Fabry disease in children and the effects of enzyme replacement treatment

Ophthalmic Manifestations in Fabry Disease: Updated Review

Fabry disease (FD) is an X-linked lysosomal storage disorder, causing Gb-3 (globotriaosylceramide) buildup in cellular lysosomes throughout the body, in particular in blood vessel walls, neuronal cells, and smooth muscle. The gradual accumulation of this glycosphingolipid in numerous eye tissues causes conjunctival vascular abnormalities, corneal epithelial opacities (cornea verticillata), lens opacities, and retinal vascular abnormalities. Although a severe vision impairment is rare, these abnormalities are diagnostic indicators and prognostics for severity. Cornea verticillata is the most common ophthalmic feature in both hemizygous men and heterozygous females. Vessel tortuosity has been linked to a faster disease progression and may be useful in predicting systemic involvement. New technologies such as optical coherence tomography angiography (OCTA) are useful for monitoring retinal microvasculature alterations in FD patients. Along with OCTA, corneal topographic analysis, confocal microscopy, and electro-functional examinations, contributed to the recognition of ocular abnormalities and have been correlated with systemic involvement. We offer an update regarding FD ocular manifestations, focusing on findings derived from the most recent imaging modalities, to optimize the management of this pathology.

Estimation of Health State Utility Values in Fabry Disease Using Vignette Development and Valuation

Background: Health state utilities are measures of health-related quality of life that reflect the value placed on improvements in patients' health status and are necessary for estimation of quality-adjusted life-years. Health state utility data on Fabry disease (FD) are limited. In this study we used vignette (scenario) construction and valuation to develop health state utilities. Objectives: The aim of this study was to use vignette construction and valuation to estimate health state utility values suitable for inclusion in economic models of FD treatments. Methods: Health state vignettes were developed from semistructured qualitative telephone interviews with patients with FD and informed by published literature and input from an expert. Each vignette was valued in an online survey by members of the United Kingdom (UK) general population using the composite time trade-off (TTO) method, which aims to determine the time the respondent would trade to live in full health compared with each impaired health state. Results: Eight adults (50% women) with FD from the UK were interviewed. They were recruited via various approaches, including patient organizations and social media. The interviewees' responses, evidence from published literature, and input from a clinical expert informed the development of 6 health state vignettes (pain, moderate clinically evident FD [CEFD], severe CEFD, end-stage renal disease [ESRD], stroke, and cardiovascular disease [CVD]) and 3 combined health states (severe CEFD + ESRD, severe CEFD + CVD, and severe CEFD + stroke). A vignette valuation survey was administered to 1222 participants from the UK general population who were members of an external surveying organization and agreed to participate in this study; 1175 surveys were successfully completed and included in the analysis. Responses to TTO questions were converted into utility values for each health state. Pain was the highest valued health state (0.465), and severe CEFD + ESRD was the lowest (0.033). Discussion: Overall, mean utility values declined as the severity of the vignettes increased, indicating that respondents were more willing to trade life-years to avoid a severe health state. Conclusions: Health state vignettes reflect the effects of FD on all major health-related quality-of-life domains and may help to support economic modeling for treatment of FD.

Palm-Plant Pain, Sign of a Severe Systemic Disease? Case Report and Review of Literature

Fabry disease is an X-linked lysosomal storage disease, second in prevalence after Gaucher disease. The onset of symptoms occurs in childhood or adolescence with palmo-plantar burning pains, hypo hidrosis, angiokeratomas, and corneal deposits. In the absence of diagnosis and treatment, the disease will progress to the late phase, characterized by progressive cardiac, cerebral and renal damage, and possible death. We present the case of an 11-year-old male boy who was transferred to the Pediatric Nephrology Department for palmo-plantar burning pain and end stage renal disease. Following the evaluations for the etiology of end stage renal disease we excluded the vasculitis, the neurologic diseases, extrapulmonary tuberculosis. Because of suggestive aspect at CT scan and lack of etiologic diagnosis of renal insufficiency we performed lymph node and kidney biopsy, with a surprising result for storage disease. The specific investigation confirmed the diagnosis.

Burden associated with Fabry disease and its treatment in 12-15 year olds: results from a European survey

Background

Fabry Disease (FD) is a rare X-linked metabolic lysosomal disorder. FD has a broad range of symptoms which vary markedly between patients. The heterogenous nature of the disease makes diagnosis difficult for health care professionals (HCPs), which in turn has a significant effect on the patient’s quality of life (QoL). As few adolescent patients are eligible for treatment, to date there has been little published data on the burden of disease and impact of treatment on these patients and their caregivers. This study was developed to provide some insight into these groups.

