potential for late-onset GALC mutations

Krabbe disease is an autosomal recessive leukodystrophy caused by a deficiency of the galactocerebrosidase (GALC) enzyme. Hematopoietic stem cells transplantation is the only available treatment option for pre-symptomatic patients. We have previously reported the chaperone effect of N-octyl-4-epi-β-valienamine (NOEV) on mutant GM1 β-galactosidase proteins, and in a murine GM1-gangliosidosis model. In this study, we examined its chaperone effect on mutant GALC proteins. We found that NOEV strongly inhibited GALC activity in cell lysates of GALC-transfected COS1 cells. In vitro NOEV treatment stabilized GALC activity under heat denaturation conditions. We also examined the effect of NOEV on cultured COS1 cells expressing mutant GALC activity and human skin fibroblasts from Krabbe disease patients: NOEV significantly increased the enzyme activity of mutants of late-onset forms. Moreover, we confirmed that NOEV could enhance the maturation of GALC precursor to its mature active form. Model structural analysis showed NOEV binds to the active site of human GALC protein. These results, for the first time, provide clear evidence that NOEV is a chaperone with promising potential for patients with Krabbe disease resulting from the late-onset mutations.

Rapid Immunochromatographic Detection of Serum Anti-α-Galactosidase A Antibodies in Fabry Patients after Enzyme Replacement Therapy

We developed an immunochromatography-based assay for detecting antibodies against recombinant α-galactosidase A proteins in serum. The evaluation of 29 serum samples from Fabry patients, who had received enzyme replacement therapy with agalsidase alpha and/or agalsidase beta, was performed by means of this assay method, and the results clearly revealed that the patients exhibited the same level of antibodies against both agalsidase alpha and agalsidase beta, regardless of the species of recombinant α-galactosidase A used for enzyme replacement therapy. A conventional enzyme-linked immunosorbent assay supported the results. Considering these, enzyme replacement therapy with agalsidase alpha or agalsidase beta would generate antibodies against the common epitopes in both agalsidase alpha and agalsidase beta. Most of the patients who showed immunopositive reaction exhibited classic Fabry phenotype and harbored gene mutations affecting biosynthesis of α-galactosidase A. As immunochromatography is a handy and simple assay system which can be available at bedside, this assay method would be extremely useful for quick evaluation or first screening of serum antibodies against agalsidase alpha or agalsidase beta in Fabry disease with enzyme replacement therapy.

Late onset variants in Fabry disease: Results in high risk population screenings in Argentina

Background

Screening for Fabry disease (FD) in high risk populations yields a significant number of individuals with novel, ultra rare genetic variants in the GLA gene, largely without classic manifestations of FD. These variants often have significant residual α-galactosidase A activity. The establishment of the pathogenic character of previously unknown or rare variants is challenging but necessary to guide therapeutic decisions.

Objectives

To present 2 cases of non-classical presentations of FD with renal involvement as well as to discuss the importance of high risk population screenings for FD.

Results

Our patients with non-classical variants were diagnosed through FD screenings in dialysis units. However, organ damage was not limited to kidneys, since LVH, vertebrobasilar dolichoectasia and cornea verticillata were also present. Lyso-Gb3 concentrations in plasma were in the pathologic range, compatible with late onset FD. Structural studies and in silico analysis of p.(Cys174Gly) and p.(Arg363His), employing different tools, suggest that enzyme destabilization and possibly aggregation could play a role in organ damage.

Conclusions

Screening programs for FD in high risk populations are important as FD is a treatable multisystemic disease which is frequently overlooked in patients who present without classical manifestations.

Nano-LC-MS/MS for Quantification of Lyso-Gb3 and Its Analogues Reveals a Useful Biomarker for Fabry Disease

