Mutations In Different Genes Research Articles

Report of the 84th ENMC Workshop: PROMM (Proximal Myotonic Myopathy) and Other Myotonic Dystrophy-Like Syndromes: 2nd Workshop. 13–15th October, 2000, Loosdrecht, The Netherlands

Report of the 84th ENMC Workshop: PROMM (Proximal Myotonic Myopathy) and Other Myotonic Dystrophy-Like Syndromes: 2nd Workshop. 13–15th October, 2000, Loosdrecht, The Netherlands

Hereditary periodic fever.

Fever of undetermined origin may be familial and have a periodic course. This article discusses three syndromes of hereditary periodic fever: familial Mediterranean fever, the hyper-IgD syndrome, and the tumor necrosis factor receptor–associated periodic syndrome. Each is caused by mutations in different genes and affects different ethnic groups. Important recent advances in our understanding of the pathophysiology of these disorders are presented in this review article.

Clinical and genetic heterogeneity in congenital hyperinsulinism.

Congenital hyperinsulinism is one of the most common causes of recurrent hypoglycaemia in early infancy. It is characterised by dysregulation of insulin secretion. Over the last few years, substantial progress has been made in understanding the molecular mechanisms of normal and pathological insulin secretion. Mutations in different genes (those for the sulphonylurea receptor, inward-rectifying potassium channel, glutamate dehydrogenase and glucokinase) are associated with different modes of inheritance. The clinical heterogeneity of the various forms is explained by different pathogenic mechanisms resulting in inappropriate, partly unregulated secretion of insulin. Early recognition of hypoglycaemia, correct differentiation between histological types (focal or diffuse), and maintenance of adequate glucose levels are of critical importance for the outcome of these patients. the recent advances in the knowledge of the basis of congenital hyperinsulinism have resulted in new diagnostic and treatment strategies. Application of these aspects to general clinical practice will lead to an improvement of the management and long-term outcome of affected patients.

Arrested differentiation and epithelial cell degeneration in zebrafish lens mutants.

In a chemical mutagenesis screen, we identified two zebrafish mutants that possessed small pupils. Genetic complementation revealed these two lines are due to mutations in different genes. The phenotypes of the two mutants were characterized using histologic, immunohistochemical, and tissue transplantation techniques. The arrested lens (arl) mutant exhibits a small eye and pupil phenotype at 48 hr postfertilization (hpf) and lacks any histologically identifiable lens structures by 5 days postfertilization (dpf). In contrast, the disrupted lens (dsl) mutants are phenotypically normal until 5 dpf, and then undergo lens disorganization and cell degeneration that is apparent by 7 dpf. Histology reveals the arl mutant terminates lens cell differentiation by 48 hpf, whereas the dsl lens exhibits a defective lens epithelial cell population at 5 dpf. Lens transplantation experiments demonstrate both mutations are autonomous to the lens tissue. Immunohistochemistry reveals the retinal cells may suffer subtle effects, possibly due to the lens abnormalities.

Molecular analysis of hepatitis B virus genomes isolated from black African patients with fulminant hepatitis B

To investigate further the possible role of mutant hepatitis B viruses in the pathogenesis of fulminant hepatitis B, the genomic sequence of hepatitis B virus isolates from 9 South African blacks with this disease, including 5 entire genomes, was analysed. Seven of the isolates were genotype A. The mutation most often reported in patients with fulminant hepatitis B, the G1896A precore stop-codon substitution, was, as expected, not present in the genotype A isolates with the exception of one in which it was accompanied by a compensatory C1858T substitution. G1896A was, however, present in the one genotype D isolate. No other precore-defective mutants were detected. The other mutation commonly found in patients with fulminant hepatitis B, the paired A1762T, G1764A substitution in the basic core promoter, was present in only one patient and G1764A in one other. The pre-surface initiation-codon mutation documented in a number of patients with fulminant hepatitis B was not found in our isolates. An 18-amino acid deletion present in the pre-surface region of one isolate has not previously been described in fulminant hepatitis B. Variations within the surface region were mainly genotype specific and not previously described. A relatively large number of mutations were present in the middle region of the core gene in those isolates without G1896A or A1762T, G1764A mutations, although the pattern was not consistent with those in published studies. Thus, as in other published series in which the entire genome of hepatitis B virus responsible for fulminant hepatitis was sequenced, we detected many mutations in different genes, but none was common to all the reported isolates.

