Gabor Matyas: «Grundlagen und Terminologie von genetischen
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Zentrum für Kardiovaskuläre Genetik und Gendiagnostik c/o Stiftung für Menschen mit seltenen Krankheiten ASA/SVV Fortbildungsreihe Genetik 2014 - Module 1 Grundlagen und Terminologie von genetischen Untersuchungen Olten, 22. Mai 2014 PD Dr. Gabor Matyas, FAMH Medizinische Genetik Leiter Zentrum für Kardiovaskuläre Genetik & Gendiagnostik Geschäftsleiter Stiftung für Menschen mit seltenen Krankheiten www.genetikzentrum.ch, www.stiftung-seltene-krankheiten.ch Human genetics describes the study of heredity and variation in humans and encompasses a variety of overlapping fields Transmission genetics (pedigree analyses) Classical genetics Epigenetics Cytogenetics Clinical genetics Genomics Transcriptomics Proteomics Bioinformatics Molecular genetics Human genetics Genetic counseling Biochemical genetics Gene diagnostics Molecular phylogenetics Comparative genomics Population genetics Developmental genetics Medical genetics is the application of genetics to medicine Cytogenetics Clinical genetics Genetic counseling Molecular genetics Medical genetics Biochemical genetics Gene diagnostics Grundlagen der Humangenetik (Einführung) Das menschliche Erbgut (DNA) Zellkern mtDNA Chatterjee et al., Oncogene (2006) 25: 4663–4674 http://commons.wikimedia.org/wiki/Image:Karyotype.png Mitochondrium Nuclear genome (nDNA) Mitochondrial genome (mtDNA) Size 3200 Mb 16.6 kb No. of different DNA molecules 23 (in XX cells) or 24 (in XY cells); all linear One circular DNA molecule Total no. of DNA molecules/cell 46 in diploid cells (varies in ploidy) Often several thousand (but variable) Associated protein Several classes of histone and nonhistone protein Largely free of protein No. of genes ~20,000 37 (13 polypeptides, 2 rRNAs, and a set of 22 tRNAs) Gene density ~1/100 kb 1/0.45 kb Repetitive DNA Over 50% of genome Very little Transcription The most genes are transcribed individually Co-transcription of multiple genes from both the H and L strands Introns Found in most genes Absent % of coding DNA ~1.5% (~50 Mb) ~93% Recombination At least once for each pair of homologs at meiosis Not evident (mtDNA can replicate independently of nDNA) Inheritance Mendelian for sequences on X and autosomes paternal for sequences on Y Exclusively maternal Codon usage Four codons are interpreted differently in the nucleus (N) and mitochondria (M): UGA = Stop(N), Trp(M); AUA = Ile (N), Met (M); AGA+AGG = Arg (N), Stop (M) mtDNA Chatterjee et al., Oncogene (2006) 25: 4663–4674 http://commons.wikimedia.org/wiki/Image:Karyotype.png The Human Genome (1) http://commons.wikimedia.org/wiki/Image:Karyotype.png http://genome-euro.ucsc.edu/index.html Das menschliche Erbgut (DNA) Janine Meienberg | www.genetikzentrum.chwww.genetikzentrum.ch www.genetikzentrum.ch Chromatin has highly complex structure with several levels of organization. The simplest level is the double-helical structure of DNA. Adapted from Pierce, Benjamin. Genetics: A Conceptual Approach, 2nd ed. Nature Education: www.nature.com/scitable/topicpage/Eukaryotic-Genome-Complexity Base pairing in DNA. In double-stranded DNA, two hydrogen bonds connect the nucleotides thymine (T) to adenine (A); three hydrogen bonds connect the nucleotides guanine (G) to cytosine (C). The sugarphosphate backbones (grey) run anti-parallel to each other, so that the 3’ and 5’ ends of the two strands are aligned. Nature Education: www.nature.com/scitable/topicpage/Discovery-of-DNA-Structure-and-Function-Watson-397 Cytosine (C): can be methylated (=> hypermethylation) and change into uracil (=> spontaneous deamination). The chemical structures of DNA (left) and RNA (right). RNA is usually single-stranded. In DNA, the sugar that composes the sugar-phosphate backbone is deoxyribose; in RNA, the sugar is ribose. The nucleotide thymine (T) is not present in RNA: rather than binding with thymine, the nitrogenous base adenine (A) base-pairs with the nitrogenous base uracil (U) in RNA. Nature Education: http://www.nature.com/scitable/topicpage/chemical-structure-of-rna-348 (a) A region of single-stranded RNA. The sugar component of the sugar-phosphate backbone is ribose and RNA does not contain the nitrogenous base thymine (T), instead, the nitrogenous base uracil (U) binds with the base adenine. (b) The primary and secondary structures of RNA. The primary structure refers to the molecule’s nucleotide sequence; the secondary structure refers to its three-dimensional conformation after folding has occurred. Nature Education: http://www.nature.com/scitable/topicpage/chemical-structure-of-rna-348 Several forms of RNA are involved in gene expression. During transcription, DNA (grey rectangle) is used as a template to produce an RNA transcript (purple rectangle). The RNA is translated to build the protein molecule (polypeptide) encoded by the original gene. Both prokaryotic and eukaryotic cells contain messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA). Premessenger RNA (pre-mRNA), small nuclear RNA (snRNA), small nucleolar RNA (snoRNA), small cytoplasmic RNA (scRNA), micro RNA (miRNA), and small interfering RNA (siRNA) are found exclusively in eukaryotic cells. Nature Education: www.nature.com/scitable/topicpage/chemical-structure-of-rna-348 Das menschliche Erbgut (DNA) Aminosäuren http://www.nature.com/scitable/topicpage/gene-expression-14121669 Das menschliche Erbgut (DNA) – Chromosom 15 DNA ... ... – Gen ... ... – 65 Exons Splicing ... Protein Synthese – Transkript: ~10 Kilobasen ... – Protein: N 2871 Aminosäuren Downing et al. 1996. Cell 85:597-605 Protein Faltung C Disulfidbrückenbildung Calcium-Bindung Ca Ca Glykosylierung Ca Ca Gen: Abschnitt der DNA, der die Information zur Herstellung eines Proteins trägt Das menschliche Erbgut (DNA) – Chromosom 15q21.1 DNA ... ... – FBN1: ~237,000 nucleotides ... ... – 65 Exons Splicing ... Protein Synthese – Transkript: ~10 Kilobasen ... – Protein: N 2871 Aminosäuren Downing et al. 1996. Cell 85:597-605 Protein Faltung C Disulfidbrückenbildung Calcium-Bindung Ca Ca Glykosylierung Ca Ca Gen: Abschnitt der DNA, der die Information zur Herstellung eines Proteins trägt FBN1 – Schematische Darstellung – Chromosom 15q21.1 DNA ... ... – FBN1: ~237 Kilobasen ... ... – 65 Exons Splicing ... Protein Synthese – Transkript: ~10 Kilobasen ... – Protein: N 2871 Aminosäuren Downing et al. 1996. Cell 85:597-605 Protein Faltung C Disulfidbrückenbildung Calcium-Bindung Ca Ca Glykosylierung Ca Ca Gen: Abschnitt der DNA, der die Information zur Herstellung eines Proteins trägt FBN1 – Schematische Darstellung – Chromosom 15q21.1 DNA ... ... – Gen: ~237 Kilobasen prä-mRNA ... ... – 65 Exons RNA Synthese Splicing ... Protein Synthese – Transkript: ~10 Kilobasen ... – Protein: N 2871 Aminosäuren Downing et al. 1996. Cell 85:597-605 Protein Faltung C Disulfidbrückenbildung Calcium-Bindung Ca Ca Glykosylierung YNYYRAY is a common sequence at the branchingCa points of introns. Ca Y indicates a pyrimidine (C, T/U); N, a nucleotide; R, a purine (A, G); and A, the base adenine. Gen: Abschnitt der DNA, der die Information zur Herstellung eines Proteins trägt Nature Education: www.nature.com/scitable/topicpage/chemical-structure-of-rna-348 FBN1 – Schematische Darstellung – Chromosom 15q21.1 DNA ... ... – Gen: ~237 Kilobasen prä-mRNA ... ... – 65 Exons RNA Synthese Splicing mRNA ... – Transkript: ~10 Kilobasen ... – Protein: N 2871 Aminosäuren Downing et al. 1996. Cell 85:597-605 Protein Faltung C Disulfidbrückenbildung mRNA Calcium-Bindung Ca Ca Glykosylierung Introns (non-coding sequences) are removed during RNA splicing to produce a Ca Ca mature mRNA transcript composed of exons (coding sequences). Gen: Abschnitt der DNA, der die Information zur Herstellung eines Proteins trägt Nature Education: www.nature.com/scitable/topicpage/chemical-structure-of-rna-348 FBN1 – Schematische Darstellung – Chromosom 15q21.1 DNA ... ... – Gen: ~237 Kilobasen prä-mRNA ... ... – 65 Exons RNA Synthese Splicing mRNA ... – Transkript: ~10 Kilobasen ... – Protein: mRNA N 2871 Aminosäuren Downing et al. 1996. Cell 85:597-605 Protein Faltung C tRNA Calcium-Bindung Ca Ca Disulfidbrückenbildung Glykosylierung Ca Ca Gen: Abschnitt der DNA, der die Information zur Herstellung eines Proteins trägt Nature Education: www.nature.com/scitable/topicpage/chemical-structure-of-rna-348 FBN1 – Schematische Darstellung DNA ... ... prä-mRNA ... ... RNA Synthese Splicing mRNA ... ... 2871 Aminosäuren Protein Faltung Downing et al. 1996. Cell 85:597-605 – Protein: mRNA N C tRNA Ca Disulfidbrückenbildung Calcium-Bindung Ca Glykosylierung Ca Ca Gen: Abschnitt der DNA, der die Information zur Herstellung eines Proteins trägt Nature Education: www.nature.com/scitable/topicpage/chemical-structure-of-rna-348 FBN1 – Schematische Darstellung DNA ... ... prä-mRNA ... ... RNA Synthese Splicing mRNA ... ... – Protein: mRNA N 2871 Aminosäuren Downing et al. 1996. Cell 85:597-605 Protein Faltung C tRNA Calcium-Bindung Ca Ca Disulfidbrückenbildung Glykosylierung Ca Ca Gen: Abschnitt der DNA, der die Information zur Herstellung eines Proteins trägt Nature Education: www.nature.com/scitable/topicpage/chemical-structure-of-rna-348 FBN1 – Schematische Darstellung DNA ... ... prä-mRNA ... ... RNA Synthese Splicing mRNA ... ... 2871 Aminosäuren Protein Faltung Downing et al. 1996. Cell 85:597-605 – Protein: mRNA N C tRNA Ca Disulfidbrückenbildung Calcium-Bindung Ca Glykosylierung Ca Ca Gen: Abschnitt der DNA, der die Information zur Herstellung eines Proteins trägt Nature Education: www.nature.com/scitable/topicpage/chemical-structure-of-rna-348 FBN1 – Schematische Darstellung – Chromosom 15q21.1 DNA ... ... – Gen: ~237 Kilobasen prä-mRNA ... ... – 65 Exons RNA Synthese Splicing Protein Synthese Protein mRNA ... – Transkript: ~10 Kilobasen ... – Protein: N 2871 Aminosäuren Downing et al. 1996. Cell 85:597-605 Protein Faltung C Disulfidbrückenbildung (Cys-Cys) Calcium-Bindung Ca Ca Glykosylierung Ca Ca 1 Gen => 1 Protein Alternative splicing a process by which a given gene is spliced into more than one type of mRNA molecule DNA prä-mRNA mRNA 1 Gen => mehrere Proteine ~20‘000 Gene => ~100‘000 Proteine Nature Education: http://www.nature.com/scitable/topicpage/chemical-structure-of-rna-348 3 Milliarden Buchstaben im Zellkern (in jeder Zelle!) 