Safety and Efficacy of Enzyme Replacement Therapy with Agalsidase Beta: An International, Open-label Study in Pediatric Patients with Fabry Disease

Safety and Efficacy of Enzyme Replacement Therapy with Agalsidase Beta: An International, Open-label Study in Pediatric Patients with Fabry Disease J. EDMOND WRAITH, MB, CHB,* ANNA TYLKI-SZYMANSKA, MD, PHD,* NATHALIE GUFFON, MD, PHD, Y. HOWARD LIEN, MD, PHD, MICHEL TSIMARATOS, MD, PHD, ASHOK VELLODI, MBBS, AND DOMINIQUE P. GERMAIN, MD, PHD

Objective To evaluate the safety and explore the efficacy of enzyme replacement therapy with agalsidase beta (recombinant human ␣-galactosidase A; Fabrazyme [Genzyme Corporation, Cambridge, MA]) in pediatric patients with Fabry disease, a genetic disorder in which deficient endogenous enzyme causes pathogenic tissue accumulation of globotriaosylceramide (GL-3). Study design Fourteen male and 2 female patients, 8 to 16 years old, were treated in this open-label study. A 12-week observation period to collect baseline data preceded the 48-week treatment period when agalsidase beta (1 mg/kg) was infused intravenously every 2 weeks. No primary efficacy end point was specified. Results Before treatment, results of skin biopsies from 12 male patients showed From Royal Manchester Children’s Hospimoderate or severe GL-3 accumulation in superficial dermal capillary endothelial cells; tal, Manchester, United Kingdom (J.E.W.); The Children’s Memorial Health Institute, with treatment, these cells were completely cleared of GL-3 in week-24 biopsies from all Warsaw, Poland (A.T.-S.); Hôpital Edouard 12 male patients and in all available week-48 biopsies. With treatment, reports of Herriot, Lyon, France (N.G.); University of Arizona, Tucson, Arizona (Y.H.L.); Assisgastrointestinal symptoms declined steadily. Patient diaries documented significant retance Publique-Hôpitaux de Marseille la ductions in school absences due to sickness. Agalsidase beta was generally well tolerated; Timone-Enfants, Marseille, France (M.T.); Great Ormond Street Hospital for Chilmost treatment-related adverse events were mild or moderate infusion-associated reacdren, London, United Kingdom (A.V.); tions involving rigors, fever, or rhinitis. and University of Versailles-St Quentin en Conclusions Agalsidase beta safely and effectively reduced the GL-3 accumulation Yvelines and Centre de référence de la maladie de Fabry et des maladies hérédiin dermal endothelium already evident in children with Fabry disease. Early intertaires du tissu conjonctif, Assistance Pubvention may prevent irreversible end-organ damage from chronic GL-3 deposition. lique-Hôpitaux de Paris, Paris, France (D.P.G.) (J Pediatr 2008;152:563-70) *

nzyme replacement therapy (ERT) for Fabry disease (OMIM#301500) involves regular intravenous (IV) infusions of recombinant human ␣-galactosidase A (r-h␣Gal). This compensates for an inherited deficiency of endogenous enzyme, which results in pathogenic accumulation of uncleaved substrates, predominantly globotriaosylceramide (GL-3).1 In the classic Fabry phenotype, symptoms emerge in childhood or adolescence, evolve through early adulthood, and culminate in life-threatening renal, cerebrovascular, and cardiac complications in the fourth or fifth decade of life. Because the gene encoding ␣-galactosidase A (␣Gal) is X-linked, disease manifestations usually arise earlier and progress more rapidly in male hemizygotes; however, female heterozygotes may experience significant clinical pathology.1,2 A series of clinical trials to evaluate ERT with agalsidase beta (r-h␣Gal; Fabrazyme [Genzyme Corporation, Cambridge, MA]) administered at 1 mg/kg every 2 weeks has

E

AE ␣Gal BMI ECG ELISA ERT IAR IV

Adverse event ␣-Galactosidase A Body mass index Electrocardiography, electrocardiogram Enzyme-linked immunoadsorbent assay Enzyme replacement therapy Infusion-associated reaction Intravenous

GFR GL-3 IgE IgG OMIM r-h␣Gal SAE

Glomerular filtration rate Globotriaosylceramide Immunoglobulin E Immunoglobulin G Online Mendelian Inheritance in Man Recombinant human ␣-Galactosidase A Serious adverse event

J. Edmond Wraith and Anna Tylki-Szymanska were equal contributors to this article. Sponsored by Genzyme Corporation. This trial has been registered at clinicaltrials. gov. The study ID# is NCT00074958. Conflict-of-Interest Disclosures: Dr Wraith has received honoraria and consulting fees from Genzyme; Dr Tylki-Szymanska has received honoraria and consulting fees from Genzyme; Dr Guffon received a research grant from Genzyme; Dr Lien has received research grants from Genzyme and Shire; Dr Tsimaratos has received honoraria from Genzyme and Shire; Dr Vellodi has received honoraria from Genzyme; and Dr Germain has receieved a research grant and consulting fees from Genzyme. Submitted for publication Dec 28, 2006; last revision received Jul 19, 2007; accepted Sep 5, 2007. Reprint requests: A.Tylki-Szymanska, The Children’s Memorial Health Institute, Warsaw, Poland. E-mail: [email protected]. 0022-3476/$ - see front matter Copyright © 2008 Mosby Inc. All rights reserved. 10.1016/j.jpeds.2007.09.007