Biomarkers useful for diagnosis and evaluation of treatment for patients with Fabry disease are urgently needed. Recently, plasma globotriaosylsphingosine (lyso-Gb3) and lyso-Gb3-related analogues have attracted attention as promising biomarkers of Fabry disease. However, the plasma concentrations of lyso-Gb3 and its analogues are extremely low or below the detection limits in some Fabry patients as well as in healthy subjects. In this paper, we introduce the novel application of a nano-liquid chromatography-tandem mass spectrometry (nano-LC-MS/MS) system to the measurement of lyso-Gb3 and its analogues in plasma. Nano-LC-MS/MS requires smaller amounts of samples and is more sensitive than conventional techniques. Using this method, we measured the plasma concentrations of lyso-Gb3 and its analogues in 40 healthy subjects, 5 functional variants (males with E66Q), and various Fabry patients (9 classic Fabry males/9 mutations; 7 later-onset Fabry males/5 mutations; and 10 Fabry females/9 mutations). The results revealed that the mean lyso-Gb3 and lyso-Gb3(-2) concentrations in all the Fabry patient subgroups were statistically higher, especially in the classic Fabry males, than those in the functional variants and healthy subjects. The plasma concentrations of lyso-Gb3 and its analogues in healthy subjects, functional variants, and some Fabry patients with specific mutations (R112H and M296I) that cannot be established by conventional techniques were successfully determined by means of nano-LC-MS/MS. The lyso-Gb3 and lyso-Gb3(-2) concentrations in male patients with these mutations were lower than those in most Fabry patients having other mutations, but higher than those in the functional variants and healthy subjects. This new method is expected to be useful for sensitive determination of the plasma concentrations of lyso-Gb3 and its analogues. This study also revealed that not only lyso-Gb3 but also lyso-Gb3(-2) in plasma is a useful biomarker for the diagnosis of Fabry disease.

Plasma mutant α-galactosidase A protein and globotriaosylsphingosine level in Fabry disease

Fabry disease is an X-linked genetic disorder characterized by deficient activity of α-galactosidase A (GLA) and accumulation of glycolipids, and various GLA gene mutations lead to a wide range of clinical phenotypes from the classic form to the later-onset one. To investigate the biochemical heterogeneity and elucidate the basis of the disease using available clinical samples, we measured GLA activity, GLA protein and accumulated globotriaosylsphingosine (Lyso-Gb3), a biomarker of this disease, in plasma samples from Fabry patients. The analysis revealed that both the enzyme activity and the protein level were apparently decreased, and the enzyme activity was well correlated with the protein level in many Fabry patients. In these cases, a defect of biosynthesis or excessive degradation of mutant GLAs should be involved in the pathogenesis, and the residual protein level would determine the accumulation of Lyso-Gb3 and the severity of the disease. However, there are some exceptional cases, i.e., ones harboring p.C142Y, p.R112H and p.M296I, who exhibit a considerable amount of GLA protein. Especially, a subset of Fabry patients with p.R112H or p.M296I has been attracted interest because the patients exhibit almost normal plasma Lyso-Gb3 concentration. Structural analysis revealed that C142Y causes a structural change at the entrance of the active site. It will lead to a complete enzyme activity deficiency, resulting in a high level of plasma Lyso-Gb3 and the classic Fabry disease. On the other hand, it is thought that R112H causes a relatively large structural change on the molecular surface, and M296I a small one in a restricted region from the core to the surface, both the structural changes being far from the active site. These changes will cause not only partial degradation but also degeneration of the mutant GLA proteins, and the degenerated enzymes exhibiting small and residual activity remain and probably facilitate degradation of Lyso-Gb3 in plasma, leading to the later-onset phenotype. The results of this comprehensive analysis will be useful for elucidation of the basis of Fabry disease.

A case of Fabry nephropathy with histological features of oligonephropathy

Newborn screening studies indicate the expected high incidence of later-onset Fabry disease with silent Fabry nephropathy while, with recent improved clinical care of premature infants, children with congenital oligonephropathy caused by premature embryonal development of the kidney are thought to be increasing. However, the coexistence of Fabry nephropathy and oligonephropathy has not been reported previously. We present the case of a 13-year-old boy who was diagnosed with Fabry nephropathy accompanied with histological features of oligonephropathy. He was born as a preterm baby, and a renal biopsy was performed because of mild renal dysfunction and mild proteinuria. He had neither characteristic early symptoms nor a family history of Fabry disease. Histologic findings demonstrated diffuse global enlargement and foamy change of podocytes with markedly decreased number and enlargement of the glomeruli. Both his plasma and leukocyte α-galactosidase A (GLA) activities were markedly decreased, and the plasma globotriaosylsphingosine and urine globotriaosylceramide levels were increased. Gene analysis revealed a missense mutation, R112H, in the GLA gene, which had been reported in the later-onset phenotype of Fabry patients. He is now under treatment with enzyme replacement therapy and an angiotensin-converting enzyme inhibitor.

CONCLUSION

This case indicated the possible co-occurrence of Fabry nephropathy and oligonephropathy. For early diagnosis and timely management, careful examinations for proteinuria and renal function, in addition to establishing an effective screening system for Fabry disease, will be necessary.

