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Gaucher disease is an autosomal recessive inherited lysosomal storage disorder due to mutations in the glucocerebrosidase gene located on chromosome 1q21. Hepatosplenomegaly and bone disease due to massive accumulation of undegraded glucocerebroside in macrophages found in the liver, spleen and bone marrow dominate the clinical picture in type 1 disease. In rare instances (type 2 and 3 disease) the central nervous system is involved. Phenotype-genotype correlations are poor. Diagnosis is possible by enzyme assay at clinical genetic centres in the Netherlands. The availability of effective therapies emphasizes the need for early recognition of the disease.

The Orphan Drugs Act has been officially implemented in all countries of the European Union since the year 2000. The Act aims to promote the development of treatments for rare diseases (prevalence < 5:10,000). Successful therapies for such diseases are granted market-monopoly for 10 years, during which no me-too products are allowed. There are problems concerning approval and reimbursement. Drugs already in use can also be registered as orphan drugs for a specific indication. In addition to this, European approval for the market authorization of new drugs does not automatically mean that the costs of the drug are reimbursed within the Netherlands, whereas that might well be the case in other EU countries. However, a faster procedure with respect to the reimbursement of drug costs in the Netherlands may not lead to the responsibilities for the carrying out of additional trials being transferred to those handling the treatment.

Fabry's disease, deficiency of the enzyme alpha-galactosidase A, is an X-linked lysosomal storage disorder. Clinical symptoms are caused by continuous deposition of specific glycolipids in endothelial cells, neural cells, skin and cornea. These depositions give rise to skin (angiokeratoma) and eye abnormalities (cornea verticillata), acroparaesthesias and anhidrosis and later in life cause renal insufficiency and cardiovascular complications. Hemizygous males suffer from Fabry's disease, whereas female carriers (heterozygotes) are usually asymptomatic. Recently, an atypical presentation of Fabry's disease was described in males who only presented with cardiac involvement. Therefore, the actual number of Fabry patients in the Netherlands could be higher than the predicted 300. Diagnosis in males can be established by measuring alpha-galactosidase enzyme activity in plasma, leukocytes or fibroblasts. Apart from kidney transplantation only symptomatic therapy is available today. Enzyme supplementation therapy (as shown in Gaucher's disease) and substrate deprivation are possible ways of treatment in the future.