Hemoglobinopathies and Thalassemias

John Onetime , in Emery and Rimoin's Principles and Practice of Medical Genetics, 2013

71.ix.4.4 Frameshift Mutations

Frameshift mutations are deletions or additions of 1, 2, or 4 nucleotides that change the ribosome reading frame and crusade premature termination of translation at a new nonsense or concatenation termination codon (TAA, TAG, and TGA). Too, insertions, deletions, and point mutations tin all generate a nonsense codon mutation, straight stopping translation. Chain termination mutations result in the majority of cases in a shortened β-mRNA that is often unstable and is apace degraded. The majority of these mutations that occur within exons 1 and 2 results in the typical recessively inherited β o-thalassemia phenotype. In contrast, frameshift and nonsense mutations that occur later in the β-globin sequence in exon 3 often produce a clinical phenotype more than severe than typical β-thalassemia trait and are said to be dominantly inherited.

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Poly peptide Synthesis and Deposition

John W. Pelley , in Elsevier's Integrated Review Biochemistry (Second Edition), 2012

Frameshift Mutations

Frameshift mutations are produced by molecules that can insert (intercalate) between the normal bases to create mistakes during DNA synthesis. These are usually apartment molecules, such as the acridine dyes, that have a hydrophobic nature (remember that hydrophobic base stacking is a contributing forcefulness in the construction of the helix). A frameshift mutation is produced either by insertion or deletion of ane or more than new bases. Because the reading frame begins at the start site, whatsoever mRNA produced from a mutated DNA sequence will be read out of frame after the point of the insertion or deletion, yielding a nonsense protein. Similarly to a signal mutation, a frameshift mutation can produce a termination codon ( Fig. 17-7). In addition, frameshift mutations, like bespeak mutations, are less deleterious if they are close to the carboxyl terminal.

Histology

Continuously Dividing Cells

Cells undergoing continuous jail cell segmentation are either differentiating mitotic cells or vegetative intermitotic cells (stem cells) that replicate both to replace themselves and to provide precursors for specialized cells. Examples of stem cells are basal cells in the epidermis, regenerative cells in the intestines, and bone marrow stem cells. Examples of differentiating mitotic cells are the prickle cells in the stratum spinosum of the epidermis and fibroblasts in the connective tissue during wound healing.

Recombination Mutations

Recombination is a normal process through which chromosomes exchange cistron alleles (culling forms of the same factor). When it occurs during meiosis, it is referred to as crossing over. During this process, genes are non created or destroyed, but if a misalignment occurs (Fig. 17-viii), then an unequal distribution of DNA results. This creates a deletion from the affected gene on i strand accompanied by a fractional duplication on the other strand. When this blazon of diff crossover occurs during meiosis, the new chromosomal arrangement becomes a heritable change. An example of such an unequal crossover is the Lepore thalassemia variant allele (Fig. 17-9). The similarity betwixt the β-globin gene and the side by side δ-globin gene led to a misalignment and an unequal crossover within the gene. Since the δ-globin protein has normal function in forming agile hemoglobin tetramers, there is no loss of function from this mutation. Instead, the defect is in the fact that the hybrid δ-β globin, which is the same length as the normal β-globin, is produced by the slower δ-globin promoter, thus classifying the mutation as a thalassemia (reduced production of a globin leading to altered hemoglobin tetramers).

Key Point Nigh Mutation

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The effect of a mutation can range from silence to devastation of the polypeptide or deletion of the factor; the effect of the mutation is determined by where in the mRNA the change occurred and what the new codon specifies (eastward.k., a termination codon vs. an amino acrid change).

