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Two novel mutations in the aquaporin 2 gene in a girl with congenital nephrogenic diabetes insipidus.

Congenital nephrogenic diabetes insipidus (CNDI) is a rare inherited disorder characterized by insensitivity of the kidney to the antidiuretic effect of vasopressin. There are three inheritance patterns of CNDI: the X-linked recessive form associated with vasopressin V2 receptor gene mutations, and the autosomal recessive and dominant forms associated with aquaporin-2 gene (AQP2) mutations. The evaluation for polyuria and polydipsia in a one-month-old Korean girl revealed no response to vasopressin and confirmed the diagnosis of CNDI. Because the child was female without family history of CNDI, her disease was thought to be an autosomal recessive form. We analyzed the AQP2 gene and detected a compound heterozygous missense point mutation: 70Ala (GCC) to Asp (GAC) in exon 1 inherited from her father and 187Arg (CGC) to His (CAC) in exon 3 inherited from her mother. The first mutation is located within the first NPA motif of the AQP2 molecule and the second one right after the second NPA motif. This is the first report to characterize AQP2 mutations in Korean patients with autosomal recessive CNDI, and expands the spectrum of AQP2 mutations by reporting two novel mutation, 70Ala (GCC) to Asp (GAC) and 187Arg (CGC) to His (CAC).

Aquaporin 2↗

LINKAGE programs: linkage analysis for monogenic cardiovascular diseases.

Identification of the genes for a human disease provides significant insights into the molecular mechanism underlying the pathogenesis of the disease. A human disease gene can be identified by its chromosomal location (positional cloning). Linkage analysis is a key step in positional cloning. For monogenic disorders with a known inheritance pattern, model-based linkage analysis is effective in mapping the disease location. Therefore, model-based linkage analysis can provide a powerful tool to positional cloning of some specific molecular determinants that co-segregate with disease phenotypes in the isolated samples (e.g., large and multiplex impaired pedigrees). This chapter describes model-based human genetic linkage analysis as implemented in the LINKAGE computer package. First, we introduce the basic concepts and principles for genetic analysis of monogenic disorders. Then, we demonstrate the usages of the programs by analyzing several examples of hypothetical pedigrees with the inheritance modes of autosomal-dominant, autosomal-recessive, and genetic heterogeneity.

Cardiovascular Diseases↗

Ethnicity greatly influences cytokine gene polymorphism distribution.

Polymorphisms in the regulatory regions of cytokine genes are associated with high and low cytokine production and may modulate the magnitude of alloimmune responses following transplantation. Ethnicity influences allograft half-life and the incidence of acute and chronic rejection. We have questioned whether ethnic-based differences in renal allograft survival could be due in part to inheritance of cytokine polymorphisms. To address that question, we studied the inheritance patterns for polymorphisms in several cytokine genes (IL-2, IL-6, IL-10, TNF-alpha, TGF-beta, and IFN-gamma) within an ethnically diverse study population comprised of 216 Whites, 58 Blacks, 25 Hispanics, and 31 Asians. Polymorphisms were determined by allele-specific polymerase chain reaction and restriction fragment length analysis. We found striking differences in the distribution of cytokine polymorphisms among ethnic populations. Specifically, significant differences existed between Blacks and both Whites and Asians in the distribution of the polymorphic alleles for IL-2. Blacks, Hispanics and Asians demonstrated marked differences in the inheritance of IL-6 alleles and IL-10 genotypes that result in high expression when compared with Whites. Those of Asian descent exhibited an increase in IFN-gamma genotypes that result in low expression as compared to Whites. In contrast, we did not find significant ethnic-based differences in the inheritance of polymorphic alleles for TNF-alpha. Our results show that the inheritance of certain cytokine gene polymorphisms is strongly associated with ethnicity. These differences may contribute to the apparent influence of ethnicity on allograft outcome.

Alleles↗

Benign mitochondrial myopathy with decreased succinate cytochrome C reductase activity.

