The limb-girdle muscular dystrophies-multiple genes, multiple mechanisms.
(49/2914)
In the field of muscular dystrophy, advances in understanding the molecular basis of the various disorders in this group have been rapidly translated into readily applicable diagnostic tests, allowing the provision of more accurate prognostic and genetic counselling. The limb-girdle muscular dystrophies (LGMD) have recently undergone a major reclassification according to their genetic basis. Currently 13 different types can be recognized. Amongst this group, increasing diversity of the mechanisms involved in producing a muscular dystrophy phenotype is emerging. Recent insights into the involvement of the dystrophin glycoprotein complex in muscular dystrophy suggests that its members may play distinct or even multiple roles in the maintenance of muscle fibre integrity. In other forms of LGMD, proteins have been implicated which may be important in intracellular signalling, vesicle trafficking or the control of transcription. As these various mechanisms are more fully elucidated, further insights will be gained into the pathophysiology of muscular dystrophy. At a practical level, despite the marked heterogeneity of this group real progress can at last be made in determining a precise diagnosis. (+info)
Forward genetics in mammalian cells: functional approaches to gene discovery.
(50/2914)
Definitive proof of function in biological systems requires genetic analysis. Only when the loss of a particular protein corresponds to the loss of a specific function can one be sure that the protein truly affects the function. Changing the pattern of gene expression through random mutagenesis or by introducing expression libraries, followed by selection of mutant or variant cells and identification of a missing or overexpressed protein, has the power to reveal or confirm the roles of specific components of signaling pathways and to provide mutant cell lines and cDNA reagents to be used in defining detailed mechanisms through structure-function analyses. These examples of forward genetics contrast with reverse genetic approaches, where the function of a known gene product is explored by knockout or replacement. Here we review a broad range of techniques that have been used to alter gene expression randomly in mammalian cells, with examples of specific discoveries that have resulted from these applications of forward genetics. (+info)
The Berkeley Drosophila Genome Project gene disruption project: Single P-element insertions mutating 25% of vital Drosophila genes.
(51/2914)
A fundamental goal of genetics and functional genomics is to identify and mutate every gene in model organisms such as Drosophila melanogaster. The Berkeley Drosophila Genome Project (BDGP) gene disruption project generates single P-element insertion strains that each mutate unique genomic open reading frames. Such strains strongly facilitate further genetic and molecular studies of the disrupted loci, but it has remained unclear if P elements can be used to mutate all Drosophila genes. We now report that the primary collection has grown to contain 1045 strains that disrupt more than 25% of the estimated 3600 Drosophila genes that are essential for adult viability. Of these P insertions, 67% have been verified by genetic tests to cause the associated recessive mutant phenotypes, and the validity of most of the remaining lines is predicted on statistical grounds. Sequences flanking >920 insertions have been determined to exactly position them in the genome and to identify 376 potentially affected transcripts from collections of EST sequences. Strains in the BDGP collection are available from the Bloomington Stock Center and have already assisted the research community in characterizing >250 Drosophila genes. The likely identity of 131 additional genes in the collection is reported here. Our results show that Drosophila genes have a wide range of sensitivity to inactivation by P elements, and provide a rationale for greatly expanding the BDGP primary collection based entirely on insertion site sequencing. We predict that this approach can bring >85% of all Drosophila open reading frames under experimental control. (+info)
A direct screen identifies new flight muscle mutants on the Drosophila second chromosome.
(52/2914)
An ethyl methanesulfonate mutagenesis of Drosophila melanogaster was undertaken, and >3000 mutagenized second chromosomes were generated. More than 800 homozygous viable lines were established, and adults were screened directly under polarized light for muscle defects. A total of 16 mutant strains in which the indirect flight muscles were reduced in volume or disorganized or were otherwise abnormal were identified. These fell into seven recessive and one semidominant complementation groups. Five of these eight complementation groups, including the semidominant mutation, have been mapped using chromosomal deficiencies and meiotic recombination. Two complementation groups mapped close to the Myosin heavy chain gene, but they are shown to be in different loci. Developmental analysis of three mutations showed that two of these are involved in the early stages of adult myogenesis while the other showed late defects. This is the first report of results from a systematic and direct screen for recessive flight muscle defects. This mutant screen identifies genes affecting the flight muscles, which are distinct from those identified when screening for flightlessness. (+info)
The effects of deleterious mutations on linked, neutral variation in small populations.