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Compensatory Evolution

N. Osada , in Encyclopedia of Evolutionary Biology, 2016

Intramolecular Compensatory Evolution

Frameshift mutations are i of the examples of intramolecular compensation. Withal, there are many other mechanisms that promote intramolecular compensatory evolution. One of the clearest evidence of intramolecular compensatory evolution has been described in stem-loop structures in RNA molecules ( Wheeler and Honeycutt, 1988). As shown in Effigy 2, transcribed RNA molecules oft form Watson–Crick pairs betwixt A and U bases, and between C and G bases, in stem-loop structure. Mutations in i strand would dismiss the pairing and secondary structure of the RNA molecules may become unstable or may shift to a different country. However, if the base of operations coding the opposite strand have another mutation that could grade correct pairing, the two ribonucleotides could form proper pairing once more. Many RNA structures such every bit tRNA and ribosomal RNA structure have the potential to promote compensatory evolution, and studies take shown that compensatory development is a prevalent mode of RNA sequence evolution (Wheeler and Honeycutt, 1988; Stephan and Kirby, 1993; Meer et al., 2010).

Effigy 2. Example of compensatory evolution in RNA stem-loop construction. Watson and Crick pairs bound with each other with hydrogen bonds. Change of RNA sequence from G to C in the stem region (which is C to G mutation in the coding strand of genome) would break upwards the coupling, but the bail could exist restored by boosted mutation in the opposite strand.

Proteins are folded into circuitous three-dimensional structures and many amino acid residues interact with one some other in the folding process, which provide huge opportunity for compensatory evolution between different amino acid sites (DePristo et al., 2005). For example, positively charged amino acid site and negatively charged amino acid sites that are physically close to each other are bound with electrostatic interaction. Change of the 1 amino acid to lose proper charge may disrupt the interaction and may exist detrimental for protein folding and stability, but the stability may exist recovered by paired change at interacting sites. Complex poly peptide structure offers large potential for other kinds of interaction between amino acid sites, such as hydrophobic interactions and covalent bonds between amino acid residues (reviewed in Ivankov et al., 2014). In laboratory experiments, many compensatory mutations that could affect the stabilization of proteins take been identified (Lunzer et al., 2010). Notation that compensatory evolution here is not restricted to two-locus interaction equally presented in the uncomplicated population genetics model. Indeed, experimental show showed that the consequence of deleterious mutations are oft compensated by many different mutations around deleterious mutations (e.one thousand., Poon and Chao, 2005). In improver, many molecular evolution studies have identified coupled amino acid substitutions along lineages particularly when the coevolving sites are shut in three-dimensional structure (due east.g., Shim et al., 2005; Wang and Pollock, 2007; Yeang and Haussler, 2007). Large part of these correlated amino acid substitutions could be due to compensatory evolution.

Another example of intermolecular compensatory evolution is the development of codon bias (Akashi, 1995). In many genomes, both in eukaryotes and prokaryotes, the preference of codon usage in degenerative codons has been observed and preferred codons ofttimes correspond to the about arable tRNA in the genomes (Ikemura, 1981). The frequency of preferred codons would be unlike among genes and correlate with cistron expression level (Duret and Mouchiroud, 1999). Because the selective effect of each codon is presumably weak and one gene harbors many degenerative codons, gain and loss of preferred codons inside genes are considered to be evolving nether compensatory weak pick evolution. Population genetics studies on codon usage bias in Drosophila showed that the force of natural selection was indeed very weak and in the range of weak selection (|Nes|~1) (Akashi, 1995). Similar argument could be applied to the evolution of nucleosome binding sites, where nucleotide A and T are preferred for nucleosome bounden and GC content at genome-wide level is under compensatory weak pick (Kenigsberg et al., 2010).

