-
Recebido em 30.01.2002. / Received in January, 30th of
2002.Aprovado pelo Conselho Consultivo e aceito para publicao em
30.07.2002. / Approved by the Consultive Council and accepted for
publication in July, 30th of 2002.* Trabalho realizado com bolsa de
ps-doutorado da Capes e da Fundao Alexander von Humboldt, no
Laboratrio de Diagnstico Gentico, Universidade de Colnia,Alemanha
(Servio do Prof. Thomas Krieg) / Work done with a post-doctorate
grant from Capes and the Alexander von Humbold Foundation, in the
Genetic DiagnosisLaboratory, University of Cologne, Germany
(Service of Prof. Thomas Krieg)
1 Professor Adjunto de Dermatologia, Universidade Federal de
Pelotas. / Adjunct Professor of Dermatology, Federal University of
Pelotas.
2002 by Anais Brasileiros de Dermatologia
Gentica Molecular das Epidermlises Bolhosas *Molecular Genetics
of Epidermolysis Bullosa *
Hiram Larangeira de Almeida Jr.
An bras Dermatol, Rio de Janeiro, 77(5):519-532, set./out.
2002.
Almeida Jr. 519
Educao Mdica Continuada / Continuing Medical Education
Resumo: O estudo das alteraes moleculares das epidermlises
bolhosas tem contribudo para que se com-preenda melhor essas
enfermidades. Na epidermlise bolhosa simples a maioria dos casos
est associada comalterao nas citoqueratinas basais 5 (gen KRT5) e
14 (gen KRT14), o que modifica o citoesqueleto na camadabasal da
epiderme, levando degenerao dessa camada, formando bolha
intra-epidrmica. Mutaes na plecti-na (gen PLEC1), componente da
placa interna do hemidesmossoma, levam tambm clivagem
intra-epidrmi-ca. Na epidermlise bolhosa juncional vrios gens esto
envolvidos, em decorrncia da complexidade da zonada membrana basal,
todos levando ao descolamento dos queratincitos basais na lmina
lcida, pela disfunoda aderncia entre esses e a lmina densa.
Alteraes na laminina 5 (gens LAMA3, LAMB3 e LAMC2), integrinaa6b4
(gens ITGA6 e ITGB4) e colgeno XVII (gen COL17A1) foram descritas.
Por fim, na epidermlise bolhosadistrfica apenas um gen est mutado,
alterando o colgeno VII (gen COL7A1), principal componente das
fibri-las ancorantes, produzindo clivagem abaixo da lmina densa,
variando fenotipicamente de acordo com a con-seqncia da mutao.
Outra aplicao importante dessas informaes refere-se ao diagnstico
pr-natal, coma perspectiva no futuro da terapia
gnica.Palavras-chave: Diagnstico pr-natal; epidermlise bolhosa;
gentica bioqumica; mutao; reao em cadeiada polimerase.
Summary: New data regarding the molecular aspects of the
heterogeneous group of epidermolysis bullosahas brought some
important information about its pathogenesis. In epidermolysis
bullosa simplex themajority of mutations are localized in the genes
of the basal cytokeratin 5 (gene KRT5) and 14 (gene
KRT14),cytolysis at this layer with intraepidermal blister is seen
under light microscopy. Mutations of plectin (genePLEC1), a protein
found in the inner hemidesmosomal plaque, leads also to
intraepidermal blisters. In junc-tional epidermolysis bullosa many
proteins from the basal membrane zone are involved, such as
laminin5 (genes LAMA3, LAMB3 and LAMC2), integrin a6b4 (genes ITGA6
and ITGB4) and collagen XVII (gene COL17A1),the dysfunction which
leads to a subepidermal blister, at the level of the lamina lucida.
In the third group,epidermolysis bullosa dystrophica, the mutations
are localized in only one gene (gene COL7A1), where theyalter the
structure of collagen VII, the principal compound of anchoring
fibrils, splitting the skin under thelamina densa. This information
can also be used in the prenatal diagnosis of epidermolysis
bullosa, withfuture perspectives of gene therapy.Key words:
prenatal diagnosis; epidermolysis bullosa; genetics, biochemical;
mutation; polymerase chainreaction.
