Non-invasive high-risk screening for Fabry disease hemizygotes and heterozygotes

Urine-derived cells: a promising diagnostic tool in Fabry disease patients

Fabry disease is a lysosomal storage disorder resulting from impaired alpha-galactosidase A (α-Gal A) enzyme activity due to mutations in the GLA gene. Currently, powerful diagnostic tools and in vivo research models to study Fabry disease are missing, which is a major obstacle for further improvements in diagnosis and therapy. Here, we explore the utility of urine-derived primary cells of Fabry disease patients. Viable cells were isolated and cultured from fresh urine void. The obtained cell culture, modeling the renal epithelium, is characterized by patient-specific information. We demonstrate that this non-invasive source of patient cells provides an adequate cellular in vivo model as cells exhibit decreased α-Gal A enzyme activity and concomitant globotriaosylceramide accumulation. Subsequent quantitative proteomic analyses revealed dysregulation of endosomal and lysosomal proteins indicating an involvement of the Coordinated Lysosomal Expression and Regulation (CLEAR) network in the disease pathology. This proteomic pattern resembled data from our previously described human podocyte model of Fabry disease. Taken together, the employment of urine-derived primary cells of Fabry disease patients might have diagnostic and prognostic implications in the future. Our findings pave the way towards a more detailed understanding of pathophysiological mechanisms and may allow the development of future tailored therapeutic strategies.

Prevalence of Fabry disease in dialysis patients: Japan Fabry disease screening study (J-FAST)

BACKGROUND

In Fabry disease, progressive glycolipid accumulation leads to damage in kidney and other organs. This study was designed to determine the prevalence rate of Fabry disease in Japanese dialysis patients.

METHODS

All dialysis patients agreeing to Japan Fabry disease screening study (J-FAST) with informed consent were selected except for Fabry disease. The screening was performed by a method of measuring plasma and/or leukocytes lysosomal α-galactosidase A protein level and α-galactosidase A activity. If positive, genetic analysis was carried out upon patient's agreement.

RESULTS

J-FAST dealt with 8547 patients (male 5408, female 3139). At the tertiary examination, 26 out of 8547 patients were found to be positive. Six out of 26 patients could not accept genetic analysis because of death. Remaining 20 patients agreed with genetic analysis; then 2 patients (male 2, female 0) had a variation of the α-Gal gene and 11 patients showed E66Q variations. Therefore, the frequency of Fabry disease in J-FAST was 0.04 % (2/5408) in males and 0 % (0/3139) in females, and then 0.02 % (2/8547) in all patients. The presumptive clinical diagnoses of end-stage kidney disease (ESKD) were 10 chronic glomerulonephritis, 7 diabetic nephropathy, 3 unknown etiology, 3 nephrosclerosis, 1 gouty nephropathy, 1 autosomal dominant polycystic kidney disease and 1 renal tuberculosis among 26 tertiary positive patients. Two male Fabry patients were initially diagnosed as nephrosclerosis and chronic glomerulonephritis.

CONCLUSIONS

The prevalence rate of Fabry disease in J-FAST was 0.02 %. Moreover, Fabry disease could not be ruled out as the clinical diagnosis of ESKD.

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.

A pharmacogenetic approach to identify mutant forms of α-galactosidase A that respond to a pharmacological chaperone for Fabry disease

Fabry disease is caused by mutations in the gene (GLA) that encodes α-galactosidase A (α-Gal A). The iminosugar AT1001 (GR181413A, migalastat hydrochloride, 1-deoxygalactonojirimycin) is a pharmacological chaperone that selectively binds and stabilizes α-Gal A, increasing total cellular levels and activity for some mutant forms (defined as “responsive”). In this study, we developed a cell-based assay in cultured HEK-293 cells to identify mutant forms of α-Gal A that are responsive to AT1001. Concentration-dependent increases in α-Gal A activity in response to AT1001 were shown for 49 (60%) of 81 mutant forms. The responses of α-Gal A mutant forms were generally consistent with the responses observed in male Fabry patient-derived lymphoblasts. Importantly, the HEK-293 cell responses of 19 α-Gal A mutant forms to a clinically achievable concentration of AT1001 (10 µM) were generally consistent with observed increases in α-Gal A activity in peripheral blood mononuclear cells from male Fabry patients orally administered AT1001 during Phase 2 clinical studies. This indicates that the cell-based responses can identify mutant forms of α-Gal A that are likely to respond to AT1001 in vivo. Thus, the HEK-293 cell-based assay may be a useful aid in the identification of Fabry patients with AT1001-responsive mutant forms. Hum Mutat 32:1–13, 2011. © 2011 Wiley-Liss, Inc.

Elevation of urinary globotriaosylceramide (GL3) in infants with Fabry disease

BACKGROUND

Fabry disease is caused by a deficiency of α-galactosidase A (α-Gal A), which results in the accumulation of globotriaosylceramide (GL3) and related glycosphingolipids in different organs. Urinary GL3 levels increase in symptomatic Fabry disease patients, but it is not clear whether urinary GL3 excretion also increases in young or pre-symptomatic patients.

SUBJECTS AND METHODS

Eighty-nine newborns with leukocyte α-Gal A activities of less than 30% of the normal mean were discovered by newborn screening. Urine samples were collected on filter paper, and GL3 levels were measured using liquid chromatography-tandem mass spectrometry.