Methods

An online-based survey was performed to gather further insights on the burden of FD in 14 adolescents aged 12–15 years old across three European countries, from the perspective of the patients, caregivers and HCPs.

Results

Symptom burden was found to be high in the adolescent population, with ‘pain’ and ‘intolerance to heat or cold’ commonly reported symptoms, both by patients and to HCPs. Eleven of the 14 patients surveyed were receiving enzyme replacement therapy (ERT), with their post-ERT symptomology showing improvement when compared to symptoms before receiving ERT. The majority of caregivers believe their child’s overall health has improved since starting ERT. While there was a positive outlook towards ERT noted by the patients and caregivers, 4/5 HCPs believed there is ‘a need for more efficacious treatment options’ and all HCPs noted that there is ‘a need for more manageable treatment options’. FD was shown to place a burden on caregivers, who reported feelings of guilt and absences from work.

Conclusions

Data show there is a significant symptom burden for the adolescent, which affects their QoL and mental health, as well as placing a burden on the wider family. While ERT is an effective treatment and provides symptom relief for many of the respondents in the survey, they still reported symptom burden. Additionally, there was reporting of reluctance to engage in treatment or difficulties associated with the treatment. Heterogeneity in symptom presentation suggests that the treatment regimen needs to be tailored to the individual. Physicians therefore need to have a choice of treatment options available to help them manage symptoms and disease where the benefit to risk ratio is in favour of undergoing treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02417-3.

Gene Therapy for Pediatric Neurologic Disease

Pediatric lysosomal and peroxisomal storage disorders, leukodystrophies, and motor neuron diseases can have devastating neurologic manifestations. Despite efforts to exploit cross-correction to treat these monogenic disorders for several decades, definitive treatment has yet to be identified. This review explores recent attempts to transduce autologous hematopoietic stem cells with functional gene or provide therapeutic gene in vivo. Specifically, we discuss the rationale behind efforts to treat pediatric neurologic disorders with gene therapy, outline the specific disorders that have been targeted at this time, and review recent and current clinical investigations with attention to the future direction of therapy efforts.

Identification of dual active sites in Caenorhabditis elegans GANA-1 protein: an ortholog of the human α-GAL a and α-NAGA enzymes

Fabry disease (FD) is caused by a defective α-galactosidase A (α-GAL A) enzyme responsible for breaking down globotriaosylceramide (Gb₃). To develop affordable therapeutics, more effort is needed to obtain insights into the underlying mechanism of FD and understanding human α-GAL A structure and function in related animal models. We adopted C. elegans as a model to elucidate the sequence and 3D structure of its GANA-1 enzyme and compared it to human α-GAL A. We constructed GANA-1 3D structure by homology modelling and validated the quality of the predicted GANA-1 structure, followed by computational docking of human ligands. The GANA-1 protein shared sequence similarities up to 42.1% with the human α-GAL A in silico and had dual active sites. GANA-1 homology modelling showed that 11 out of 13 amino acids in the first active site of GANA-1 protein overlapped with the human α-GAL A active site, indicating the prospect for substrate cross-reaction. Computational molecular docking using human ligands like Gb₃ (first pocket)_, 4-nitrophenyl-α-D-galactopyranoside (second pocket), α-galactose (second pocket), and N-acetyl-D-galactosamine (second pocket) showed negative binding energy. This revealed that the ligands were able to bind within both GANA-1 active sites, mimicking the human α-GAL A and α-NAGA enzymes. We identified human compounds with adequate docking scores, predicting robust interactions with the GANA-1 active site. Our data suggested that the C. elegans GANA-1 enzyme may possess structural and functional similarities to human α-GAL A, including an intrinsic capability to metabolize Gb₃ deposits.Communicated by Ramaswamy H. Sarma.

X Chromosome Inactivation in Carriers of Fabry Disease: Review and Meta-Analysis

Anderson-Fabry disease is an X-linked inborn error of glycosphingolipid catabolism caused by a deficiency of α-galactosidase A. The incidence ranges between 1: 40,000 and 1:117,000 of live male births. In Italy, an estimate of incidence is available only for the north-western Italy, where it is of approximately 1:4000. Clinical symptoms include angiokeratomas, corneal dystrophy, and neurological, cardiac and kidney involvement. The prevalence of symptomatic female carriers is about 70%, and in some cases, they can exhibit a severe phenotype. Previous studies suggest a correlation between skewed X chromosome inactivation and symptoms in carriers of X-linked disease, including Fabry disease. In this review, we briefly summarize the disease, focusing on the clinical symptoms of carriers and analysis of the studies so far published in regards to X chromosome inactivation pattern, and manifesting Fabry carriers. Out of 151 records identified, only five reported the correlation between the analysis of XCI in leukocytes and the related phenotype in Fabry carriers, in particular evaluating the Mainz Severity Score Index or cardiac involvement. The meta-analysis did not show any correlation between MSSI or cardiac involvement and skewed XCI, likely because the analysis of XCI in leukocytes is not useful for predicting the phenotype in Fabry carriers.

