Enzymatically amplified RNA transcripts were used to analyze the full coding region of the glucocerebrosidase gene from Gaucher disease patients. Two previously undescribed mutations were identified. One mutation consists of a single-base substitution in three different codons: codon 444, Leu (CTG) to Pro (CCG); codon 456, Ala (GCT) to Pro (CCT); and codon 460, Val (GTG) to Val (GTC). This mutant is called "pseudo pattern" (psi) because it is identical in sequence to a small region of the pseudogene in exon 10 (Horowitz et al., 1989). The other new mutation is a single-base substitution (C to T) resulting in the substitution of Cys for Arg in codon 463. These mutations in the human gene were duplicated in wild-type cDNA and expressed in 3T3 cells. The human mutant proteins were isolated by immunoaffinity and shown to have altered enzymatic properties demonstrating the causality of these two allelic mutations for Gaucher disease.