Phenotype of FAECB (Facility for Automated Experiments in Cell Biology) Chinese hamster ovary mutants with minimal UV-sensitivity

The Facility for Automated Experiments in Cell Biology (FAECB) collection of over 200 lines of ultraviolet (UV)-sensitive mutant Chinese hamster ovary (CHO) cells has previously been studied for complementation group assignment (CG), with representatives of rodent UV CGs 1–6 (ERCC1–6) and the new rodent XRCC9/FANCG group identified. Ten mutants from the collection, including a further six derived from wildtype AA8, three UV-sensitive double-mutants of CHO ERCC1 cell line UV4, and a UV-sensitive mutant of CHO XRCC1 cell line EM9, had not been assigned or characterized in these previous studies. These 10 mutants include 8 with approximately 1.5-fold the UV-sensitivity of the parental line (AA8, EM9, or UV4), and 2 with about 2-fold the UV-sensitivity of AA8. The present study reports the partial characterization of these 10 mutants in terms of sensitivity to UV (with and without caffeine), ionizing radiation, mitomycin C (MMC) and ethyl methanesulfonate (EMS); proficiency in DNA repair (unscheduled DNA synthesis (UDS)); and UV-mutability. The phenotypes of the 10 cell lines were heterogeneous, a number showed reduced UDS or UV-sensitization by caffeine, whilst others showed marked sensitivity to EMS or MMC, and they may have mutations in different genes involved in nucleotide excision repair, post-replicational repair, base excision repair or recombinational repair. Previous mutants isolated as part of the FAECB collection have proved to be extremely important in characterizing mammalian DNA repair processes and cloning human repair genes and these current mutants, whilst not as hypersensitive to UV, may still have the potential to make further contributions.

Temperature-sensitive mutations in various genes of Escherichia coli K12 can be suppressed by the ssrA gene for 10Sa RNA (tmRNA).

An Escherichia coli strain with a deletion in the ssrA gene that encodes 10Sa RNA (tmRNA) was used to screen for temperature-sensitive (ts) mutants whose ts phenotypes were suppressible by introduction of the wild-type ssrA gene. Mutants in four different genes were isolated. Ts mutants of this type were also obtained in a screen for mutations in thyA, the structural gene for thymidylate synthase. The ThyA activity in crude extracts prepared from the ts mutants was temperature-sensitive. The presence of the ssrA gene caused an increase in the total amount of the temperature-sensitive enzyme expressed, rather than suppressing the ts activity of the enzyme itself. SsrA-DD, a mutant form of 10Sa RNA, suppressed the ts phenotype of a thyA mutant, suggesting that degradation of a tagged peptide was not required for suppression of the ts phenotype. Considering the fact that ssrA-suppressible mutants could be isolated as temperature-sensitive mutants with mutations in different genes, it seems evident that trans-translation can occur on mRNA that is not lacking its stop codon.

Early loss of synaptic protein PSD-95 from rod terminals of rhodopsin P347L transgenic porcine retina