Current and experimental therapeutics for Fabry disease

Fabry (or Anderson‐Fabry) is a rare pan‐ethnic disease affecting males and females. Fabry is an X‐linked lysosomal storage disease, affecting glycosphingolipid metabolism, that is caused by mutations of the GLA gene that codes for α‐galactosidase A. Fabry disease (FD) can be classified into a severe, classical phenotype, most often seen in men with no residual enzyme activity, that usually appear before 18 years and a usually milder, nonclassical (later‐onset) phenotype that usually appear above 18 years. Affected patients show multifactorial complications, including renal failure, cardiovascular problems, and neuropathy. In this review, we briefly report the clinical trials so far performed with the available therapies, and then we focus on the in vitro and the in vivo experimental models of the disease, to highlight the relevance in improving the existing therapeutics and understand the mechanism of this rare disorder. Current available in vivo and in vitro models can assist in better comprehension of the pathogenesis and underlying mechanisms of FD, thus the existing therapeutic approaches can be optimized, and new options can be developed.

Enfermedad de Fabry clásica en pacientes pediátricos asintomáticos

El propósito de este artículo es proponer un marco bioético para la administración de la terapia enzimática en niños con enfermedad de Fabry asintomáticos. Se realizó un estudio de campo transversal, observacional, descriptivo, con análisis cuantitativo y cualitativo, a la luz de la bioética en médicos que han diagnosticado y tratado pacientes con la enfermedad a nivel nacional e internacional, mediante una encuesta con preguntas cerradas validada por juicio de expertos, se evaluó la aplicación de los principios de no maleficencia, justicia y sacralidad de la vida en la administración del tratamiento enzimático para estos pacientes. La información se agrupó y procesó con estadística descriptiva. El 83,33 % de los encuestados consideró que un niño con enfermedad de Fabry asintomático debe recibir tratamiento enzimático específico, independientemente de su costo (justicia), además, que el tratamiento debe ser financiado por el Estado a fin de prevenir las complicaciones de la enfermedad; esto fue reconocido por el 75 % de los médicos encuestados (no maleficencia). El 66,66 % consideró que la sacralidad de la vida está en función de prevenir las complicaciones que condicionan la muerte. Así, con base en la bioética principialista se justifica iniciar la terapia enz- imática específica para el tratamiento de niños con enfermedad de Fabry asintomáticos.

Variable clinical features of patients with Fabry disease and outcome of enzyme replacement therapy

Fabry disease (FD) is an X-linked lysosomal storage disorder caused by a deficiency in the enzyme α-galactosidase A due to mutations in the GLA gene. This leads to an accumulation of globotriaosylceramide (GL-3) in many tissues, which results in progressive damage to the kidneys, heart, and nervous system. We present the molecular and clinical characteristics and long-term outcomes of FD patients from a multidisciplinary clinic at the University of California, Irvine treated with agalsidase beta enzyme replacement therapy (ERT) for 2-20 years. This cohort comprised 24 adults (11 males, 13 females) and two male children (median age 45; range 10-68 years). Of the 26 patients in this cohort, 20 were on ERT (12 males, 8 females). We describe one novel variant not previously reported in the literature in a patient with features of 'classic' FD. The vast majority of patients in this cohort presented with symptoms of 'classic' FD including peripheral neuropathic pain, some form of cardiac involvement, angiokeratomas, corneal verticillata, hypohidrosis, tinnitus, and gastrointestinal symptoms, primarily abdominal pain. The majority of males had clinically evident renal involvement. An annual eGFR reduction of -1.88 mL/min/1.73 m2/yr during the course of ERT was seen in this cohort. The most common renal presentation was proteinuria, and one individual required a renal transplant. Other common findings were pulmonary involvement, lymphedema, hearing loss, and significantly, three patients had strokes. Notably, there was a high prevalence of endocrine dysfunction and low bone mineral density, including several with osteoporosis. While enzyme replacement therapy (ERT) cleared plasma GL-3 in this cohort, there was limited improvement in renal function or health-related quality of life based on the patient-reported SF-36 Health Survey. Physical functioning significantly declined over the course of ERT treatment, which may be, in part, due to the late initiation of ERT in several patients. Further delineation of the phenotypic and genotypic spectrum in patients with FD and the long-term outcome of ERT will help improve management and treatment options for this disease.

