H. Galjaard

Identification of a gene (FMR-1) containing a CGG repeat coincident with a breakpoint cluster region exhibiting length variation in fragile X syndrome

Fragile X syndrome is the most frequent form of inherited mental retardation and is associated with a fragile site at Xq27.3. We identified human YAC clones that span fragile X site-induced translocation breakpoints coincident with the fragile X site. A gene (FMR-1) was identified within a four cosmid contig of YAC DNA that expresses a 4.8 kb message in human brain. Within a 7.4 kb EcoRI genomic fragment, containing FMR-1 exonic sequences distal to a CpG island previously shown to be hypermethylated in fragile X patients, is a fragile X site-induced breakpoint cluster region that exhibits length variation in fragile X chromosomes. This fragment contains a lengthy CGG repeat that is 250 bp distal of the CpG island and maps within a FMR-1 exon. Localization of the brain-expressed FMR-1 gene to this EcoRI fragment suggests the involvement of this gene in the phenotypic expression of the fragile X syndrome.

A new gene, encoding an anion transporter, is mutated in sialic acid storage diseases.

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.

Elevated plasma chitotriosidase activity in various lysosomal storage disorders

SummaryRecently a striking elevation of the activity of chitotriosidase, an endo β-glucosaminidase distinct from lysozyme, was found in plasma from patients with Gaucher type I disease (McKusick 230800). Plasma chitotriosidase originates from activated macrophages and this elevation is secondary to the basic defect in Gaucher disease. To investigate the specificity of this phenomenon, we have investigated 24 different lysosomal storage diseases. In 11 different diseases increased chitotriosidase activity in plasma was found (in 28% of the patients). None of these diseases showed elevations as high as in Gaucher disease. Chitotriosidase was not significantly elevated in plasma from 20 different non-lysosomal enzymopathies or in plasma from patients with infectious diseases associated with hepatomegaly. The results show that marked elevation of chitotriosidase activity in plasma appears to be specific for Gaucher disease. The data further suggest that elevated levels of chitotriosidase activity in plasma from patients with unexplained diseases may be indicative for a lysosomal disorder.

Rapid antibody test for fragile X syndrome

Fragile X syndrome is the most common known cause of inherited mental retardation. Identification of patients and carriers of fragile X syndrome is usually done with a DNA test system but we have developed a rapid antibody to identify fragile X patients. This non-invasive test requires only 1 or 2 drops of blood and can be used for screening large groups of mentally retarded people and neonates for fragile X syndrome.

A fluorimetric enzyme assay for the diagnosis of Morquio disease type A (MPS IV A)

4-Methylumbelliferyl-beta-D-galactopyranoside-6-sulphate was synthesized and used for the determination of galactose-6-sulphate sulphatase activity. Fibroblasts and leucocytes from 12 different Morquio A patients, showed 0.0-2.7% of mean normal galactose-6-sulphate sulphatase activity. Heterozygotes showed intermediate activities. The enzymatic liberation of the fluorochrome from 4-methylumbelliferyl-beta-D-galactopyranoside-6-sulphate requires the sequential action of galactose-6-sulphate sulphatase and beta-galactosidase. Normal beta-galactosidase activity caused nearly complete hydrolysis of non-fluorescing 4-methylumbelliferyl-galactoside, formed during incubation. In cell extracts with a beta-galactosidase deficiency however, a second incubation in the presence of excess beta-galactosidase is needed to avoid underestimation of galactose-6-sulphate sulphatase activity.

Rapid antibody test for diagnosing fragile X syndrome : a validation of the technique

Abstract To date, the identification of patients and carriers of the fragile X syndrome has been carried out by DNA analysis by means of the polymerase chain reaction and Southern blot analysis. This direct DNA analysis allows both the size of the CGG repeat and methylation status of the FMR1 gene to be determined. We have recently presented a rapid antibody test on blood smears based on the presence of FMRP, the protein product of the FMR1 gene, in lymphocytes from normal individuals and the absence of FMRP in lymphocytes from patients. Here, we have tested the diagnostic value of this new technique by studying FMRP expression in 173 blood smears from normal individuals and fragile X patients. The diagnostic power of the antibody test is “perfect” for males, whereas the results are less specific for females.