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Proteases in Health and Illness

Stefano Lancellotti , Raimondo De Cristofaro , in Progress in Molecular Biology and Translational Science, 2011

2 Frameshift Mutations

In five frameshift mutations, c.1783_1784del, c.2376_2401del, c.2549_2550del, c.3770dupT, and c.4143dupA, ADAMTS13 is expressed as a truncated mutant with an abnormal C-final end. The c.1783_1784del mutation replaces L595-T1427 sequence in the spacer domain with the peptide sequence dGGEDRRALCRGWEDEHLP, the c.2376_2401del mutation in the TSP1-4 domain (A793-T1427) with the sequence PALPCQVGGVRAQLMHISWWSRPGLGERDLCARGRWPGGSSD, the c.2549_2550del mutation in the TSP1-5 domain (D850-T1427) with the GEAACP sequence, the c.3770dupT in the CUB-1 domain (L1258-T1427) with VGHDFQL QDQHAGGEAALRAARRWGAAAVWEPACS, and the c.4143dupA frameshift mutation in the CUB-2 domain (E1382-T1427) with the REQPG sequence. These aberrant mutants cannot be secreted, whereas others are secreted in sufficient amounts but are dysfunctional. However, information technology cannot exist excluded that mRNAs with these frameshift mutations may be eliminated by factor expression quality command systems. Finally, it should be noted that the c.3254_3255del mutation, which is responsible for the congenital thrombotic thrombocytopenic purpura chosen Upshaw–Schulman syndrome, is often reported in the literature as the R1096X mutation. 98

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Dystonia

Marker S. LeDoux , in Move Disorders (2d Edition), 2015

24.6.1.three DYT10/DYT19 (PKD)

Numerous missense and frameshift mutations leading to protein truncation or nonsense-mediated decay in the gene for proline-rich transmembrane protein 2 ( PRRT2) have been associated with PKD in numerous Han Chinese, Caucasian, and African-American families (Chen et al., 2011; Li et al., 2012; Liu et al., 2012; Wang et al., 2011). Several of the frameshift mutations are predicted to cause protein truncation or nonsense-mediated decay (Hedera et al., 2012). PRRT2 contains two predicted transmembrane domains and is highly expressed in the developing nervous arrangement, particularly the cerebellum (Chen et al., 2011). In addition to classic carbamazepine-responsive PKD, the phenotypic spectrum of PRRT2 mutations includes infantile convulsions and paroxysmal choreoathetosis, beneficial familial infantile seizures, hemiplegic migraine, a "PNKD-like" syndrome, and PED (Liu et al., 2012; Gardiner et al., 2012).

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Pancreatic ß-Cell Biology in Health and Disease

Laura Sanchez Caballero , ... Mariana Igoillo-Esteve , in International Review of Cell and Molecular Biological science, 2021

ii.15.ane Genetic alteration and clinical phenotype

Homozygous nonsense or frameshift mutations in the NKX2.ii gene coding for the transcription factor NKX2.2 cause permanent neonatal diabetes mellitus (Flanagan et al., 2014). Upwards to date, three patients from 2 independent consanguineous families have been reported. The three patients had very important insulin secretion defects but no alterations in the exocrine pancreas role (Flanagan et al., 2014), and ii of them also had several extrapancreatic manifestations including moderate to severe developmental delay affecting motor and intellectual part, hypotonia, bilateral hearing harm, cortical blindness and short stature amongst others (Flanagan et al., 2014).

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GENETICS | Genetics of Lafora and Juvenile Myoclonic Epilepsies

A.V. Delgado-Escueta , in Encyclopedia of Basic Epilepsy Enquiry, 2009

Factor replacement therapy is the time to come

For deletions, frameshifts, missense or nonsense mutations in laforin or malin, gene replacement treatment would exist the ideal handling. Cornford and Hyman have successfully transported laforin across the claret–encephalon barrier of laforin-deficient KO mice after intravenous administration of an expression plasmid containing laforin packaged in the interior of neutral pegylated immunoliposomes (PIL). The external PIL is conjugated with OX26 monoclonal antibodies against transferrin receptor, which transports the vehicle across the claret–brain barrier. Presently, these investigators are administering PIL packaged with all iv exons of laforin, with SV40 promotor, using mice epm2a polyclonal antibodies to confirm passage of epm2a through the claret–brain barrier in exon 4 KO homozygous null mutant mice. So far, laforin has been shown to rescue the pathology of LD in epm2a KO mice when administered in utero and in early postnatal months. Laforin replacement is now beingness studied in older mice with Lafora disease. In the most hereafter, the aforementioned method of delivering epm2a/laforin tin can be applied to Laforin deficient humans.