Retinitis pigmentosa (RP), a type of retinal degeneration involving first rod and then slow cone photoreceptor degeneration, can be caused by any of a number of mutations in different genes. In the cases of mutations affecting rod-specific genes such as rhodopsin, it is unclear how the mutations may cause degeneration of cones. We have used the porcine retina, which is rod-dominated and has an abundance of cones, to study the mutation-induced changes in both rod and cone photoreceptors. Like patients with the same mutation, rhodopsin P347L transgenic swine manifest rod–cone degeneration. In addition, the rod bipolar cells fail to form synaptic connections with rods; instead, they form ectopic synapses with cones. The mechanisms that prevent the formation of the rod–rod bipolar cell synaptic connection are not known. We used specific antibodies and immunocytochemistry to show that the synaptic protein, PSD-95, is present in both normal and transgenic porcine retinas. During neonatal development, however, PSD-95 is lost from rod terminals in the transgenic swine. This loss is virtually complete (90%) by postnatal day 5, at a time when greater than 80% of rod cell bodies still remain. Furthermore, the remaining rods retain their outer segments and their gross morphology appears relatively normal. In contrast, PSD-95 expression continues in cone terminals, even in 10-month-old transgenic swine, where the rods have all disappeared and the cones show signs of severe degeneration. These results suggest that loss of PSD-95 may not be a general consequence of the deteriorating cell. Rather, the very early and selective loss of PSD-95 from the rod terminals may be causally related to the absence of rod–rod bipolar cell synapses in the rhodopsin P347L transgenic retina.

Mutation-selection balance, dominance and the maintenance of sex.

A leading hypothesis for the evolutionary function of sex postulates that sex is an adaptation that purges deleterious mutations from the genome, thereby increasing the equilibrium mean fitness of a sexual population relative to its asexual competitor. This hypothesis requires two necessary conditions: first, the mutation rate per genome must be of order one, and, second, multiple mutations within a genome must act with positive epistasis, that is, two or more mutations of different genes must be more harmful together than if they acted independently. Here, by reconsidering the theory of mutation-selection balance at a single diploid gene locus, we demonstrate a significant advantage of sex due to nearly recessive mutations provided the mutation rate per genome is of order one. The assumption of positive epistasis is unnecessary, and multiple mutations may be assumed to act independently.

Genetic analysis of artificial pigmentation mutants in Porphyra yezoensis Ueda (Bangiales, Rhodophyta)

SUMMARY Porphyra yezoensis Ueda artificial pigmentation mutants, yel (green), fre (red-orange) and bop (pink), obtained by treatment with /V-methyl-/V′-nitro-N-nitrosoguanidine, were genetically analysed. The mutations associated with color phenotypes are recessive because all of the heterozygous conchocelis resembled the wild type color when they were crossed with the wild type (wt). In the reciprocal crosses of yel × wt, both parental colors and eight types of blades appeared in the F1 gametophytic blades from the heterozygous conchocelis. Both colors segregated in the sectored F1 blades in a 1:1 ratio, indicating that the color pheno-type of yel resulted from a single mutation in the nuclear gene. In the reciprocal crosses of fre × wt, however, four colors and more than 40 types of blades appeared in the F1 blades from the heterozygous conchocelis, indicating that the color phenotype of fre resulted from two mutations in different genes. In the reciprocal crosses of bop×wt, three colors and 12 types of blades were observed in the F1 blades from the heterozygous conchocelis. Both parental colors appeared far more frequently than the third new color. These results indicated that the color phenotype of bop resulted from two closely linked mutations in different genes, and the epistasis occurred in the F1 blades. The mutants, yel, fre and bop, differ from the spontaneous green (C-O), the red (H-25) and the violet (V-O) mutants of P. yezoensis, respectively.

Stress-reactivity and juvenile hormone degradation in Drosophila melanogaster strains having stress-related mutations

Juvenile hormone (JH) degradation was studied under normal and stress conditions in young and matured females of Drosophila melanogaster strains having mutations in different genes involved in responses to stress It was shown that (1) the impairment in heat shock response elicits an alteration in stress-reactivity of the JH system; (2) the impairment JH reception causes a decrease of JH-hydrolysing activity and of stress-reactivity in young females, while in mature ones stress reactivity is completely absent; (3) the absence of octopamine results in higher JH-hydrolysis level under normal conditions and altered JH stress-reactivity; (4) the higher dopamine content elicits a dramatic decrease of JH degradation under normal conditions and of JH stress-reactivity. Thus, the impairments in any component of the Drosophila stress reaction result in changes in the reponse of JH degradation system to stress. The role of JH in the development of the insect stress reaction is discussed.