(53/2914)
The effects of recessive, deleterious mutations on genetic variation at linked neutral loci can be heterozygosity-decreasing because of reduced effective population sizes or heterozygosity-increasing because of associative overdominance. Here we examine the balance between these effects by simulating individual diploid genotypes in small panmictic populations. The haploid genome consists of one linkage group with 1000 loci that can have deleterious mutations and a neutral marker. Combinations of the following parameters are studied: gametic mutation rate to harmful alleles (U), population size (N), recombination rate (r), selection coefficient (s), and dominance (h). Tight linkage (r +info)
The pathophysiological and molecular basis of Bartter's and Gitelman's syndromes.
(54/2914)
Molecular defects affecting the transport of sodium, potassium and chloride in the nephron through the ROMK K+ channel, Na+/K+/2Cl- cotransporter, the Na+/Cl- cotransporter and chloride channel have been identified in patients with Bartter's and Gitelman's syndromes. Defects of the angiotensin II type I receptor and CFTR have also being described. These defects are simple (i.e., most are single amino acid substitutions) but affect key elements in tubular transport. The simplicity of the genetic defects may explain why the inheritance of these conditions remains unclear in most kindreds (i.e., not just recessive or dominant) and emphasises the crucial importance of the conformational structure of these channels. Application of this molecular information will allow the early genetic identification of patients with these syndromes and enable us to differentiate between the various disorders at a functional level. It may also identify a subgroup in which the heterozygous form may make patients potentially exquisitely sensitive to diuretics. (+info)
Clinical and morphological correlations for transglutaminase 1 gene mutations in autosomal recessive congenital ichthyosis.
(55/2914)
Autosomal recessive congenital ichthyosis (ARCI) is a group of inherited disorders of cornification in which progress has recently been made in the identification of pathogenic mechanisms causing the disease. Transglutaminase 1 (TGM1) has been found as a defective gene in a large fraction of patients with lamellar ichthyosis (LI), a severe inherited scaling disorder of the skin. We have previously performed molecular genetic studies of 38Finnish ARCI families and found six different mutations in 13 families of 38 (34%). In this study we compared the molecular genetic alterations with clinical and electron microscopic findings of these patients. Families were classified by electron microscopy in ichthyosis congenita (IC) types I, II, III, IV and a non-defined group. TGM 1 gene mutation was found in all of the IC type II and 1/3 of the IC type 1 families. Although electron microscopy is not always used to classify ARCI patients, it can distinguish groups which are parallel with molecular genetic findings. This finding might be useful in the classification of ARCI patients for further linkage studies. Clinically typical phenotype of the TGM1 mutation carrier includes large, thick, brownish scales, but ichthyosis of some of these patients tends to be milder. (+info)
Chediak-Higashi syndrome associated with maternal uniparental isodisomy of chromosome 1.
(56/2914)
Chediak-Higashi syndrome (CHS) is a rare autosomal recessive disorder (incidence around 1 in 106 births), characterised by a complex immunologic defects, reduced pigmentation, and presence of giant granules in many different cell types. It most likely results from defective organellar trafficking or protein sorting. The causative gene (LYST) has recently been identified and shown to be homologous to the beige locus in the mouse. CHS has always been reported associated with premature-termination-codon mutations in both alleles of LYST. We report a unique patient with CHS, who was homozygous for a stop codon in the LYST gene on chromosome 1 and who had a normal 46,XY karyotype. The mother was found to be a carrier of the mutation, whereas the father had two normal LYST alleles. Non-paternity was excluded by the analysis of microsatellite markers from different chromosomes. The results of 13 informative microsatellite markers spanning the entire chromosome 1 revealed that the proband had a maternal isodisomy of chromosome 1 encompassing the LYST mutation. The proband's clinical presentation also confirms the absence of imprinted genes on chromosome 1. (+info)