The inhibition of glutathione S-transferases: mechanisms, toxic consequences and therapeutic benefits.

Inhibition of the enzymes belonging to the family of glutathione S-transferases is important from several points of view. These involve applications in studies of the catalytic mechanism, e.g. studying the topology and binding characteristics of the active site. Also, from a therapeutic standpoint, inhibition of glutathione S-transferases steadily becomes more interesting, since these enzymes appear to be involved in drug resistance, and in the biosynthesis of a number of important arachidonic acid metabolites such as prostaglandins and leukotrienes. Modulation of the glutathione S-transferase activity could be used to regulate the concentrations of these compounds, Thirdly, unwanted inhibition by xenobiotics makes a cell more vulnerable for alkylating agents and can thus have toxic consequences. This review describes the state of the art, dealing with the various types of inhibiton employed (reversible, irreversible or nonsubstrate ligands). Furthermore, isoenzyme selectivity, organ distribution and interindividual differences are discussed.     

Germinal mosaicism increases the recurrence risk for ''new'' Duchenne muscular dystrophy mutations.

In 288 Dutch and Belgian Duchenne and Becker muscular dystrophy families, the parental origin of 41 new deletion or duplication mutations was determined. Twenty seven of the new mutations occurred in the maternal X chromosome and nine in the grandmaternal and five in the grandpaternal X chromosome. The grandparental data are compatible with equal mutation rates for DMD in male and female X chromosomes. New mutations were defined by their presence in one or more progeny and absence in the lymphocytes of the mother or the grandparents. In one family a fraction of the maternal lymphocytes was found to carry the mutation, suggesting somatic mosaicism. In six cases out of 41, the mutation was transmitted more than once by a parent in whom the mutation was absent in lymphocytes, suggesting gonadal mosaicism as the explanation for the multiple transmission. Using our data for the recurrence of the mutations among the total of at risk haplotypes transmitted, we arrive at a recurrence risk of 14% for the at risk haplotype. The observation of this high risk of germinal mosaicism is crucially important for all physicians counselling females in DMD families. Recently, germinal mosaicism has been observed also in a number of other X linked and autosomal disorders. The implications and appropriate diagnostic precautions are discussed.     

Sex ratio of the mutation frequencies in haemophilia A: coagulation assays and RFLP analysis.

Coagulation and RFLP data from 41 families with an isolated haemophilia A patient were used to estimate the sex ratio of mutation frequencies (nu/mu). Based on the results of coagulation assays in all the female relatives investigated, nu/mu was estimated to be 12.1 by the maximum likelihood method (95% confidence interval 3.8 to 62.5). In order to avoid the possible influence of germline mosaicism, an additional analysis was performed in which only the results in the mothers and grandmothers of an isolated patient were included. The nu/mu ratio was then estimated to be 5.2 (95% confidence interval 1.8 to 15.1). Because an estimate of nu/mu based on all available RFLP data can easily be biased in favour of males, we set up a model in which only information on the grandparental derivation of the patient's X chromosome was used, irrespective of the generation in which the mutation actually occurred. In this way nu/mu was estimated to be minimally 4. The probability of carriership for mothers of an isolated haemophilia A patient amounts to 86% with a sex ratio of 5.2. Although this would imply that 14% of the mothers are not carriers of the disease in the classical sense, they may be mosaic for the mutation and, therefore, also at risk of transmitting the mutation more than once.     

DNA probe analysis for carrier detection and prenatal diagnosis of Duchenne muscular dystrophy: a standard diagnostic procedure.

Thirteen marker loci localised on the short arm of the X chromosome are available for use in genetic studies for Duchenne muscular dystrophy (DMD). This large number of probes detecting about 20 RFLPs encouraged us to set up a standard procedure using a sequence of selected probes and restriction enzymes for the diagnosis of DMD families. The application of DNA probe analysis for carrier detection and prenatal diagnosis, involving 61 pedigrees of both familial and isolated cases, has yielded the following results. Carrier detection using flanking markers was possible in more than 75% of the cases (104 out of 136 females) with a reliability of better than 98%. Prenatal diagnosis was possible in 95% of the cases (65 out of 68 proven carriers or women at risk). Twenty-three prenatal diagnoses were performed on male fetuses; 13 appeared to have a low risk for DMD (less than 1%) and thus the pregnancies continued. Seven have since come to term and the male infants have normal CK levels. The genetic distances of the loci relative to the DMD locus and their order on the short arm of the X chromosome were deduced from our total DMD family material and are not significantly different from those reported earlier. For 754 (DXS84) we found a genetic distance of 5 cM with a lod score of +12.4 and 95% confidence limits between 2 and 12 cM. Similar data were obtained for pERT87 (DXS164), suggesting that in our family material both loci are tightly linked. Multiply informative recombination showed that both 754 and pERT87 map proximal to the DMD mutations in the cases studied. The high frequency of DMD mutations and its relation to the observed instability in this part of the genome will be discussed. Unequal crossing over is proposed as one of the mechanisms contributing to the high mutation frequency.     