New nomenclature and DNA testing guidelines for myotonic dystrophy type 1 (DM1). The International Myotonic Dystrophy Consortium (IDMC).

Myotonic (DM; OMIM 160900, also known as dystrophia myotonica, myotonia atrophica and Steinert disease) is an autosomal dominant associated with abnormalities of other organs, including eyes, heart, endocrine system, central and peripheral nervous systems, gastrointestinal organs, bone, and skin.1 The mutation underlying DM is an expansion of an unstable cytosine-thymine-guanine (CTG) trinucleotide repeat in the 3' untranslated region of the protein kinase (DMPK) gene in chromosome 19q13.3.2-4 In 1994, Thornton et al.5 described an autosomal dominant disorder similar to DM without CTG repeat expansion at the DM locus. Ricker et al.6 named this disease myopathy (PROMM; OMIM 600109) because of predominantly proximal muscle weakness without atrophy as opposed to the distal muscle involvement seen in DM. Subsequently, Meola et al.7 described a variant of PROMM with unusual and myopathic features, which they named syndrome, and Udd et al.8 described a PROMM-like family with dystrophic features, which they named dystrophy (PDM). Researchers at the University of Minnesota9,10 found another multisystemic disorder that closely resembles DM with distal muscle weakness but no CTG repeat expansion. Because of the close phenotypic resemblance to DM, they called this disease myotonic type 2 (DM2; OMIM 602668). In 1998, Ranum et al.9 assigned the DM2 locus to chromosome 3q in a large kindred. Shortly after that, Ricker et al.11 found that the majority of German PROMM families show linkage to the DM2 locus. PDM was also mapped to this region (Krahe and Udd, personal communication, 1999). Whether PROMM, PDM, and DM2 represent different phenotypic expressions of a disease caused by the same mutation or if they are allelic disorders remains to be determined. It is also possible that these disorders are caused by mutations in different genes that are closely linked in the chromosome 3q region.12 Furthermore, the disease loci in some typical PROMM families11 and other families with multisystemic disorders have been excluded from both DM and DM2 loci. Because of the genetic and phenotypic heterogeneity in this group of disorders, it became necessary to establish a new nomenclature foreseeing the future discovery of new disease loci and phenotypic variability.

SEVERE COMBINED IMMUNODEFICIENCY CAUSED BY DEFECTS IN COMMON CYTOKINE RECEPTOR γc SIGNALING PATHWAYS

Severe combined immunodeficiency (SCID) syndromes are a group of congenital disorders characterized by severe impairment of cellular and humoral immunity, leading to death at an early age. Human SCID comprises genotypically and phenotypically heterogeneous conditions of which the genetic basis for many of the underlying immunologic defects have been recently elucidated. All SCID phenotypes are defined by the absence of mature T cells. Other characteristics, including the presence or absence of B cells and natural killer (NK) cells and the particular genes involved, help to distinguish the various subtypes of these disorders (Fig. 1). One of the principal difficulties inherent in deciphering the pathogenesis of SCID syndromes is that different mutations in a single gene may give rise to distinct clinical conditions and that a similar clinical phenotype can result from mutations in different genes (Figs. 1 and 2). Complete deficiencies in the recombinase activating genes RAG1 and RAG2 block the generation of mature T and B lymphocytes by preventing antigen receptor gene rearrangements, 70 whereas NK cell development proceeds normally (T − NK + B − SCID). Deficiencies in RAG may not be the only cause of this SCID subtype: defects in other genes involved in the recombination process, such as Ku 70 and 86 proteins and DNA-dependent protein kinases, 4 could result in T − NK + B − SCID. Not all defects in the RAG genes generate typical T − NK + B − SCID. Mutations associated with partial RAG function recently were described in Omenn's syndrome, an immunodeficiency characterized by oligoclonal T- and B-cell development. 86 Defining the genetic basis of SCID syndromes remains a challenge. One prominent clinical immunologist described SCID syndromes as experiments of nature: a fitting characterization in that through these rare conditions, scientists and clinicians often can extract information regarding the essential roles of various gene products in the differentiation of the human lymphoid system. One of the most common subtypes of SCID is characterized by the selective blockade of T- and usually NK-cell differentiation, with the presence of poorly functioning B cells (T − NK − B + SCID). This immunologic phenotype is caused by deficiencies in signaling through a group of cytokine receptors that share the common cytokine receptor γ chain (γ c ). Like all SCIDs, disorders characterized by perturbations in the function of γ c -dependent cytokines can give rise to considerable heterogeneity with respect to the immunologic presentation and the molecular basis for the underlying disease pathology. This article summarizes the clinical considerations for T − NK − B + SCID and its atypical variants, the role of the γ c cytokine network in normal lymphopoiesis and in the pathophysiology of these diverse human SCID syndromes, and analyzes γ c mutations in typical and atypical SCID syndromes.