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demonstrated reduction or clearance of accumulated substrates from the vascular endothelium of the kidney, heart, and skin.3-7 These trials, conducted in adult male and female patients, also suggested that agalsidase beta therapy may confer enhanced clinical benefit when initiated before irreversible tissue damage has occurred.5-7 The advantages of early intervention, together with increasing awareness of the extent of disease burden in pediatric patients,8-12 have promoted discussion of the appropriate role of ERT in children with this lifelong disease. Since 2001, marketing approval for agalsidase beta has been granted in ⬎40 countries. This report describes the post-approval trial undertaken to evaluate the safety and efficacy of agalsidase beta in pediatric patients when administered at the same dosage regimen that is used in adults (1 mg/kg/2 weeks).

METHODS Study Population Patient enrollment began in October 2002; the last study visit occurred in May 2005. Of 17 patients screened, 16 were enrolled at 7 sites in 4 countries (France, Poland, United Kingdom, United States); 15 completed the study. At enrollment, participants had to be ⱖ7 and ⱕ15 years of age, and at or below Tanner Stage III of pubertal development. Inclusion criteria required a clinical diagnosis of Fabry disease, documentation of reduced ␣Gal activity for male patients and gene mutation for female patients, and at least 1 of the following: history of Fabry pain crises, chronic pain not effectively controlled with pain medication, or both; urine albumin level ⬎30 mg/dL; estimated glomerular filtration rate ⬍80 mL/ min; history of post-prandial abdominal pain, nausea, or vomiting; autonomic neuropathy evidenced by hypohidrosis, impaired pupillary constriction, or reduced tear production; low body mass index (BMI); abbreviated P-R interval. All patients met between 2 and 6 of these criteria. Patients who previously received ERT were not eligible. Each site’s ethics committee or institutional review board approved the protocol; before any intervention, informed consent was obtained from the patient and his/her legal guardian. Study Design This was an open-label study; no primary efficacy end point was specified. To establish baseline data for each patient, assessments were conducted at monthly visits during a 12-week observation period that preceded the first infusion. During the subsequent 48-week treatment period (weeks 0 to 48), visits were scheduled every 2 weeks for the conduct of protocol-specified assessments and administration of agalsidase beta by IV infusion at 1 mg/kg body weight. This was a post-approval trial, and to comply with product labelling in the European Union and United States, acetaminophen or ibuprofen was administered at least 1 hour before infusions to minimize infusion-associated reactions; patients could also receive an antihistamine. For the first 8 treatments, infusions were initiated at a rate of 0.05 mg/kg/hr; rates were increased 564

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incrementally, as tolerated, to a maximum of 15 mg/hr. After the eighth treatment, incremental rate increases up to 5 mg/hr were permitted with these limits: for patients weighing ⱖ30 kg, the infusion rate could exceed 15 mg/hr, as long as the infusion duration was ⬎2 hours; for patients weighing ⬍30 kg, the infusion duration could be ⬍2 hours, but the infusion rate could not exceed 15 mg/hr. After every infusion, patients remained at the site for observation for at least 1 hour.

Efficacy Assessments SKIN GL-3. Skin biopsies (3-mm punch) were obtained from all patients during the observation period and at week 24 and from 5 male patients and 1 female patient at week 48. Tissues were prepared for and evaluated with light microscopy, as described.13 Slides were masked for patient identification and sampling period. The degree of GL-3 accumulation in designated cell types was assessed independently by 3 dermatopathologists who had been trained in the 4-category scoring system (none, mild, moderate, severe). For each sample, the majority score was determined from the 3 pathologists’ scores. PLASMA GL-3. Pre-infusion plasma samples were obtained at week 0 and every 4 weeks thereafter for determination of GL-3 concentrations with tandem mass spectrometry.14 With this method, 7.03 ␮g/mL was considered the upper limit of normal. RENAL FUNCTION. Serum creatinine level, assayed by a central laboratory, was used to estimate glomerular filtration rate (GFR) with the Schwartz equation.15 For assessment of protein excretion, 24-hour urine collections obtained during an overnight hospital stay were assayed by a central laboratory. CARDIAC FUNCTION. Simultaneous 12-lead electrocardiography (ECG) and 2-dimensional Doppler echocardiography were performed during the observation period and at weeks 24 and 48. Standard analyses were conducted by central laboratories. GASTROINTESTINAL PARAMETERS. At 4-week intervals throughout observation and treatment, investigators asked patients about the frequency of nausea, vomiting, and postprandial pain during the previous month. GROWTH. Height and weight measurements were made at study visits. Sex-specific growth charts (Center of Disease Control and Prevention, National Center for Health Statistics, Hyattsville, MD) were used to assess normal weight (kg), height (cm), and BMI (kg/m2). ELECTRONIC PATIENT DIARY. A questionnaire was developed for daily self-assessment of quality-of-life measures; the instrument was not validated. Patients were trained in the use of the electronic diary, which only permitted entries between 17:00 and 20:00 for the current day. The Journal of Pediatrics • April 2008

School attendance. Patients were asked whether they attended school that day, and, if not, the reason why (I am sick; there is no school today; I had a doctor visit). Physical activity. Patients were asked whether they had difficulty performing activities that require low energy (such as dressing, eating, bathing, getting out of bed), moderate energy (such as climbing stairs, walking to school), high energy (such as playing football, running). General health. Patients placed a mark on a visual analogue scale from 0 (poor) to 100 (excellent) that “best shows your general health today.” Scores were determined from marked positions.