RESULTS

Five newborns with classic Fabry disease mutations all had elevated urinary GL3 levels (mean=5.2 mg/mmol creatinine (creat.), range=0.80-14.39, normal <0.6). Among the 84 newborns with later-onset mutations, 45 (54%) had a mild elevation of urinary GL3 levels (mean=1.1 mg/mmol creat., range=0.60-3.07, normal <0.6). The urinary GL3 levels decreased in all newborns over the course of a three-year follow-up period. However, four children with classic mutations and seven with IVS4+919G>A mutations still had elevated GL3 levels at the end of the study.

CONCLUSION

Elevated urinary GL3 levels can be present at birth in Fabry disease patients, suggesting an early involvement of the kidneys in this disease. The increased urinary GL3 excretion in those with later-onset mutations supports a pathogenic role for these mutations.

Fabry disease: a review of current management strategies

Fabry disease is an X-linked inherited condition due to the absence or reduction of alpha-galactosidase activity in lysosomes, that results in accumulation of globotriaosylceramide (Gb3) and related neutral glycosphingolipids. Manifestations of Fabry disease include serious and progressive impairment of renal and cardiac function. In addition, patients experience pain, gastrointestinal disturbance, transient ischaemic attacks and strokes. Additional effects on the skin, eyes, ears, lungs and bones are often seen. The first symptoms of classic Fabry disease usually appear in childhood. Despite being X-linked, females can suffer the same severity of symptoms as males, and life expectancy is reduced in both females and males. Enzyme replacement therapy (ERT) can stabilize the progression of the disease. The rarity of the classic form of Fabry disease, however, means that there is a need to improve the knowledge and understanding that the majority of physicians have concerning Fabry disease, in order to avoid misdiagnosis and/or delayed diagnosis. This review aims to raise awareness of the signs and symptoms of Fabry disease; to provide a general diagnostic algorithm and to give an overview of the effects of ERT and concomitant treatments. We highlight a need to develop comprehensive international guidelines to optimize ERT and adjunctive therapy in patients with Fabry disease, including females and children.

Plasma globotriaosylsphingosine as a biomarker of Fabry disease

Fabry disease is an X-linked genetic disorder caused by a deficiency of alpha-galactosidase A (GLA) activity. As enzyme replacement therapy (ERT) involving recombinant GLAs has been introduced for this disease, a useful biomarker for diagnosis and monitoring of therapy has been strongly required. We measured globotriaosylsphingosine (lyso-Gb3) and globotriaosylceramide (Gb3) in plasma samples from ten hemizygous males (six classic and four variant cases) and eight heterozygous females with Fabry disease, and investigated the responses of plasma lyso-Gb3 and Gb3 in a male Fabry patient who had undergone ERT for 4years to determine whether plasma lyso-Gb3 and Gb3 could be biomarkers of Fabry disease. The results revealed that plasma lyso-Gb3 was apparently increased in male patients and was higher in cases of the classic form than those of the variant one. In Fabry females, plasma lyso-Gb3 was moderately increased in both symptomatic and asymptomatic cases, and there was a correlation between the increase in lyso-Gb3 and the decrease in GLA activity. As to plasma Gb3, the levels in the variant Fabry hemizygotes and Fabry heterozygotes could not be distinguished from those in the controls, although those in the classic Fabry hemizygotes were increased. The plasma lyso-Gb3 level in the Fabry patient who had received ERT was elevated at the baseline and fell more dramatically on ERT than that of Gb3. Plasma lyso-Gb3 could thus be a potential biomarker of Fabry disease.

Expression of the disease on female carriers of X-linked lysosomal disorders: a brief review

Most lysosomal diseases (LD) are inherited as autosomal recessive traits, but two important conditions have X-linked inheritance: Fabry disease and Mucopolysaccharidosis II (MPS II). These two diseases show a very different pattern regarding expression on heterozygotes, which does not seem to be explained by the X-inactivation mechanism only. While MPS II heterozygotes are asymptomatic in most instances, in Fabry disease most of female carriers show some disease manifestation, which is sometimes severe. It is known that there is a major difference among X-linked diseases depending on the cell autonomy of the gene product involved and, therefore, on the occurrence of cross-correction. Since lysosomal enzymes are usually secreted and uptaken by neighbor cells, the different findings between MPS II and Fabry disease heterozygotes can also be due to different efficiency of cross-correction (higher in MPS II and lower in Fabry disease). In this paper, we review these two X-linked LD in order to discuss the mechanisms that could explain the different rates of penetrance and expressivity observed in the heterozygotes; this could be helpful to better understand the expression of X-linked traits.

Fabry disease

Fabry disease, an X-linked disorder of glycosphingolipids that is caused by the deficiency of alpha-galactosidase A, is associated with dysfunction of many cell types and includes a systemic vasculopathy. As a result, patients have a markedly increased risk of developing small-fiber peripheral neuropathy, stroke, myriad cardiac manifestations and chronic renal disease. Virtually all complications of Fabry disease are non-specific in nature and clinically indistinguishable from similar abnormalities that occur in the context of more common disorders in the general population. Although Fabry disease was originally thought to be very rare, recent studies have found a much higher incidence of mutations of the GLA gene, suggesting that this disorder is under-diagnosed. Although the etiology of Fabry disease has been known for many years, the mechanism by which the accumulating alpha-D-galactosyl moieties cause this multi-organ disorder has only recently been studied and is yet to be completely elucidated. Specific therapy for Fabry disease has been developed in the last few years but its role in the management of the disorder is still being investigated. Fortunately, standard 'non-specific' medical and surgical therapy is effective in slowing deterioration or compensating for organ failure in patients with Fabry disease. All these aspects are discussed in detail in the present review.