A total of 101 different examples of point mutations, which lie in the vicinity of mRNA splice junctions, and which have been held to be responsible for a human genetic disease by altering the accuracy of efficiency of mRNA splicing, have been collated. These data comprise 62 mutations at 5' splice sites, 26 at 3' splice sites and 13 that result in the creation of novel splice sites. It is estimated that up to 15% of all point mutations causing human genetic disease result in an mRNA splicing defect. Of the 5' splice site mutations, 60% involved the invariant GT dinucleotide; mutations were found to be non-randomly distributed with an excess over expectation at positions +1 and +2, and apparent deficiencies at positions -1 and -2. Of the 3' splice site mutations, 87% involved the invariant AG dinucleotide; an excess of mutations over expectation was noted at position -2. This non-randomness of mutation reflects the evolutionary conservation apparent in splice site consensus sequences drawn up previously from primate genes, and is most probably attributable to detection bias resulting from the differing phenotypic severity of specific lesions. The spectrum of point mutations was also drastically skewed: purines were significantly over-represented as substituting nucleotides, perhaps because of steric hindrance (e.g. in U1 snRNA binding at 5' splice sites). Furthermore, splice sites affected by point mutations resulting in human genetic disease were markedly different from the splice site consensus sequences. When similarity was quantified by a 'consensus value', both extremely low and extremely high values were notably absent from the wild-type sequences of the mutated splice sites. Splice sites of intermediate similarity to the consensus sequence may thus be more prone to the deleterious effects of mutation. Regarding the phenotypic effects of mutations on mRNA splicing, exon skipping occurred more frequently than cryptic splice site usage. Evidence is presented that indicates that, at least for 5' splice site mutations, cryptic splice site usage is favoured under conditions where (1) a number of such sites are present in the immediate vicinity and (2) these sites exhibit sufficient homology to the splice site consensus sequence for them to be able to compete successfully with the mutated splice site. The novel concept of a "potential for cryptic splice site usage" value was introduced in order to quantify these characteristics, and to predict the relative proportion of exon skipping vs cryptic splice site utilization consequent to the introduction of a mutation at a normal splice site.
All molybdenum‐containing enzymes other than the bacterial nitrogenase share an identical molybdenum cofactor (MoCo), which is synthesized via a conserved pathway in all organisms and therefore also is called “universal molybdenum cofactor.” In humans, four molybdoenzymes are known: aldehyde oxidase, mitochondrial amidoxime reducing component (mARC), xanthine oxidoreductase, and sulfite oxidase. Mutations in the genes encoding the biosynthetic MoCo pathway enzymes abrogate the activities of all molybdoenzymes and result in the “combined” form of MoCo deficiency, which is clinically very similar to isolated sulfite oxidase deficiency, caused by mutations in the gene for the corresponding apoenzyme. Both deficiencies are inherited as an autosomal‐recessive disease and result in progressive neurological damage and early childhood death in most cases. The majority of mutations leading to MoCo deficiency have been identified in the genes MOCS1 (type A deficiency), MOCS2 (type B deficiency), with one reported in GPHN. For type A deficiency an effective substitution therapy has been described recently. Hum Mutat 32:10–18, 2011. © 2010 Wiley‐Liss, Inc.
Molybdenum cofactor deficiency (MoCD) is a rare metabolic disorder characterized by severe and rapidly progressive neurologic damage caused by the functional loss of sulfite oxidase, 1 of 4 molybdenum-dependent enzymes. To date, no effective therapy is available for MoCD, and death in early infancy has been the usual outcome. We report here the case of a patient who was diagnosed with MoCD at the age of 6 days. Substitution therapy with purified cyclic pyranopterin monophosphate (cPMP) was started on day 36 by daily intravenous administration of 80 to 160 microg of cPMP/kg of body weight. Within 1 to 2 weeks, all urinary markers of sulfite oxidase (sulfite, S-sulfocysteine, thiosulfate) and xanthine oxidase deficiency (xanthine, uric acid) returned to almost normal readings and stayed constant (>450 days of treatment). Clinically, the infant became more alert, convulsions and twitching disappeared within the first 2 weeks, and an electroencephalogram showed the return of rhythmic elements and markedly reduced epileptiform discharges. Substitution of cPMP represents the first causative therapy available for patients with MoCD. We demonstrate efficient uptake of cPMP and restoration of molybdenum cofactor-dependent enzyme activities. Further neurodegeneration by toxic metabolites was stopped in the reported patient. We also demonstrated the feasibility to detect MoCD in newborn-screening cards to enable early diagnosis.
The molybdenum cofactor (Moco), a highly conserved pterin compound complexing molybdenum, is required for the enzymatic activities of all molybdenum enzymes except nitrogenase. Moco is synthesized by a unique and evolutionarily old pathway that requires the activities of at least six gene products. Some of the proteins involved in bacterial, plant, and invertebrate Moco biosynthesis show striking homologies to the primary structure of gephyrin, a polypeptide required for the clustering of inhibitory glycine receptors in postsynaptic membranes in the rat central nervous system. Here, we show that gephyrin binds with high affinity to molybdopterin, the metabolic precursor of Moco. Furthermore, gephyrin expression can reconstitute Moco biosynthesis in Moco-deficient bacteria, a molybdenum-dependent mouse cell line, and a Moco-deficient plant mutant. Conversely, inhibition of gephyrin expression by antisense RNA expression in cultured murine cells reduces their Moco content significantly. These data indicate that in addition to clustering glycine receptors, gephyrin also is involved in Moco biosynthesis and illustrate the remarkable conservation of its function in Moco biosynthesis throughout phylogeny.
All molybdoenzymes other than nitrogenase require molybdopterin as a metal-binding cofactor. Several genes necessary for the synthesis of the molybdenum cofactor (MoCo) have been characterized in bacteria and plants. The proteins encoded by the Escherichia coli genes moaA and moaC catalyse the first steps in MoCo synthesis. The human homologues of these genes are therefore candidate genes for molybdenum cofactor deficiency, a rare and fatal disease. Using oligonucleotides complementary to a conserved region in the moaA gene, we have isolated a human cDNA derived from liver mRNA. This transcript contains an open reading frame (ORF) encoding the human moaA homologue and a second ORF encoding a human moaC homologue. Mutations can be found in the majority of MoCo-deficient patients that confirm the functional role of both ORFs in the corresponding gene MOCS1 (for 'molybdenum cofactor synthesis-step 1'). Northern-blot analysis detected only full-length transcripts containing both consecutive ORFs in various human tissues. The mRNA structure suggests a translation reinitiation mechanism for the second ORF. These data indicate the existence of a eukaryotic mRNA, which as a single and uniform transcript guides the synthesis of two different enzymatic polypeptides with disease-causing potential.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.