Molecular basis of 1-deoxygalactonojirimycin arylthiourea binding to human α-galactosidase a: pharmacological chaperoning efficacy on Fabry disease mutants

Fabry disease (FD) is an X-linked lysosomal storage disorder caused by mutations in the GLA gene often leading to missense α-galactosidase A (α-Gal A) variants that undergo premature endoplasmic reticulum-associated degradation due to folding defects. We have synthesized and characterized a new family of neutral amphiphilic pharmacological chaperones, namely 1-deoxygalactonojirimycin-arylthioureas (DGJ-ArTs), capable of stabilizing α-Gal A and restoring trafficking. Binding to the enzyme is reinforced by a strong hydrogen bond involving the aryl-N'H thiourea proton and the catalytic aspartic acid acid D231 of α-Gal A, as confirmed by a 2.55 Å resolution cocrystal structure. Selected candidates enhanced α-Gal A activity and ameliorate globotriaosylceramide (Gb3) accumulation and autophagy impairments in FD cell cultures. Moreover, they acted synergistically with the proteostasis regulator 4-phenylbutyric acid, appearing to be promising leads as pharmacological chaperones for FD.

Comparative study on mannose 6-phosphate residue contents of recombinant lysosomal enzymes

As most recombinant lysosomal enzymes are incorporated into cells via mannose 6-phosphate (M6P) receptors, the M6P content is important for effective enzyme replacement therapy (ERT) for lysosomal diseases. However, there have been no comprehensive reports of the M6P contents of lysosomal enzymes. We developed an M6P assay method comprising three steps, i.e., acid hydrolysis of glycoproteins, derivatization of M6P, and high-performance liquid chromatography, and determined the M6P contents of six recombinant lysosomal enzymes now available for ERT and one in the process of development. The assay is easy, specific, and reproducible. The results of the comparative study revealed that the M6P contents of agalsidase alfa, agalsidase beta, modified α-N-acetylgalactosaminidase, alglucosidase alfa, laronidase, idursulfase, and imiglucerase are 2.1, 2.9, 5.9, 0.7, 2.5, 3.2, and <0.3 mol/mol enzyme, respectively. The results were correlated with those of the biochemical analyses previously performed and that of the binding assay of exposed M6P of the enzymes with the domain 9 of the cation-independent M6P receptor. This assay method is useful for comparison of the M6P contents of recombinant lysosomal enzymes for ERT.

Structural and clinical implications of amino acid substitutions in α-L-iduronidase: insight into the basis of mucopolysaccharidosis type I

Allelic mutations, predominantly missense ones, of the α-l-iduronidase (IDUA) gene cause mucopolysaccharidosis type I (MPS I), which exhibits heterogeneous phenotypes. These phenotypes are basically classified into severe, intermediate, and attenuated types. We previously examined the structural changes in IDUA due to MPS I by homology modeling, but the reliability was limited because of the low sequence identity. In this study, we built new structural models of mutant IDUAs due to 57 amino acid substitutions that had been identified in 27 severe, 1 severe-intermediate, 13 intermediate, 1 attenuated-intermediate and 15 attenuated type MPS I patients based on the crystal structure of human IDUA, which was recently determined by us. The structural changes were examined by calculating the root-mean-square distances (RMSD) and the number of atoms influenced by the amino acid replacements. The results revealed that the structural changes of the enzyme protein tended to be correlated with the severity of the disease. Then we focused on the structural changes resulting from amino acid replacements in the immunoglobulin-like domain and adjacent region, of which the structure had been missing in the IDUA model previously built. Coloring of atoms influenced by an amino acid substitution was performed in each case and the results revealed that the structural changes occurred in a region far from the active site of IDUA, suggesting that they affected protein folding. Structural analysis is thus useful for elucidation of the basis of MPS I.

Development of a highly sensitive immuno-PCR assay for the measurement of α-galactosidase A protein levels in serum and plasma