INTRODUO Antes da descoberta e padronizao da reao em
cadeia da polimerase (PCR) o seqenciamento gnico eratarefa
lenta, levando-se muito tempo para analisar peque-nos segmentos. A
PCR permite a amplificao rpida desegmentos de DNA, os quais so
posteriormente seqencia-
INTRODUCTION Before the discovery and standardization of
polyme-
rase chain reaction (PCR), gene sequencing was anarduous task,
requiring a long time to analyze small seg-ments. PCR allows the
fast amplification of DNA segments,which are then sequenced,
thereby contributing to enor-
-
Figure 1: Example of gene sequencing
Figura 1: Exemplo de
seqenciamento gnico
520 Almeida Jr.
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2002.
dos, tendo trazido enorme evoluo nessa rea. Por ocasiodessa
reviso, ao se utilizar PCR como palavra-chave noMedline, estavam
disponveis mais de 150.000 publicaescom essa tcnica, num perodo de
pouco mais de 12 anos,ilustrando a importncia da mesma na pesquisa
mdica.
O princpio da PCR bastante simples: o primeiropasso o isolamento
de DNA, por exemplo a partir de san-gue, fazendo uso de sua
insolubilidade e precipitao emalguns solventes e de sua
hidrossolubilidade, havendo co-mercialmente vrios kits para essa
funo.
Posteriormente uma parte do DNA obtido incubadocom uma
polimerase termorresistente (j que o mesmo aquecido para que a
cadeia dupla se desfaa) juntamente comseqncias conhecidas de DNA,
os chamados primers (inicia-dores). Havendo no DNA em questo
seqncia igual doprimer, a polimerase amplificar esse segmento de
DNA. Osnucleotdeos (adenina, timidina, citosina e guanina)
fazemparte da reao, para que obviamente a enzima tenha a
mat-ria-prima necessria polimerizao. Ciclos de aquecimentoe
resfriamento so repetidos inmeras vezes, aumentandocada vez mais o
produto da PCR. Posteriormente feita ele-troforese para identificar
a presena de uma banda de DNA,mostrando a positividade ou no da
reao.
Numa etapa posterior o produto obtido pela PCR seqenciado, o que
feito com uma variante da PCR. Oseqenciamento atualmente
automatizado, sendo feitauma leitura a laser, obtendo-se grficos
policromticos,representando a cor azul, citosina; a cor vermelha,
timidina;o preto, guanina; e o verde, adenina (Figura 1). A
compara-o do resultado obtido no paciente investigado e em
seusgenitores com a seqncia normal do gen pode demonstrarmutao e o
padro da herana.
Cada conjunto de trs bases do DNA codifica umaminocido para a
sntese protica no ribossoma; havendouma mutao, ou seja, a troca de
uma base, haver durantea sntese protica a insero de outro
aminocido, alterandoa estrutura da protena, com as conseqncias que
isso podeacarretar.
Inmeros gens j foram seqenciados, estando suacomposio disponvel
em bancos de dados digitais. O maisutilizado o Genbank, doCentro
Nacional de Infor-mao em Biotecnologia dosEstados Unidos,
disponvelno endereo eletrnico:www.ncbi.nlm.nih.gov.
As mutaes so des-critas citando-se os aminoci-dos ou as bases
envolvidas.Primeiro citado o aminoci-
mous progress in this field. To date, inputting PCR as a keyword
in the Medline database, lists over 150,000 publica-tions using
this technique, in a period of little over 12 years,thus
illustrating the importance of PCR to medical research.
The principle of PCR is quite simple: the first step isto
isolate the DNA, for instance taking blood and makinguse of its
insolubility and precipitation in certain solventsand its water
solubility, several commercial kits are availa-ble for this
function.
Then, part of the DNA obtained is incubated with
athermoresistant polymerase (since the DNA is heated inorder to
separate the double chain) together with knownsequences of DNA, the
so-called primers. If the DNA inquestion has the same sequence as
that of the primer, thepolymerase will amplify this segment of DNA.
The nucleoti-des (adenine, thymidine, cytosine and guanine) are
part ofthe reaction, such that obviously the enzyme has the
neces-sary raw material for the polymerization. Heating and
coo-ling cycles are repeated innumerous times, thereby increa-sing
the product of PCR more and more. After which, elec-trophoresis is
performed to identify the presence of a bandof DNA, demonstrating
the positivity or otherwise of thereaction.
