Homozygosity for the p.K136E mutation in the SLC17A5 gene as cause of an Italian severe Salla disease.

Lysosomal free sialic acid storage diseases are recessively inherited allelic neurodegenerative disorders that include Salla disease (SD) and infantile sialic acid storage disease (ISSD) caused by mutations in the SLC17A5 gene encoding for a lysosomal membrane protein, sialin, transporting sialic acid from lysosomes. The classical form of SD, enriched in the Finnish population, is related to the p.R39C designed Salla(FIN) founder mutation. A more severe phenotype is due both to compound heterozygosity for the p.R39C mutation and to different mutations. The p.R39C has not been reported in ISSD. We identified the first case of SD caused by the homozygosity for p.K136E (c.406A>G) mutation, showing a severe clinical picture, as demonstrated by the early age at onset, the degree of motor retardation, the occurrence of peripheral nerve involvement, as well as cerebral hypomyelination. Recently, in vitro functional studies have shown that the p.K136E mutant produces a mislocalization and a reduced activity of the intracellular sialin. We discuss the in vivo phenotypic consequence of the p.K136E in relation to the results obtained by the in vitro functional characterization of the p.K136E mutant. The severity of the clinical picture, in comparison with the classical SD, may be explained by the fact that the p.K136E mutation mislocalizes the protein to a greater degree than p.R39C. On the other hand, the presence of a residual transport activity may account for the absence of hepatosplenomegaly, dysostosis multiplex, and early lethality typical of ISSD and related to the abolished transport activity found in this latter form.

[Computer-assisted instruction in training and continuing education in veterinary medicine]. / Computer ondersteund onderwijs ten behoeve van onderwijs en nascholing in de diergeneeskunde.

The microcomputer is an excellent instrument for stimulation in training in clinical problem-solving. However, the construction of computerprogrammes requires far too much time of teachers. At the Department of Surgery of the University Hospital at Leiden, a software package was developed, called 'CASES' (Computer-Assisted Simulation and Education System). This authoring system enables the clinical teacher to create a new 'case' within a few hours. When this type of computer-assisted instruction is used a student must attempt to solve a problem and in doing so will make a few, or possibly several, mistakes. The author of the programme will comment upon all the mistakes which are made. It is, as if the teacher were personally present and giving private instruction to his student. To create a case the teacher does not need any knowledge of computers nor of programming-languages. Other fields of use could be post-graduate training. By mailing floppy-discs to the doctor's home he could have his interactive training by experts at home in his own study. With little if any modifications, this system may also be used in veterinary medicine. It runs on IBM-PC's (128 K) and all compatible hardware.

The chromosomal localization of human beta-galactosidase revisited: a locus for beta-galactosidase on human chromosome 3 and for its protective protein on human chromosome 22.

A series of man-Chinese hamster and man-mouse somatic cell hybrids was investigated to study the localization of the genes coding for the human lysosomal enzyme beta-galactosidase (EC 3.2.1.23) and for its protective protein. Using a monoclonal antibody, raised against human placental beta-galactosidase, it was observed that the structural locus for the beta-galactosidase polypeptide is located on chromosome 3. The nature of the involvement of chromosome 22 in the expression of human beta-galactosidase was elucidated by metabolic labelling of the hybrids with radioactive amino acids, immunoprecipitation with monoclonal and polyclonal antibodies against beta-galactosidase, followed by analysis via gel electrophoresis and fluorography. The data show that the presence of chromosome 22 coincides with the presence of a 32 kd protein. This polypeptide, the "protective protein" was previously shown to be intimately associated with human beta-galactosidase. In addition, the protective protein was found to be essential for the in vivo stability of beta-galactosidase by aggregating beta-galactosidase monomers into high molecular weight multimers. Both chromosome 3 and 22 are therefore necessary to obtain normal levels of beta-galactosidase activity in human cells.

A rapid and simple microfractionation method for the analysis of hexosaminidase A and B activities in small numbers of cultured (amniotic fluid) cells.

A simple and rapid microfractionation procedure is described which enables the separate analysis of hexosaminidase A and B activities in as little as a few hundred to a thousand cultured human cells. 25 microliter cell homogenate is added to a pellet of DEAE-cellulose and 50 microliter 0.1 M NaCl in buffer. After centrifugation the hex B and I forms are measured in the supernatant, whereas hex A is determined by direct incubation of the DEAE pellet with methylumbelliferyl substrate. The reliability and reproducibility of the method is compared with that of heat inactivation and column chromatography. The application of the procedure is illustrated by analyses of fibroblasts and cultured amniotic fluid cells from pregnancies at risk for Tay-Sachs disease and by serum assays for the diagnosis and heterozygote testing of this disease.