In most of the cases previously described, the defect on complex II was suggested by low activity of succinate cytochrome C reductase (SCCR). The clinical pattern of the previous 10 cases is heterogeneous and may be limited to one particular tissue or be of a more general nature. We report a 22-year-old-woman, daughter of consanguineous parents, with generalized muscle weakness, easy fatigability and benign course, who showed a decrease of SCCR activity in mitochondria of muscle fibers. Free carnitine (FC) concentration was decreased in muscle as well. The muscle biopsy showed a mild variation in fiber size, with fiber type I predominance, subsarcolemmal oxidative DPNH accumulations, excess of neutral lipids and abnormally large mitochondria with paracrystalline inclusions. A possible inheritance pattern is discussed. Coenzyme Q10 therapy in this patient induced a significant increase of global MRC index score and a decrease of the turns-mean amplitude ratio in the automatic analysis of the EMG.

Adult↗

Inherited and noninherited risk factors in rheumatoid arthritis.

Rheumatoid arthritis (RA) is likely the result of a concerted action of several inherited and noninherited factors. Although there is a high suspicion that environmental factors are important, proof is missing. Most information has been collected on genetic risk factors. The inheritance pattern for RA is complex, and there is good evidence that HLA as well as non-HLA genes are involved. Almost all racial-ethnic groups share the association of RA with the HLA-DRB1-encoded sequence motif QKRAA or QRRAA. However, the completeness of the association varies significantly in different ethnic cohorts, as can be expected in a multigene model. The sequence motif translates into a pocket in the antigen-binding site of the HLA-DR molecule. The "rheumatoid pocket" accommodates peptide side chains and has distinct binding characteristics. Epidemiologic evidence points toward a role for non-HLA genes. Candidate genes, such as transporter in antigen processing (TAP) genes are currently explored. Major advances in defining and understanding the contribution of inherited and noninherited factors in RA may come from abandoning the concept of RA as a single entity and accepting a heterogeneity model for RA. Distributions of HLA-DR genes indicate that several subsets of RA patients exist. Seronegative (prognostically good) and seropositive (prognostically worse) patients can be distinguished by the arginine versus lysine substitution at position 71 of the HLA-DRB1 gene. A different dimension of disease, rheumatoid organ disease, appears to be reached in patients with two HLA-DRB1*0401 alleles. Identification of distinct RA subsets may allow us to stratify patients into categories that differ with respect to etiology, disease course, clinical pattern, and treatment response.

Amino Acid Sequence↗

Population genetics of the bovine/cattle lungworm (Dictyocaulus viviparus) based on mtDNA and AFLP marker techniques.

Mitochondrial DNA (mtDNA) sequence data and amplified fragment length polymorphism (AFLP) patterns were compared for the lungworm Dictyocaulus viviparus, a nematode parasite of cattle. Eight individual D. viviparus samples from each of 8 herds in Sweden and 1 laboratory isolate were analysed, with the aim of describing the diversity and genetic structure in populations using different genetic markers on exactly the same DNA samples. There was qualitative agreement between the whole-genome AFLP data and the mtDNA sequence data, both indicating relatively strong genetic differentiation among the Swedish farms. However, the AFLP data detected much more genetic variation than did the mtDNA data, even after allowing for the different inheritance patterns of the markers, and indicated that there was much less differentiation among the populations. The mtDNA data therefore seemed to be more informative about the most recent history of the parasite populations, as the general patterns were less obscured by detailed inter-relationships among individual worms. The 4 mtDNA genes sequenced (1542 bp) showed consistent patterns, although there was more genetic variation in the protein-coding genes than in the structural RNA genes. Furthermore, there appeared to be at least 3 distinct genetic groups of D. viviparus infecting Swedish cattle, 1 of which was predominant and showed considerable differentiation between farms, but not necessarily within farms. Second, the 2 smaller genetic groups occurred on farms where the predominant group also occurred, suggesting that these farms have had multiple introductions of D. viviparus.

Animals↗

Foot polydactyly and polysyndactyly: genetic implications in two families.