Exercise-induced metallothionein expression in human skeletal muscle fibres

Exercise induces free oxygen radicals that cause oxidative stress, and metallothioneins (MTs) are increased in states of oxidative stress and possess anti-apoptotic effects. We therefore studied expression of the antioxidant factors metallothionein I and II (MT-I + II) in muscle biopsies obtained in response to 3 h of bicycle exercise performed by healthy men and in resting controls. Both MT-I + II proteins and MT-II mRNA expression increased significantly in both type I and II muscle fibres after exercise. Moreover, 24 h after exercise the levels of MT-II mRNA and MT-I + II proteins were still highly increased and the MT-II mRNA expression reached a 15-fold increase. As expected, immunohistochemical detection of malondialdehyde (MDA) and nitrotyrosine (NITT) showed that formation of free radicals and oxidative stress were clearly increased in exercising muscle peaking shortly after the end of exercise in both type I and II muscle fibres. This is the first report demonstrating that MT-I + II are significantly induced in human skeletal muscle fibres following exercise. As MT-I + II are antioxidant factors that protect various tissues during pathological conditions, the MT-I + II increases post exercise may represent a mechanism whereby contracting muscle fibres are protected against cellular stress and injury.     

Pitt-Rogers-Danks syndrome and Wolf-Hirschhorn syndrome are caused by a deletion in the same region on chromosome 4p 16.3.

Recently, a deletion of chromosome 4pter was found in three patients with Pitt-Rogers-Danks syndrome. We investigated two of these patients, by means of DNA and FISH studies, together with two additional patients with Pitt-Rogers-Danks syndrome, to determine the critical region of the deletion in these patients and to compare this with the critical region in Wolf-Hirschhorn syndrome. All four patients showed terminal deletions of chromosome 4p of different sizes. One of them appeared to have an unbalanced karyotype caused by a cryptic translocation t(4;8) in the mother, resulting in a deletion of chromosome 4pter and a duplication of chromosome 8pter. The localisation of the Wolf-Hirschhorn critical region has been confined to approximately 1 Mb between D4S43 and D4S115. Our study shows that the deletions in four patients with the Pitt-Rogers-Danks syndrome overlap the Wolf-Hirschhorn critical region and extend beyond this in both directions. This study, combined with the fact that our third patient, who was previously described as a Pitt-Rogers-Danks patient, but who now more closely resembles a Wolf-Hirschhorn patient, makes it likely that Pitt-Rogers-Danks and Wolf-Hirschhorn syndromes are different clinical phenotypes resulting from a deletion in the same microscopic region on chromosome 4p16.     

Is MED13L-related intellectual disability a recognizable syndrome?

Introduction

MED13L-related intellectual disability is characterized by moderate intellectual disability (ID), speech impairment, and dysmorphic facial features. We present 8 patients with MED13L-related intellectual disability and review the literature for phenotypical and genetic aspects of previously described patients.

DGGE-based whole-gene mutation scanning of the dystrophin gene in Duchenne and Becker muscular dystrophy patients

Duchenne and Becker muscular dystrophy (DMD and BMD) are caused by mutations in the dystrophin gene. Large rearrangements in the gene are found in about two-thirds of DMD patients, with approximately 60% carrying deletions and 5-10% carrying duplications. Most of the remaining 30-35% of patients are expected to have small nucleotide substitutions, insertions, or deletions. To detect these subtle changes within the coding and splice site determining sequences of the dystrophin gene, we established a semiautomated denaturing gradient gel electrophoresis (DGGE) mutation scanning system. The DGGE scan covers the dystrophin gene with 95 amplicons, PCRed either individually or in a multiplex setup. PCR and pooling were performed semiautomatically, using a pipetting robot and 384-well plates, enabling concurrent amplification of DNA of four patients in one run. Amplification of individual fragments was performed using one PCR program. The products were pooled just before gel loading; DGGE requires only a single gel condition. Validation was performed using DNA samples harboring 39 known DMD variants, all of which could be readily detected. DGGE mutation scanning was applied to analyze 135 DMD/BMD patients and potential DMD carriers without large deletions or duplications. In DNA from 25 out of 44 DMD patients (57%) and from 5 out of 39 BMD patients (13%), we identified clear pathogenic changes. All mutations were different, with the exception of one DMD mutation, which occurred twice. In DNA from 10 out of 44 potential DMD carriers, including four obligate carriers, we detected causative changes, including one pathogenic change in every obligate carrier. In addition to these pathogenic changes, we detected 15 unique unclassified variants, i.e., changes for which a pathogenic nature is uncertain.