Harvy Mauricio Velasco PGenética Humana

UNAL

1* 1015 células adultas17 2*1017 divisiones

celularesó6 *109 nucleótidos

para cada división l lcelular

1*10 -6 -8 Eficiencia de l DNA li la DNA polimerasa

Proliferación, Noxas externasDivisión yapoptosis

Noxas externas

Oncogenes y Genes

Reparación delDNA

supresores

UN GEN SE UN GEN SE ENCUENTRA ENCUENTRA AFECTADO

GENERADAS POR LA EVOLUCION

ERRORES EN LA REPLICACION

DNA POLIMERASANOVEDADADAPTACION

DNA POLIMERASA

TAMAÑO DE DNA3 000 MILLONES DE pb

ENFERMEDADMUERTE

3.000 MILLONES DE pb

AGRESION DIRECTA A DNADEGRADACION INTERNA DEGRADACION INTERNA DE NUCLEOTIDOS

MUTACIONMUTACIONCualquier cambio en el material genético(DNA

POLIMORFISMOV i ió étimaterial genético(DNA

nuclear y mitocondrial), que se herede a las

Variación genética que tiene más de

i tgeneraciones siguientes. una variante alélica en una

i DNAsecuencia DNAFrecuencia >1%

MUTACIONES GERMINALES

MUTACIONES SOMATICASM t ió GERMINALES

El cambio en el DNA se da lí t l

Mutación que no compromete líneas germinalesen línea parental en

celulas germinales y esta mutación se HEREDA

germinalesEn un tejido especifico

mutación se HEREDA

GERMINALES SOMATICAS

INDUCIDAS POR ELAMBIENTE O

EN EL LABORATORIOESPONTANEAS

A GRAN ESCALA O MUTACIONES

A PEQUEÑA ESCALA O CITOGENETICAMENTE MUTACIONES

CITOGENETICAMENTE VISIBLES

CITOGENETICAMENTE INVISIBLES

VISIBLES

EXISTE ALTERACION DE ALGUNOS DE LOS COMPONENTES DEL MATERIAL GENETICO O EN EL FLUJO DE INFORMACION DEL DNA HACIA EL FLUJO DE INFORMACION DEL DNA HACIA PROTEINAS

ERROR EN LA EXPRESION DE LA INFORMACION GENETICAGENETICA

TIPO DEFINICIONSUSTITUCION Reemplazo de una(s) base(s)SUSTITUCION Reemplazo de una(s) base(s)

por otra(s)

DELECION P did li i ió dDELECION Perdida o eliminación de uno o más nucleótidos

INSERCION Uno o más nucleótidos están adicionados en una secuencia

–Transposición con duplicaciónde material genético–Transposición sin duplicación(translocación)

MUTACIONES

Sustitución de Inserciones Delecionesbases

Transiciones Transversiones

1 o pocos nucleótidos

1 o pocos nucleótidos

Sustitución i ó i ( t )

Expansión de i l

Grandes delecionessinónima (neutra)

y no sinónimatripletas deleciones

Conversión génica, múltiple sustitución de

Otras grandes inserciones: elementos

ibl

En el marco de lectura

bases transponibles

Transiciones: Pirimidina por

Transversiones:Purina por pirimidina o p

pirimidina (C-T)Más comunes (ISLAS

p pviceversa

(CpG)

Purina por purina (A-G)G)

A C

G TG T

SINÓNIMAS (SILENCIOSAS): Ó(SILENCIOSAS):NeutralNo cambia secuencia

NO SINÓNIMASAltera secuenciaNo cambia secuencia

a.a.En DNA no codificante

á ú

TIPOSDeletéreasSin efectoMás común en DNA

codificante En DNA codificante

Sin efecto Efecto benéfico

En DNA codificante cambia el A.A. en posición 3 de codón

Mayor frecuencia Transversiones que transicionesMayor frecuencia en secuencias no codificantesCualquier secuencia puede ptener sustituciones No