In a subsequent stage the product obtained by PCR issequenced
using a variant of PCR. The sequencing is nowautomated with laser
readings providing polychromaticgraphs, with blue representing
cytosine, red thymidine,black guanine and green adenine (Figure 1).
Comparisonof the result obtained in the investigated patient and
theirprogenitors with the normal gene sequence can demonstra-te
mutation and an inherited pattern.
Each set of three bases of DNA codifies an aminoacid for the
protein synthesis in the ribosome; leading to amutation, or in
other words, the change of a base, duringthe protein synthesis
there will be an insertion of anotheramino acid, thus altering the
structure of the protein andresultant consequences.
Countless genes have already been sequenced andtheir composition
is available in digital databases. Thesecan be accessed at the
Genbank of the National Center of
Biotechnology Informationof the United
States:www.ncbi.nlm.nih.gov.
The mutations aredescribed by citing theamino acids or bases
invol-ved. Firstly the aminoa-cid/base is given that
shouldconstitute the protein/gene,followed by a number, which
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Almeida Jr. 521
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2002.
corresponds to the location of the same in the protein/geneunder
investigation and finally the aminoacid/base insertedin the place
of the first, such as, for instance, Glu20Arg, inother words, the
twentieth amino acid should be a glutami-ne, but the mutation leads
to an insertion in the protein ofan arginine, which alters its
structure. Some sequences ofbases codify the end of the protein
synthesis; a mutation canlead to this interruption, the so-called
premature termina-tion codon, which is described in the following
manner:Lys472Stop, in other words, instead of the insertion of a
lysi-ne, at the 472 position, the protein synthesis was
interrup-ted. Abbreviated descriptions with only a single letter
canbe found, for example such an interruption of this synthesisis
denoted by an X; in the above example this would then beL472X.
The bullous dermatoses make a fascinating chapterin dermatology,
they comprise acquired or congenitaldefects of the intraepidermal
or dermoepidermal adhesion,leading to blisters which can be
spontaneous or provokedby minimal trauma.
In epidermolysis bullosa (EB) these defects are con-genital and
can be identified by gene sequencing, whichaffords a greater
understanding of their molecular base,1,2
complements the clinicohistological diagnosis and maybein the
medium term will partly modify the classification ofthese
dermatoses.
Three subgroups of EB are recognized:2 epidermoly-sis bullosa
simplex (EBS), in the which the cleaving occursinside the
epidermis; junctional epidermolysis bullosa(EBJ), with subepidermal
cleaving in the lamina lucida; andepidermolysis bullosa dystrophica
(EBD), also subepider-mal, but below the lamina densa. EBJ and EBD
cannot bedifferentiated by optical microscopy alone. There are
seve-ral classifications, but in this work the second
internationalconsensus has been adopted regarding the diagnosis
andclassification of epidermolysis bullosa.3
Epidermolysis bullosa simplexThe group of EBS has several
subtypes, according to
the intensity and location of the blisters, all of which
withautosomal dominant inheritance;4 these are also called
epi-dermolytic EB, since the defect is intraepidermal.3 The
his-tological aspect most commonly found is degeneration ofthe
basal layer, in the absence of any inflammatory infiltra-tion and
without deposit of antibodies in the tissue.
The most serious form of EBS is Dowling-Mearasyndrome (EBS-DM),5
in which disseminated blisters thatalso involve the mucous
membranes, are accompanied bypalmoplantar hyperkeratosis. The
mildest form is Weber-Cockayne syndrome (EBS-WC) with lesions
restricted to thepalmar and plantar regions.5 An intermediate form
exists,again with disseminated blisters, but with a less intense
pic-ture than that of EBS-DM, denominated EBS-Koebner (EBS-K),
although certain authors consider this to be a mildvariant of
EBS-DM.6
do/base que deveria constituir a protena/gen, seguido porum
nmero, o qual corresponde localizao do mesmo naprotena/gen
investigado, e por fim o aminocido/base inse-rido no lugar do
primeiro, como, por exemplo, Glu20Arg,ou seja, o vigsimo aminocido
deveria ser uma glutamina,mas a mutao leva insero na protena de uma
arginina,o que altera sua estrutura. Algumas seqncias de
basescodificam o final da sntese protica; uma mutao podelevar a
essa interrupo, o chamado premature terminationcodon (cdon
finalizador prematuro), a qual descrita daseguinte forma:
Lys472Stop, ou seja, em vez da insero deuma lisina, na posio 472,
foi interrompida a sntese pro-tica. Encontram-se tambm descries
abreviadas comapenas uma letra, sendo a interrupo da sntese
descritacom X; o exemplo acima ficaria L472X.