Safety Monitoring ADVERSE EVENTS. At study visits, investigators reviewed the results of scheduled physical examinations and laboratory tests and asked patients an open-ended question about their health status. Any symptom or abnormality considered clinically significant was reported as an adverse event (AE) and assessed by the investigator for seriousness, severity, and treatmentrelatedness. Infusion-associated reactions (IARs) were defined as treatment-related AEs occurring on the day of infusion excluding ECG, echocardiography, and laboratory abnormalities based on pre-infusion assessments. An independent data and safety monitoring board, comprising 1 immunologist and 2 pediatricians, convened regularly to review safety data; the board was authorized to recommend study termination when warranted. IMMUNOGLOBULIN G ANTIBODIES. Pre-infusion serum samples were obtained at week 0 and every 4 weeks thereafter for detection and titering of Immunoglobulin G (IgG) antibodies to agalsidase beta with an enzyme-linked immunosorbent assay (ELISA), and antibody specificity was confirmed by radioimmunoprecipitation.5 Patients with positive results in both assays were considered to be seropositive. IgG titers are reported as the inverse of the highest serum dilution yielding a positive ELISA result.

Table I. Patient demographics and Fabry disease history Fabry medical history*

Patient 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Mean (SD) Median (minimum, maximum) Number (%) positive

Age at baseline (years) 8.5 8.7 9.3 9.7 10.3 11.1 11.7 11.9 13.5 13.7 14.4 15.6 15.9 16.0 11.1 11.7 12.1 (2.5) 11.7 (8.5, 16.0)

Age at symptom Gastrointestinal onset (years) symptoms Angiokeratoma 6 8 9 7 5 7 6 6 9 9 6 8 5 8 11 10 7 (1) 7 (5, 11)

⫺ ⫹ ⫹ ⫹ ⫹ ⫺ ⫺ ⫹ ⫹ ⫹ ⫹ ⫹ ⫺ ⫹ ⫺ ⫹

⫹ ⫺ ⫹ ⫺ ⫺ ⫹ ⫹ ⫹ ⫹ ⫹ ⫹ ⫺ ⫹ ⫹ ⫹ ⫺

11 (68.8)

11 (68.8)

*Fabry medical history data were obtained from a medical history conducted before treatment, with the exception of “angiokeratoma” data, which were obtained from a physical examination. Gastrointestinal symptoms reported were nausea, vomiting, diarrhea, constipation, and post-prandial pain. All patients were male except patients 15 and 16, all patients were positive for hypohidrosis, and all patients except 1 and 15 were positive for Fabry-related pain.

Role of the Sponsor The trial was sponsored by Genzyme Corporation, whose project team designed the trial in conjunction with study investigators. Data management and statistical analyses were conducted by the sponsor, and site monitoring and source data verification was conducted by a contract research organization. The manuscript was drafted by Drs Tylki-Szymanska, Wraith, and Germain, with writing services provided by the sponsor, who reviewed the manuscript for accuracy but was not involved in the decision to submit it for publication.

RESULTS Statistical Analyses Analyses were conducted on available data from all 16 patients. The exact binomial matched pairs procedure was used to evaluate changes in each patient’s skin biopsy score from pre-treatment to week 24 and week 48 and the change in gastrointestinal symptoms reported at least once by patients during the 12-week observation period relative to sequential 12-week treatment intervals. To compare pre- and posttreatment values, Wilcoxon-signed rank tests were applied to plasma GL-3 data and repeated measures models were applied to e-diary data. The World Health Organization Adverse Reaction Thesaurus (WHOART) was used to code AEs; frequency data for AEs reported during the treatment period are presented in summary form.

