医学遗传学课件：Principles of Molecular Disease

PrinciplesofMolecularDisease

Gene

Thebasichereditaryunit,aDNAsequence

requiredforproductionofafunctionalproduct,usuallyaprotein,butrarely,anuntranslatedRNA.

Genemutation

Achange

inbasessequenceororganizationof

DNA,usuallyconferringadeleteriouseffect.

BasesubstitutionPointmutationCodonmutation

StaticmutationFrame-shiftMutationmutationFragmentmutationDynamicmutation

Pointmutation

AchangeinoneorfewbasesofDNA,includingbasesubstitution,Codonmutationandframe-shiftmutation.

samesensemutation(silent)

non-sensemutation

1.Basesubstitution

missensemutation

terminatorcodonmutation

2.

Codonmutation

3.Frame-shiftmutation

deletion

insertion

Fragmentmutation

inversion

duplication

fusiongeneDynamicmutation

Unstabletrinucleotiderepeatamplification,E.g.FragileXsyndrome(CGG)>200,Huntington’sDisease(CAG)>35.

harmfulness

Consequenceofgenemutation

neutrality

advantage

Theeffectofmutationonproteinfunction

Disease-causingmutation

1.loss-of-FunctionMutationα-thalassemiapku

2.Gain-of-FunctionMutation

EnhanceoneNormalFunctionofaprotein

hemoglobinKempsey

IncreaseproductionofaNormalproteintrisomy21

3.NovelpropertyMutation

sicklecelldisease

4.MutationAssociatedwithHeterochronicorEctopicGeneExpression

r-globingene→adult

oncogene→cancer

Moleculardisease

Thediseasesiscausedbygenemutationwhichleadtoproteinvariants.

HemoglobinsandHemoglobinopathies

WHO:world’spopulation

>5%carriersofgenesforclinicallyimportantdisordersofhemoglobin

HumanHemoglobinsandTheGenesHumanHemoglobins

twoαchains.141aa（ζ）

FourSubunits

twoβchains.146aa（ε.γ.δ）

Eachsubunits:aglobinchainandaheme.

HemoglobinGenesGenecluster

1.αandα-likegenescluster5’→ζ→Ψζ→Ψα1→α2→α1→3

’

16p13.1－p13.3,2n→4α

1313299100141

1

2

1

5‘3’16pter-p13.32.βandβ-likegenescluster

5’→ε→Gγ→Aγ→Ψβ→δ→β→3’

11p15.5,2n→2β

11p15.513031104105146

εG

A

ψ

δβ5’3’

Pseudogene

Thegenesaresimilartothenormalgene,butwithoutnormalgenefunction.

e.gΨζ,Ψα,ΨβDevelopmentalExpressionofGlobingene

Transcription→modification→Translation→modification→Assembly

1.tissuepropertyRegulation2.timeproperty3.amounts(Dosage)balance

1.Structuralvariants(Abnormalhemoglobin)>800

Hemoglobinopathies

2.Thalassemias(amountsimbalance)>400

3.Hereditarypersistenceoffetalhemoglobin

Abnormalhemoglobin

Sicklecellanemia(OMIM#603903)

Sicklecellhemoglobin(HbS)

1949PaulingThefirstabnormalhemoglobintobedetected

Itisduetoasinglenucleotidesubstitutionthatchangesthecodonofthesixthaminoacidofβglobinfromglutamicacidtovaline

(GAGGTG:Glu6val).

SicklecellanemiaClinicalfeatures

HbSHbS:Homozygotes→sicklecellAnemia.HbAHbS:Heterozygotes→sicklecelltraitinlowoxygenpressureIncidence

About1in600AfricanAmericansGeographicdistribution

MostfrequentlyinequatorialAfricaWorldwide

GeographicdistributionGenetics

Autosomalrecessive(AR),genelocation11P15.5Basicdefect

βgene

β6GAG→GTG

βmRNA

β6GAG→GUG

βglobin

β6glu→Val

HbS(α2β6Val2)(α2βs2)

Pathology

The

mutation(GAGGTG:Glu6val)

inβglobindecreasesthesolubilityofdeoxygenatedhemoglobinandcauseittoformagelatinousnetworkoffibrouspolymers.Thus,erythrocytesbecomefirmanddeformintosickle-shapedcells.

Sicklecellsareunabletopassthroughsmallarteriesandcapillaries.Thesebecome

clogged

andcauselocaloxygendeficiency

inthetissues.

Defectiveerythrocytesaredestroyed(hemolysis).Chronicanemiaanditsnumeroussequelaesuchasheartfailure,liverdamage,andinfectionaretheresult.

sicklecellsnormalcells粘滞性僵硬Prenataldiagnosis

possiblewithDNAtechniques.

Treatment

MolecularBasisofAbnormalhemoglobin

1.Missensemutation:

HbS（β6glu→val)

2.Non-sensemutation:

HbMckees-Rock

(β145UAU→UAA)

3.Terminationcodonmutation:

Hbconstantspring

（α142UAA→CAA）

4.Frame-shiftmutation:

Hbwayne

（α138UCC↑）

5.Codonmutation:

HbGumHiu

(β91-95↑)

6.Fusiongene:

Hblepore

（δβ）

Hbanti-lepore（βδ）

Thalassemia

AnImbalanceofGlobin-Chainsynthesis

Themutationsreducethesynthesisorstabilityofeithertheα-orβ-globinchain,tocauseα-orβ-thalassemia,respectively.

