A new severity score index for phenotypic classification and evaluation of responses to treatment in type I Gaucher disease

Background: Gaucher disease is the first lysosomal storage disease for which specific therapy became available. Over 4800 patients have been treated with enzyme replacement therapy. Analysis of Gaucher disease registry data has outlined the clinical heterogeneity of the disease and the different responses to treatment from patient to patient, and for different organs. This variability in clinical response justifies the development of a severity score index to assess disease activity, stage and prognosis, and to quantify the effects of treatment. Design and Methods: The new scoring system proposed here, the "Gaucher Disease Severity Score Index - Type I" (GauSSI-I), is based on the clinical experience of the authors and an extensive literature review, including data from the International Gaucher Registry. In particular for skeletal disease, all the available scoring systems have been reviewed and compared in order to provide a skeletal scoring system that allows use of any of the different methods on an equivalent basis. Results: The new scoring system, GauSSI-I, was developed. Six specific domains, in which different items were scored according to their impact on morbidity, were characterized. GauSSI-I was evaluated in 53 type I Gaucher patients treated with imiglucerase, and it was compared to the Zimran score, the only severity index score so far available. Conclusions: The GauSSI-I is a reliable method for staging the severity of adult type I Gaucher disease, and it is more sensitive than the Zimran score for monitoring the response to treatment.