Study Population Demographic and medical history data are presented in Table I for the 14 male and 2 female participants, who ranged in age from 8 to 15 years at enrollment; 2 male patients turned 16 before the first treatment. Patient histories indicated that the onset of symptoms occurred at a mean (SD) age of 7 (1) years, with disease diagnosis at 9 (4) years. Only 2 male patients and 1 female patient had their disease diagnosed before symptom onset, although at least 1 family member of all patients had been diagnosed with Fabry disease. Of the 16 patients, 15 completed the study, having received between 22 and 25 of the 25 scheduled infusions; 1 male patient stopped participating at week 26 after 15 infusions. Infusion rates were more strictly limited for the first 8 treat-

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Figure 1. GL-3 accumulation in the superficial dermal capillary endothelium of the skin of male pediatric patients. Cells were scored from none to severe on the basis of the amount of GL-3 observed in skin biopsy samples obtained during the pre-treatment period and at weeks 24 and 48 of treatment. The percentage of male patients assigned each score is shown for each time point. *P ⬍ .001, compared with the respective pre-treatment value.

ments, and the mean (SD) time to complete infusions decreased from 4.5 (0.4) to 2.9 (0.7) hours from week 0 to week 48. SKIN GL-3. Before treatment, 12 male patients exhibited GL-3 deposits in the superficial dermal capillary endothelium that ranged from perinuclear inclusions in moderate cases to large cytoplasmic aggregates that sometimes protruded into the vessel lumen in a severe case. Complete clearance of GL-3 from the superficial dermal capillary endothelium was observed at week 24 for the 12 male patients and at week 48 for 5 of the male patients with available samples (Figure 1). For 2 male patients (and both female patients; not shown), no pre- or post-treatment GL-3 deposits were detected. Before treatment, the deep dermal capillary/arteriolar endothelium showed moderate or severe accumulation in 12 male patients and mild accumulation in 1 female patient; deposits were cleared or reduced to mild at week 24 in these 13 patients and at week 48 in the 5 male patients with available samples. PLASMA GL-3. Before the first infusion, plasma GL-3 levels were elevated in all male patients, with a median of 15.9 ␮g/mL (normal, ⱕ7.03 ␮g/mL). By week 4, the median decreased to 6.3 ␮g/mL (P ⫽ .001) and remained in reference range through week 48 (Figure 2; available at www.jpeds. com). For the 2 female patients, plasma GL-3 was ⱕ5 ␮g/mL from week 0 through week 48.

Gastrointestinal Symptoms Patient reports of post-prandial pain, nausea, and vomiting declined steadily with time on treatment, showing statistically significant improvements by week 24 (Figure 3). Although 11 patients reported vomiting at least once, only 1 566

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Figure 3. Gastrointestinal symptoms. The percentage of patients reporting each symptom at least once during the respective 12-week interval is shown. The total number of patients ⫽ 15-16. *P ⫽ .031; #P ⫽ .008, compared with the pre-treatment observation period.

patient reported this symptom as occurring often through the first 12 weeks of treatment. Chronic diarrhea was not noted in any patient during observation or treatment.

Renal Function No patient received angiotensin-converting enzyme inhibitors or angiotensin receptor blockers during the trial. The mean (SD) rate of urinary protein excretion was 118 (55) mg/m2/24 hr at baseline (n ⫽ 15), 77 (29) at week 24 (n ⫽ 15), and 95 (35) at week 48 (n ⫽ 13). Mild proteinuria, evidenced by levels at or higher than the reference range threshold of 100 mg/m2/24 hr established for pediatric patients,16 was seen in 8 of 15 patients at baseline. Only 3 of the 8 patients (described below) had values ⱖ100 mg/m2/24 hr at week 48, and an increase from 93 to 157 mg/m2/24 hr from baseline to week 48 was noted for 1 patient. Serum creatinine levels ranged from 0.6 to 0.9 mg/dL in the 16 patients at baseline and did not vary significantly during the course of treatment. Mean (SD) estimated GFR was 126 (29) mL/min/ 1.73 m2 at baseline (n ⫽ 16), 128 (29) at week 24 (n ⫽ 16), and 125 (26) at week 48 (n ⫽ 15). By using the Schwartz equation to estimate GFR, the normal mean (SD) is approximately 140 (30) mL/min/1.73 m2 for male patients younger than 21 years.17 Patient 5, a 10-year-old boy, had an estimated GFR of 86 mL/min/1.73 m2 at baseline, although his serum creatinine (0.8 mg/dL) and protein excretion levels (69 mg/m2/24 hr) were in the reference range. His estimated GFR values ranged from 72 to 92 mL/min/1.73 m2 during the study, but inulin clearance determined at week 24 was 127 mL/min/1.73 m2. This patient was small in stature, with height measurements ⬍10th percentile throughout the study, which may account for the low values for estimated GFR, as height is a variable in the Schwartz equation. Patient 12, a 15-year-old boy, had an estimated GFR of 185 mL/min/1.73 m2 and protein excretion of 275 mg/m2/24 hr at baseline; at week 48, these values were 184 mL/min/1.73 m2 and 153 mg/m2/24 hr, respectively. Albumin excretion also decreased The Journal of Pediatrics • April 2008

for this patient during 48 weeks of treatment, from 74 to 40 mg/m2/24 hr. Two other adolescent male patients exhibited baseline estimated GFR in the hyperfiltrative range, accompanied by mild proteinuria. Patient 11 had an estimated GFR of 166 mL/min/1.73 m2 and protein excretion of 133 mg/ m2/24 hr at baseline, decreasing to 142 mL/min/1.73 m2 and 105 mg/m2/24 hr, respectively, at week 48. Albumin excretion was 3 mg/m2/24 hr at week 48, but baseline data were not available. Patient 13 had estimated GFR of 177 mL/min/ 1.73 m2 and 157 mL/min/1.73 m2, protein excretion of 103 mg/m2/24 hr and 94 mg/m2/24 hr, and albumin excretion of 46 mg/m2/24 hr and 26 mg/m2/24 hr at baseline and week 24, respectively. No week-48 data were available for this patient.

