Genetic heterogeneity in Gaucher disease: Physicokinetic and immunologic studies of the residual enzyme in cultured fibroblasts from non‐neuronopathic and neuronopathic patients

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Abstract
To elucidate the genetic heterogeneity in the three major phenotypic subtypes of Gaucher disease, the residual acid β-glucosidase in fibroblasts from patients with all three subtypes from different ethnic and demographic groups was investigated by comparative kinetic, thermostability, and immunotitration studies. The kinetic studies delineated three distinct groups (designated A, B, and C) of residual activities with characteristic responses to the enzyme modifiers, taurocholate (or phosphatidylserine), and glucosyl sphingosine (or N-hexyl glucosyl sphingosine); Group A residual enzymes responded normally to these modifiers. All neuronopathic patients (types 2 and 3) and most non-Jewish, non-neuronopathic patients (type 1) had group A residual activities and thus could not be distinguished by their kinetic properties. Group B residual enzymes had markedly abnormal responses to these modifiers. All Ashkenazi and only two non-Jewish type 1 patients had group B residual activities. Group C residual activity had an intermediate response to all modifiers and represented a single Afrikaner type 1 patient. Pedigree studies indicated that this patient was a genetic compound for the group A (type 2) and group B (type 1) mutations. Thermostability studies showed additional heterogeneity of the residual activities within the three kinetic groups. Group A (type 2) and group B (type 1) enzymes had similarily decreased thermostabilities. In contrast, group A (type 1) residual activities were heterogeneous; three classes of thermostabilities were found among these enzymes: normal, decreased, and increased Immunotitration of equal amonuts of the normal or Gaucher dieseas β-glucosidase activities with monospecific IgG indicated that the enzyme proteins from most Gaucher disease patients were antigenically altered and/or that large amounts of catalytically abnormal or inactive antigen were present. A decreased amount of antigenically and catalytically normal enzyme was present in a group A, type 1 African black patient, suggesting decreased stability or synthesis of his mutant acid β-glucosidase. These kinetic, immunologic, and thermostability studies indicated that 1 type (1) Gaucher disease is biochemically heterogeneous and results from at least from distinct allelic acid β-glucosidase mutations that alter enzyme structuer and/or function, 2 neuronopathic and non-Jewish non-neuronopathic phenotypes cannot be distinguished reliably by kinetic analyses alone, and 3) the Ashkenzi type 1 Gaucher disease results from a unique mutation that alters a specific active site domain of acid β-glucosidase.