sinónimas

Sinonimias

Sinónimas

Algunas sustituciones en secuencias no codificantes afectan la expresión

SUST

MUTAC

ON

enerac

ón

de

ás

ca

de

a

MUTAC

ON

erac

ón

de

o

CONS

p

azado

qu

m

NO

CON

qu

m

camen

eSUSTITUCIONES

TUC

ONES

NES

NONSESE

codon

de

pa

func

ón

o

e

ES

M

SSENSE

ro

A

A

d

f

EVAT

VA

camen

e

s

m

SERVAT

VA

a

emp

azaarada

expres

ón

gén

feren

e

a

3

a

pos

ado

a

y

2dan

ca

c

ón

codon

pos

c

ón

coddon

Gene No. of codons Nonsynonymous Synonymous

Histone H3 135 0.00 6.38

Histone H4 101 0 00 6 12Histone H4 101 0.00 6.12

Actin α 376 0.01 3.68

Aldolase A 363 0.07 3.59

HPRT 217 0.13 2.13

Insulin 51 0.13 4.02

α-Globin 141 0.55 5.14

β-Globin 144 0.80 3.05

Albumin 590 0.91 6.63

Ig VH 100 1.07 5.66

Growth hormone 189 1.23 4.95

Ig κ 106 1.87 5.66

Interferon-β1 159 2.21 5.88

Interferon-γ 136 2.79 8.59

•MUTACIONES QUE GENERAN GANANCIA O PERDIDA DE MATERIAL GENETICO•DNA CODIFICANTE Y NO CODIFICANTE•INVOLUCRA GENERALMENTE

•“REPETICIONES CORTAS EN TANDEM”• FENOMENOS DE RECOMBINACION

Short Tandem Repeats (STRs)AATGAATG

7 repeats

8 repeats

Homologous equal crossover Homologous equal crossover can result in fusion genes.The example shows how intragenic equal crossover occurring between alleles on occurring between alleles on nonsister chromatids can generate novel fusion genes composed of adjacent

t f th t segments from the two alleles. Note that similar exchanges between genes on sister chromatids do not

l i i l result in genetic novelty because the gene sequences on the interacting sister chromatids would be expected to be identical.

Unequal crossover and unequal Unequal crossover and unequal sister chromatid exchange cause insertions and deletions. The examples illustrate unequal pairing of chromatids within a tandemly

d U l repeated array. Unequal crossover involves unequal pairing of nonsister chromatids followed by chromatid breakage and rejoining. Unequal sister chromatid exchange Unequal sister chromatid exchange involves unequal pairing of sister chromatids followed by chromatidbreakage and rejoining. For the sake of simplicity, the breakages of the chromatids are shown to occur the chromatids are shown to occur between repeats, but of course breaks can occur within repeats. Note that both types of exchange are reciprocal - one of the

ti i ti h tid l participating chromatids loses some DNA, while the other gains some.

Unequal crossover in a tandem repeat Unequal crossover in a tandem repeat array can result in sequence homogenization. Note that the initial spread of the novel sequence variant to the same position in the chromosomes of other members of a sexual population p pcan result by random genetic drift. Once the mutation has achieved a reasonable population frequency (left panel) it can spread to other positions within the array (right panel). This can occur by successive gain of mutant repeats as a successive gain of mutant repeats as a result of unequal crossover (or unequal sister chromatid exchanges) and occasional loss of normal repeats. Eventually the mutant repeat can replace the original repeat sequence at replace the original repeat sequence at all positions within the array, leading to sequence homogenization for the mutant repeat. Such sequence homogenization is thought to result in species-specific concerted evolution for repetitive DNA

UEC l sequences. UEC, unequal crossover.

Tandem gene duplication Tandem gene duplication can result from unequal crossover or unequal sister chromatid exchange, facilitated by short facilitated by short interspersed repeats. The double arrow indicates the extent of the tandem gene d li ti f t duplication of a segment containing gene A and flanking sequences. Original mispairing of chromatids

ld b f ili d b hi h could be facilitated by a high degree of sequence homology between nonallelic short repeats (R1, R2). Note that p ( 1, 2)the same mechanism can result in large-scale deletions.

Gene conversion involves a nonreciprocalGene conversion involves a nonreciprocalsequence exchange between allelic ornonallelic genes. (A) Interallelic geneconversion. Note the nonreciprocal natureof the sequence exchange - the donorsequence is not altered but the acceptorq psequence is altered by incorporatingsequence copied from the donor sequence.(B) Interlocus gene conversion. This isfacilitated by a high degree of sequencehomology between nonallelic sequences, asin the case of tandem repeats (C) Mismatchin the case of tandem repeats. (C) Mismatchrepair of a heteroduplex. This is one ofseveral possible models to explain geneconversion. The model envisages invasion byone strand of the donor sequence (-) to forma heteroduplex with the complementary (+)a heteroduplex with the complementary ( )strand of the acceptor sequence, therebydisplacing the other strand of the acceptor.Mismatch repair enzymes recognize themispaired bases in the heteroduplex and‘correct' the mismatches so that the (+)

i ‘ d' bacceptor sequence is ‘converted' to beperfectly complementary in sequence to the(-) donor strand. Subsequent replication ofthe (-) acceptor strand and sealing of nicksresults in completion of the conversion.