Cardiac Function No clinically significant cardiac abnormalities were evident in any of the ECG or echocardiogram assessments at baseline, and no changes occurred in the 48 weeks of treatment. No sinus arrhythmias or conduction abnormalities were noted on ECGs. Echocardiogram evaluations revealed normal ejection fractions, and no regional wall motion abnormalities were identified. Aortic valve morphology and function were normal in all patients, but myxomatous mitral valves, accompanied by trace regurgitation, were noted in 3 male patients. A left ventricular mass index ⬎51 g/m2, suggestive of left ventricular hypertrophy,18 was determined in 1 male patient; no change was observed at week 24, but week-48 data were not available for this patient. Body Mass Index Before treatment, BMI was between the seventh and 62nd percentiles for all patients, except 1 overweight 13-yearold boy in the 97th percentile. During 48 weeks of treatment, BMI fluctuated slightly, but notable changes were only seen in a 16-year-old boy who gained 9.7 cm and 3.6 kg, but dropped slightly below the fifth percentile for BMI, and the overweight boy who gained 10.6 cm and lost 3.8 kg, and dropped to 75th percentile for BMI. Electronic Patient Diary Diary entries for all 16 patients were available through week 24 and for 11 patients through week 48 because 1 patient withdrew and there were technical problems with electronic transmission of data for 4 patients during the latter part of the study. For the 11 patients, the mean (SD) percentage of days when diary entries were made was 75% (15%) from observation through week 48. From the 12-week observation period to weeks 37 to 48, statistically significant reductions were noted in the mean percentage of days absent from school because of sickness (12% to 7%; odds ratio ⫽ 0.56; P ⫽ .04). Significant improvements were also observed in the mean percentage of days with difficulty performing low-energy activities (12% to 3%; odds ratio ⫽ 0.25; P ⬍ .001), with non-significant improvements for the percentage

Table II. Most frequently reported adverse events and infusion-associated reactions Number Number (%) (%) Number of AE Number of patients AEs that of patients with AE were IARs with IAR description of AEs Headache Abdominal pain Fever Nausea Fabry pain Rhinitis Pharyngitis Rigors Vomiting Pain All others Total AEs

38 36

9 (56) 9 (56)

5 1

3 (19) 1 (6)

28 23 21 20 15 15 12 9 133 350

8 (50) 8 (50) 4 (25) 6 (38) 9 (56) 3 (19) 7 (44) 6 (38) 15 (94) 15 (94)

9 5 0 8 2 14 1 0 15 60

2 (13) 3 (19) 0 1 (6) 1 (6) 3 (19) 1 (6) 0 5 (31) 6 (38)

The 10 most frequently reported AEs without regard to causality are listed in order of frequency, with the numbers and percentages of patients who experienced each type of AE. Data are also provided for AEs that were IARs.

of days with difficulty performing moderate-energy (18% to 12%; odds ratio ⫽ 0.65; P ⫽ .325) and high-energy (29% to 27%; odds ratio ⫽ 0.93; P ⫽ .81) activities. The mean percentage of days when patients recorded good general health (scores ⱖ75) increased from 69% to 77% (P ⫽ .11) from observation to weeks 37 to 48. Overall, consistent results were found for electronic diary entries from all 16 patients from the observation period to weeks 13 to 24.

Adverse Events During the 48-week treatment period, 350 AEs were reported for 15 patients (Table II). More than 90% of AEs were mild or moderate in severity; 82% were not related to treatment. Of the 62 AEs that were treatment-related, 60 (97%) were IARs experienced by 6 male patients, 3 of whom reported events during ⬎1 infusion. The most frequently reported IARs were rigors, fever, and rhinitis (Table II); 85% were mild in severity. All patients recovered: one-third of IARs did not require any intervention; the remainder were managed by reductions in infusion rates, administration of antipyretics, antihistamines, and/or steroids, or both. The frequency of IARs decreased with time, with 68% occurring within the first 24 weeks of treatment. The only serious adverse event (SAE) reported in this study was an IAR experienced by patient 13, a 16-year-old boy, during his 15th infusion. The patient’s pre-infusion blood pressure and heart rate were 122/49 mm Hg and 63 beats per minute. Approximately 2 hours after the infusion began, the patient developed itching, facial redness, and hives on his chest, along with shortness of breath and tightness in the chest. Blood pressure was 82/44 mm Hg, heart rate was 38 beats per minute, and oxygen saturation was 100%. The patient never presented with tachycardia; rather, the episode was associated with

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bradycardia, which responded to treatment with atropine. Tryptase levels (an indicator of mast cell degranulation) were in the reference range in serum collected within 1 hour of symptom onset; IgE antibodies to agalsidase beta were not detected in serum collected immediately before and 3 days after the infusion. The patient’s serum IgG antibody titer was 800. The event was assessed by the investigator as severe in intensity and definitely related to treatment. The patient recovered the same day without sequelae, but discontinued his participation in the study. (Of note, the patient later began ERT with commercial agalsidase beta outside of the study setting. After approximately 3 months, he developed generalized hives during an infusion; no respiratory or cardiovascular symptoms were noted. He subsequently tested positive for serum IgE antibodies to agalsidase beta.)