Induction and characterization of pigmentation mutants in Porphyra yezoensis (Bangiales, Rhodophyta)

Porphyra yezoensis Ueda conchospore germlings (1–4-cell stages) were treated with N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) for inducing mutations. Three kinds of color-mutated gametophytic blades, which were composed of the mutated cells wholly, sectorially or spottedly, were obtained; and most of them were sectorially variegated blades. The highest frequency of these mutated blades was 1.3%. Four different pigmentation mutant strains were obtained by regenerating single cells and protoplasts that were enzymatically isolated from the mutated sectors of the sectorially variegated blades. The mutants were relatively stable in color in both gametophytic blade and conchocelis phases. In the two phases, each mutant strain showed characteristic differences in the in vivo absorption spectra, and had different pigment contents of major photosynthetic pigments (chlorophyll a, phycoerythrin and phycocyanin) as compared with the wild-type and with each other. The gametophytic blades from the four mutant lines showed significant differences in growth and photosynthetic rates, when they were cultured in the same conditions. By crossing the mutant with the wild-type, it was found that the color phenotypes of two mutants reported above, were resulted from two mutations in different genes, respectively.

Somatic Mutation as Mechanism for Cyst Formation in Autosomal Dominant Polycystic Kidney Disease

One of the most striking aspects of certain inherted disease is the high degree of variability that is ometimes observed in the clinical presentation of ffected individuals. Differences between families an be easily explained by a variety of mechanisms. or example, mutations in different genes may afect the severity of a disease phenotype; or alternaively, mutations in different functional domains of he same gene may give rise to significant differnces between families in the clinical manifestations hat are associated with the disease. Differences etween family members inheriting the same germine mutation can be more difficult to understand ut a number of explanations can still be postulated. t is well recognized, for example, in animal breedng studies that the genetic background on which a ermline mutation occurs can have a significant imact on the phenotypic expression. Furthermore, for ost inherited diseases, the role of environmental actors is poorly understood, but it is certainly coneivable that they could modify the phenotypic exression of a specific mutant allele. For certain disases with focal manifestations, however, these actors do not tell the entire story (1). In this review e will use autosomal dominant polycystic kidney isease (ADPKD) as a model to explore the factors hat might contribute to phenotypic variability and ocal disease manifestations.

Craniosynostosis Syndromes: From Genes to Premature Fusion of Skull Bones

The calvarian bones in humans are formed by ntramembranous ossification, beginning around he ninth week of gestation (1). At the sites of bone pproximation narrow sutures are formed, which ontain immature, rapidly dividing osteogenic stem ells (2). These sutures allow the necessary adaptaion of the skull shape during delivery and, by apositional bone growth along the sutures, sufficient ncrease of the skull volume for the brain to develop n utero and in the first years of life. When these unctions are fulfilled, the cranial sutures ossify and orm a single protective helmet-like structure for the rain. Premature fusion of one or several sutures of the kull (craniosynostosis) is one of the most common raniofacial anomalies at birth and occurs with a revalence of approximately 1 in 2100–3000. More han 100 distinct genetic syndromes with craniosynstosis have been described (reviewed in Ref. 3). The ecent observation of mutations in different genes in atients and families with syndromal craniosynososis confirmed the proposed genetic heterogeneity nd at the same time supported the idea of addiional genetic and/or environmental factors modifyng the initial mutation effect and/or contributing to he pathogenesis in isolated cases of unknown etiolgy (2). Sporadic cases of craniosynostosis without dentified mutation most often present with premaure fusion of the sagittal suture, accounting for pproximately 56–58% of all craniosynostosis pan c c t

A cascade of genes related to Waardenburg syndrome.