LUGARES DE DNA

CARACTERISTICA

SECUENCIAS CODIFICANTES DEL GEN

•La mayoría patológicas (sustituciones) (1ra y 2da posicíón)GEN (sustituciones) (1ra y 2da posicíón)•Sitios mas susceptibles : islas CpGcerca a hotspotscerca a hotspots

SECUENCIAS INTRAGENIAS NO •Menor porcentaje mutacional

(10 15%)CODIFICANTES (10-15%)•Afecta regiones intronicas

SECUENCIAS REGULADORAS FUERA DE EXONES

•En las regiones promotoras de los genes (antes del Exon 1)g ( )•Alteración en la metilación

Mutations at conserved splice donor (SD) Mutations at conserved splice donor (SD) or splice acceptor (SA) sequences (see Figure 1.15 for consensus sequences) result in (A) intron retention where there is failure of splicing and an intervening intron sequence is not g qexcised; or in exon skipping where the spliceosome brings together the splice donor and splice acceptor sites of non-neighbouring exons. (B) Sequences that are very similar to the consensus splice donor or splice acceptor sequences may donor or splice acceptor sequences may coincidentally exist in introns and exons(sd and sa). These sequences are not normally used in splicing and so are known as cryptic splice sites. A mutation can activate a cryptic splice site by can activate a cryptic splice site by making the sequence more like the consensus splice donor or acceptor sequence and the cryptic splice site can now be recognized and used by the spliceosome (activation of the cryptic

li i ) S Fi 9 12 d 9 13splice site). See Figures 9.12 and 9.13for examples of activation of an exonicand an intronic cryptic splice site, respectively

GANANCIA DE INTRON

PERDIDA DE EXONDE EXON

GENERACION DE INSERCIONES O DELECIONES EN EL DNA PRODUCIENDO MUTACIONES TIPO “FRAMESHIFT”

Location and nature of mutation Effect on gene function CommentsExtragenic mutation Normally none Rare mutations may result in inactivation of distant regulatory elements required for normal

gene expression (see Figure 8.23)

Multigene deletion Abolition Associated with contiguous gene syndromes (see Figure 16.9)

Whole gene deletion AbolitionWhole gene duplication Can have effect due to altered gene

dosageLarge duplications including the peripheral myelin protein 22 gene can cause Charcot-Marie-Tooth syndrome (see Figure 16.7)

Whole exon deletion Abolition or modification May cause shift in reading frame; protein often unstable

Within exon Abolition If loss/change of key amino acids, shift of the reading frame or introduction of premature stopcodon

Modification If nonconservative substitutions, small in-frame insertions or other mutations at somelocations

None If conservative/silent substitutions or mutation at nonessential sites

Whole intron deletion NoneSplice site mutation Abolition or modulation of expression Conserved GT and AG signals are critically important for normal gene expression. Mutations

i d ki i i t t timay induce exon skipping or intron retention

Promoter mutation Abolition or modulation of expression Deletion, insertion or substitution of nucleotides within promoter may alter expression.Complete deletion abolishes function

Mutation of termination codon Modification Additional amino acids are included at the end of the protein until another stop codon isreached

Mutation of poly(A) signal Abolition or modulation of expression Deletion, insertion or substitution of nucleotides within poly(A) site may alter expression.Complete deletion abolishes functionComplete deletion abolishes function

Elsewhere in introns/UTS Usually none

Change Example

Delete:

(i) the entire gene Most α thalassemia mutations(i) the entire gene Most α‐thalassemia mutations 

(ii) part of the gene 60% of Duchenne muscular dystrophy 

Insert a sequence into the gene Insertion of LINE‐1 repetitive sequence  into F8C gene in hemophilia A

Disrupt the gene structure:

(i) by a translocation X‐autosome translocations in women with Duchennemuscular dystrophy 

(ii) by an inversion Inversion in F8C gene(ii) by an inversion Inversion in F8C gene 

Prevent the promoter working:

(i) by mutation β‐Globin ‐29A → G mutation 

(ii) by methylation Fragile‐X full mutation (FMR1) 

Destabilize the mRNA:

(i) by a polyadenylation site mutation α‐globin AATAAA → AATAGA mutation

(ii) by nonsense‐mediated RNA decay Fibrillin mutations (FBN1)

Prevent correct splicing :Prevent correct splicing :