Seroconversion IgG antibodies to agalsidase beta were detected in sera from 11 male patients; 3 male and both female patients remained seronegative. Seroconversion occurred in a mean time of 56 days after treatment initiation, with antibodies first detected after the second to sixth infusion. The highest titer did not exceed 800 in 5 patients and ranged from 1600 to 6400 in 6 patients (Figure 4; available at www.jpeds.com). Seroconversion was not associated with elevations in plasma or dermal GL-3 levels. Five of the 6 patients who experienced IARs were seropositive, but no correlation between IAR frequency and IgG titer was discerned.

DISCUSSION This report describes the first clinical trial of agalsidase beta therapy in pediatric patients with Fabry disease. The safety profile and exploratory efficacy data that emerged from the 12-month study are similar to findings in adults treated with the same dosage regimen. As recently reported,9,12 agalsidase alfa, another form of r-h␣Gal (Replagal, Shire, Cambridge, MA) was also well tolerated by children during openlabel trials, but the administered dose was lower than for agalsidase beta (0.2 versus 1 mg/kg). Before agalsidase beta therapy was initiated, intracellular deposits of GL-3 were detected in the superficial dermal capillary endothelium of 12 of the male patients, including the 3 youngest. Histologically, the appearance of the deposits and the range of severity of accumulation were similar to those observed in untreated adult patients.13 Glycolipid inclusions have been described in tissues from children with Fabry disease,19,20 and fetal autopsies have indicated that substrate deposition begins in utero.21 Because the failure to metabolize GL-3 and related glycolipid substrates underlies the pathogenesis of Fabry disease, it is encouraging that agalsidse beta treatment resulted in complete clearance of accumulated substrate from the superficial dermal capillary endothelium of all patients, along with normalization of plasma GL-3. In some adult Fabry patients, particularly those who exhibit severe renal disease (extensive glomerulosclerosis or high proteinuria) before the initiation of ERT, reductions in GL-3 levels 568

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in cells or plasma have not corresponded to reversal of preexisting organ dysfunction.6 However, it remains to be seen whether initiation in young patients of biweekly infusions of agalsidase beta at 1 mg/kg will provide long-term maintenance of normal tissue levels of GL-3 and prevent organ damage later in life. Gastrointestinal symptoms are common in Fabry disease and generally increase in frequency and severity with age.22 In this pediatric study, some degree of post-prandial pain, nausea, and/or vomiting was experienced by all patients before treatment. Reports of these symptoms declined steadily with treatment, and statistically significant improvements were seen by week 24. These results are supported by data from adult patients who experienced reductions in gastrointestinal symptoms after 6 months of agalsidase beta treatment, which were sustained for as long as 3 years of therapy.23,24 Renal and cardiac manifestations of Fabry disease were not present in most children in this study. For the 3 adolescent male patients with possible hyperfiltration and mild proteinuria at baseline, it is notable that further deterioration of renal function was not observed. In addition, no transient ischemic attacks or strokes were reported in this 12-month study. However, to determine whether ERT ultimately can prevent development of end-organ complications, long-term monitoring of patients is required. Because clinical trials can not be ethically or logistically managed for extended periods, the Fabry Registry,25 a voluntary observational program, has been established for long-term tracking of clinical outcomes in patients with Fabry disease, regardless of whether the patient is undergoing ERT. Registry data will be useful in elucidating the natural history of the disease and determining the extent to which ERT improves outcomes when initiated in pediatric and adult patients. Patient self-assessments during agalsidase beta therapy suggested improvements in some quality-of-life measures, such as school attendance and the ability to undertake lowenergy physical activities. These results must be interpreted cautiously because of the design of the study (inclusion of a small, heterogeneous patient population with varying expression of Fabry disease symptoms and the lack of a placebo control) and the use of non-validated questionnaires. However, the results of these exploratory measures can be viewed as encouraging trends. The overall safety profile for agalsidase beta in this pediatric cohort mirrors that observed in adult populations.4,7 Most AEs were not related to treatment and included pain symptoms typically associated with Fabry disease. Almost all the treatment-related AEs were IARs, which were reported for 38% of the pediatric patients. For the 3 boys with recurrent IARs, most events occurred in the first 6 months and subsided thereafter, the same pattern seen in adult patients.5 In accordance with study protocols for trials in both pediatric and adult patients, acetominophen or ibuprofen was administered before infusions, and antihistamines or steroids may have been administered to individuals with recurrent IARs. Therefore, the decline in IAR frequency with time may reflect The Journal of Pediatrics • April 2008

