β-thalassemia mutations in the Portuguese population

Summary In this study we have carried out haplotype analysis on the -globin gene cluster and characterized the -thalassemia mutation by oligonucleotide hybridization in 14 patients with thalassemia major and 5 with sickle cell/-thalassemia originating from southern Portugal. We found that three mutations, namely the °-39, ° IVS-1 nt 1 and ⁺ IVS-1 nt 110 are prevalent accounting for 53%, 32% and 10% of the -thalassemia chromosomes respectively. In general each mutation was associated with a specific chromosomal haplotype; the ° mutation, however, was linked to three different haplotypes. These results indicate that three oligo-probes complementary to the most common mutations allow prenatal diagnosis by oligonucleotide analysis in 96% of the couples at risk of having offspring with thalassemia major in southern Portugal.     

Molecular characterization of β-thalassemia mutations in Egypt

Summary The relative frequency of different -thalassemia mutations and their association with -globin haplotypes were studied in patients from the Nile delta region, Egypt, by means of the polymerase chain reaction, oligonucleotide hybridization and restriction analysis. We found that 8 mutations account for 77% of -thalassemia chromosomes in this population, the commonest being IVS-1 nt 110, IVS-1 nt 6 and IVS-1 nt 1. Each mutation was associated with a specific haplotype, with the exception of IVS-1 nt 110, found on 3 different chromosomal backgrounds. Our data show that testing for the 8 detectable mutations makes feasible prenatal diagnosis in 65% of at risk couples and exclusion testing in an additional 25% of cases.     

How do Parkin mutations result in neurodegeneration?

The gene product responsible for autosomal recessive juvenile Parkinsonism, Parkin, has been observed to have ubiquitin ligase activity. This finding has changed the direction of studies on Parkinson's disease by suggesting that abnormal protein turnover might be involved in its pathogenesis. A number of potentially neurotoxic Parkin-specific substrates have been identified. Further investigation of Parkin knockout mice will hopefully provide new evidence in the search for Parkin's substrates and further clarify their role in Parkinson's disease.     

Half chromatid mutations: transmission in humans?

Attention is drawn to the possibility of half chromatid and early somatic mutations and to several implications of these mosaic-yielding events. There is suggestive evidence that spontaneous mutations can result in mosaics. A world-wide cooperative study of Lesch-Nyhan families could determine the extent of half chromatid mutation transmission and early somatic mutation in humans.     

Frequency of mutations in “thrombophilic state” genes in Uzbekistan

The frequency of mutations in a number of genetic markers, specifically factor V gene (G1691A), blood coagulation factor II gene (G20210A), and the methylenetetrahydrofolate reductase (MTHFR) gene (C677T), is studied in ethnic Uzbek patients with deep vein thrombosis of the lower extremities and in healthy donors. It is established that the incidence of mutant alleles among patients in Uzbekistan for FV Leiden is 12.9%; for prothrombin, 4%; and for MTHFR, 47.8%. The mutant allele C677T of the MTHFR gene has the highest expressivity in the appearance of MTHFR (47.8%). It is noted that this mutation in the MTHFR gene is encountered significantly more frequently in females with deep vein thrombosis than in males with deep vein thrombosis. The G20210A mutation in the prothrombin gene is encountered more rarely in the Uzbek population. The penetrance is studied and the role of these mutations in the appearance of deep vein thrombosis is estimated.     

Disease mutations in disordered regions--exception to the rule?

Intrinsically disordered proteins (IDPs) have been implicated in a number of human diseases, including cancer, diabetes, neurodegenerative and cardiovascular disorders. Although for some of these conditions molecular mechanisms are now better understood, the big picture connecting distinct structural properties and functional repertoire of IDPs to pathogenesis and disease progression is still incomplete. Recent studies suggest that signaling and regulatory roles carried out by IDPs require them to be tightly regulated, and that altered IDP abundance may lead to disease. Here, we propose another link between IDPs and disease that takes into account disease-associated missense mutations located in the intrinsically disordered regions. We argue that such mutations are more prevalent and have larger functional impact than previously thought. In addition, we demonstrate that deleterious amino acid substitutions that cause disorder-to-order transitions are particularly enriched among disease mutations compared to neutral polymorphisms. Finally, we discuss potential differences in functional outcomes between disease mutations in ordered and disordered regions, and challenge the conventional structure-centric view of missense mutations.     

Does caffeine induce dominant lethal mutations in mice?