The purpose of this study was to determine the genetic characteristics of foot polydactyly and identify its inheritance pattern by analyzing familial pedigree. Five cases from 2 Korean families were studied: 1 is a family whose members have been affected for 4 generations and the other for 2 generations. Using peripheral blood samples, we performed chromosomal analysis using the banding technique with Giemsa stain and karyotyping. We investigated the shape and structure of 46 chromosomes, looking for translation, deletion, inversion, ring chromosome, and isochromosome abnormalities. All peripheral blood samples demonstrated no chromosomal abnormalities, though the genetic nature of foot polydactyly and a new genetic locus was identified recently by other studies. Familial pedigree analysis suggested that polydactyly was inherited as an autosomal dominant trait in the first family. The mode of inheritance for the second family could not be determined due to an insufficient number of family members. The result of this study brought us to the conclusion that, while genetic factors play a major role in polydactyly, other factors may contribute to its occurrence.

Adult↗

Grain Development Mutants of Barley ([alpha]-Amylase Production during Grain Maturation and Its Relation to Endogenous Gibberellic Acid Content).

Barley (Hordeum vulgare L. Himalaya) mutants with altered grain morphology were isolated to investigate whether defects in grain development, possibly involving gibberellins (GAs) and abscisic acid, would lead to altered patterns of [alpha]-amylase gene expression. Following treatment with sodium azide, 75 mutants, typically showing grain shriveling, were identified. At grain maturity 15 of the 75 mutants had higher [alpha]-amylase activities in shriveled grains compared with either phenotypically normal grains that developed on the same heterozygous plant or with grains of cv Himalaya. Studies of four of these mutants demonstrated increased levels of both high- and low-isoelectric point [alpha]-amylase isozymes midway through grain development. This category of mutant has been designated pga, for premature grain [alpha]-amylase. One such mutant (M326) showed an endosperm-determined inheritance pattern. When crossed into a (GA-deficient) dwarfing background there was a 10- to 20-fold reduction in [alpha]-amylase activity, suggesting a requirement for GA biosynthesis. Endogenous GAs and abscisic acid were quantified by combined gas chromatography-specific ion monitoring in normal and mutant grains of heterozygous M326 plants during the period of [alpha]-amylase accumulation. Mutant grains had significantly higher (5.8-fold) levels of the bioactive GA1 compared with normal grains but much lower (approximately 10-fold) levels of the 2[beta]-hydroxylated ("inactive") GAs, typical of developing barley grains (e.g. GA8, GA34, GA48). We propose that a reduced extent of 2[beta]-hydroxylation in the mutant grains results in an increased level of GA1, which is responsible for premature [alpha]-amylase gene expression.

Journal Article↗

The evolutionary dynamics of extrachromosomal DNA in human cancers.

Oncogene amplification on extrachromosomal DNA (ecDNA) is a common event, driving aggressive tumor growth, drug resistance and shorter survival. Currently, the impact of nonchromosomal oncogene inheritance-random identity by descent-is poorly understood. Also unclear is the impact of ecDNA on somatic variation and selection. Here integrating theoretical models of random segregation, unbiased image analysis, CRISPR-based ecDNA tagging with live-cell imaging and CRISPR-C, we demonstrate that random ecDNA inheritance results in extensive intratumoral ecDNA copy number heterogeneity and rapid adaptation to metabolic stress and targeted treatment. Observed ecDNAs benefit host cell survival or growth and can change within a single cell cycle. ecDNA inheritance can predict, a priori, some of the aggressive features of ecDNA-containing cancers. These properties are facilitated by the ability of ecDNA to rapidly adapt genomes in a way that is not possible through chromosomal oncogene amplification. These results show how the nonchromosomal random inheritance pattern of ecDNA contributes to poor outcomes for patients with cancer.

Biological Evolution↗

C8A and C8B polymorphisms in Norwegians and Norwegian lapps.

C8 inheritance patterns in 364 mother-child pairs formed the basis for evaluation of the existence of silent alleles (null alleles) in the genes determining the two known polymorphic C8 systems. While evidence for such alleles was not found in C8A (alpha-gamma complex), two observations of null allele segregation in C8B (beta chain) indicate a C8BQ*0 allele frequency of about 0.07. Two population samples comprising 150 Lappish and 1,264 non-Lappish Norwegians were examined for phenotype distributions in C8A and C8B. The phenotype distributions were mainly in accordance with the expected Hardy-Weinberg distribution. The results for C8A indicated simple, codominant inheritance of two frequent and several rare alleles. Allele frequencies were similar in the two populations. The C8A B gene frequency in Norwegians was significantly lower than that in FRG and higher than that in Negroes. C8B allele frequencies were also calculated from gene counts in the population material, but with due corrections for the C8BQ*0 frequency observed in the mother-child material.

