Hexosaminidase A activity in skin fibroblasts from various types of GM2 gangliosidosis using a fluorogenic sulphated substrate

Improved behavior and neuropathology in the mouse model of Sanfilippo type IIIB disease after adeno-associated virus-mediated gene transfer in the striatum

Sanfilippo syndrome is a mucopolysaccharidosis (MPS) caused by a lysosomal enzyme defect interrupting the degradation pathway of heparan sulfates. Affected children develop hyperactivity, aggressiveness, delayed development, and severe neuropathology. We observed relevant behaviors in the mouse model of Sanfilippo syndrome type B (MPSIIIB), in which the gene coding for alpha-N-acetylglucosaminidase (NaGlu) is invalidated. We addressed the feasibility of gene therapy in these animals. Vectors derived from adeno-associated virus serotype 2 (AAV2) or 5 (AAV5) coding for NaGlu were injected at a single site in the putamen of 45 6-week-old MPSIIIB mice. Normal behavior was observed in treated mice. High NaGlu activity, far above physiological levels, was measured in the brain and persisted at 38 weeks of age. NaGlu immunoreactivity was detected in neuron intracellular organelles, including lysosomes. Enzyme activity spread beyond vector diffusion areas. Delivery to the entire brain was reproducibly obtained with both vector types. NaGlu activity was higher and distribution was broader with AAV5-NaGlu than with AAV2-NaGlu vectors. The compensatory increase in the activity of various lysosomal enzymes was improved. The accumulation of gangliosides GM2 and GM3 present before treatment and possibly participating in neuropathology was reversed. Characteristic vacuolations in microglia, perivascular cells, and neurons, which were prominent before the age of treatment, disappeared in areas in which NaGlu was present. However, improvement was only partial in some animals, in contrast to high NaGlu activity. These results indicate that NaGlu delivery from intracerebral sources has the capacity to alleviate most disease manifestations in the MPSIIIB mouse model.

Amniotic fluid for screening of lysosomal storage diseases presenting in utero (mainly as non-immune hydrops fetalis)

Seventy amniotic fluids (AF) were sampled because of abnormal ultrasound findings (mainly non-immune hydrops fetalis (54 cases) or of the presence of vacuolated lymphocytes in fetal blood (3 cases)). They were analysed by a procedure involving AF supernatant analysis (glycosaminoglycans, oligosaccharides, free sialic acid and acid hydrolase activities) and biochemical study of cultured AF cells. Ten cases of lysosomal storage diseases (LSD) were diagnosed. The reported procedure allows an orientating screening within 3 days by analysis of 15 ml of third trimester AF supernatant (except for Gaucher and Niemann-Pick diseases). In some cases, the results allow an LSD diagnosis and a medical abortion without waiting for the formal diagnosis (in cultured AF cells that needs 3 more weeks), considering the poor prognosis of these LSD presenting in utero. Furthermore, the formal assessment of the diagnosis in the cultured fetal cells allows accurate genetic counselling for the couple.

Characteristics of hexosaminidase A in homogenates of white blood cells using methylumbelliferyl-N-acetyl-beta-D-glucosaminide-6-sulphate as substrate

Using methylumbelliferyl-N-acetyl-beta-D-glucosaminide-6-sulphate as a substrate hexosaminidase A activity was measured in leukocyte homogenates with a one-step method without the need of thermoinactivation. According to the buffer system used--acetate or citrate--the enzyme has pH optima of 3.5 and 4, respectively, and is linear during at least 1 h of incubation. The enzyme is resistant to mechanical inactivation by homogenization or to freezing and thawing and is thermostable between 0 and 37 degrees C but it is rapidly inactivated at 50 degrees C. This thermoinactivation is retarded by acidification of the homogenate. The latency of the enzyme is in agreement with its known lysosomal localization. Like most lysosomal enzymes, hexosaminidase A binds to Concanavalin A. After homogenization of leukocytes and repeated freezing and thawing, about 60% of the enzyme is present in the supernatant. Hexosaminidase A activity was stimulated by taurocholate between 0.05 and 0.1 M and inhibited by dimethylsulfoxide, dimethylformamide, N-acetylglucosamine and N-acetylgalactosamine. No pronounced difference was noted in specific activity of a homogenate of mononuclear cells, granulocytes or total leukocytes.