a combination of effective prophylaxis with pre-infusion medications, optimization of infusion rates, and increased tolerance to the exogenous protein (see below). For treating new patients, a sound strategy for children and adults involves initiation of infusions at a slow rate, followed by incremental rate increases, and careful patient monitoring to assess how individuals tolerate treatment and to determine the need for prophylactic medications. The development of serum IgG antibodies to agalsidase beta by at least some children was anticipated because seroconversion has been observed in 68% to 90% of adults who are treated.5,7 Of the 16 study participants, 11 (69%) seroconverted. Although IgG antibodies did not develop in either of the girls, seroconversion has been observed in 50% of adult female patients.5,7 No effect on GL-3 clearance from skin or plasma could be discerned in any seropositive patient, suggesting that the antibodies did not impair the efficacy of the enzyme infused at 1 mg/kg every other week. During a 54-month extension trial of adult patients receiving agalsidase beta, IgG antibody titers declined with time in most patients who were seropositive, and 17% of them reverted to seronegative status.6 Although antibody titers for the 11 seropositive juveniles did not fall below detectable levels within the 12month time frame of this study, last-available titers for 7 of them ranged from 100 (the minimum dilution) to 800. The decline in IgG antibody titers parallels—and may contribute to—the decline in IAR frequency in both pediatric and adult patients. Yet, the susceptibility of patients to IARs cannot be predicted on the basis of IgG antibody titers alone, and the nature of the immune response involved in IARs has not been elucidated. These issues are evident in the only SAE reported in this study. IgG antibodies developed after the fourth infusion in patient 13, but he experienced no IAR until the 15th infusion. Although some features of the event were characteristic of a type 1 hypersensitivity reaction, uncharacteristically substantial respiratory symptoms were absent and tachycardia was not observed. Instead, the patient was bradycardic and responded to atropine. Because these developments are more indicative of a vasovagal response, the unusual clinical course of this event may entail both Fabry-related autonomic dysfunction and immune-mediated reactions. In summary, IV infusions of agalsidase beta at 1 mg/kg every 2 weeks can be safely administered to children and adolescents with Fabry disease, resulting in rapid clearance of accumulated substrate from dermal endothelium and plasma. As seen in this study, substantial tissue accumulation of substrate may be present in young patients in the absence of serious symptoms. However, it is not yet known whether initiation of enzyme replacement in pediatric patients will prevent the widespread tissue damage and multisystemic complications associated with disease morbidity and mortality in adult patients. Because there is currently no widely accepted biomarker to monitor treatment effects in Fabry disease, systematic tracking of clinical outcomes for several years is needed to determine whether ERT, when initiated in

young patients, can play a preventative role in mitigating disease progression. Finally, because the natural course of Fabry disease varies markedly among individuals, no generalizations can be made about the appropriate disease stage or optimal age at which to begin enzyme replacement and the decision to initiate therapy must be evaluated on a case-bycase basis by treating physicians. We thank the patients and their families and the study personnel who participated in the trial. The dermatopathologists who scored the histology specimens were: Robert G. Phelps, MD, H. Randolph Byers, MD, PhD, and Scott R. Granter, MD. The Genzyme project team included: Bernard Bénichou, MD, PhD, Tim Foley, Mathilde Kaper, MA, Andrea Norfleet, PhD, Crystal Sung, PhD, Beth Thurberg, MD, PhD, Catherine Weenink, and Karen Welch.

