Clinical outcomes following hematopoietic stem cell transplantation for the treatment of mucopolysaccharidosis VI

Mucopolysaccharidosis VI (MPS VI, Maroteaux-Lamy Syndrome) is one of approximately 50 known lysosomal storage disorders. MPS VI is characterized by an absence or deficiency of N-acetylgalactosamine 4-sulfatase (arylsulfatase B) resulting in accumulation of dermatan sulfate. Prior to the availability of enzyme replacement therapy (ERT), the clinical management of MPS VI was limited to supportive care and allogeneic hematopoietic stem cell transplantation (HSCT); however, due to the rarity of this disease, little is known about the long-term outcomes of HSCT for MPS VI. The following retrospective study was performed using aggregate data gathered by the Center for International Blood and Marrow Transplant Research (CIBMTR) between 1982 and 2007 to determine survival probability for patients with MPS VI following allogeneic HSCT. This analysis identified 45 MPS VI patients with a median age of 5 years (range, 1-22 years) at the time they received an allogeneic HSCT. Cumulative incidence (95% CI) of acute graft-vs.-host disease at 100 days was 36% (21-53%). Probability of survival was 78% (65-89%) at 100 days and 66% (52-79%) at 1 and 3 years. While these data are based upon small numbers of recipients, they represent the largest series to date and may help clinicians assess the relative risks and benefits of currently available therapies.

Current therapy for Lambert-Eaton myasthenic syndrome: development of 3,4-diaminopyridine phosphate salt as first-line symptomatic treatment

BACKGROUND

Lambert-Eaton myasthenic syndrome (LEMS) is a rare pre-synaptic auto-immune disorder of neuromuscular transmission that is characterised by proximal muscle weakness, depressed tendon reflexes and autonomic dysfunction. This review summarises the clinical symptoms, aetiology, diagnosis and treatment options for LEMS. Focus is placed on symptomatic treatment with the potassium channel blocker 3,4-diaminopyridine (3,4-DAP).

RESEARCH METHODS

English-language publications were searched in MEDLINE and EMBASE to retrieve relevant literature on LEMS. The data submitted to obtain regulatory approval of 3,4-DAP phosphate by the European Medicines Agency (EMA) were also used.

FINDINGS

LEMS is a rare disease with few treatment options which are generally categorised as anti-tumour, immunomodulating or immunosuppressing, and symptomatic treatments. Anti-tumour treatment is recommended for patients with the paraneoplastic form of LEMS. While several immunomodulating or immunosuppressing treatments have been identified, these treatments should be initiated when symptomatic treatments are inadequate. As expected, due to the rarity of the disease, few reports of randomised controlled trials (RCTs) exist. Seven RCTs have been conducted to evaluate treatment of patients with LEMS. One RCT evaluated immunomodulating treatment with intravenous immunoglobulin (ivIg), while six evaluated symptomatic treatment with the potassium channel blocker 3,4-DAP. Improvements in LEMS symptoms after ivIg treatment were observed, leading to the recommendation for treatment in patients when symptomatic treatment does not provide satisfactory improvement. Potassium channel blockers evaluated for the treatment of LEMS include guanidine, 4-aminopyridine (4-AP) and 3,4-DAP. However, only 3,4-DAP has been evaluated in RCTs. Results of these RCTs demonstrated that treatment with 3,4-DAP is efficacious in treatment of LEMS and has an acceptable tolerability profile. Hence, 3,4-DAP has been recommended as first-line symptomatic treatment for LEMS by the European Federation of Neurological Societies. While 3,4-DAP base has only been available via named-patient programmes, requiring ad hoc preparations in compounding pharmacies, tablets containing 3,4-DAP phosphate salt, equivalent to 10 mg base, have become available. This formulation has obtained the orphan medicinal product status both in the European Union and in the United States of America, and has received marketing authorisation in Europe as Firdapse*. These tablets have been shown to be essentially bioequivalent with the base preparation.