Cardiomyopathies in children: classification, diagnosis and treatment

PURPOSE OF REVIEW

Cardiomyopathies are rare in the pediatric population, but significantly impact on morbidity and mortality. The present review aims to provide an overview of cardiomyopathies in children and some practical guidelines for their prognostic stratification and management.

RECENT FINDINGS

Pediatric cardiomyopathies may present as isolated cardiac muscle disease or in the context of complex clinical syndromes. The etiologic characterization represents an important step in the diagnosis and treatment of cardiomyopathies because of its impact on prognosis and on therapeutic measures. Indeed, replacement therapy is nowadays widely available and changes the natural history of the disease. More complex is the management of isolated cardiomyopathies, which lack specific therapies, mainly aimed at symptomatic relief. In this context, heart transplantation shows excellent outcomes in children, but wait-list mortality is still very high. Device therapy for sudden cardiac death prevention and the use of mechanical assist devices are becoming more common in the clinical practice and may help to reduce mortality.

SUMMARY

Providing insight into pediatric cardiomyopathies classification helps in the prognostication and management of such diseases. Recent years witnessed a significant improvement in mortality, but future research is still needed to improve quality of life and life expectations in the pediatric population.

Ocular findings in Fabry disease in Colombian patients

Fabry disease is a rare X-linked disorder caused by an alpha-galactosidase enzyme deficiency, which leads to a progressive lysosomal glycosphingolipids accumulation, mainly globotriaosylceramide, in multiple organism tissues including the eye.This case series describes the first ophthalmological Colombian report of Fabry disease highlighting the importance of ocular signs as markers of the disease, useful in diagnosis and treatment to avoid long-term complications that lead to a morbi-mortality increment.We describe five cases of Fabry disease from Bogotá, Colombia, including a complete clinical history, ophthalmologic, optometric examination, and photographs. We found that all patients had refractive defects and that in all cases corneal verticillata pattern was found. Four patients presented with posterior capsule lens brown-beige deposits and four patients had conjunctival and retinal tortuous vessels. A complete ophthalmologic examination is important for prompt diagnosis, which is key to starting a multidisciplinary treatment and reducing morbi-mortality.

Home infusion program with enzyme replacement therapy for Fabry disease: The experience of a large Italian collaborative group

Fabry disease (FD) [OMIM 301500] is an X-linked lysosomal storage disorder caused by a deficiency of the lysosomal enzyme alpha-galactosidase A, resulting in progressive multisystem accumulation of globotriaosylceramide (Gb3). Although the introduction of Enzyme Replacement Therapy (ERT) resulted in a variety of clinical benefits, life-long intravenous (IV) treatment with ERT with an every other week schedule, may interfere with daily life activities and impact on QoL. We report here a multicentric, observational, longitudinal data analysis on a large cohort of 85 Italian FD patients (45 males, 40 females) from 11 out of 20 Italian regions, who received a cumulative number of 4269 home infusions of agalsidase alfa. For the whole cohort, the average duration of home therapy was 1 year and 11 months (range 3 months–4 years and 6 months), and during this period, compliance to treatment (number of infusions performed vs scheduled) reached 100%. The EQ-5 VAS scale was administered to patients to evaluate the self-reported QoL, 58% of patients showing an increase of EQ-5 VAS score at follow up compared to baseline (home treatment start) or remaining stable. A mild increase of average disease severity, measured through Mainz Severity Score Index (MSSI), was found during hospital treatment (p < 0,007), while it remained stable between the first home therapy infusion and last follow up. Interestingly, 4 out of 7 (57%) patients, showing an improvement in FD-related clinical status after starting home therapy, had previously a sub-optimal compliance to treatment during the period of hospital treatment management. Only 4 adverse non serious reactions (0,093%) were reported totally in 2 patients during home treatment.

We conclude that home infusions in eligible patients with FD are safe, contribute to improve treatment compliance and therapeutic clinical outcomes, and may have a positive impact on self-perceived QoL.