Fabry disease is an X-linked genetic disorder caused by defects in the α-galactosidase A (GLA) gene, and heterogeneous mutations lead to quantitative and/or qualitative defects in GLA protein in male patients with Fabry disease. Random X-chromosomal inactivation modifies the clinical and biochemical features of female patients with Fabry disease. Functional polymorphisms have been frequently reported in recent times, and these increase the difficulty of understanding the pathogenetic basis of the disease. To date, GLA protein level has been measured using an enzyme-linked immunosorbent assay (ELISA). However, ELISA is not highly sensitive due to the high background noise. In this paper, we introduce a novel application of the immuno-polymerase chain reaction (PCR) method (termed Multiple Simultaneous Tag [MUSTag]) for measurement of the GLA protein level in blood samples. We compared the sensitivities of the MUSTag method with plates or magnetic beads with those of ELISA for recombinant human GLA and found that the apparent maximal sensitivity was higher for the former than for the latter. We then measured the GLA concentrations in serum and plasma from male patients with classic Fabry disease (Male Fabry), females with Fabry disease (Female Fabry), male subjects harboring the functional polymorphism p.E66Q (E66Q), and control (Control) subjects. Our results revealed that compared to the MUSTag plate and ELISA, the MUSTag beads assay afforded a clearer estimation of the GLA protein levels in the serum and plasma with minimal or no background noise, although all the methods could differentiate between the Male Fabry, E66Q, and Control groups. The Female Fabry group showed characteristic heterogeneity, which was consistent with the X-linked inheritance. This novel method is expected to be useful for the sensitive determination of GLA level in blood and elucidation of the pathogenetic basis of Fabry disease.

Impaired neural differentiation of induced pluripotent stem cells generated from a mouse model of Sandhoff disease

Sandhoff disease (SD) is a glycosphingolipid storage disease that arises from mutations in the Hexb gene and the resultant deficiency in β-hexosaminidase activity. This deficiency results in aberrant lysosomal accumulation of the ganglioside GM2 and related glycolipids, and progressive deterioration of the central nervous system. Dysfunctional glycolipid storage causes severe neurodegeneration through a poorly understood pathogenic mechanism. Induced pluripotent stem cell (iPSC) technology offers new opportunities for both elucidation of the pathogenesis of diseases and the development of stem cell-based therapies. Here, we report the generation of disease-specific iPSCs from a mouse model of SD. These mouse model-derived iPSCs (SD-iPSCs) exhibited pluripotent stem cell properties and significant accumulation of GM2 ganglioside. In lineage-directed differentiation studies using the stromal cell-derived inducing activity method, SD-iPSCs showed an impaired ability to differentiate into early stage neural precursors. Moreover, fewer neurons differentiated from neural precursors in SD-iPSCs than in the case of the wild type. Recovery of the Hexb gene in SD-iPSCs improved this impairment of neuronal differentiation. These results provide new insights as to understanding the complex pathogenic mechanisms of SD.

A mutant mRNA expression in an endomyocardial biopsy sample obtained from a patient with a cardiac variant of Fabry disease caused by a novel acceptor splice site mutation in the invariant AG of intron 5 of the α-galactosidase A gene

We herein describe the case of a 58-year-old man who presented with dilated-phase hypertrophic cardiomyopathy (HCM) and required an implantable cardioverter defibrillator implant. Subsequently, the patient was diagnosed with Fabry disease (FD), which was suspected based on the results of an endomyocardial biopsy and diagnosed following demonstration of deficient α-galactosidase A (GLA) activity. Molecular studies showed a novel point mutation in the 3' splice site consensus sequence of intron 5 in the gene encoding GLA that created a new splicing site, resulting in the expression of mutant mRNA. FD should be considered a cause of HCM in patients with severe tachyarrhythmia without other remarkable manifestations of FD.

Mutant α-galactosidase A with M296I does not cause elevation of the plasma globotriaosylsphingosine level

Recently, plasma globotriaosylsphingosine (lyso-Gb3) has attracted attention as a biomarker of Fabry disease. However, we found a subset of Fabry disease patients who did not show any increase in the plasma lyso-Gb3 concentration, although other patients exhibited apparent enhancement of it. This subset predominantly exhibited the clinical phenotype of later-onset Fabry disease, and gene analysis revealed that the patients harbored the M296I mutation common to Japanese Fabry patients. This amino acid substitution is predicted to cause a small conformational change on the surface of the α-galactosidase A molecule, resulting in residual enzyme activity. Plasma lyso-Gb3 is a good biomarker of Fabry disease but care should be taken when it is used for a definitive diagnosis.

Crystallization, X-ray diffraction analysis and SIRAS phasing of human α-L-iduronidase

Human lysosomal α-L-iduronidase, whose deficiency causes mucopolysaccharidosis type I, was crystallized using sodium/potassium tartrate and polyethylene glycol 3350 as a precipitant. Using synchrotron radiation, a native data set was collected from a single crystal at 100 K to 2.3 Å resolution. The crystal belonged to space group R3 with unit-cell dimensions of a=b=259.22, c=71.83 Å. To obtain the phase information, mercury-derivative crystals were prepared and a single-wavelength anomalous dispersion (SAD) data set was collected at the Hg peak wavelength. Phase calculation with the single isomorphous replacement with anomalous scattering (SIRAS) method successfully yielded an interpretable electron-density map.