B.A. van Oost

New Polymorphic DNA Marker Close to the Fragile Site FRAXA

DNA from a human-hamster hybrid cell line, 908-K1B17, containing a small terminal portion of the long arm of the human X chromosome as well as the pericentric region of 19q was used as starting material for the isolation of an X-chromosome-specific DNA segment, RN1 (DXS369), which identifies a XmnI RFLP. Linkage analysis in fragile X families resulted in a maximum lod score of 15.3 at a recombination fraction of 0.05 between RN1 and fra(X). Analysis of recombinations around the fra(X) and distal to DXS105. Analysis of the marker content of hybrid cell line 908K1B17 suggests the localization of RN1 between DXS98 and fra(X). Heterozygosity of DXS369 is approximately 50%, which extends the diagnostic potential of RFLP analysis in fragile X families significantly.

Myotonic dystrophy is closely linked to the gene for muscle-type creatine kinase (CKMM)

SummaryWe have studied genetic linkage between the gene for creatine kinase muscle type (CKMM) and the gene for myotonic dystrophy (DM). In a panel of 65 myotonic dystrophy families from Canada and the Netherlands, a maximum lod score (Zmax) of 22.8 at a recombination frequency (Θ) of 0.03 was obtained. Tight linkage was also demonstrated for CKMM and the gene for apolipoprotein C2 (ApoC2). This establishes CKMM as a useful marker for myotonic dystrophy.

Myopathology and a mitochondrial DNA deletion in the pearson marrow and pancreas syndrome

A patient with the Pearson marrow and pancreas syndrome is presented. She showed an anaemia with neutropenia and thrombopenia, failure to thrive, diarrhoea, disturbed glucose homeostasis and lactic acidosis. An exocrine pancreatic insufficiency was lacking. The disease followed a fatal course. Biochemical investigations of skeletal muscle revealed a disturbed mitochondrial energy metabolism, while many ultrastructural abnormal features were observed in the muscle tissue. Molecular genetic studies showed a de novo deletion in the mitochondrial DNA (mtDNA), different in size from the already published deletions and flanked by two 4 bp direct repeats, interspaced by 4-5 non-repeated nucleotides. mtDNA from 12 other tissues showed the same deletion in different percentages. No obvious relation between these percentages and tissue dysfunction was found. In spite of an open reading frame of 74 codons, only little transcription product of the genomic region resulting from the deletion was found.

New distal marker closely linked to the fragile X locus

SummaryWe have isolated II-10, a new X-chromosomal probe that identifies a highly informative two-allele TaqI restriction fragment length polymorphism at locus DXS466. Using somatic cell hybrids containing distinct portions of the long arm of the X chromosome, we could localize DXS466 between DXS296 and DXS304, both of which are closely linked distal markers for fragile X. This regional localization was supported by the analysis, in fragile X families, of recombination events between these three loci, the fragile X locus and locus DXS52, the latter being located at a more distal position. DXS466 is closely linked to the fragile X locus with a peak lod score of 7.79 at a recombination fraction of 0.02. Heterozygosity of DXS466 is approximately 50%. Its close proximity and relatively high informativity make DXS466 a valuable new diagnostic DNA marker for fragile X.

Detection of extremely low levels of wild-type mitochondrial DNA in the liver of a patient with pearson syndrome by a sensitive PCR assay

Pearsons marrow and pancreas syndrome is characterized by refractory sideroblastic anaemia with vacuolization of bone marrow precursors and exocrine pancreatic insufficiency (Pearson et al 1979). Onset is in early infancy and many patients die before the age of 3 years. Recently it has become apparent that patients with Pearson syndrome have large deletions in part of their mitochondrial DNA (mtDNA) (Rotig et al 1989, 1990, 1991; Cormier et al 1990; McShane et al 1991)

Benign mitochondrial encephalomyopathy in a patient with complex I deficiency

Mitochondrial encephalomyopathies are very heterogeneous disorders. They can be associated with a broad spectrum of clinical manifestations, including muscle weakness, cardiac failure, movement disorders, renal failure, liver dysfunction, gastrointestinal disturbances, blindness, deafness, diabetes and dementia. In a substantial number of the patients with a mitochondrial encephalomyopathy a deficiency in the pyruvate dehydrogenase complex or in one or more of the complexes of the respiratory chain has been established. Most of these patients die at early age. Five cases of benign infantile mitochondrial myopathy have been described so far, all of them exhibiting a cytochrome c oxidase deficiency (DiMauro et al 1983 ; Zeviani et al 1987 ; Servidei et al 1988 ; Salo et al 1992). Recently, a patient with a benign form of succinate : cytochrome c oxidoreductase activity has been described (Arpa et al 1994). In this paper a patient with a benign mitochondrial encephalomyopathy due to a complex I deficiency is described.

Enzymological versus DNA investigations in mitochondrial (encephalo-)myopathies

The molecular basis of most types of deficiency in mitochondrial energy metabolism is still unknown. Application of newly developed DNA technology to the relatively small mtDNA molecule with known base sequence has resulted in the detection of deletions, duplications and point mutations in many patients (Zeviani and Antozzi 1992). However, the relatively large group of patients with disturbance in the respiratory chain has not yet been characterized at the DNA level. Thirteen proteins of the oxidative phosphorylation system are encoded by mitochondrial DNA (mtDNA), which also encodes for the ribosomal and transfer RNA of the organelle. The nuclear genome encodes for the other mitochondrial proteins and regulates the biogenesis of mitochondria (Attardi and Schatz 1988)

Biogenic Amine Metabolite Patterns in the Urine of Monoamine Oxidase A-Deficient Patients. A Possible Tool for Diagnosis

Recently we studied the urine patterns of biogenic amines and their metabolites in a family with X-linked mild mental retardation and prominent behavioural disturbanoes. These were characterized by periodic outbursts of aggression, and sometimes violence, as an uncontrollable reaction to stressful or depressing events. Characteristically abnormal excretion patterns of biogenic amine metabolites were found in affected males. This finding, combined with previous assignment of the locus for this disorder to the MAO-A (monoamine oxidase A) gene on the X-chromosome and normal platelet MAO-B activity was compatible with isolated MAO-A deficiency (Brunner et al 1993)