23 ChromosomenPaare ca. 20‘000 Gene Das menschliche Erbgut (DNA) • Chromosomen (Karyotyp) The Human Genome (2): X Chromosome Inactivation In the early XX female zygote, both X chromosomes are active. In der Embryonalentwicklung findet die X-Inaktivierung etwa zum Zeitpunkt der Differenzierung der pluripotenten Zellen zu verschiedenen Zellschichten statt, also während des Blastozystenstadiums (ca. 5 Tage nach der Befruchtung; ~100 Zellen) Around the late blastocyst stage a choice is made randomly in each cell to inactivate either the paternal or the maternal X. The choice that a cell makes is preserved in all its descendants. Adapted from Migeon, Trends Genet (1994) 10:230-235 The Human Genome (2): X Chromosome Inactivation X-linked (dominant) Incontinentia pigmenti (IP) (one X chromosome harbors a mutation) An adult XX female has clonal populations of cells with the paternal (here normal) or maternal (here mutated) inactivated X chromosome. Skin abnormalities known as Blaschko's lines X-chromosomale Inaktivierung Definition: Gendosis-Kompensation in weiblichen somatischen Zellen weiblicher Karyotyp: 46, XX männlicher Karyotyp: 46, XY Lyon-Hypothese (Mary F. Lyon, Nature, 1961): in weiblichen somatischen Zellen ist nur ein X-Chromosom aktiv Inaktivierung des zweiten X erfolgt früh in der Embryonalentwicklung ist zufällig und irreversibel (in somatischen Zellen) Das menschliche X-Chromosom: ca. 160 Millionen Basenpaare ~1000 Gene Eigenschaften des inaktiven X-Chromosoms: spät replizierend hypermethyliert hypoazetyliert Mechanismen der X-Inaktivierung: Markierung des aktiven X-Chromosoms Inaktivierung aller weiteren X-Chromosomen X-Inaktivierungszentrum (XIC): Xq13.3 (Region mit einer Grösse von ca. 1 Mbp enthält XIST-Gen (X inactive specific transcript) 17 kb Transkript, nicht-kodierend XIST-Transkript ´umhüllt´ das inaktive X-Chromosom => Hypoazetylierung der Histone => DNA-Methylierung X0?? (R. Knippers: Molekulare Genetik) Das menschliche X-Chromosom: ca. 160 Millionen Basenpaare ~1000 Gene Eigenschaften des inaktiven X-Chromosoms: spät replizierend hypermethyliert hypoazetyliert Mechanismen der X-Inaktivierung: Markierung des aktiven X-Chromosoms Inaktivierung aller weiteren X-Chromosomen X-Inaktivierungszentrum (XIC): Xq13.3 (Region mit einer Grösse von ca. 1 Mbp enthält XIST-Gen (X inactive specific transcript) 17 kb Transkript, nicht-kodierend XIST-Transkript ´umhüllt´ das inaktive X-Chromosom => Hypoazetylierung der Histone => DNA-Methylierung NICHT alle Gene des X-Chromosoms werden inaktiviert (etwa 10%-25% werden ausgenommen) (R. Knippers: Molekulare Genetik) RPS4Y (R. Knippers: Molekulare Genetik) Expressed genes on the inactive X chromosome • Many of the genes which escape inactivation are also present on the Y chromosome, e.g. genes in the pseudoautosomal region (PAR) or RPS4. Thus, individuals of either sex will receive two copies of these genes (like on autosomes). • The existence of genes not silenced explains the defects in humans with abnormal numbers of the X chromosome, such as Turner syndrome (X0) or Klinefelter syndrome (XXY). (R. Knippers: Molekulare Genetik) Random monoallelic expression on the human autosomes (A) ~5 to 10% of assessed autosomal genes display random monoallelic transcription in human cells. (B) Distribution along autosomes of randomly monoallelically expressed and biallelic genes (brown boxes mark centromeres). (C) Gene-level view of allele-specific expression on chromosome 18 in clonal cell lines from three individuals. BUT, monoallelic expression also occurs due to genomic imprinting (*) (e.g. on chromosomes 11p, 15q): Paternally imprinted, maternally expressed maternal Gene 1 paternal* Gene 1 Maternally imprinted, paternally expressed maternal* Gene 2 paternal Gimelbrant et al., Science (2007) 318:1136-1140 Gene 2 *Imprinting: genetic information can be manifested in a different way when it is inherited from the mother than when it is inherited from the father Veränderung der DNA Classification of Mutations by Effect on Structure 1. Genome