Alleles↗

A molecular approach to the stratification of cardiovascular risk in families with Marfan's syndrome.

BACKGROUND: The fibrillin gene encodes a protein in the extracellular matrix, and this protein is widely distributed in elastic tissues. The fibrillin gene is the site of mutations causing Marfan's syndrome. This disorder shows a high degree of clinical variability both between and within families. Each family appears to have a unique mutation in the fibrillin gene, which precludes the routine use of mutation screening for presymptomatic diagnosis of the disorder. The goal of this study was to develop a widely applicable method of molecular diagnosis. METHODS: We used three newly characterized intragenic sites of normal DNA repeat-sequence variation (i.e., polymorphisms) as markers to follow the inheritance pattern of specific copies (alleles) of the fibrillin gene in multiple kindreds with various clinical features of Marfan's syndrome. RESULTS: The polymorphic markers allowed identification of the particular copy of the fibrillin gene that cosegregated with Marfan's syndrome in 13 of the 14 families tested. In 11 families a definite presymptomatic diagnosis of Marfan's syndrome could be made in family members who had only equivocal manifestations of the disorder. In two other families, some family members demonstrated either classic Marfan's syndrome or a milder but closely related phenotype. The copy of the fibrillin gene that cosegregated with classic Marfan's syndrome was not inherited by family members with the latter, atypical, form of the disease. These milder phenotypes, previously diagnosed as Marfan's syndrome, were not associated with aortic involvement. CONCLUSIONS: These results document the usefulness of novel polymorphic DNA repeat sequences in the presymptomatic diagnosis of Marfan's syndrome. Our findings also demonstrate that the various clinical phenotypes seen in selected families may be due not to single fibrillin mutations, but rather to different genetic alterations. These findings underscore the need for a modification of the current diagnostic criteria for Marfan's syndrome in order to achieve accurate risk assessment.

Alleles↗

Genetic studies in Parkinson's disease.

In a previous paper (2), we had demonstrated the existence of familial cases of Parkinson's disease. We have now identified two main patterns to these familial cases within our own clinical material. The total familial subgroup of 50 kinships that we report represents 13% of our 342 kinships personally examined in detail. Only 2 of these familial cases turn out to be phenocopies of Parkinson's disease. A further 34 kinships (10% of all Parkinson's disease) are classified within the essential-tremor related Parkinsonism subgroup that we have previously described and 10 kinships (3% of all Parkinson's disease) form what we now call the recessive akineto-rigid syndrome. A further 4 kinships (called pseudodominant) are probably examples of this same entity. These subgroups have quite distinct inheritance patterns and deserve more thorough metabolic investigations and clinical characterization. On the basis of these studies, we propose that a genetic type of Parkinson's disease be included in any classification of the disorder.

Genes, Dominant↗

Four Japanese male patients with juvenile retinoschisis: only three have mutations in the RS1 gene.

PURPOSE: To describe the clinical phenotypes of four unrelated Japanese male patients with juvenile retinoschisis and to investigate occurrences of mutations in the RS1 gene. DESIGN: Observational case series and experimental study. METHODS: Fundus examinations, fluorescein angiography, and single-flash electroretinography (ERG) were carried out. In one patient, optical coherence tomography (OCT) was performed. The coding regions of the RS1 gene that encodes retinoschisin were amplified by polymerase chain reaction (PCR). The PCR products were purified and directly sequenced. RESULTS: The four affected patients showed cystoid- or wheel-like foveal changes with a little or no fluorescein leakage and negative b-wave patterns in both eyes. The OCT images of foveal retinoschisis disclosed that splitting occurs in the putative fibers of Henle. In three patients, we identified three different missense mutations (p.S73P, p.Y89C, p.R209C) in the functionally important discoidin domain of the RS1 gene. The p.S73P mutation has not been previously reported. In contrast, no nucleotide substitutions were detected in the fourth patient whose parents were unrelated and asymptomatic. No other member of this family for three generations has had juvenile retinoschisis. CONCLUSION: Because serine 73 is conserved in the mouse ortholog and other discoidin proteins, the proline 73 allele is therefore very likely to encode a defective retinoschisin. Although the inheritance pattern is uncertain in the patient without the RS1 mutation, the clinical and ERG findings were indistinguishable from those of patients with RS1 mutations. This finding points to the genetic heterogeneity of juvenile retinoschisis.

