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  • 8/12/2019 0130 Explanation Slides Classification of Genetic Disorders (1)

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    2009 NHS National Genetics Education and Development Centre Genetics and Genomics for Healthcarewww.geneticseducation.nhs.uk

    Classification of Genetic Disorders

    This PowerPoint file contains a number of slides that may be useful forteaching of genetics concepts.

    You may use these slides and their contents for non-commercial

    educational purposes.

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    2009 NHS National Genetics Education and Development Centre Genetics and Genomics for Healthcarewww.geneticseducation.nhs.uk

    Fig. 13.3Scion Publishing Ltd

    Etiology of diseases.For any condition the overall balance of genetic and environmental determinants can be represented by a pointsomewhere within the triangle.

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    2009 NHS National Genetics Education and Development Centre Genetics and Genomics for Healthcarewww.geneticseducation.nhs.uk

    Classification of genetic disorders

    Multifactorial

    Single gene

    Chromosomal

    Mitochondrial

    Somatic mutations (cancer)

    Male

    + environment

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    2009 NHS National Genetics Education and Development Centre Genetics and Genomics for Healthcarewww.geneticseducation.nhs.uk

    Fig. 1.15Scion Publishing Ltd

    Continuum of penetrance.

    There is a continuum of penetrance from fully penetrant conditions, where other genes and environmentalfactors have no effect, through to low-penetrance genes that simply play a small part, along with other geneticand environmental factors, in determining a persons susceptibility to a disease.

    Multiple sclerosis is used as an example of a multifactorial condition where genetic factors play a major part indetermining susceptibility, but current research suggests that each individual factor has a very low penetrance.

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    2009 NHS National Genetics Education and Development Centre Genetics and Genomics for Healthcarewww.geneticseducation.nhs.uk

    Genetic factors

    Male

    Mutations in singlegenes (often causing loss

    of function)

    Variants in genes causingalterationof function

    Chromosomal imbalancecauses alteration ingene

    dosage

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    2009 NHS National Genetics Education and Development Centre Genetics and Genomics for Healthcarewww.geneticseducation.nhs.uk

    Classification of genetic disorders

    Male

    Mutations in single genes

    Variants in genes

    Chromosomal imbalance

    Single Gene Disorders

    Multifactorial diseases

    Chromosome disorders

    + environment

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    2009 NHS National Genetics Education and Development Centre Genetics and Genomics for Healthcarewww.geneticseducation.nhs.uk

    Recessive

    Homozygotes with two copiesof the altered gene areaffected

    Dominant

    Heterozygotes with one copyof the altered geneare affected

    X-linked recessive

    Males with one copyof the altered gene on theX-chromosome are affected

    Male

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    2009 NHS National Genetics Education and Development Centre Genetics and Genomics for Healthcarewww.geneticseducation.nhs.uk

    Genetic disorders Multifactorial (common)

    - Environmental influences act on a genetic predisposition to produce a liability toa disease.

    - One organ system affected.

    - Person affected if liability above a threshold.

    Single gene (1% liveborn)-Dominant/recessive pedigree patterns (Mendelian inheritance).- Can affect structural proteins, enzymes, receptors, transcription factors.

    Chromosomal (0.6% liveborn)

    - Thousands of genes may be involved.- Multiple organ systems affected at multiple stages in gestation.- Usually de novo (trisomies, deletions, duplications) but can be inherited(translocations).

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    2009 NHS National Genetics Education and Development Centre Genetics and Genomics for Healthcarewww.geneticseducation.nhs.uk

    GENETIC ENVIRONMENTAL

    Duchennemuscular dystrophy

    HaemophiliaOsteogenesis imperfecta

    Club footPyloric stenosisDislocation of hip

    Peptic ulcerDiabetes

    Tuberculosis

    Phenylketonuria

    Galactosaemia

    Spina bifidaIschaemic heart disease

    Ankylosing spondylitis

    Scurvy

    The contributions of genetic and environmentalfactors to human diseases

    RareGenetics simple

    UnifactorialHigh recurrence rate

    CommonGenetics complexMultifactorialLow recurrence rate

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    2009 NHS National Genetics Education and Development Centre Genetics and Genomics for Healthcarewww.geneticseducation.nhs.uk

    Multifactorial

    Environmental influences act on a genetic predispositionOne organ system affected

    Single geneDominant/recessive pedigree patternsStructural proteins, enzymes, receptors, transcription factors

    ChromosomalMultiple organ systems affectedInherited or de novo

    EnvironmentalDrugs, infections

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    2009 NHS National Genetics Education and Development Centre Genetics and Genomics for Healthcarewww.geneticseducation.nhs.uk

    Single gene disorders

    - High risks to relatives

    - Dominant/recessive pedigree patterns

    - Some isolated cases due to new dominant mutations

    - Structural proteins, enzymes, receptors, transcription factors

    I:1AA

    I:2AB

    II:1AA

    II:2AB

    II:3BB

    ?

    III:1BB

    Tom

    I:2I:1 I:3

    II:1 II:2 II:3 II:4 II:5 II:6 II:7 II:8 II:9 II:10 II:11 II:12 II:13 II:14 II:15

    III:1 III:2 III:3

    IV:1 IV:2 IV:3 IV:4

    III:4 III:5

    IV:5 IV:6 IV:7

    III:6 III:7

    IV:8 IV:9 IV:10

    III:8 III:9 III:10 III:11 III:12 III:14III:13 III:15 III:16 III:17

    IV:11 IV:12 IV:13

    I:1 I:2

    II:1 II:2 II:3 II:5 II:6 II:8

    III:1 III:2

    IV:1