REFERENCES 1. Desnick RJ, Ioannou YA, Eng CM. Alpha-galactosidase A deficiency: Fabry disease. In: Scriver CR, Beaudet A, Sly W, Valle D, Childs R, Kinzler K, editors. Metabolic and molecular bases of inherited disease. 8 ed. New York: McGraw Hill; 2001. p. 3733-74. 2. Gupta S, Ries M, Kotsopoulos S, Schiffmann R. The relationship of vascular glycolipid storage to clinical manifestations of Fabry disease: a cross-sectional study of a large cohort of clinically affected heterozygous women. Medicine 2005;84:261-8. 3. Eng CM, Banikazemi M, Gordon RE, Goldman M, Phelps R, Kim L, et al. A phase 1/2 clinical trial of enzyme replacement in Fabry disease: pharmacokinetic, substrate clearance, and safety studies. Am J Hum Genet 2001;68:711-22. 4. Eng CM, Guffon N, Wilcox WR, Germain DP, Lee P, Waldek S, et al. Safety and efficacy of recombinant human alpha-galactosidase A—replacement therapy in Fabry’s disease. N Engl J Med 2001;345:9-16. 5. Wilcox WR, Banikazemi M, Guffon N, Waldek S, Lee P, Linthorst GE, et al. Long-term safety and efficacy of enzyme replacement therapy for Fabry disease. Am J Hum Genet 2004;75:65-74. 6. Germain DP, Waldek S, Banikazemi M, Bushinsky DA, Charrow J, Desnick RJ, et al. Sustained, long-term renal stabilization after 54 months of agalsidase beta therapy in patients with Fabry disease. J Am Soc Nephrol 2007;18:1547-57. 7. Banikazemi M, Bultas J, Waldek S, Wilcox WR, Whitley CB, McDonald M, et al. Agalsidase beta therapy for advanced Fabry disease: a randomized trial. Ann Intern Med 2007;146:77-86. 8. Ries M, Gupta S, Moore DF, Sachdev V, Quirk JM, Murray GJ, et al. Pediatric Fabry disease. Pediatrics 2005;115:e344-55. 9. Ramaswami U, Wendt S, Pintos-Morell G, Parini R, Whybra C, Leon Leal JA, et al. Enzyme replacement therapy with agalsidase alfa in children with Fabry disease. Acta Paediatr 2007;96:122-7. 10. Ries M, Ramaswami U, Parini R, Lindblad B, Whybra C, Willers I, et al. The early clinical phenotype of Fabry disease: a study on 35 European children and adolescents. Eur J Pediatr 2003;162:767-72. 11. Desnick RJ, Brady RO. Fabry disease in childhood. J Pediatr 2004;144(5 Suppl):S20-6. 12. Ries M, Clarke JT, Whybra C, Timmons M, Robinson C, Schlaggar BL, et al. Enzyme-replacement therapy with agalsidase alfa in children with Fabry disease. Pediatrics 2006;118:924-32. 13. Thurberg BL, Byers HR, Granter SR, Phelps RG, Gordon RE, O’Callaghan M. Monitoring the 3-year efficacy of enzyme replacement therapy in Fabry disease by repeated skin biopsies. J Invest Dermatol 2004;122:900-8. 14. Roddy TP, Nelson BC, Sung CC, Araghi S, Wilkens D, Zhang XK, et al. Liquid chromatography-tandem mass spectrometry quantification of globotriaosylceramide in plasma for long-term monitoring of Fabry patients treated with enzyme replacement therapy. Clin Chem 2005;51:237-40. 15. Schwartz GJ, Brion LP, Spitzer A. The use of plasma creatinine concentration for estimating glomerular filtration rate in infants, children, and adolescents. Pediatr Clin North Am 1987;34:571-90. 16. Hogg RJ, Portman RJ, Milliner D, Lemley KV, Eddy A, Ingelfinger J. Evaluation and management of proteinuria and nephrotic syndrome in children: recommendations from a pediatric nephrology panel established at the National Kidney Foundation conference on proteinuria, albuminuria, risk, assessment, detection, and elimination (PARADE). Pediatrics 2000;105:1242-9. 17. Hogg RJ, Furth S, Lemley KV, Portman R, Schwartz GJ, Coresh J, et al. National

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Kidney Foundation’s Kidney Disease Outcomes Quality Initiative clinical practice guidelines for chronic kidney disease in children and adolescents: evaluation, classification, and stratification. Pediatrics 2003;111(6 Pt 1):1416-21. 18. de Simone G, Devereux RB, Daniels SR, Koren MJ, Meyer RA, Laragh JH. Effect of growth on variability of left ventricular mass: assessment of allometric signals in adults and children and their capacity to predict cardiovascular risk. J Am Coll Cardiol 1995;25:1056-62. 19. Gubler MC, Lenoir G, Grunfeld JP, Ulmann A, Droz D, Habib R. Early renal changes in hemizygous and heterozygous patients with Fabry’s disease. Kidney Int 1978;13:223-35. 20. Raas-Rothschild A, Friedlaender MM, Pizov G, Backenroth R. The kidney in Fabry disease. J Pediatr 2005;146:148. 21. Tsutsumi O, Sato M, Sato K, Mizuno M, Sakamoto S. Early prenatal diagnosis

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of inborn error of metabolism: a case report of a fetus affected with Fabry’s disease. Asia Oceania J Obstet Gynaecol 1985;11:39-45. 22. O’Brien BD, Shnitka TK, McDougall R, Walker K, Costopoulos L, Lentle B, et al. Pathophysiologic and ultrastructural basis for intestinal symptoms in Fabry’s disease. Gastroenterology 1982;82(5 Pt 1):957-62. 23. Banikazemi M, Ullman T, Desnick RJ. Gastrointestinal manifestations of Fabry disease: clinical response to enzyme replacement therapy. Mol Genet Metab 2005; 85:255-9. 24. Guffon N, Fouilhoux A. Clinical benefit in Fabry patients given enzyme replacement therapy—a case series. J Inherit Metab Dis 2004;27:221-7. 25. Eng CM, Fletcher J, Wilcox WR, Waldek S, Scott CR, Sillence DO, et al. Fabry disease: baseline medical characteristics of a cohort of 1765 males and females in the Fabry Registry. J Inherit Metab Dis 2007;30:184-92.

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Figure 2. Plasma GL-3 concentrations in the male study patients. The horizontal line inside each box plot represents the median; the bottom and top of the box represent the 25th and 75th percentiles, respectively, and the error bars span the last observed values within (1.5*interquartile range). The dotted line at 7.03 ␮g/mL shows the upper limit of normal plasma GL-3. At each time point, n ⫽ 11-14. P ⱕ .001, compared with week 0.

Figure 4. Titers of IgG antibodies to algasidase beta in the 11 patients who were seropositive. The dark portion of each column indicates the highest antibody titer, and the light portion shows the last-available titer for the patient during the study. For patients 2, 8, and 1, the final titer was the same as the highest titer observed earlier in the study. Data for the 3 male and 2 female patients who remained seronegative are not shown.

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