Summary The problem of mutagenic activity of caffeine (1-3-7-trimethylxanthine) in man became more and more urgent because it is; first, one of the most frequently used stimulants in beverages and drugs and; second, recently several contradictory reports have been published [37, 29, 1, 43] which were followed up in public with great interest. We, therefore, tested the spermatogenesis of mice with the method of induction of dominant lethal mutations [42] in order to find a mutagenic effect, and by fractionating the spermatogenesis in eight breeding groups to detect some sensitive stages after a single treatment with a high caffeine dose. The animals used were of the C3H inbred strain of mice, the dose just tolerated by these animals was 0.25 g caffeine/kg body weight. Two experiments were carried out under same conditions with 29 males treated and 10 males in the control group. 373 pregnant females fertilized by the treated males showed among their 3495 implants 15% dead implantations while 201 females fertilized by the control males had 2139 implants, 13.6% of which died during pregnancy. This slight difference does not indicate any mutagenic function of caffeine on the spermatogenesis of mice as a whole. The tested stages of spermatogenesis revealed no sensitivity. A slight increase in pseudopregnancy (P0.007) could be observed, which might be physiologically caused. Copulation frequency was considerably decreased, especially in the first week after treatment.With the support of the Deutsche Forschungsgemeinschaft.     

Unique pattern of mutations in β-thalassemia patients in Western Uttar Pradesh

CONTEXT:

β-thalassemia is one of the most common heterogeneous inherited single gene disorders. The disease results from one or more of 380 different mutations in the β-globin gene. Uttar Pradesh (U.P.) is the most populous state of India, comprising various ethnic groups and Bareilly is one of the largest cities situated in Western U.P.

AIMS:

To examine the prevalence of five common β-thalassemian mutations: Intervening Sequence IVS 1-5 (c. 92 + 5 G > C), codon 8/9 (c. 27_28insG), codon 41/42 (c. 124_127delTTCT), IVS 1-1 (c. 92 + 1 G > T) and codon 26 G-A (c. 79G > A) in Western U.P.

SETTINGS AND DESIGN:

Patients attending camps organized by the Thalassemia Society, Bareilly were selected for the study.

MATERIALS AND METHODS:

A total of 48 blood samples were collected from the patients of transfusion dependent β-thalassemia from July 2011 to May 2012. All the samples were analyzed for five common mutations by using the Amplification Refractory Mutation System (ARMS)-hot start-polymerase chain reaction (PCR) technique.

RESULTS:

Among the five common mutations prevalent in India, we were able to detect all except codon 26 G-A (c. 79G > A), which is prevalent in northeast India. These four mutations accounted for 58% of the total number of our patients. The IVS 1-5 (G-C) was found to be the most common mutation with a frequency of 46% and the 2 ^ndmost common mutation was Fr8/9 (+G) with a frequency of 21%. The frequency of other mutations was IVS1-1 (12%) and Cd 41/42 (4%).

CONCLUSION:

This study provides evidence that the pattern of mutations in Western U.P. is different from the rest of India and even from the neighboring states (Delhi and Punjab). To the best of our knowledge, mutation Fr8/9, the 2^ndmost common mutation in our study has never been reported to be so common from anywhere in India. Some mutations, which are prevalent in other regions are absent in our region (mutation for ε-globin). Hence, these findings can be called unique to Western U.P.     

Identification of 28 novel mutations in the Bardet–Biedl syndrome genes: the burden of private mutations in an extensively heterogeneous disease

Bardet–Biedl syndrome (BBS), an emblematic disease in the rapidly evolving field of ciliopathies, is characterized by pleiotropic clinical features and extensive genetic heterogeneity. To date, 14 BBS genes have been identified, 3 of which have been found mutated only in a single BBS family each (BBS11/TRIM32, BBS13/MKS1 and BBS14/MKS4/NPHP6). Previous reports of systematic mutation detection in large cohorts of BBS families (n > 90) have dealt only with a single gene, or at most small subsets of the known BBS genes. Here we report extensive analysis of a cohort of 174 BBS families for 12/14 genes, leading to the identification of 28 novel mutations. Two pathogenic mutations in a single gene have been found in 117 families, and a single heterozygous mutation in 17 families (of which 8 involve the BBS1 recurrent mutation, M390R). We confirm that BBS1 and BBS10 are the most frequently mutated genes, followed by BBS12. No mutations have been found in BBS11/TRIM32, the identification of which as a BBS gene only relies on a single missense mutation in a single consanguineous family. While a third variant allele has been observed in a few families, they are in most cases missenses of uncertain pathogenicity, contrasting with the type of mutations observed as two alleles in a single gene. We discuss the various strategies for diagnostic mutation detection, including homozygosity mapping and targeted arrays for the detection of previously reported mutations.     

Two novel missense mutations in the cystathionine β-synthase gene in homocystinuric patients

Direct sequencing of the coding region of the cystathionine -synthase (CBS) gene in two homocystinuric patients revealed the presence of two novel missense mutations. The first mutation, a 1111G A transition, resulted in the substitution of the evolutionary conserved valine-371 by a methionine residue (V371M) and created a new NlaIII restriction site. The second mutation, a GA transition at base-pair 494, resulted in an amino acid change from cysteine to tyrosine (C165Y) and abolished a BsoFI restriction site. Both mutations were found in a compound heterozygous state with the previously described 833T C transition.     