As dermatoses bolhosas so captulo fascinante dadermatologia,
constitudas por defeitos adquiridos ou natosda adeso
intra-epidrmica ou dermoepidrmica, levando abolhas espontneas ou
provocadas por trauma mnimo,decorrentes do defeito dessa adeso.
Nas epidermlises bolhosas (EB) esses defeitos sonatos e podem
ser identificados por seqenciamento gni-co, o que traz maior
compreenso base molecular dasmesmas,1,2 complementa o diagnstico
clnico-histolgico etalvez a mdio prazo modifique em parte a
classificaodessas dermatoses.
Trs subgrupos de EB so reconhecidos:2 a epider-mlise bolhosa
simples (EBS), na qual a clivagem ocorredentro da epiderme; a
epidermlise bolhosa juncional(EBJ), cuja clivagem subepidrmica, na
lmina lcida; e aepidermlise bolhosa distrfica (EBD), sendo tambm
sube-pidrmica, mas abaixo da lmina densa. A EBJ e a EBD nopodem ser
diferenciadas apenas por microscopia tica.Existem diversas
classificaes, sendo adotada aqui a dosegundo consenso international
sobre diagnstico e classifi-cao das epidermlises bolhosas.3
Epidermlise Bolhosa Simples O grupo da EBS tem vrios subtipos de
acordo com
a intensidade e localizao das bolhas, sendo todos deherana
autossmica dominante;4 so tambm chamados deEB epidermoltica, pois o
defeito intra-epidrmico.3 Oaspecto histolgico mais comumente
encontrado a dege-nerao da camada basal, na ausncia de infiltrado
inflama-trio e sem depsito de anticorpos no tecido.
A forma mais grave da EBS a Dowling-Meara(EBS-DM),5 na qual
bolhas disseminadas, envolvendo tam-bm as mucosas, so acompanhadas
de hiperqueratose pal-moplantar. A forma mais leve a Weber-Cockayne
(EBS-WC) com leses restritas s palmas e plantas.5 Existe umaforma
intermediria com bolhas disseminadas, mas comquadro menos intenso
do que o da EBS-DM, denominadoEBS - Koebner (EBS-K), que certos
autores consideramvariante leve da EBS-DM.6
Algumas citoqueratinas so expressadas nas clulas
-
Figure 2: Schematic represen-tation of the molecule
ofcytokeratin 5 and 14. Themutations of cytokeratin 5
arerepresented above the schemeand those of cytokeratin 14below, in
that each line couldrepresent more than onemutation. It can be
observedthat the mutations of epider-molysis bullosa
simplexDowling-Meara (EBS-DM) arelocated in the extremities ofthe
molecule, while most ofthose of EBS Weber-Cockayne(EBS-WC), in the
non-helicalsegment between 1B and 2A.
Figura 2: Representaoesquemtica da molcula das
citoqueratinas 5 e 14. Asmutaes da citoqueratina 5
esto representadas acima doesquema e as da citoqueratina
14 abaixo, sendo que cada traopode representar mais de uma
mutao. Note-se que asmutaes da epidermlise bol-
hosa simples Dowling-Meara(EBS-DM) localizam-se nas
extremidades da molcula, e amaioria das da EBS Weber-
Cockayne (EBS-WC), no segmen-to no helicoidal entre 1B e 2A
522 Almeida Jr.
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2002.
epiteliais aos pares,7 os quais formam heterodmeros, ouseja, a
unio das duas molculas, configurando o citosque-leto dos epitlios,
havendo especificidade de acordo com oepitlio envolvido.7 A camada
basal diferencia-se de outrosepitlios e dos segmentos suprabasais
da epiderme pelaexpresso das citoqueratinas 5 e 14.