Gastrointestinal Symptoms of Patients with Fabry Disease

In order to characterize gastrointestinal (GI) symptoms of 50 patients with Fabry disease (FD) (22 M; age range: 4–70 y; 35 adults and 15 children), validated questionnaires of GI symptoms were used to diagnose the functional gastrointestinal disorders (FGIDs) of the patients with GI symptoms (33/50 (66%); 25/35 adults and 8/15 children) according to Rome III criteria. In 16/25 of these adults and 2/8 of these children, the symptoms mimicked FGID. The adult subgroup included patients with unspecified functional bowel disorder (n = 9), functional bloating (n = 7), and IBS (n = 5), and the child subgroup included patients with abdominal migraine (n = 1) and IBS (n = 1). Among the 25 adults, 14 reported feeling full after a regular-size meal, and 12 complained of abdominal bloating/distension. All of the children with GI symptoms complained of low abdominal pain associated with changes in the form of the stool/improvements with defecation. In conclusion, according to Rome III criteria, the most frequent diagnoses of FGID among the adults with FD were unspecified functional bowel disorder, followed by functional bloating and IBS. The most frequent GI symptom in the children in our population was IBS-like abdominal pain, while the adults exhibited a full feeling following a regular-size meal and abdominal bloating/distension.

Carboxyl-terminal truncations alter the activity of the human α-galactosidase A

Fabry disease is an X-linked inborn error of glycolipid metabolism caused by deficiency of the human lysosomal enzyme, α-galactosidase A (αGal), leading to strokes, myocardial infarctions, and terminal renal failure, often leading to death in the fourth or fifth decade of life. The enzyme is responsible for the hydrolysis of terminal α-galactoside linkages in various glycolipids. Enzyme replacement therapy (ERT) has been approved for the treatment of Fabry disease, but adverse reactions, including immune reactions, make it desirable to generate improved methods for ERT. One approach to circumvent these adverse reactions is the development of derivatives of the enzyme with more activity per mg. It was previously reported that carboxyl-terminal deletions of 2 to 10 amino acids led to increased activity of about 2 to 6-fold. However, this data was qualitative or semi-quantitative and relied on comparison of the amounts of mRNA present in Northern blots with αGal enzyme activity using a transient expression system in COS-1 cells. Here we follow up on this report by constructing and purifying mutant enzymes with deletions of 2, 4, 6, 8, and 10 C-terminal amino acids (Δ2, Δ4, Δ6, Δ8, Δ10) for unambiguous quantitative enzyme assays. The results reported here show that the k_cat/K_m approximately doubles with deletions of 2, 4, 6 and 10 amino acids (0.8 to 1.7-fold effect) while a deletion of 8 amino acids decreases the k_cat/K_m (7.2-fold effect). These results indicate that the mutated enzymes with increased activity constructed here would be expected to have a greater therapeutic effect on a per mg basis, and could therefore reduce the likelihood of adverse infusion related reactions in Fabry patients receiving ERT treatment. These results also illustrate the principle that in vitro mutagenesis can be used to generate αGal derivatives with improved enzyme activity.

Fabry disease in infancy and early childhood: a systematic literature review

PURPOSE

Fabry disease is a pan-ethnic, progressive, X-linked genetic disorder that commonly presents in childhood and is caused by deficient activity of the lysosomal enzyme alpha-galactosidaseA (α-gal A). Symptoms of Fabry disease in the pediatric population are well described for patients over five years of age; however, data are limited for infancy and early childhood. The purpose of this article is to delineate the age of detection for specific Fabry symptoms in early childhood.

METHODS

A systematic retrospective analysis of PubMed indexed, peer-reviewed publications and case reports in the pediatric Fabry population was performed to review symptoms in patients reported before 5 years of age.

RESULTS

The most frequently reported symptom in all age groups under 5 years was acroparesthesias/neuropathic pain, reported in 9 children, ranging in age from 2.0-4.0 years. Also notable is the frequency of gastrointestinal issues reported in 6 children aged 1.0-4.1 years of age.

CONCLUSION

This article finds clear evidence that symptoms can occur in early childhood, before age 5 years. Given early presenting symptoms and the ability to monitor these disease hallmarks, a timely referral to a medical geneticist or other specialty clinician experienced in managing children with Fabry disease is strongly indicated.

Altered dynamics of a lipid raft associated protein in a kidney model of Fabry disease

Accumulation of globotriaosylceramide (Gb3) and other neutral glycosphingolipids with galactosyl residues is the hallmark of Fabry disease, a lysosomal storage disorder caused by deficiency of the enzyme alpha-galactosidase A (α-gal A). These lipids are incorporated into the plasma membrane and intracellular membranes, with a preference for lipid rafts. Disruption of raft mediated cell processes is implicated in the pathogenesis of several human diseases, but little is known about the effects of the accumulation of glycosphingolipids on raft dynamics in the context of Fabry disease. Using siRNA technology, we have generated a polarized renal epithelial cell model of Fabry disease in Madin-Darby canine kidney cells. These cells present increased levels of Gb3 and enlarged lysosomes, and progressively accumulate zebra bodies. The polarized delivery of both raft-associated and raft-independent proteins was unaffected by α-gal A knockdown, suggesting that accumulation of Gb3 does not disrupt biosynthetic trafficking pathways. To assess the effect of α-gal A silencing on lipid raft dynamics, we employed number and brightness (N&B) analysis to measure the oligomeric status and mobility of the model glycosylphosphatidylinositol (GPI)-anchored protein GFP-GPI. We observed a significant increase in the oligomeric size of antibody-induced clusters of GFP-GPI at the plasma membrane of α-gal A silenced cells compared with control cells. Our results suggest that the interaction of GFP-GPI with lipid rafts may be altered in the presence of accumulated Gb3. The implications of our results with respect to the pathogenesis of Fabry disease are discussed.