CONCLUSIONS

The results of this review show that anti-tumour treatment is recommended for patients with the paraneoplastic form of LEMS and that one RCT has shown that immunomodulating treatments should be initiated when symptomatic treatments do not provide satisfactory results. A number of RCTs have shown that 3,4-DAP is effective in symptomatic treatment of patients with LEMS and has been recommended as first-line symptomatic treatment of patients with LEMS. The 3,4-DAP phosphate salt formulation was shown to be safe and effective in the treatment of LEMS with a positive benefit:risk ratio.

Clinical utility of endurance measures for evaluation of treatment in patients with mucopolysaccharidosis VI (Maroteaux-Lamy syndrome)

Increased functional capacity of major organ systems improves the quality of life and contributes to reductions in the morbidity associated with chronic debilitating diseases. Routine endurance tests can be used to gauge the progression of disease and the impact of therapeutic modalities in disorders with multiple organ system involvement such as with Mucopolysaccharidosis type VI (MPS VI). MPS VI is a progressive disorder affecting multiple organs and tissues due to the deficient activity of N-acetylgalactosamine-4-sulfatase leading to the accumulation of glycosaminoglycan (GAG) dermatan sulfate. Since 2005, enzyme replacement therapy (ERT) with human recombinant N-acetylgalactosamine-4-sulfatase (galsulfase) has been an available treatment option for MPS VI. These patients are routinely evaluated for extent of disability, disease progression and the impact of ERT. Evaluations are made by a combination of urinary GAG measurement and submaximal intensity endurance tests such as the 3-minute stair climb (3-MSC), and the 6- and 12-minute walk tests (6-MWT and 12-MWT). This review highlights the clinical validity of endurance measures as inexpensive diagnostic tools for diseases affecting multiple organ systems and evaluating the impact of therapeutic modalities, such as ERT for MPS VI.

In Vitro Stability of Sapropterin Dihydrochloride From Crushed Tablets Mixed in Applesauce, Pudding, and Infant Formula

Sapropterin is approved to reduce blood phenylalanine levels in patients with hyperphenylalaninemia due to tetrahydrobiopterin-responsive phenylketonuria. The current Food and Drug Administration—approved labeling states that sapropterin tablets should be dissolved in 4 to 8 oz of water or apple juice; however, numerous requests for information regarding the feasibility of administering crushed sapropterin tablets in infant formula or soft foods such as applesauce and pudding suggest that the current recommendations for administration may not be suitable for many infants and small children. To determine the safety of administering the medication in formula or soft foods, powdered tablets representing 200 mg of sapropterin were thoroughly mixed with applesauce, lemon pudding, and 3 brands of phenylalanine-free infant formula, incubated for up to 60 minutes at room temperature and then analyzed for sapropterin content. The results indicate there was no significant change in the amount of sapropterin present in any mixture after 60 minutes.

Reversed papilledema in an MPS VI patient with galsulfase (Naglazyme) therapy

MPS VI (mucopolysaccharidosis VI, known as Maroteaux-Lamy syndrome) is a multi-systemic inherited disease, resulting from a deficiency of N-acetylgalactosamine-4-sulfatase, causing accumulation of the glycosaminoglycan (GAG) dermatan sulfate in all tissues. It is one of almost 50 lysosomal storage disorders. Ocular pathology is common in patients with MPS VI, with complications including ocular hypertension, progressive corneal clouding, optic nerve swelling (or papilledema) often associated with communicating hydrocephalus (Ashworth et al., Eye 20(5), 553-563, 2006; Goldberg et al., AJO 69(6), 969-975), and raised intracranial pressure (ICP) progressing to atrophy with loss of vision (Goodrich et al., Loss of vision in MPS VI is a consequence of increased intracranial pressure, 2002). This is the first case report of reversed papilledema and improved visual acuity in an 11-year-old MPS VI patient receiving galsulfase (Naglazyme), an enzyme-replacement therapy (ERT) of recombinant human arylsulfatase B (rhASB) (Harmatz et al., J Pediatr 148(4), 533-539, 2006).