Assignment of the gene coding for human β-glucocerebrosidase to the region q21-q31 of chromosome 1 using monoclonal antibodies

SummaryA series of man-Chinese hamster somatic cell hybrids with a variable content of human chromosomes was used to study the localization of the human gene coding for the lysosomal enzyme β-glucocerebrosidase (EC 3.2.1.45). In lysates made from hybrid cells, the human enzyme was specifically recognized by a mouse monoclonal antibody raised against human placental β-glucocerebrosidase. This monoclonal antibody did not cross-react with Chinese hamster β-glucocerebrosidase. After reaction of the antibody with the enzyme, β-glucocerebrosidase was precipitated by addition of Protein A-Sepharose beads, and was detected on the beads by its enzymatic activity. From the analysis of a series of man-Chinese hamster hybrids, among which were hybrids with specific segments of chromosome 1, we conclude that the gene coding for human β-glucocerebrosidase is localized in the region q21-q31 of chromosome 1.

Genetic heterogeneity in GM1-gangliosidosis.

GM1-GANGLIOSIDOSIS is an inherited lysosomal storage disease which is due to a deficiency of the acid hydrolase GM1-β-galactosidase1. During the past few years several clinical variants have been described2–6 that differ in time of onset of symptoms, involvement of visceral organs or skeletal tissue and in the degree of neuronal and mental deterioration. Some of these variants have been related to different properties of the deficient β-galactosidases5,7 but the significance of the experimental data8 has been questioned. Several investigators have speculated on the genetic background of the different variants2,8,9 but no experimental evidence has been provided to support the hypotheses.

Prenatal diagnosis of genetic disorders.

Three hundred and fifty pregnancies were monitored by transabdominal amniocentesis in the fourteenth to sixteenth week of gestation followed by karyotyping or biochemica assays of cultured amniotic fluid cells and analysis of alpha-fetoprotein in the amniotic fluid supernatant. The pregnancy was interrupted in 36 cases (10%) either becasue of a fetal abnormality or the presence of a male fetus in pregnancies at risk for an X-linked disease. Four chromosomal aberrations were found in 87 pregnancies tested because of advanced maternal age. In 101 pregnancies with a recurrence risk of Downs syndrome, 2 fetuses with an abnormal karyotype were detected. In 11 cases, in which 1 parent was a carrier of a balanced translocation, 2 unbalanced fetal karyotypes were found. Fetal chromosome studies in 43 pregancies at risk for an X-linked disease indicated the presence of a male fetus in 21 cases. Prenatal diagnosis of 11 different metabolic diseases was performed in a total of 34 cases. Microchemical techniques were used to allow completion of the diagnosis of seven different enzyme deficiencies within 9 to 22 days after amniocentesis. Alpha-fetoprotein assay in the amniotic fluid supernatant of 47 pregnancies at risk for an open neural tube defect resulted in the detection of 3 anencephalic fetuses during the second half of pregnancy. The safety and reliability of amniocentesis and the possible effects on the outcome of pregnancy are evaluated. Prenatal diagnosis offers a promising alternative for parents who are at risk of having a child with a genetic disease which can be detected in amniotic fluid or in cultured amniotic fluid cells.

Purification of acid β-galactosidase and acid neuraminidase from bovine testis: Evidence for an enzyme complex

Abstract The isolation of an acid neuraminidase from bovine testis is described. Under all experimental conditions this neuraminidase copurifies with acid β-galactosidase, but not with other lysosomal hydrolases. Immunotitration with an antiserum raised against purified human placental β-galactosidase results in the coprecipitation of both enzyme activities. Our data indicate that acid neuraminidase and β-galactosidase are present as an enzyme complex. The possible physiological relevance is discussed.