Neuropathic pain in children

Neuropathic pain (NP), due to a lesion or disease of the somatosensory nervous system, is not well documented or researched in children. NP is a clinical diagnosis that can be difficult, especially in younger children. Nevertheless, it is important to recognise NP, as pain mechanisms and consequently management and prognosis differ from other types of long-term pain. NP is common in adult pain clinics but many of the underlying disease states in which it occurs are infrequently or never encountered in paediatric practice. However, NP in childhood has been reported, even in the very young in certain clinical situations. Causes of NP include traumatic injury, complex regional pain syndrome type II, cancer and chemotherapy, chronic infection, neurological and metabolic disease, and inherited sensory nerve dysfunction. The clinical and laboratory study of traumatic peripheral nerve injury has revealed important age-related differences in clinical presentation and prognosis. It is clear that mechanisms operating during development can profoundly modify the consequences of nerve damage and NP. Clinically, diagnosis, assessment and treatment of NP are based on methods and evidence derived from data in adults. Improvements in the understanding and management of NP are likely to come from developmentally appropriate improvements in the clarity and consistency of diagnosis and systematic, well-researched approaches to treatment.

Enzyme replacement therapy partially prevents invariant Natural Killer T cell deficiency in the Fabry disease mouse model

Fabry disease is a lysosomal storage disease caused by deficient activity of the α-Galactosidase A (α-Gal A) enzyme, which leads to abnormal accumulation of glycosphingolipids, mainly globotriaosylceramide (Gb3), in the lysosome. Glycosphingolipids are known to be invariant Natural Killer T (iNKT) cell antigens. Several animal models of lysosomal storage diseases, including Fabry disease, present a defect in iNKT cell selection by the thymus. We have studied the effect of age and the impact of enzyme replacement therapy on Gb3 accumulation and iNKT cells of Fabry knockout mice. At 4 weeks of age, Fabry knockout mice already showed Gb3 accumulation and a reduction in the percentage of iNKT cells. In older mice (12-week old), we observed an accentuated peripheral iNKT deficiency. 12-week old animals also showed a reduced splenic CD4+/CD4- iNKT cell ratio due to greater loss in the iNKT CD4+ subset. Treatment of Fabry knockout mice with α-Gal A replacement therapy efficiently reduced Gb3 deposition in the liver and spleen. Moreover, enzyme replacement therapy had a positive effect on the number of iNKT cells in an organ-dependent fashion. Indeed, treatment of Fabry knockout mice with α-Gal A did not alter iNKT cell percentage in the thymus and liver but increased splenic iNKT cell percentage when compared to untreated mice. Study of animals prior to treatment indicates that enzyme replacement therapy stabilized iNKT cell percentage in the spleen. This stabilization is due to a specific effect on the iNKT CD4+ subset, preventing the decrease on the number of these cells that occurs with age in Fabry knockout mice. This study reveals that enzyme replacement therapy has a positive organ and subset-dependent effect in iNKT cells of Fabry knockout mice.

Impact of growing up with Fabry disease on achievement of psychosocial milestones and quality of life

Little is known on the impact of growing up with Fabry disease (FD) on psychosocial development. Children with FD may suffer from severe recurrent pains in hands and feet, gastro-intestinal symptoms and heat intolerance. These symptoms may influence quality of life and may interfere with a normal psychosocial development. It is important to evaluate psychosocial outcomes of patients with FD into adulthood to be able to optimize support of children with FD. The current cross-sectional questionnaire study investigated psychosocial development and quality of life of 28 young adults with FD, aged 18-35 years (9 males, 19 females), using the Course of Life questionnaire and the Short Form-36 questionnaire for quality of life. The results were compared with an age-matched normative population. We found significant differences in the achievement of milestones in social development of male Fabry patients. The milestones that were affected were 'going out to bars' and 'participation in sports activities'. Other than that FD patients appear to be able to achieve a rather normal psychosocial development until adulthood. Quality of life was decreased in Fabry males in the domains of physical functioning and bodily pain and of general health perception in females.