Adolescent↗

Mapping of genes predisposing to idiopathic generalized epilepsy.

Idiopathic generalized epilepsy (IGE) is characterized by recurring generalized seizures in the absence of detectable brain lesions and/or metabolic abnormalities. Twin and family studies suggest that genetic factors play a key part in IGE. A multilocus model appears to best fit the observed inheritance patterns. Mapping of IGE-related genes has been previously attempted using parametric methods, with conflicting results. In particular, recent evidence argues both for and against a chromosome 6p locus (EJM1) for juvenile myoclonic epilepsy, a subtype of IGE. We have approached the problem of mapping IGE loci using non-parametric methods, which have recently been successful for other complex diseases. No evidence for linkage to chromosome 6p was obtained. However, we obtained evidence for involvement of a locus at chromosome 8q24, close to the marker D8S256. The same 8q24 region was previously implicated in families with benign neonatal familial convulsions (BNFC), a generalized epilepsy syndrome that is inherited as a simple dominant mendelian trait. There is an apparent conserved syntenic group of genes in human 8q24 and a region of mouse chromosome 15, which harbors the stargazer (stg) locus. Homozygous mutant mice at the stg locus show a form of generalized epilepsy that resembles human absence epilepsy. Our findings may have implications for a locus on 8q24 predisposing to IGE.

Chromosome Mapping↗

Multi-step genetic regulation of oncogene expression in fish hereditary melanoma.

Melanoma occurring spontaneously in Xiphophorus fish hybrids is a model system in which involvement of cellular oncogenes and multi-step regulation of their expression have been identified by classical genetics. The macromelanophore gene in platyfish (Xiphophorus maculatus) is a sex-linked codominant gene which determines the black spot patterns of macromelanophores in the skin. The macromelanophore locus includes a cellular oncogene which potentially induces neoplasms of the pigment cells. Expression of the oncogene is regulated by a multi-step genetic process and brings about a characteristic phenotype associated with pigment cell differentiation at each step. The multi-step genetic regulation of oncogene expression can be recognized by interspecific hybridization of the platyfish with swordtails (Xiphophorus helleri) which have not developed the macromelanophore gene. When platyfish are hybridized with swordtails, the F1 offspring carrying this gene develop a preneoplastic state. When the F1 offspring are back-crossed to swordtails, the backcross offspring develop a heritable form of melanoma with a characteristic inheritance pattern. This heritable form of melanoma occurs at an early age and has a well differentiated character. Thus, the first and second steps of oncogene expression bring about a preneoplastic state in the F1 offspring and a heritable form of melanoma in the backcross offspring, respectively. These steps may be due to progressive substitution of platyfish chromosomes with swordtail chromosomes in germ line cells, resulting in a progressive reduction of the dosage of regulatory genes in the platyfish genome. The third step of oncogene expression brings about a sporadic form of melanoma in the hybrid offspring bearing the preneoplastic state and heritable form of melanoma spontaneously or through induction by carcinogens. This form of melanoma has a poorly differentiated character. The incidence of this form is considerably enhanced by aging in adult life, thus exhibiting age-specific incidence. It is likely that this step is due to mutational events in regulatory genes, which occur in somatic cells following chromosome substitution in germ line cells by hybridization. The albino gene enhances the malignancy of the two forms of melanoma and the incidence of the sporadic form of melanoma, possibly by suppressing the differentiation of transformed pigment cells. These facts and speculations are summarized in Fig. 6. The molecular identification of oncogenes in this melanoma system and their transfer into the swordtail eggs may provide a useful means for studying oncogene expression during development, growth, and aging of animals.

Age Factors↗

Retinal degeneration in motor neuron degeneration: a mouse model of ceroid lipofuscinosis.