(i) by inactivating donor splice site PAX3 451 + 1G → T mutation 

(ii) by inactivating acceptor splice site PAX3 452‐2A → G mutation 

(iii) by activating a cryptic splice site β‐Globin intron 1 ‐110G → A mutation 

Introduce a frameshift in translation PAX3 874–875insG mutation

Convert a codon into a stop codon PAX3 Q254X mutation

Replace an essential aminoacid PAX3 R271C mutation

Prevent post‐transcriptional processing Cleavage‐resistant collagen N‐terminal propeptide inPrevent post transcriptional processing Cleavage resistant collagen N terminal propeptide in Ehlers Danlos VII syndrome

Prevent correct cellular localization of product F508del mutation in cystic fibrosis

NOMENCLATURA EFECTO EN EL ALELO

ALELO NULO El alelo no genera prod ctoALELO NULO El alelo no genera producto proteico

A. HIPOMORFO Genera una reducida cantidad del producto

A.HIPERMORFO Genera una excesiva cantidad del producto p

A. NEOMORFO Genera un nuevo producto

A ANTIMORFO G d tA. ANTIMORFO Genera un producto que antagoniza la actividad o f ió d d tfunción de un producto normal

óSustitución a.a.R117H: arginina por hi tidi 117 (A 117

Deleciones –i ihistidina en 117 (Arg117

His) G542X: glicina por Stop

insercionesDelta - F508 o ∆F508

G542X: glicina por Stop (Gly Stop) Sustitución nucleótidos

nt6232(del5) o nt6232(del ACCTG) Sustitución nucleótidos

1162(G>A) 621(G>T)

( )nt409(insC)

( )

IVS4+1G>T :Cambio de G por T en la primera base del intron44

409-410insC :I ió d C l l id 409 410Inserción de C entre los nucleotidos 409 y 410

PERDIDA DE FUNCION

Enfermedades A.R.

HaploinsuficienciaA.D.

Efecto dominante negativo A.D. Toxicidad celularA.R.

< 50% de la actividad

A.D. negativo A.D.

Expansión de tripletas actividad

enzimaticatripletas

(GRANDES)

GANANCIA DE FUNCION

Proteínas hiperfuncionantes o

autoestimuladas

Proteínas neoformadas

Enfermedades A.D.

Repetición de tripletas con presencia de

proteínas con poli glutamina (MEDIANA)

ABL -BCL

Loss of function mutations in the PAX3 gene. The 10 exons of the gene are shown as boxes, with the connecting intronsnot to scale. The shaded areas show the sequences encoding the two DNA-binding domains of the PAX3 protein. Note that mutations that completely destroy the structure of the PAX3 protein (drawn above the gene diagram) are scattered that mutations that completely destroy the structure of the PAX3 protein (drawn above the gene diagram) are scattered over at least the first six exons of the gene, but missense mutations (shown below the gene diagram) are concentrated in two regions, the 5′ part of the paired domain and the third helix of the homeodomain. A196T is believed to affect splicing. The 874–875insG mutation introduces a seventh G into a run of six Gs; it has arisen independently several times and illustrates the relatively high frequency of slipped-strand mispairing

HPRT activity (% of normal) Phenotype>60 Normal8–60 Neurologically normal; hyperuricemia (gout)1.6–8 Neurological problem (choreoathetosis)1 4 1 6 h h d ( h h i lf1.4–1.6 Lesch-Nyhan syndrome (choreoathetosis, self-

mutilation) but intelligence normal<1.4 Classical Lesch-Nyhan syndrome (MIM 308000;y y ( ;

choreoathetosis, self-mutilation and mentalretardation)

DELECIONES E INSERCIONES CON

α GLOBINA (α talasemia) DELECION

FORMACON DE FRAMESHIFT

talase a) C ONFACTOR 8 (Hemofilia A) INSERCION

SUSTITUCIONES TIPO NONSENSE

INSERCIONDISTOFINA (Distrofia de Duchenne) MUTACIONES CON

ALTERACION EN EL

Duchenne) FRAMESHIFTPAX 3 (S W d b ) SPLICING PAX 3 (S. Waardenburg) I,D,S,Splic

Condition MIM no. Gene

Alagille syndrome

118450 JAG1

Multiple exostoses

133700 EXT1

Tomaculous 162500 PMP22Tomaculous neuropathy

162500 PMP22

Supravalvular aortic stenosis

185500 ELN

Tricho-rhino-phalangeal syndrome

190350 TRPS1

Waardenburg syndrome Type 1

193500 PAX3

Malfunction Gene Disease MIM no.