As citoqueratinas 5 e 14 so reguladas pelos gensKRT5 e KRT14,
localizados nos cromossomas 17 e 12, res-pectivamente. interessante
observar que defeitos genti-cos distintos na EBS, um afetando a
citoqueratina 5, outro,a 14,6,8,9 levam mesma alterao histolgica,
pois todosesses defeitos produzem alteraes estruturais de uma
ououtra citoqueratina,10 impedindo a funo estrutural dasmesmas no
citoesqueleto 11 a formao dos heterodmeros,responsveis pela
configurao tridimensional da clula.Essa alterao vista facilmente na
histologia e culminacom a formao das bolhas, sendo esse o nico
subgrupodas EB decorrente de citlise e no de defeito de adeso.
As citoqueratinas so constitudas por quatro seg-mentos
helicoidais, 1A, 1B, 2A e 2B,12 tendo sido a maioriadas mutaes da
EBS-DM descrita no incio do segmento 1Ae no final do segmento 2B
(Figura 2)13,14 das citoqueratinasbasais. As mutaes da EBS-K tm
localizao semelhan-te,15 reforando a hiptese de ser variante da
EBS-DM. NaEBS-WC a maioria das mutaes localiza-se no
segmentono-helicoidal entre 1B e 2A das mesmas citoqueratinas,sem
que com isso se explique a localizao palmoplantardas leses.
Um quarto tipo de EBS descrito, no qual no ocor-re citlise na
camada basal. a EBS com distrofia musculartardia, decorrente de
alterao da plectina, presente na placainterna do hemidesmossoma
(Figura 3). Como a clivagemocorre dentro da epiderme, includa nesse
grupo. A plec-tina regulada pelo gen PLEC11 e est tambm envolvida
nocitoesqueleto da musculatura lisa,16 da a miopatia
associa-da.1,17 Outro componente da placa interna do
hemidesmos-soma o antgeno do penfigide bolhoso de 230 KD de
pesomolecular, no havendo at o momento descrio de muta-o no gen que
o regula.1
Some cytokeratins are expressed in the epithelialcells in
pairs,7 which form heterodimers, in other words, theunion of two
molecules, configuring the cytoskeleton of theepithelia, with
specificity according to the epithelium invol-ved.7 The basal layer
differs from other epithelia and supra-basal segments of the
epidermis by the expression of cyto-keratins 5 and 14.
Cytokeratins 5 and 14 are regulated by the genesKRT5 and KRT14,
located in chromosomes 17 and 12, res-pectively. It is interesting
to note that different geneticdefects in EBS, one affecting
cytokeratin 5 and the other14,6,8,9 lead to the same histological
alteration, because allthese defects produce structural alterations
in one or ano-ther cytokeratin,10 impeding their structural
function in thecytoskeleton11 i.e. the formation of the
heterodimers, res-ponsible for the three-dimensional configuration
of the cell.This alteration is easily seen in the histology and
culmina-tes with the formation of blisters, making this the only
sub-group of EB due to cytolysis and not to an adhesion defect.
The cytokeratins are constituted by four helical seg-ments, 1A,
1B, 2A and 2B,12 the majority of the mutations ofEBS-DM are
described in the beginning of segment 1A and atthe end of segment
2B (Figure 2)13,14 of the basal cytokeratins.The mutations of EBS-K
have a similar location,15 reinforcingthe hypothesis that it is a
variant of EBS-DM. In EBS-WCmost of the mutations are located in
the non-helical segmentbetween 1B and 2A of the same cytokeratins,
though thisdoes not explain the palmoplantar location of the
lesions.
A fourth type of EBS is described, in which cytolysis inthe
basal layer does not occur. It is EBS with tardive
musculardystrophy, due to alteration of the plectin, present in the
inter-nal plaque of the hemidesmosome (Figure 3). Since the
clea-ving occurs within the epidermis, it is included in this
group.The plectin is regulated by the gene PLEC11 and is also
invol-ved in the cytoskeleton of the smooth musculature,16 hence
theassociated myopathy.1,17 Another component of the internalplaque
of the hemidesmosome is the bullous pemphigoid anti-gen with 230 KD
molecular weight. To date mutation in thegene that regulates this
has not been described.1
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2002.
