Non-neuronopathic Gaucher disease due to saposin C deficiency

Abstract

Gaucher disease is generally caused by a deficiency of the lysosomal enzyme glucocerebrosidase. The degradation of glycosphingolipids requires also the participation of sphingolipid activator proteins. The prosaposin PSAP gene codes for a single protein which undergoes post-translational cleavage to yield four proteins named saposins A, B, C and D. Saposin (SAP-) C is required for glucosylceramide degradation, and its deficiency results in a variant form of Gaucher disease. In this report, we present clinical, biochemical, and molecular findings in a 36-year-old man and his 30-year-old sister with non-neuronopathic Gaucher disease due to SAP-C deficiency. Very high levels of chitotriosidase activity, chemokine CCL18, and increased concentration of glucosylceramide in plasma and normal beta-glucosidase activity in skin fibroblasts were observed in the patients. A molecular genetics study of the PSAP gene enabled the identification of one missense mutation, p.L349P, located in the SAP-C domain and another mutation, p.M1L, located in the initiation codon of the prosaposin precursor protein. The presented findings describe the first cases where the non-neuronopathic Gaucher disease has been definitely demonstrated to be a consequence of SAP-C deficiency. Three previously described cases in the literature displayed a Gaucher type 3 phenotype.