On some occasions, mutations of a gene cause different syndromes that may have similar phenotypes. For example, mutations of the MITF gene cause Waardenburg syndrome type 2 (Tassabehji et al, 1994; Nobukuni et al, 1996) as well as Tietz syndrome (Smith et al, 1997). On other occasions, mutations of different genes cause an identical syndrome. Molecular analyses of these genes may provide a good opportunity to not only understand such syndromes themselves but also the biologic aspects of cells relevant to these syndromes. By analyzing the genes for Waardenburg syndrome, we showed that PAX3, the gene responsible for Waardenburg syndrome type 1, regulates MITF, the gene responsible for Waardenburg syndrome type 2. Such epistatic relationships have been shown between other genes related to Waardenburg syndrome, and likely to construct a cascade. This paper proposes such a cascade, one that involves genes for PAX3, MITF, human MyoD, MYF5, c-MET, c-KIT, tyrosinase, TRP-1, human QNR-71, SOX10, EDNRB, and EDN3.

The inheritance of hypertrophic cardiomyopathy.

The inheritance of hypertrophic cardiomyopathy is autosomal dominant, "sporadic" cases are now recognised to be uncommon. In the past 5 years molecular genetic advances have isolated >100 different mutations in genes encoding sarcomeric proteins. The cardiac morphology and prognosis are linked to the underlying genetic defect, but intra and interfamilial variation suggest polymorphism or mutation of other genes, or environmental factors. Penetrance is age related and negative echocardiographic screening cannot guarantee absence of disease. Currently mutation analysis is not routine in clinical practice.

Progression as exemplified by human astrocytic tumors

The last 10 years has seen major improvements in our understanding of the g enetic anomalies that lie behind the development and progression of human astrocytic tumors. The least aggressive astrocytomas frequently show loss of wild type p53 as well as losses of alleles from a number of regions of the genome. The genes targeted have yet to be identified. The most aggressive tumors, the glioblastomas, show mutations affecting the cellular mechanisms controlling entry into the S–phase of the cell cycle. The picture has become more complex as regards the mechanisms targeted. The heterogeneous genetic abnormalities reported previously in individual tumors of the same type have become easier to understand with the realization that they represent the mutation of different genes that code for components of the same cellular control mechanisms. There remain many routes to explore before we understand in detail the molecular mechanisms behind the phenotype of these tumors.

Splicing Variants in Sheep CLN3, the Gene Underlying Juvenile Neuronal Ceroid Lipofuscinosis

Mutations in different genes underlie different forms of the neuronal ceroid lipofuscinoses (NCLs, Batten disease). Subunit c of mitochondrial ATP synthase specifically accumulates in most of them, including the juvenile CLN3 form and a sheep form orthologous to CLN6. Products of these genes are likely to be components of a complex or pathway for subunit c turnover, and their expression may be cross-regulated. Different bands, some with different subcellular distributions, were detected by antisera against different regions of CLN3 on Western blots of sheep tissues. Affected liver blots were the same as controls but a specific 50-kDa band was at higher concentration in affected brain homogenates than in controls. Others have also reported bands reacting differently to different CLN3 antibodies. When the 3′ end of sheep CLN3 cDNA was amplified by RT-PCR, four mRNA splicing variants were found. Different CLN3 splicing variants at the 5′ end of the human cDNA have been reported. These mRNA splicing variants may account the variation of epitope distribution and the different subcellular locations of the CLN3 gene product(s). The predicted size of the unmodified CLN3 protein is 48 kDa. Significantly higher molecular weight bands may correspond to oligomers of a CLN3 isoform or to a CLN3 isoform tightly bound to another protein.