Overexpression PMP22 Charcot-Marie-Tooth 118200pdisease

Receptor permanently ‘on'

GNAS1 McCune-Albright disease

174800on disease

Acquire new substrate PI (Pittsburgh allele) α1-Antitrypsin deficiency

107400

Ion channel inappropriately open

SCN4A Paramyotonia congenita

168300

Structurally abnormal multimers

COL2A1 Osteogenesis imperfecta

Various

Protein aggregation HD Huntington disease 143100

Chimeric gene BCR-ABL Chronic myeloid 151410leukemia

Tumor Rearrangement Chimeric gene Nature of chimeric product

CML t(9;22)(q34;q11) BCR-ABL Tyrosine kinase

Ewing sarcoma t(11;22)(q24;q12) EWS-FLI1 Transcription factor

Ewing sarcoma (variant)

t(21;22)(q22;q12) EWS-ERG Transcription factor( )Malignant melanoma of soft parts

t(12;22)(q13;q12) EWS-ATF1 Transcription factor

Desmoplastic small round cell tumor

t(11;22)(p13;q12) EWS-WT1 Transcription factor

Liposarcoma t(12;16)(q13;p11) FUS-CHOP Transcription factor

AML t(16;21)(p11;q22) FUS-ERG Transcription factor

Papillary thyroid carcinoma

inv(1)(q21;q31) NTRK1-TPM3(TRKoncogene)

Tyrosine kinasecarcinoma oncogene)

Pre-B cell ALL t(1;19)(q23;p13.3) E2A-PBX1 Transcription factor

ALL t(X;11)(q13;q23) MLL-AFX1 Transcription factor

ALL T(4;11)(q21;q23) MLL-AF4 Transcription factor

ALL t(9;11)(q21;q23) MLL-AF9 Transcription factor

ALL t(11;19)(q23;p13) MLL-ENL Transcription factor

Acute promyelocytic leukemia

t(15;17)(q22;q12) PML-RARA Transcriptionfactor+retinoic acidleukemia factor+retinoic acidreceptor

Alveolar rhabdomyosarcoma

t(2;13)(q35;q14) PAX3-FKHR Transcription factor

Rearreglos cromosómicos con producción de genes quiméricos

Gene Location Diseases Symbol MIM no.PAX3 2q35 Waardenburg syndrome type 1 WS1 193500

Alveolar rhabdomyosarcoma RMS2 268220

CFTR 7p31.2 Cystic fibrosis CF 219700Bilateral absence of vas deferens

RET 10q11.2 Multiple endocrine neoplasia type 2A MEN2A 171400

Multiple endocrine neoplasia type 2B MEN2B 162300

Medullary thyroid carcinoma FMTC 155420Hirschsprung disease HSCR 142623p g

PMP22 17p11.2 Charcot-Marie-Tooth neuropathy type 1A CMT1A 118220

Tomaculous neuropathy HNPP 162500SCN4A 17q23.1-q25.3 Paramyotonia congenita PMC 168300

Hyperkalemic periodic paralysis HYPP 170500Acetazolamide-responsive myotonia congenita

PRNP 20p12 pter Creutzfeldt Jakob disease CJD 123400PRNP 20p12-pter Creutzfeldt-Jakob disease CJD 123400Familial fatal insomnia FFI 176640

GNAS1 20q13.2 Albright hereditary osteodystrophy AHO 103580

McCune Albright syndrome PFD 174800McCune-Albright syndrome PFD 174800AR Xcen-q22 Testicular feminization syndrome TFM 313700

Kennedy disease SBMA 313200

Gran heterogeneidad genéticaCMT

PMP22, peripheral myelinprotein 22MPZ m elin protein eroMPZ, myelin protein zeroGJB1, connexin 32EGR2, early growth response proteinproteinNDRG1, N-myc down regulated gene 1,MTMR2, myotubularin relatedMTMR2, myotubularin relatedprotein 2 kinaseGAN1, gigaxoninNEFL, neurofilament light chainKIF1B, kinesin 1BβPRX, periaxin

Gene Location Mutations Syndrome

COL1A1 17 22 N ll ll l OI t ICOL1A1 17q22 Null alleles OI type I

Partial deletions; C-terminalsubstitutions

OI type II

N terminal s bstit tions OI t pes I III or IVN-terminal substitutions OI types I, III or IV

Deletion of exon 6 EDS type VII

COL1A2 7q22.1 Splice mutations; exon deletions OI type I

C-terminal mutations OI type II, IV

N-terminal substitutions OI type III

D l ti f 6 EDS t VIIDeletion of exon 6 EDS type VII

COL2A1 12q13 Point mutations SED

Nonsense mutation Stickler syndrome

f i i i d l iDefect in conversion Kniest dysplasia

Missense Achondrogenesis II, spondylo-meta-epiphyseal dysplasia

COL11A2 6p21.3 Splicing mutation Stickler syndrome