Theimbalanceintheratioofα:βchain→theexcessnormalchainsprecipitateinthecell→damagingthemembraneandleadingtoredbloodcelldestruction→anemia

FirstdiscoveredinpersonofMediterraneanorigin

Widedistributeintheworld

MediterraneanMiddleEastPortsofAfricaIndiaandAsiaDistributeintheworld

Alpha-Thalassemias

αgenemutationordeletion,β-globinisinrelativeexcess

α0(α1)Thalassemias

genotype(――)twoα-geneinsame16chromosomearedeletion

α＋(α2)Thalassemias

genotype(－α)oneα-geneinone16chromosomeisdeletion

DeletionsoftheAlpha-Globingenes

1.HbBart’s

――/――，Υ4（HbBart’s）hydropsfetalis

2.HbH

――/－α，ααT/――orααCS/――

α↓,β↑→β4(HbH)precipitation

moderatelyseverehemolyticanemia

3.Alpha-thalassemiatrait

――/ααor－α/－α

mildanemia

4.Silentcarrier

―α/αα

Themolecularmechanismofα-thalassemia

1.DeletionForms

Homologouschromosomemistakepairingandunequal

crossover

Mostcommonform

2.NondeletionForms

α-gene

mutation

less

Beta-Thalassemias

βgenemutationordeletion,α-globinisinrelativeexcess

β0–thalassemiaβ-genemutationordeletion,noβ-globin

β＋

-thalassemiaβ-genevariants,Someβ-globin

1.β-thalassemiamajor

Mostpatientswithoutnormalβ-thalassemiaalleles.

Severeanemia

needforlifelongmedicalmanagement.

β0/β0、β0/β＋、β0/δβ0、δβ0/δβ0

2.β-thalassemiaminor

patientshavehypochromic,microcyticredbloodcell,slightanemia

β＋/βA、β0/βAorδβ0/δβA，

HbA2（α2δ2）↑orHbF（α2γ2）↑

3.Hereditarypersistenceoffetalhemoglobin

highlevelthepersistenceofr-globingeneexpressionthroughoutadultlife

δ.β↓,r↑→HbF（α2γ2）

TheMolecularBasisofBeta-thalassemia

1.Nondeletion

β-genemutation

most

commonform

2.Deletion

Homologousmistakeparingandunequalcrossover

less

Mutationsite:

1.Codingsequencesinβ-gene→β02.5’-regulationsequencesinβ­gene→β0orβ＋

3.splicejunctionsequencesinβ-gene→β04.5’-cappingsequencesinβ-gene→β＋

5.3’-tailingsequencesinβ-gene→β＋

Master:

GeneandGenemutationMoleculardiseaseHemoglobinopathiesAbnormalhemoglobin,SicklecellanemiaMolecularBasisofAbnormalhemoglobinThalassemiaAlpha-Thalassemias,Beta-Thalassemias

Understand:ConsequenceofgenemutationTheeffectofmutationonproteinfunctionHumanHemoglobinsandTheirGenesThemolecularmechanismofα-thalassemiaThemolecularmechanismofβ-thalassemia

TheMolecularandBiochemicalBasisofGeneticDiseases

TaoZhangDepartmentofMedicalGeneticsHealthScienceCenterPekingUniversity

EnzymedefectsandDiseases

Hereditaryenzymopathy(Enzymopathy)

Theinbornerrorsofmetabolismiscausedby

genemutationwhichleadtoenzymeproteinvariants200+(AR)

metabolismS1E12S2E23S3E3PPS4S5

Gene G1 G2

G3

(mutation)

Enzyme EAB EBC

ECD（defect）

MetabolismA B C∥DPathologyerrorsofmetabolism

ThemechanismofHereditaryenzymopathy.

1.Productdeficience

Albinism

A→B→C∥D↓

PAHTyrosinaseMelaninDopaPheTyr

×2.Substrateaccumulation

Glycogenstoragedisease

A↑BC

∥D↓

3.Middleproductaccumulation

Galactosemia

AB↑C↑∥D↓4.Sideproductaccumulation

Phenylketonuria(PKU)

A→B→C∥DE↑→F↑5.Productincrease

GoutA→B→C→D↑6.Lossofnormalfeedbackinhibition

Lesch-nyhansyndrome

ABCD↓E∥㈠

Phenylketonuria(PKU)

PKU(OMIM#261600)

Animportantcauseofmentalretardation,PKUiscausedbydefectivefunctionofthe

phenylalaninehydroxylase(PAH)gene.Clinicalfeatures

1.

Mentalretardation2.“Mousy”odorinurine3.Seizuredisorder4.Hypopigmentationofskinandhair

PKUIncidence

1in16000inpopulationGenetics

Autosomalrecessive(AR),genelocation12q24,13exons,12introns,90kb,mRNA2.4kbAllelicHeterogeneity>400LocusHeterogeneitycofactBH4Basicdefect

Mutationinthegene,phenylalaninehydroxylase,whichconvertsphenylalaninetotyrosine

Phenylketonuria(PKU)

HypopigmentationofskinandhairPAHPhenyllacticacidBenzophenoneTyrosinaseMelaninDopaPheProteinTyr

ProteinPhenylpyruvicacidPhenylaceticacidMentalretardation“Mousy”odorinurine(－)(－)(－)∥↑↑↑BH4Autosomalrecessive(AR)PathologyThederivativesof

Phenylalaninedamagethedevelopingbrain,tocausethe“Mousy”odorinurineandHypopigmentationofskinandhairPrenataldiagnosis

PossiblewithDNAtechniquesTreatment

Dietaryreductionofphenylalanine

Pharmacogenetics

Thespecialareaofbiochemicalgenetics

thatdealswiththevariabilityinresponsetodrugsthatisduetogeneticvariation.Drugresponse:

absorb,transport,metabolize,reaction,excretedrugs.

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