Novel therapeutic targets for the treatment of Fabry disease

Agalsidase-β should be proposed as first line therapy in classic male Fabry patients with undetectable α-galactosidase A activity

BACKGROUND

Fabry disease (FD) is a rare X-linked lysosomal storage disease caused by mutations in the α-galactosidase A (GLA) gene leading to deficiency of α-galactosidase A (α-gal A). This results in progressive multisystemic glycosphingolipid accumulation, especially globotriaosylceramide (Gb3) and globotriaosylsphingosine (Lyso-Gb3). Enzyme replacement therapy with two recombinant enzymes, agalsidase-α and -β is approved for two different dosages. However, little is known about which enzyme is more effective in decreasing the metabolite load in male and female patients with the classic form of the disease.

METHODS

In this prospective observational study, 14 consecutive adult Fabry patients (10 males) with a classic GLA-mutation, were switched from agalsidase-α to agalsidase-β at the respective licensed doses. Lyso-Gb3 levels were measured before the switch and for a period of 12 months after the switch in dried blood spots by tandem mass spectrometry.

RESULTS

Mean age at start of the switch was 36.7 ± 14 years. Plasma Lyso-Gb3 levels decreased from 27.2 ± 17.9 ng/mL before the switch to 16.8 ± 10.5 ng/mL after the switch (mean reduction of 30.1%; p = 0.004). The decrease was maximal in the subgroup of 7 male patients with no or very low residual enzyme activity (mean reduction of 40.4%). However, two females with high residual enzyme activity also showed a reduction >30% after the switch. In male patients, the reduction of plasma Lyso-Gb3 correlated negatively with the residual α-gal A activity: r = -0.803; p = 0.009.

CONCLUSION

Agalsidase-β at licensed dose is significantly more effective than agalsidase-α to reduce Lyso-Gb3 levels in classic Fabry patients, and should be used as first line therapy in classic males with no residual enzyme activity.

Global research on Fabry's disease: Demands for a rare disease

Background

Fabry disease (FD), the second most prevalent lysosomal storage disorder, is classified as a rare disease. It often leads to significant quality of life impairments and premature death. Many cases remain undiagnosed due to the rarity and heterogeneity. Further, costs related to treatment often constitute a substantial financial burden for patients and health systems. While its epidemiology is still unclear, newborn screenings suggest that its actual prevalence rate is significantly higher than previously suspected.

Methods

Based on well‐established methodologies, this study gives an overview about the background of the development of FD‐related research and provides a critical view of future needs.

Results

On the grounds of benchmarking findings, an increasing research activity on FD can be observed. Most publishing countries are the USA, some European countries, Japan, Taiwan, and South Korea. In general, high‐income countries publish comparably more on FD than low‐ or middle‐income economies. The countries' financial and infrastructural background are unveiled as crucial factors for the FD research activity.

Conclusions

Overall, there is a need to foster FD research infrastructure in developing and emerging countries with focus on cost‐intensive genetic research that is independent from economic interests of big pharmaceutical companies.

Pharmacological small molecules for the treatment of lysosomal storage disorders

IMPORTANCE OF THE FIELD

Inherited lysosomal storage diseases often cause severe disability and have a devastating effect on quality of life. Enzyme replacement therapy (ERT) forms a cornerstone in the treatment of lysosomal enzyme deficiencies. Although for some lysosomal disorders ERT is lifesaving, important intrinsic restrictions of the approach are limited access of infused enzyme to less accessible body compartments such as the CNS, the burden of frequent intravenous administration, the emergence of antibodies and the high associated costs. Pharmacological small molecules may overcome these limitations.

AREAS COVERED IN THIS REVIEW

Several novel therapeutic approaches using small molecules are emerging: substrate reduction therapy, pharmacological chaperone therapy, premature nonsense mutation suppressors and proteostasis regulators.

WHAT THE READER WILL GAIN

Based on an extensive literature search up until June 2010, we here review the various therapeutic approaches with small compounds, including those currently in clinical use and those that have entered clinical trials. Compounds that are still in the preclinical phase are also briefly discussed.

TAKE HOME MESSAGE

pharmacological small molecules are a new class of agents that show great promise for the treatment of lysosomal storage disorders.

Misdiagnosis in Fabry disease

OBJECTIVE

To evaluate the most frequent diagnostic errors in patients with Fabry disease and the types of specialists most often consulted before diagnosis.

STUDY DESIGN

We evaluated 45 consecutive symptomatic patients with Fabry disease confirmed by enzymatic tests in males and genetic studies in females. We interviewed the patients, their mothers, or both regarding symptoms, age at onset, medical consultations, and recommended treatments.

RESULTS

Neuropathic pain was the most frequent initial complaint, and rheumatic fever was the most common diagnosis. Seven patients were treated with penicillin for many years. Ten patients sought medical consultation because of abdominal pain and were diagnosed with food intoxication or nonspecific pain. Six patients sought consultation because of anhidrosis, considered of unclear cause, and angiokeratomas diagnosed as petechiae. Internists and pediatricians were the most frequently consulted specialists. The correct diagnosis was obtained after a mean of 19.7 years.