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Neurogenetics, Part Two

Leonel T. Takada , ... Michael D. Geschwind , in Handbook of Clinical Neurology, 2018

PRNP nonsense mutations

PRNP nonsense (or frameshift mutation leading to premature cease codon) mutations are very rare and cause gPrD with atypical clinical and neuropathologic features, as discussed beneath. The pathogenic mechanisms underlying these mutations are withal unclear, but the lack of the GPI ballast in the truncated protein appears to play an important function ( Mead et al., 2013). Experiments with transgenic mice expressing anchorless PrP showed that not only can they develop a transmissible PrP amyloidosis, but also that following infection by PrPSc, PrP degradation can exist found in extraneural tissues such equally center, kidney, pancreas and gut (Stohr et al., 2011).

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GPCR'due south and Endocrinology

Caroline K. Gorvin , in Reference Module in Biomedical Sciences, 2021

ii.two.1 Mutations in MC4R cause severe obesity in humans

In 1998, heterozygous frameshift mutations in MC4R were identified in two cohorts of severely obese children (Yeo et al., 1998). Subsequently, ~   160 dissimilar loss-of-function mutations have been described and defects in MC4R are now recognized as the near common genetic cause of obesity, associated with upward to 6% of cases (Farooqi et al., 2003). MC4R mutations have a ascendant way of inheritance. The majority of mutations are heterozygous, and individuals in which homozygous mutations have been identified have an earlier onset of severe obesity (Farooqi et al., 2003, 2000). Most of the MC4R mutations are missense, although nonsense, frameshift and small insertions and deletions have been described (Novoselova et al., 2018; Farooqi et al., 2003, 2000). In vitro expression of MC4R mutations demonstrates partially-impaired cAMP generation (Yeo et al., 2003). Lacking prison cell surface expression is commonly observed for missense mutations and is due to retentiveness in the endoplasmic reticulum (ER) (Yeo et al., 2003; Granell et al., 2010). The development of pharmacochaperones that better poly peptide folding or decrease ER degradation could be used as treatments in hereditary obesity (Granell et al., 2010).

In add-on to early-onset obesity, patients with MC4R have alpine stature, increased lean mass, high os mineral density, hyperphagia and hyperinsulinemia (Farooqi et al., 2003, 2000). Additionally, both humans and mice with MC4R deficiency have low claret pressure due to impaired sympathetic nervous arrangement activation (Fan et al., 2000; Farooqi et al., 2003; Greenfield et al., 2009; Lotta et al., 2019). In overweight and obese humans without MC4R mutations, the infusion of a highly-selective MC4R agonist led to dose-dependent increases in blood pressure level and centre rate (Greenfield et al., 2009), limiting the use of MC4R agonists for the handling of obesity. More recently, modified agonists with reduced adverse effects on the cardiovascular organization have been adult which show hope equally an obesity treatment (Chen et al., 2015; Kievit et al., 2013). However, off-target effects on other melanocortin receptors have been observed and further modifications may be required (Chen et al., 2015).

In 2019, studies of MC4R mutations in >   l,000 individuals in the UK Biobank demonstrated that some individuals harbor variants that exhibit a gain-of-function and biased signaling to preferentially increase β-arrestin recruitment rather than military camp production (Lotta et al., 2019). Individuals with these variants had significantly lower BMI, and up to a l% lower take a chance of obesity, type-2 diabetes and coronary artery disease (Lotta et al., 2019). Therefore the development of biased agonists for MC4R that favor β-arrestin recruitment may exist required to improve obesity treatments and limit off-target effects. The recent elucidation of the MC4R crystal structure may help in designing small molecules that selectively bias MC4R signaling (Yu et al., 2020).