Functional characterization of mutations in inherited human cPLA₂ deficiency

Group IVA cytosolic phospholipase A(2) (cPLA(2)α) catalyzes the first step in the arachidonic acid cascade leading to the synthesis of important lipid mediators, the prostaglandins and leukotrienes. We previously described a patient deficient in cPLA(2)α activity, which was associated with mutations in both alleles encoding the enzyme. In this paper, we describe the biochemical characterization of each of these mutations. Using saturating concentrations of calcium, we showed that the R485H mutant was nearly devoid of any catalytic activity, that the S111P mutation did not affect the enzyme activity, and that the known K651R polymorphism was associated with activity slightly higher than that of the wild type. Using MDCK cells, we showed that translocation to the Golgi in response to serum activation was impaired for the S111P mutant but not for the other mutants. Using immortalized mouse lung fibroblasts lacking endogenous cPLA(2)α activity, we showed that both mutations S111P and R485H/K651R caused a profound defect in the enzyme catalytic activity in response to cell stimulation with serum. Taken together, our results show that the S111P mutation hampers calcium binding and membrane translocation without affecting the catalytic activity, and that the mutation R485H does not affect membrane translocation but blocks catalytic activity that leads to inactivation of the enzyme. Interestingly, our results show that the common K651R polymorphism confers slightly higher activity to the enzyme, suggesting a role of this residue in favoring a catalytically active conformation of cPLA(2)α. Our results define how the mutations negatively influence cPLA(2)α function and explain the inability of the proband to release arachidonic acid for eicosanoid production.     

Cantú syndrome is caused by mutations in ABCC9

Cantú syndrome is a rare disorder characterized by congenital hypertrichosis, neonatal macrosomia, a distinct osteochondrodysplasia, and cardiomegaly. Using an exome-sequencing approach applied to one proband-parent trio and three unrelated single cases, we identified heterozygous mutations in ABCC9 in all probands. With the inclusion of the remaining cohort of ten individuals with Cantú syndrome, a total of eleven mutations in ABCC9 were found. The de novo occurrence in all six simplex cases in our cohort substantiates the presence of a dominant disease mechanism. All mutations were missense, and several mutations affect Arg1154. This mutation hot spot lies within the second type 1 transmembrane region of this ATP-binding cassette transporter protein, which may suggest an activating mutation. ABCC9 encodes the sulfonylurea receptor (SUR) that forms ATP-sensitive potassium channels (K(ATP) channels) originally shown in cardiac, skeletal, and smooth muscle. Previously, loss-of-function mutations in this gene have been associated with idiopathic dilated cardiomyopathy type 10 (CMD10). These findings identify the genetic basis of Cantú syndrome and suggest that this is a new member of the potassium channelopathies.     

Why are some human disease-associated mutations fixed in mice?

A recent comparative genomic analysis revealed the presence of nucleotide sequences in mouse that are known to be disease-associated in humans, yet the mouse appears normal. In this article we formulate and test several hypotheses in an attempt to explain why these apparently deleterious mutations become fixed in mice. We find that except for one case, the fixations of the disease-associated mutations occurred before the separation of Mus musculus and Mus spretus at least 1 million years ago and that the fixations are not attributable to a founder effect during the recent history of mouse breeding. About 80% of the cases involve diseases that occur before reproductive age in humans and these substitutions are unlikely to have been fixed because of the inefficiency of natural selection against late-onset diseases. We conclude that the compensatory mutation hypothesis remains the most probable explanation for the majority of the fixations of disease mutations in mice.     

What keeps cells in tissues behaving normally in the face of myriad mutations?

The use of a reporter gene in transgenic mice indicates that there are many local mutations and large genomic rearrangements per somatic cell that accumulate with age at different rates per organ and without visible effects. Dissociation of the cells for monolayer culture brings out great heterogeneity of size and loss of function among cells that presumably reflect genetic and epigenetic differences among the cells, but are masked in organized tissue. The regulatory power of a mass of contiguous normal cells is expressed in its capacity to normalize the appearance and growth behavior of solitary homophilic neoplastic cells, and to redirect differentiation of solitary heterophilic stem-like cells. Intimate contact between the interacting cells is required to induce these changes. The normalization of the neoplastic phenotype does not require gap junctional communication between cells, though transdifferentiation might. These varied relationships are manifestations of the unifying biological principle of "order in the large over heterogeneity in the small".     

The spectrum of β-thalassemia mutations in northern and northeastern Thailand

Summary A total of 123 -thalassemia genes from northern (n = 113) and northeastern (n = 10) Thailand were examined. Using five oligonucleotide probes, the mutation in 108 genes (88%) was identified: 50 nonsense 17, 49 frameshift 41-42, 4-28(AG), 2IVS1 nt5(GC), 2IVS2 nt654, and 1 deletion removing the entire -globin gene. The nonsense 17 mutation (n = 39) was linked to a single haplotype, whereas the frameshift 41-42 mutation occurred with several haplotypes. The results of the present study indicate that prenatal diagnosis of clinically important -thalassemia syndromes using a limited set of oligonucleotides is feasible in approximately 80% of affected families in northern Thailand and most of the families with -thalassemia-Hb E disease in northeastern Thailand.