Progressive renal failure despite long-term biweekly enzyme replacement therapy in a patient with Fabry disease secondary to a new α-galactosidase mutation of Leu311Arg (L311R)

A 37-year-old Japanese man affected by Fabry disease secondary to a novel mutation of Leu311Arg (L311R) in α-galactosidase demonstrated progressive renal failure despite biweekly enzyme replacement therapy (ERT) for approximately 10 years. Kidney biopsy revealed foamy glomerular epithelial cells, compatible with the typical pathologic features of Fabry disease. The patient entered a phase III study of Replagal (agalsidase alfa) in 2001, allowing him to continue ERT with biweekly dosing for almost 10 years. During 2 years of that period, he was continued on Fabrazyme (agalsidase beta) biweekly dosing. His estimated GFR was calculated to decrease by 9.9 mL/min/1.73 m(2) per year. Patients with Fabry disease have been reported to have a mean decrease in GFR of 12.2 ± 8.1 mL/min/1.73 m(2) per year. This result suggests that biweekly ERT is only mildly effective at preventing loss of kidney function.

Safety of agalsidase alfa in patients with Fabry disease under 7 years

AIM

To evaluate the safety and explore the efficacy of enzyme replacement therapy (ERT) for Fabry disease with agalsidase alfa in young children enrolled in the Fabry Outcome Survey (FOS).

METHODS

This retrospective chart review identified eight children (mean age= 5.0±1.6 [mean ±SD]) in FOS who began treatment with agalsidase alfa (0.2 mg/kg, i.v., every other week) when <7 years old. Vital signs and adverse events were monitored throughout the study period. Glomerular filtration rate (GFR) was estimated, and left ventricular mass indexed to height(2.7) (LVMi) was assessed with echocardiography. Patients received 1.2-6.7 years of treatment (mean=4.2 years).

RESULTS

Infusion reactions occurred in three patients and were of mild or moderate severity. IgG antibodies to agalsidase alfa were found in one patient who experienced two mild and one moderate infusion reactions. Mean GFR was within the normal range at baseline and remained normal. LVMi was above the 75th percentile of age-matched children in 5 of 6 patients evaluated at baseline. Only two patients exceeded this threshold at their last assessment.

CONCLUSION

Long-term observation will be needed to determine whether early initiation of ERT will prevent major organ dysfunction in these patients.

Therapeutic goals in the treatment of Fabry disease

PURPOSE

Fabry disease is a progressive multiorgan, multisystem disorder that is caused by a deficiency in the lysosomal enzyme α-galactosidase A. Serious renal, cardiac, and cerebrovascular involvement are responsible for much of the morbidity and premature mortality associated with Fabry disease, and neuropathic pain, gastrointestinal problems, and hypohidrosis negatively affect quality of life of patients with Fabry disease. Fabry disease is X-linked, but women are often symptomatic and may be as severely affected as men.

METHODS

We propose a series of therapeutic and symptomatic goals for use in setting the expectations of enzyme replacement therapy and for assessing the response to enzyme replacement therapy in the treatment of Fabry disease.

RESULTS

Enzyme replacement therapy has been available since 2001 and has been associated with benefit in clinical trials, including stabilization of kidney function, improvement of cardiac structure and function, reduction in severity of neuropathic pain, and improvement in gastrointestinal involvement.

CONCLUSIONS

The presentation of these therapeutic goals will aid in the evaluation of response to enzyme replacement therapy and be useful in establishing an overall management plan for individual patients.

Effects of enzyme replacement therapy in Fabry disease--a comprehensive review of the medical literature

Enzyme replacement therapy with α-galactosidase A has been used to treat Fabry disease since 2001. This article reviews the published evidence for clinical efficacy of the two available enzyme preparations. We focused on heart, kidney, and nervous system manifestations, which impact both quality of life and overall prognosis. A literature search was undertaken to identify prospective open or randomized controlled trials of enzyme replacement therapy in patients with Fabry disease published since 2001. To date, no definitive conclusion can be drawn from studies that have directly compared therapeutic responses between the two commercially available enzyme preparations. Significant clinical benefits of enzyme replacement therapy have been demonstrated, mainly in patients at an early phase of the disease, with beneficial effects on heart, kidneys, pain, and quality of life in treated patients. Incidence of antibodies against agalsidase alfa and agalsidase beta observed during major clinical studies suggests a greater antigenic response to agalsidase beta. Further studies are required to confirm the long-term clinical benefits of enzyme replacement therapy. More studies with female patients are needed as are investigations of early initiation of enzyme replacement therapy to determine the optimal time to start treatment to prevent irreversible organ damage. The value of adjunctive and supportive therapies should also be rigorously analyzed.

