Abstract: Of the 488 studies retrieved by the electronic searches, eight met the inclusion criteria and were analysed (300 participants). Response parameters were restricted to haemoglobin concentration, platelet count, spleen and liver volume and serum biomarkers (chitotriosidase and CCL18). Only one publication reported a 'low risk of bias' score in all parameters assessed, and all studies included were randomized. Four studies reported the responses to enzyme replacement therapy of previously untreated individuals with type 1 Gaucher disease. Two studies investigated maintenance enzyme replacement therapy in people with stable type 1 Gaucher disease previously treated for at least two years. One study compared substrate reduction therapy, enzyme replacement therapy and a combination thereof as maintenance therapy in people with type 1 Gaucher disease previously treated with enzyme replacement therapy. One study examined substrate reduction therapy in people with chronic neuronopathic (type 3) Gaucher disease who continued to receive enzyme replacement therapy. Treatment-naïve participants had similar increases in haemoglobin when comparing those receiving imiglucerase or alglucerase at 60 units/kg, imiglucerase or velaglucerase alfa at 60 U/kg, taliglucerase alfa at 30 units/kg or 60 units/kg, and velaglucerase alfa at 45 units/g or 60 units/kg. For platelet count response in participants with intact spleens, a benefit for imiglucerase over velaglucerase alfa at 60 units/kg was observed, mean difference -79.87 (95% confidence interval -137.57 to -22.17). There were no other significant differences in platelet count response when comparing different doses of velaglucerase alfa and of taliglucerase alfa, and when comparing imiglucerase to alglucerase. Spleen and liver volume reductions were not significantly different in any enzyme replacement therapy product or dose comparison study. Although a dose effect on serum biomarkers was not seen after nine months, a significantly greater reduction with higher dose was reported after 12 months in the velaglucerase study, mean difference 16.70 (95% confidence intervaI 1.51 to 31.89). In the two enzyme replacement therapy maintenance studies comparing infusions every two weeks and every four weeks, there were no significant differences in haemoglobin concentration, platelet count, and spleen and liver volumes over a 6 to 12 month period when participants were treated with the same cumulative dose. A total of 25 serious adverse events were reported, nearly all deemed unrelated to treatment. There are, as yet, no randomized trials of substrate reduction therapy in treatment-naïve patients that can be evaluated. Miglustat monotherapy appeared as effective as continued enzyme replacement therapy for maintenance of hematological, organ and biomarker responses in people with type 1 Gaucher disease previously treated with imiglucerase for at least two years. In those with neuronopathic Gaucher disease, no significant improvements in haemoglobin concentration, platelet count or organ volumes occurred when enzyme replacement therapy was augmented with miglustat. One randomized controlled study assessing substrate reduction therapy was published immediately prior to producing the final version of this review, and this, along with a further ongoing study (expected to be published in the near future), will be assessed for eligibility in a future update of the review. The results reflect the limitations of analysing evidence restricted to prospective randomized controlled trials, especially when dealing with chronic rare diseases. This analysis suggests that, during the first year of treatment, different recombinant glucocerebrosidases are bio-similar and non-inferior in safety and efficacy for surrogate biological response parameters. Enzyme replacement therapy given at 30 to 45 units/kg body weight every two to four weeks was generally as effective as the 60 unit/kg dose for the assessed clinical outcomes. The analysis emphasise the need to determine whether it is realistic to carry out multi-decade prospective clinical trials for rare diseases such as type 1 Gaucher disease. With large treatment effects on the classical manifestations of the disorder, therapeutic investigations in Gaucher disease mandate innovative trial designs and methodology to secure decisive data concerning long-term efficacy and safety – with the realization that knowledge about disease-modifying actions that are sustained are of crucial importance to people with this chronic condition.

Plain-language summary: Although there are many published studies about treatment of Gaucher disease, those that are based on randomized controlled clinical studies are considered to provide the strongest evidence. Eight such studies (300 participants) were identified by systematically reviewing the medical literature. Potential risks of bias in the methods employed in the original studies and in the data reported were assessed; only one study scored 'low' in all bias domains. Six evaluated the possible beneficial effects on the disease by enzyme replacement therapy using different products, doses or frequencies of administration; two studies examined the effects of substrate reduction therapy. Owing to different study methods and data formats, the original results could not be pooled or combined in order to obtain summary measures of efficacy. Our analysis, despite being limited by the small number of studies, suggests that, at least during the first year of treatment, different enzyme replacement therapy drugs appear to have a similar safety profile and all improve some of the most obvious manifestations of the disease. One randomized controlled study assessing substrate reduction therapy was published immediately prior to producing the final version of this review, and this, along with a further ongoing study (expected to be published in the near future), will be assessed for eligibility in a future update of the review.