Sialic acid storage diseases (SASD, MIM 269920) are autosomal recessive neurodegenerative disorders that may present as a severe infantile form (ISSD) or a slowly progressive adult form, which is prevalent in Finland (Salla disease). The main symptoms are hypotonia, cerebellar ataxia and mental retardation; visceromegaly and coarse features are also present in infantile cases. Progressive cerebellar atrophy and dysmyelination have been documented by magnetic resonance imaging (ref. 4). Enlarged lysosomes are seen on electron microscopic studies and patients excrete large amounts of free sialic acid in urine. A H+/anionic sugar symporter mechanism for sialic acid and glucuronic acid is impaired in lysosomal membranes from Salla and ISSD patients. The locus for Salla disease was assigned to a region of approximately 200 kb on chromosome 6q14-q15 in a linkage study using Finnish families. Salla disease and ISSD were further shown to be allelic disorders. A physical map with P1 and PAC clones was constructed to cover the 200-kb area flanked by the loci D6S280 and D6S1622, providing the basis for precise physical positioning of the gene. Here we describe a new gene, SLC17A5 (also known as AST), encoding a protein (sialin) with a predicted transport function that belongs to a family of anion/cation symporters (ACS). We found a homozygous SLC17A5 mutation (R39C) in five Finnish patients with Salla disease and six different SLC17A5 mutations in six ISSD patients of different ethnic origins. Our observations suggest that mutations in SLC17A5 are the primary cause of lysosomal sialic acid storage diseases.

We compared intraindividual and interindividual variability in the plasma levels of fibrinogen, tissue-type plasminogen activator (TPA) antigen, plasminogen activator inhibitor (PAI) activity, and C-reactive protein (CRP) in 20 healthy, young individuals and 26 patients with stable angina pectoris (AP) who were at higher risk for cardiovascular disease. For each of the four parameters, the contribution of the intraindividual variation to the total variance (13% and 9% for fibrinogen, 3% and 5% for TPA antigen, 4% and 20% for In[PAI activity], and 14% and 9% for In[CRP] for the healthy volunteers and AP patients, respectively) was smaller than the contribution from the interindividual variation. These results indicate that single sampling is sufficient to assess an individual level for TPA antigen and PAI activity, whereas duplicate sampling for fibrinogen and triplicate sampling for CRP are recommended. In an epidemiological study the sample sizes, based on the variances found in the transverse part of the study, needed to detect a 15% difference between the two groups (with alpha = 0.01 and a statistical power = .90) are 31 and 40 for fibrinogen, 568 and 146 for TPA antigen, 603 and 119 for PAI activity, and 1490 and 2263 for CRP in healthy volunteers and patients with AP, respectively. Additionally, we studied the contribution of genetic polymorphisms of the B beta-fibrinogen (Bcl I and G-->A-455) and PAI activity (HindIII and CA-repeat) genes to intraindividual and interindividual variation. Fibrinogen genotypes were associated with plasma fibrinogen levels in the volunteers but not in the AP patients. No effects of fibrinogen or PAI polymorphisms on intraindividual variation were observed in either healthy individuals or AP patients. In this study intraindividual variation in plasma levels of the cardiovascular risk indicators fibrinogen, TPA antigen, PAI activity, and CRP was small when compared with the interindividual variation in healthy, young volunteers and patients with stable AP.

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Lysosomes are thought to play a role in various aspects of heavy metal metabolism. In the present study we demonstrate for the first time the presence of a heavy metal ion transport protein in the lysosomal membrane. Uptake of radioactive silver both in highly purified lysosomal membrane vesicles and in purified intact lysosomes showed the typical kinetics of a carrier-mediated process. This transport was stimulated by ATP hydrolysis, and showed specificity for Ag + , Cu P+ , and Cd P+ . All biochemical properties of this lysosomal metal ion transporter could classify it as a heavy metal transporting P-type ATPase. Long Evans Cinnamon (LEC) rats, an animal model for the copper transport disorder Wilson disease, showed normal lysosomal silver transport.z 1998 Federation of European Biochemical Societies.

Deficiency of a microsomal phosphate transporter in the liver has been suggested in some patients affected by glycogen storage disease type Ic (GSD Ic). Several Na(+)/phosphate co-transporters have been characterized as members of the anion-cation symporter family. Recently, the cDNA sequence of two phosphate transporters, NPT3 and NPT4, expressed in liver, kidney and intestine, has been determined. We studied expression of human NPT4 in COS cells and observed an ER localization of the transporter by immunofluorescence microscopy. We speculated that this transporter could play a role in the regulation of the glucose-6-phosphatase (G6-Pase) complex. We revealed the genomic structure of NPT4 and analysed the gene as a candidate for GSD Ic. DNA was collected from five patients without mutations in G6-Pase or the G6-P transporter gene. DNA analysis of NPT4 revealed that one patient was heterozygous for a G>A transition at nucleotide 601 which would result in a G201R substitution. Our results do not confirm the hypothesis that this gene is mutated in GSD Ic patients. However, we cannot exclude that the mutation found reduces the phosphate transport efficiency, possibly modulating the G6-Pase complex.