PURPOSE: To evaluate the retinal degeneration of the motor neuron degeneration (mnd) mouse, and to confirm its inheritance pattern and gene location. METHODS: In screening the mnd/mnd mouse for ocular disease, a retinal degeneration was found that was evaluated by serial electroretinography, histology, electron microscopy, indirect ophthalmoscopy, and genetic and linkage analysis. RESULTS: In homozygous mnd mice, photoreceptor and outer nuclear layers show cell loss by 5 weeks after birth. By 2 months, the peripheral retina is preferentially thinner than central retina, and by 6 months the entire retina is reduced in thickness. The electroretinogram was extinguished by 6 months. Transmission electron microscopy at 3 and 6 months showed distinct cytoplasmic inclusions characteristic of the curvilinear profiles seen in human ceroid lipofuscinosis. Genetic analyses show that the retinal degeneration in mnd mice is inherited as a single autosomal gene with recessive expression, and a three-point cross placed the retinal degeneration at the mnd locus on the proximal end of mouse chromosome 8. Crosses with other known strains with retinal degeneration were normal. CONCLUSIONS. The mnd mouse model is similar to the juvenile onset Spielmeyer-Vogt form of ceroid lipofuscinosis (Batten disease), and provides a good model for the retinal degeneration found in these patients.

Alleles↗

Inheritance of open-angle glaucoma in the Barbados family study.

The majority of genetic studies on open-angle glaucoma (OAG) have been conducted in primarily white populations, with investigations of inheritance patterns largely based on self-reported information. The Barbados Family Study of Open-Angle Glaucoma (BFSG) is the first study to investigate the transmission pattern(s) for OAG in a predominantly black population, based on standardized examinations. Each BFSG participant received a comprehensive examination including anthropometric and other measurements, best-corrected visual acuity, perimetry, tonometry, lens gradings, fundus photography, venipuncture, an extensive interview including ocular, medical and family history information and a comprehensive ophthalmologic evaluation. Conservative criteria were used to define glaucoma status, including the presence of both visual field defects and optic disc damage. The study included 207 OAG-affected probands (median age: 68 years) and 1,056 of their relatives (median age: 47 years). Among the relatives examined 10% (n = 106) had OAG and 13% (n = 141) had probable OAG. Segregation analyses were performed to determine the mode of inheritance for glaucoma in these families. The results indicate that transmission of OAG or probable OAG is most likely due to a major codominant gene. Both age and gender are shown to be significant factors as well; with an increase in risk being associated with each year of age over 54 years and an increase in risk for all ages and genotypes observed in males. These analyses do not, however, preclude the possible existence of an environmental component or other genetic determinants in OAG. Further evidence for the existence of a major gene may be obtained by additional follow-up of the relatively young cohort of relatives, as well as ongoing linkage analyses.

Adult↗

Genetic and epigenetic modifications associated with human ooplasm donation and mitochondrial heteroplasmy - considerations for interpreting studies of heritability and reproductive outcome.

The mitochondrial heteroplasmy present in offspring from IVF and human ooplasm donation is troublesome and merits further exploration in a debate that is already complex and controversial. Improving the understanding of mitochondrial genomics in this context is important because mitochondriopathies can impact crucial cellular processes in renal, cardiovascular, central nervous, and endocrine systems. Relevant epigenetic consequences of mitochondrial heteroplasmy include associated abnormalities in mitochondrial translation products. Furthermore, as transmission and inheritance patterns of mtDNA are species-specific, it remains to be proven if findings derived from animal studies are applicable to human offspring. As an alternative to gamete research and proteomics based on animal experimentation, continued molecular characterization of the de novo human mitochondriopathies is posed to offer further insights regarding mitochondrial heteroplasmy. In this context, because knowledge of human mitochondrial genetics remains limited and the risks associated with ooplasm donation cannot be quantified, we do not favor its use for our patients at present. However, the small number of infants already conceived from this experimental approach warrant careful longitudinal evaluation. In particular, observational study of the few children born after ooplasm donation could provide opportunities to assess human mtDNA transmission and inheritance. Such findings could help identify features distinguishing natural mtDNA heteroplasmy from heteroplasmy observed after ooplasm donation. Future investigations should also quantify the degree any such heteroplasmy can exist innocuously. Disclosure of mtDNA mutations potentially affecting children conceived from IVF and ooplasm donation must be included during patient education at centers contemplating such treatment.

Animals↗