CONCLUSIONS

Pediatricians as well as internists commonly misdiagnose Fabry disease. Neuropathic pain, hypohidrosis, and recurrent abdominal pain in childhood or adolescence should include Fabry disease in the differential diagnosis to facilitate earlier diagnosis and treatment of these patients.

Lysosomal storage disorders in the newborn

Lysosomal storage disorders are rare inborn errors of metabolism, with a combined incidence of 1 in 1500 to 7000 live births. These relatively rare disorders are seldom considered when evaluating a sick newborn. A significant number of the >50 different lysosomal storage disorders, however, do manifest in the neonatal period and should be part of the differential diagnosis of several perinatal phenotypes. We review the earliest clinical features, diagnostic tests, and treatment options for lysosomal storage disorders that can present in the newborn. Although many of the lysosomal storage disorders are characterized by a range in phenotypes, the focus of this review is on the specific symptoms and clinical findings that present in the perinatal period, including neurologic, respiratory, endocrine, and cardiovascular manifestations, dysmorphic features, hepatosplenomegaly, skin or ocular involvement, and hydrops fetalis/congenital ascites. A greater awareness of these features may help to reduce misdiagnosis and promote the early detection of lysosomal storage disorders. Implementing therapy at the earliest stage possible is crucial for several of the lysosomal storage disorders; hence, an early appreciation of these disorders by physicians who treat newborns is essential.

Enzyme replacement improves ataxic gait and central nervous system histopathology in a mouse model of metachromatic leukodystrophy

Inherited deficiencies of lysosomal hydrolases cause lysosomal storage diseases (LSDs) that are characterized by a progressive multisystemic pathology and premature death. Repeated intravenous injection of the active counterpart of the deficient enzyme, a treatment strategy called enzyme replacement therapy (ERT), evolved as a clinical option for several LSDs without central nervous system (CNS) involvement. To assess the efficacy of long-term ERT in metachromatic leukodystrophy (MLD), an LSD with prevailing nervous system disease, we treated immunotolerant arylsulfatase A (ASA) knockout mice with 52 doses of either 4 or 50 mg/kg recombinant human ASA (rhASA). ERT was tolerated without side effects and improved disease manifestations in a dose-dependent manner. Dosing of 4 mg/kg diminished sulfatide storage in kidney and peripheral nervous system (PNS) but not the CNS, whereas treatment with 50 mg/kg was also effective in the CNS in reducing storage in brain and spinal cord by 34 and 45%, respectively. Histological analyses revealed regional differences in sulfatide clearance. While 70% less storage profiles were detectable, for example, in the hippocampal fimbria, the histopathology of the brain stem was unchanged. Both enzyme doses normalized the ataxic gait of ASA knockout mice, demonstrating prevention of nervous system dysfunctions that dominate early stages of MLD.

Replacement of alpha-galactosidase A in Fabry disease: effect on fibroblast cultures compared with biopsied tissues of treated patients

The function and intracellular delivery of enzyme therapeutics for Fabry disease were studied in cultured fibroblasts and in the biopsied tissues of two male patients to show diversity of affected cells in response to treatment. In the mutant fibroblasts cultures, the final cellular level of endocytosed recombinant alpha-galactosidases A (agalsidases, Fabrazyme, and Replagal) exceeded, by several fold, the amount in control fibroblasts and led to efficient direct intra-lysosomal hydrolysis of ((3)H)Gb3Cer. In contrast, in the samples from the heart and some other tissues biopsied after several months of enzyme replacement therapy (ERT) with Fabrazyme, only the endothelial cells were free of storage. Persistent Gb3Cer storage was found in cardiocytes (accompanied by increase of lipopigment), smooth muscle cells, fibroblasts, sweat glands, and skeletal muscle. Immunohistochemistry of cardiocytes demonstrated, for the first time, the presence of a considerable amount of the active enzyme in intimate contact with the storage compartment. Factors responsible for the limited ERT effectiveness are discussed, namely post-mitotic status of storage cells preventing their replacement by enzyme supplied precursors, modification of the lysosomal system by longstanding storage, and possible relative lack of Sap B. These observations support the strategy of early treatment for prevention of lysosomal storage.

Biomarkers for lysosomal storage disorders: identification and application as exemplified by chitotriosidase in Gaucher disease

A biomarker is an analyte that indicates the presence of a biological process linked to the clinical manifestations and outcome of a particular disease. An ideal biomarker provides indirect but ongoing determinations of disease activity. In the case of lysosomal storage disorders (LSDs), metabolites or proteins specifically secreted by storage cells are good candidates for biomarkers. Potential clinical applications of biomarkers are found in improved diagnosis, monitoring of disease progression and assessment of therapeutic correction. These applications are illustrated by reviewing the use of plasma chitotriosidase in the clinical management of patients with Gaucher disease, the most common LSD. The ongoing debate on the value of biomarkers in patient management is addressed. Novel analytical methods have revolutionized the identification and measurement of biomarkers at the protein and metabolite level. Recent developments in biomarker discovery by proteomics are described and the future for biomarkers of LSDs is discussed.

CONCLUSION

Besides direct applications for biomarkers in patient management, biomarker searches are likely to render new insights into pathophysiological mechanisms and metabolic adaptations, and may provide new targets for therapeutic intervention.