Natural disease course of chronic visceral acid sphingomyelinase deficiency in adults: A first step toward treatment criteria.

Acid sphingomyelinase deficiency (ASMD) is an ultra-rare lysosomal storage disease with a broad spectrum of manifestations ranging from severe neuropathic forms to attenuated, chronic visceral forms. Manifestations of the chronic visceral subtype are variable and encompass different degrees of hepatosplenomegaly, pulmonary disease and dyslipidemia. The aim of this study was to provide insights into the natural course of adult patients with the chronic visceral subtype. Based on these insights, we proposed tentative criteria for initiation and follow-up of enzyme replacement therapy (ERT). The data of 23 adult patients were collected in a prospective study. Clinical, genetic and demographic data, plasma measurements, abdominal imaging, pulmonary imaging, pulmonary function tests and quality of life questionnaires were collected. Stability of disease based on several clinical, biochemical and radiological markers (i.e., spleen volume, platelet levels, liver volume, alanine aminotransferase [ALT] levels, diffusion capacity of the lungs for carbon monoxide [DLCO] chitotriosidase activity and lysosphingomyelin [LSM]) was assessed. Cardiovascular risk was estimated based on sex, age, smoking, systolic blood pressure and lipid profile. Quality of life was evaluated with the 36-Item Short Form Health Survey and the Health Assessment Questionnaire. Median follow-up was 6.1 years (range 1.3-19.5 years). The most common manifestations were splenomegaly (100%), decreased high-density lipoprotein cholesterol (HDL-C) plasma levels (83%), (signs of) steatosis measured with transient elastography (82%), thrombocytopenia (64%), hepatomegaly (52%) and decreased diffusion capacity (45%). The majority of markers remained stable during follow-up. Twelve patients showed progression of disease: four for spleen volume, two for liver volume, three for DLCO, seven for chitotriosidase activity and three for LSM. One patient showed progression of disease based on four markers, although this patient did not report any problems at the last visit. Cardiovascular risk was estimated and was increased in half of the patients older than 40 years. Patient-reported quality of life did not differ from the general population, but differences in median 36-Item Short Form Health Survey (SF-36) scores of patients with severe pulmonary involvement and those of patients without pulmonary involvement were observed. Tentative criteria for initiation and effect of therapy were proposed. In conclusion, the chronic visceral subtype of ASMD showed a predominantly stable disease course in this cohort. We propose that ERT should be initiated on an individual basis and only in case of progression or symptomatic disease. Collection and analysis of real world data are necessary to refine start, stop and follow-up criteria in the future.

Glycoprotein non-metastatic protein B (GPNMB) plasma values in patients with chronic visceral acid sphingomyelinase deficiency.

Acid sphingomyelinase deficiency (ASMD) is a rare LSD characterized by lysosomal accumulation of sphingomyelin, primarily in macrophages. With the recent availability of enzyme replacement therapy, the need for biomarkers to assess severity of disease has increased. Glycoprotein non-metastatic protein B (GPNMB) plasma levels were demonstrated to be elevated in Gaucher disease. Given the similarities between Gaucher disease and ASMD, the hypothesis was that GPNMB might be a potential biochemical marker for ASMD as well. Plasma samples of ASMD patients were analyzed and GPNMB plasma levels were compared to those of healthy volunteers. Visceral disease severity was classified as severe when splenic, hepatic and pulmonary manifestations were all present and as mild to moderate if this was not the case. Median GPNMB levels in 67 samples of 19 ASMD patients were 185 ng/ml (range 70-811 ng/ml) and were increased compared to 10 healthy controls (median 36 ng/ml, range 9-175 ng/ml, p < 0.001). Median plasma GPNMB levels of ASMD patients with mild to moderate visceral disease compared to patients with severe visceral disease differed significantly and did not overlap (respectively 109 ng/ml, range 70-304 ng/ml and 325 ng/ml, range 165-811 ng/ml, p < 0.001). Correlations with other biochemical markers of ASMD (i.e. chitotriosidase activity, CCL18 and lysosphingomyelin, respectively R = 0.28, p = 0.270; R = 0.34, p = 0.180; R = 0.39, p = 0.100) and clinical parameters (i.e. spleen volume, liver volume, diffusion capacity and forced vital capacity, respectively R = 0.59, p = 0.061, R = 0.5, p = 0.100, R = 0.065, p = 0.810, R = -0.38, p = 0.160) could not be established within this study. The results of this study suggest that GPNMB might be suitable as a biomarker of visceral disease severity in ASMD. Correlations between GPNMB and biochemical or clinical markers of ASMD and response to therapy have to be studied in a larger cohort.