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Cellular and Molecular Aspects of Myeloproliferative Neoplasms - Part A

Kotaro Shide , in International Review of Cell and Molecular Biology, 2021

four.3 Significance of CALR localization changes due to mutation

Another consequence of a frameshift mutation in CALR is the loss of the C-terminal KDEL sequence for ER retention ( Fig. 1). Every bit a result, in comparing with the wild-type CALR protein, mutant CALR proteins exhibit localization shift to ERGIC and Golgi apparatus (Fig. ii) (Chachoua et al., 2016). In mouse MEF cells, mutant CALR proteins were shown to accrue primarily in ERGIC, through which glycosylated proteins, including MPL, pass during their maturation procedure. The R102P mutant of MPL, which is plant in hereditary thrombocytopenia, remains in the ER, but CALR mutants tin induce its transport to the cell surface, as well equally the activation of MPL (Pecquet et al., 2019). This indicates that the mutant CALR proteins acquit as abnormal chaperones that transport activated immature MPL molecules from the ER to the cell surface via the Golgi apparatus (Pecquet et al., 2019). The location of MPL activation past CALR mutants is likewise an important question to be answered. Enhancement of STAT5 transcriptional activeness is not observed when the complex is retained in the ER by treatment with Brefeldin A, an ER-Golgi transport inhibitor. Therefore, the activation of MPL occurs in organelles between ERGIC and cell surface, and the circuitous that reaches the cell surface fully activates the function of the MPL receptor (Fig. 2) (Chachoua et al., 2016; Pecquet et al., 2019).

The wild-type CALR protein is not simply localized on the cell surface but also secreted from the cells (Eggleton et al., 1994; Ogden et al., 2001). Experiments using jail cell lines have shown that mutant CALR proteins are also secreted from the cells (Fig. ii) (Garbati et al., 2016; Han et al., 2016). In fact, the mutant CALR proteins are detected in the plasma of patients and knock-in mice at a concentration of 20–100   ng/mL (Balligand et al., 2020; Pecquet et al., 2019). In addition, MPN patients with CALR exon9 mutation have elevated levels of CALR in the plasma compared to healthy people (Liu et al., 2020). The exact production source of the secreted CALR mutants is not known, which could exist whatever blood jail cell, including clones that do not express MPL. The question arises equally to whether mutant CALR proteins have the power to activate MPL expressed in adjacent cells that do not take CALR mutants using paracrine signaling. CALR mutants interact simply with the immature MPL protein that is in the maturation process in the ER and Golgi appliance and do not interact with mature MPL, even extracellularly. In experiments using co-culture and supernatants, secreted mutant CALR proteins did not actuate mature MPL expressed in cells without CALR mutations (Araki et al., 2016; Han et al., 2016). In contrast, a written report using Nano-BRET and Nano-Luciferase found that mutant CALR proteins bind in trans to the young MPL of CALR-mutant cells, activating the JAK-STAT pathway as an abnormal cytokine (Pecquet et al., 2019). It is unclear to what extent this paracrine mechanism contributes to the activation of MPL in MPN patients (Pecquet et al., 2019).

The localization shift of mutant CALR proteins due to the loss of the C-terminal KDEL sequence is not limited to the Golgi apparatus, cell surface, or extracellular space. A recent report showed that mutant CALR proteins take increased binding affinity with FLI1, which is a known transcription cistron involved in megakaryocyte differentiation, compared to the wild-blazon CALR poly peptide, and that the mutant CALR proteins translocate FLI1 to the nucleus as chaperones, regulating the MPL promoter (Fig. 2) (Pronier et al., 2018). This newly discovered action of CALR mutants explains an early on finding that endogenous mouse c-mpl mRNA is highly expressed in Ba/F3 and 32D cells expressing the type i CALR-mutant protein (Han et al., 2016; Nivarthi et al., 2016). Furthermore, the sustained control of FLI1 may have a significant outcome on hematopoiesis, especially that of megakaryocytes. It is currently not known to what extent this action of CALR mutants in the nucleus contributes to the MPN phenotype.

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