Fabry disease

Fabry disease (FD) is a progressive, X-linked inherited disorder of glycosphingolipid metabolism due to deficient or absent lysosomal α-galactosidase A activity. FD is pan-ethnic and the reported annual incidence of 1 in 100,000 may underestimate the true prevalence of the disease. Classically affected hemizygous males, with no residual α-galactosidase A activity may display all the characteristic neurological (pain), cutaneous (angiokeratoma), renal (proteinuria, kidney failure), cardiovascular (cardiomyopathy, arrhythmia), cochleo-vestibular and cerebrovascular (transient ischemic attacks, strokes) signs of the disease while heterozygous females have symptoms ranging from very mild to severe. Deficient activity of lysosomal α-galactosidase A results in progressive accumulation of globotriaosylceramide within lysosomes, believed to trigger a cascade of cellular events. Demonstration of marked α-galactosidase A deficiency is the definitive method for the diagnosis of hemizygous males. Enzyme analysis may occasionnally help to detect heterozygotes but is often inconclusive due to random X-chromosomal inactivation so that molecular testing (genotyping) of females is mandatory. In childhood, other possible causes of pain such as rheumatoid arthritis and 'growing pains' must be ruled out. In adulthood, multiple sclerosis is sometimes considered. Prenatal diagnosis, available by determination of enzyme activity or DNA testing in chorionic villi or cultured amniotic cells is, for ethical reasons, only considered in male fetuses. Pre-implantation diagnosis is possible. The existence of atypical variants and the availability of a specific therapy singularly complicate genetic counseling. A disease-specific therapeutic option - enzyme replacement therapy using recombinant human α-galactosidase A - has been recently introduced and its long term outcome is currently still being investigated. Conventional management consists of pain relief with analgesic drugs, nephroprotection (angiotensin converting enzyme inhibitors and angiotensin receptors blockers) and antiarrhythmic agents, whereas dialysis or renal transplantation are available for patients experiencing end-stage renal failure. With age, progressive damage to vital organ systems develops and at some point, organs may start to fail in functioning. End-stage renal disease and life-threatening cardiovascular or cerebrovascular complications limit life-expectancy of untreated males and females with reductions of 20 and 10 years, respectively, as compared to the general population. While there is increasing evidence that long-term enzyme therapy can halt disease progression, the importance of adjunctive therapies should be emphasized and the possibility of developing an oral therapy drives research forward into active site specific chaperones.

Agalsidase alfa for enzyme-replacement therapy in Fabry disease

Fabry disease is an X-linked lysosomal storage disorder that is caused by a deficiency in the enzyme α-galactosidase A. Manifestations emerge during childhood, including neuropathic pain, hypohidrosis and gastrointestinal problems. Major organ involvement typically occurs during adulthood and includes progressive kidney dysfunction, cardiomyopathy and valve disease, and stroke. Enzyme-replacement therapy with agalsidase alfa has been available since 2001 and is associated with clinical benefit in adult men and women, as well as in children, with Fabry disease. The responses to agalsidase alfa include reduction in the severity of neuropathic pain, stabilization of kidney function and reduction in left ventricular mass in patients with baseline left ventricular hypertrophy. Several issues, including when to initiate treatment and whether long-term treatment will extend survival, remain to be answered. This article covers the clinical development of agalsidase alfa and the postmarketing reports of its safety and effectiveness.

Multi-system disorders of glycosphingolipid and ganglioside metabolism

Glycosphingolipids (GSLs) and gangliosides are a group of bioactive glycolipids that include cerebrosides, globosides, and gangliosides. These lipids play major roles in signal transduction, cell adhesion, modulating growth factor/hormone receptor, antigen recognition, and protein trafficking. Specific genetic defects in lysosomal hydrolases disrupt normal GSL and ganglioside metabolism leading to their excess accumulation in cellular compartments, particularly in the lysosome, i.e., lysosomal storage diseases (LSDs). The storage diseases of GSLs and gangliosides affect all organ systems, but the central nervous system (CNS) is primarily involved in many. Current treatments can attenuate the visceral disease, but the management of CNS involvement remains an unmet medical need. Early interventions that alter the CNS disease have shown promise in delaying neurologic involvement in several CNS LSDs. Consequently, effective treatment for such devastating inherited diseases requires an understanding of the early developmental and pathological mechanisms of GSL and ganglioside flux (synthesis and degradation) that underlie the CNS diseases. These are the focus of this review.