Patients' view on gene therapy development for lysosomal storage disorders: a qualitative study.

INTRODUCTION: Several new treatment modalities are being developed for lysosomal storage disorders (LSDs), including gene therapy. As the currently available treatment options and their influence on disease progression differ greatly within the spectrum of LSDs, willingness to undergo gene therapy might vary among patients with LSDs and/or their representatives. The width of the LSD spectrum is illustrated by the differences between type 1 Gaucher disease, Fabry disease and Mucopolysaccharidosis type III (MPS III). For type 1 Gaucher and Fabry disease several therapies are available, resulting in a near normal or improved, but individually varying, prognosis. No treatment options are available for MPS III. AIM: To identify factors influencing patients' and/or their representatives' decisions regarding undergoing gene therapy. METHODS: Focus group discussions and semi-structured interviews were conducted with patients with type 1 Gaucher disease, Fabry disease and MPS III. Parents of MPS III patients were included as patients' representatives. RESULTS: Nine Gaucher patients, 23 Fabry patients, two adult MPS III patients and five parents of MPS III patients participated in the study. The five main themes that arose were: outcome of gene therapy, risks and side effects, burden of gene therapy treatment, current situation and ethical aspects. Participants' views ranged from hesitance to eagerness to undergo gene therapy, which seemed to be mostly related to disease severity and currently available treatment options. Severe disease, limited treatment options and limited effectiveness of current treatment augmented the willingness to choose gene therapy. Gaucher and Fabry patients deemed the burden of treatment important. Fabry and MPS III patients and parents considered outcome important, suggesting hope for improvement. When asked to rank the factors discussed in the focus group discussions, Gaucher patients ranked outcome low, which could indicate a more cautious attitude towards gene therapy. CONCLUSION: This study underlines the importance of exploring patients' needs and expectations before using limited resources in the development of therapies for patient groups of which a significant subset may not be willing to undergo that specific therapy.

Renal involvement in a patient with the chronic visceral subtype of acid sphingomyelinase deficiency resembles Fabry disease.

Acid sphingomyelinase deficiency (ASMD) is a lysosomal storage disease (LSD) in which sphingomyelin accumulates due to deficient acid sphingomyelinase. In the chronic visceral subtype, organ manifestations are generally limited to the spleen, liver, and lungs. We report a male patient with the chronic visceral subtype who developed proteinuria and renal insufficiency at the age of 49. In renal tissue, foam cells were observed in the glomeruli as well as sphingomyelin accumulation within podocytes, mesangial cells, endothelial cells, and tubular epithelial cells. Although macrophages are the primary storage cells in both ASMD and Gaucher disease, comparison to the histopathological findings in Gaucher and Fabry disease revealed a diffuse storage pattern in multiple renal cell types, closer resembling the pattern found in Fabry disease.

Biochemical and imaging parameters in acid sphingomyelinase deficiency: Potential utility as biomarkers.

Acid Sphingomyelinase Deficiency (ASMD), or Niemann-Pick type A/B disease, is a rare lipid storage disorder leading to accumulation of sphingomyelin and its precursors primarily in macrophages. The disease has a broad phenotypic spectrum ranging from a fatal infantile form with severe neurological involvement (the infantile neurovisceral type) to a primarily visceral form with different degrees of pulmonary, liver, spleen and skeletal involvement (the chronic visceral type). With the upcoming possibility of treatment with enzyme replacement therapy, the need for biomarkers that predict or reflect disease progression has increased. Biomarkers should be validated for their use as surrogate markers of clinically relevant endpoints. In this review, clinically important endpoints as well as biochemical and imaging markers of ASMD are discussed and potential new biomarkers are identified. We suggest as the most promising biomarkers that may function as surrogate endpoints in the future: diffusion capacity measured by spirometry, spleen volume, platelet count, low-density lipoprotein cholesterol, liver fibrosis measured with a fibroscan, lysosphingomyelin and walked distance in six minutes. Currently, no biomarkers have been validated. Several plasma markers of lipid-laden cells, fibrosis or inflammation are of high potential as biomarkers and deserve further study. Based upon current guidelines for biomarkers, recommendations for the validation process are provided.