mutations Numerical change of the whole chromosome set (e.g. triploidy (3n), tetraploidy (4n)) Numerical change of a single chromosome (e.g. trisomy 21, 18, 13) http://en.wikipedia.org/wiki/Image:Types-of-mutation.png 2. Chromosomal mutations http://www.nature.com/scitable/topicpage/genetic-mutation-441 Classification of Mutations by Effect on Structure Numerical change of the whole chromosome set (e.g. triploidy (3n), tetraploidy (4n)) Numerical change of a single chromosome (e.g. trisomy 21, 18, 13) 2. Chromosomal mutations 3. Gene mutations Point mutations, deletions, insertions A>G C>T http://en.wikipedia.org/wiki/Image:Types-of-mutation.png Single nucleotide polymorphisms (SNP) SNP is a DNA sequence variation occurring when a single nucleotide in the genome (or other shared sequence) differs between members of a species (or between paired chromosomes in an individual). http://en.wikipedia.org/wiki/Image:Dna-SNP.svg 1. Genome mutations Classification of Mutations by Effect on Structure 1. Genome mutations Numerical change of the whole chromosome set (e.g. triploidy (3n), tetraploidy (4n)) Numerical change of a single chromosome (e.g. trisomy 21, 18, 13) 2. Chromosomal mutations 3. Gene mutations Point mutations, deletions, insertions A>G http://en.wikipedia.org/wiki/Image:Types-of-mutation.png C>T Classification of Mutations by Effect on Structure 1. Genome mutations Numerical change of the whole chromosome set (e.g. triploidy (3n), tetraploidy (4n)) Numerical change of a single chromosome (e.g. trisomy 21, 18, 13) 2. Chromosomal mutations 3. Gene mutations Point mutations, deletions, insertions http://www.nature.com/scitable/topicpage/genetic-mutation-441 http://en.wikipedia.org/wiki/Image:Types-of-mutation.png C>T A>G In vitro (Transkript) Analyse Stille Mutation c.6354C>T (p.I2118I) C>T Exon 50 Exon 51 Intron 51 ...C… Intron 50 380bp 150bp cF 66bp 244bp Exon 52 Intron 52 2247bp 117bp Exon 53 cR 120bp PD Dr. G. Matyas | www.genetikzentrum.ch | www.stiftung-seltene-krankheiten.ch 22.05.2014 Genetic Assessment in Patients with a Large Aorta Difficulties in sequence data interpretation • Prediction of the effect of novel sequence variants Silent mutation c.6354C>T (p.I2118I) Deletion of 66bp (22 amino acids) c.6314_6379del (p.Glu2105_Val2126del) C>T Exon 50 Intron 50 380bp 150bp cF 400bp Exon 51 Intron 51 ...C… M 1. 2. 66bp 3. 244bp Exon 52 117bp Intron 52 2247bp Exon 53 cR 120bp a. Heteroduplex of b. + c. + 300bp b. Normal transcript (317bp) 200bp M 1. 2. 3. 100bp marker FBN1 c.6354C>T FBN1 c.6354C>T Control c. Transcript with deletion of exon 51 PD Dr. G. Matyas | www.genetikzentrum.ch | www.stiftung-seltene-krankheiten.ch (251bp) 22.05.2014 / 40 FBN1 – Schematische Darstellung DNA RNA Synthese ... ... ... ... Splicing Auswirkung intronischer (+ exonischer) ... ... Mutationen: - Exon Skipping - Cryptic/Novel Splice Site - Intron Retention Ca Ca PD Dr. G. Matyas | www.genetikzentrum.ch | www.stiftung-seltene-krankheiten.ch 22.05.2014 / 41 hnRNP = heterogeneous nuclear ribonucleoproteins snRNP = small nuclear ribonucleoproteins (contain snRNAs U1, U2, U4/6, and U5) SR = serine/arginine-rich proteins 35 = U2AF35 22.05.2014 42 22.05.2014 PD Dr. G. Matyas | www.genetikzentrum.ch | www.stiftung-seltene-krankheiten.ch Several forms of RNA are involved in gene expression. During transcription, DNA (grey rectangle) is used as a template to produce an RNA transcript (purple rectangle). The RNA is translated to build the protein molecule (polypeptide) encoded by the original gene. Both prokaryotic and eukaryotic cells contain messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA). Premessenger RNA (pre-mRNA), small nuclear RNA (snRNA), small nucleolar RNA (snoRNA), small cytoplasmic RNA (scRNA), micro RNA (miRNA), and small interfering RNA (siRNA) are found exclusively in eukaryotic cells. Nature Education: www.nature.com/scitable/topicpage/chemical-structure-of-rna-348 43 Int J Mol Sci. 2013, 14: 14374–14394. Trends Cardiovasc Med. 2011, 21:172-7. Das menschliche Erbgut (DNA) Aminosäuren http://www.nature.com/scitable/topicpage/gene-expression-14121669 In vitro (Transkript) Analyse Stille Mutation c.6354C>T (p.I2118I) C>T Exon 50 150bp cF Intron 50 380bp Exon 51 Intron 51 ...C… 66bp 244bp Exon 52 117bp PD Dr. G. Matyas | www.genetikzentrum.ch | www.stiftung-seltene-krankheiten.ch Intron 52 2247bp Exon 53 cR 120bp 22.05.2014 Die Änderung im Kodon für dieselbe Aminosäure (silent mutation) führt zu veränderter Proteintranslation 22.05.2014 PD Dr. G. Matyas | www.genetikzentrum.ch | www.stiftung-seltene-krankheiten.ch 48 Li et al. compared RNA sequences … of 27 individuals to the corresponding DNA sequences from the same individuals and uncovered … RNA sequences do not match that of the DNA. …These differences … were found in multiple individuals and in different cell types …. Using mass spectrometry, Li et al. detected peptides that are translated from the discordant RNA sequences and thus do not correspond exactly to the DNA sequences. These widespread RNA-DNA differences in the human transcriptome provide a yet unexplored aspect of genome variation. Das Projekt ENCODE (the Encyclopedia of DNA Elements) zeigt, dass das Genom aus viel mehr als nur aus Genen besteht: Die rund 20'000 proteinkodierenden Gene werden von etwa vier Millionen «molekularen Schaltern», die je nach Zelltyp gewisse Abschnitte des Erbguts an oder ausschalten, kontrolliert. Classification of Mutations by Effect on Structure 1. Genome mutations Numerical change of the whole chromosome set (e.g. triploidy (3n), tetraploidy (4n)) Numerical change of a single chromosome (e.g. trisomy 21, 18, 13) 2. Chromosomal mutations 3. Gene mutations Point mutations, deletions, insertions, inversions A>G C>T Dynamic mutations http://en.wikipedia.org/wiki/Image:Types-of-mutation.png (tandem repeats that often change size on transmission to children) Anticipation: Dynamic mutations can lead to the earlier onset of disease Size standards Das haploide Genom des Menschen besteht aus ~3*109 Basenpaaren (bp) ~20% Gene (~20‘000) ~10% kodierend (Exons) ~90% nichtkodierend (Introns) 49 CAG-Repeats 15 CAG-Repeats 23 Chromosomen (22 Autosomen, 1 Geschlechtschromosom) verschiedener Längen mit 50 Mb (Chr. 21) und bis zu 263 Mb (Chr. 1) ~80% extragenische DNA ~70% Einzelkopie-Sequenzen ~30% vielfach wiederholte (repetitive) Sequenzen ~40% verstreut liegende Wiederholungen (LINES, SINES) ~60% gehäufte Wiederholungen (Satelliten-DNA) LINE-Abschnitte (6-7kb): long interspersed repetitive elements Minisatelliten (15-200bp)n: Centromere, Subtelomere SINE-Abschnitte (100-500bp): short interspersed repetitive elements (z.B. Alu-Repeats) Mikrosatelliten (1-10bp)n: Telomere, extragenische DNA Trinukleotidwiederholung (xxx)n (R. Knippers, 2006: Molekulare Genetik) Das haploide Genom des Menschen besteht aus ~3*109 Basenpaaren (bp) ~20% Gene (~20‘000) ~80% extragenische DNA ~90% nichtkodierend (Introns) ~10% kodierend (Exons) 23 Chromosomen (22 Autosomen, 1 Geschlechtschromosom) verschiedener Längen mit 50 Mb (Chr. 21) und bis zu 263 Mb (Chr. 1) ~70% Einzelkopie-Sequenzen ~30% vielfach wiederholte (repetitive) Sequenzen ~40% verstreut liegende Wiederholungen (LINES, SINES) ~60% gehäufte Wiederholungen (Satelliten-DNA) LINE-Abschnitte (6-7kb): long interspersed repetitive elements Minisatelliten (15-200bp)n: Centromere, Subtelomere SINE-Abschnitte (100-500bp): short interspersed repetitive elements (z.B. Alu-Repeats) Mikrosatelliten (1-10bp)n: Telomere, extragenische DNA FRAXA & AD Trinukleotidexpansionskrankheiten Risiko für Vollmutation bei Nachkommen Krankheit Prämutation Vollmutation Normalbereich Anzahl (n) der Basentripletts (n) STABIL 5‘UTR Position der Basentripletts Auswirkung INSTABIL ATG (CGG)n fehlendes oder vermindertes Genprodukt infolge Hypermethylierung Krankheit Fragiles X-Syndrom Vererbung X-chromosomal (Xq27.3), jedoch weder rezessiv noch dominant! offenes Leseraster (ORF) Stop (CAG)n Verlust der Proteinaktivität Effekte auf andere Proteine Effekte der Aggregatbildung Toxizität 3‘UTR (CTG)n verminderte Proteinsynthese Polyglutaminkrankheiten: HD, DRPLA SCA 1, 2, 3, 6, 7 autosomal dominant DM 1 SCA 8 (Gusella & MacDonald, 2000, Nat Rev Neurosci 1:109-115) Frühere Manifestation von Trinukleotidexpansionskrankheiten bei zunehmender Anzahl von Tripletts Zunahme der Anzahl von Triplettwiederholungen bei aufeinanderfolgenden Generationen + Frühere Manifestation von Trinukleotidexpansionskrankheiten bei zunehmender Anzahl von Tripletts Antizipation: zunehmender Schweregrad oder frühere Manifestation einer genetisch bedingten Krankheit bei aufeinanderfolgenden Generationen http://www.nature.com/scitable/topicpage/genetic-mutation-441 Types of DNA Mutations and Their Impact Classification of Disorders 1. Monogenic disorders Heteroplasmy: a mixture of mutant and wild-type mtDNA Inheritance recessive maternal dominant Penetrance: full penetrance, reduced penetrance Expressivity: describes quantitative differences in the manifestation of the disease Imprinting: genetic information can be manifested in a different way when it is inherited from the mother than when it is inherited from the father Classification of Disorders 1. Monogenic disorders Heteroplasmy: a mixture of mutant and wild-type mtDNA Inheritance Beschreibung eines Erbgangs recessive maternal dominant 1. Anzahl involvierter Loci (Gene): monogen (ein Locus), oligogen (wenige Loci), polygen (viele Loci) 2. Betroffene Chromosomen: autosomal – Loci liegen nicht auf den Geschlechtschromosomen gonosomal – Loci liegen auf einem Geschlechtschromosom (X-chromosomal, Y-chromosomal) mitochondrial – Loci liegen auf der mitochondrialen DNA 3. Zusammenhang Genotyp – Phänotyp: dominant, rezessiv, kodominant, intermediär Vererbung Vererbung Vererbung oft letal Vererbung Classification of Disorders 2. Chromosomal disorders • Not due to single defect • Usually due to deficiency in number of genes within chromosome • Phenotypically obvious, usually incompatible with life • Classic example: Down syndrome (Trisomy 21) • • Incidence (per newborn) Trisomy 21 Trisomy 18 Trisomy 13 45,X0 47 XXY, (XYY, XXX) 1:700-800 1:3500 1:6000 1:3000 1:1500 Incidence Trisomy 21 depending on maternal age 20 J. 1: 1500 35 J. 1: 380 40 J. 1: 110 Classification of Disorders 3. Complex (multifactorial, polygenic) disorders • Multiple single code defects • Usually form a pattern • Modifying or synergetic effect of other loci • Influence of environment • Example: cleft lip/palate, neural tube defects, Alzheimer disease Veränderung der DNA Erfassung (Gentest) Beschreibung (Nomenklatur) Bedeutung (Interpretation) ASA/SVV Fortbildungsreihe Genetik 2014 – Module 2 Erfassung, Beschreibung und Bedeutung von Sequenzvarianten sowie Umgang mit Datenbanken Olten, 28. August 2014