Junctional Epidermolysis BullosaGiven the complexity of the
basal membrane zone,
alterations in several proteins involved in the dermoepider-mal
adhesion can lead to the various clinical pictures ofEBJ; for these
molecular alterations to be understood, it isimportant to be
familiar with the substances responsible forthe adhesion between
the basal keratinocytes and the colla-gen IV the lamina densa
(Figure 3).
The antigen of bullous pemphigoid (180 KD) andintegrin a6b4,
which are transmembranous proteins, arefound in the external
plaque.18
The antigen of bullous pemphigoid (180 KD) is inreality a
transmembranous collagen, denominated collagenXVII, and is
regulated by the gene COL17A1.1 Each segmentof the integrin a64 is
regulated by two different genes,ITGA6 and ITGB4, which are also
expressed in the skin anddigestive tract.1,18
Finally, some substances present in the lamina luci-da
complement this molecular net,1 of which the mostimportant is
laminin 5. The laminins are heterotrimers, orthat is, they are
constituted by three distinct classes of poly-peptides a, b e
g,18-20 and hence regulated by three genes.Laminin 5 is composed of
one a3, one b3 and one g2, regu-lated by the genes LAMA3, LAMB3 and
LAMC2, respectively.
An absence or alteration of these substances produ-ces a rupture
of this adhesion net, with the formation of blis-ters.2 Some
mutations occur due to the so-called prematuretermination codon
(PTC), which provokes an interruption ofthe protein synthesis and
consequently absence of protein inthe tissue, resulting in a more
serious clinical picture.
Several genophenotype correlations have alreadybeen made. Such
as integrin a6b4 is expressed in the skinand intestine, mutations
of which lead to forms of EBJ withatresia pilori, the clinical
picture varies according to whe-ther or not it is associated to
PTC.
Regarding generalized, benign and atrophic EBJ, cha-racterized
by disseminated blisters with nail dystrophy, inwhich the
immunohistochemistry with antibody against colla-gen XVII is
negative, PTC has been demonstrated in the gene
Epidermlise Bolhosa Juncional Dada a complexidade da zona da
membrana basal,
alteraes de vrias protenas envolvidas na adeso dermoe-pidrmica
podem levar aos diversos quadros clnicos daEBJ; para que se
compreendam essas alteraes molecula-res, importante conhecer as
substncias responsveis pelaadeso entre os queratincitos basais e o
colgeno IV almina densa (Figura 3).
Na placa externa do hemidesmossoma encontram-seo antgeno do
penfigide bolhoso de 180 KD e a integrinaa6b4, os quais so protenas
transmembranosas.18
O antgeno do penfigide bolhoso de 180 KD narealidade um colgeno
transmembranoso, sendo denomina-do colgeno XVII, e regulado pelo
gen COL17A1.1 Cadasegmento da integrina a64 regulado por dois gens
dis-tintos, ITGA6 e ITGB4, sendo a mesma expressa na pele e notubo
digestivo.1,18
Finalmente algumas substncias presentes na lminalcida
complementam essa rede molecular,1 sendo a maisimportante a
laminina 5. As lamininas so heterotrmeros,ou seja, so constitudas
por trs classes distintas de polipep-tdeos a, b e g,18-20 e da
reguladas por trs gens. A laminina5 composta por uma classe a3, uma
b3 e uma g2, regula-das pelos gens LAMA3, LAMB3 e LAMC2,
respectivamente.
A ausncia ou alterao dessas substncias produz aruptura dessa
rede de adeso, com a formao das bolhas.2
De algumas mutaes decorre o chamado premature termi-nation codon
(PTC), o que provoca a interrupo da snte-se protica e
conseqentemente a ausncia da protena notecido, com quadro clnico
mais grave.
Vrias correlaes genofenotpicas j foram feitas.Como a integrina
a6b4 expressa na pele e no intestino,suas mutaes levam a formas de
EBJ com atresia pilrica,sendo o quadro clnico varivel de acordo com
sua associa-o com PTC ou no.
Na EBJ generalizada atrfica benigna, caracterizadapor bolhas
disseminadas com distrofia ungueal, na qual aimuno-histoqumica com
anticorpo contra o colgeno XVII negativa, foi demonstrada PTC no
gen COL17A,1,21 o que
Figure 3: The adherence betweenthe basal keratinocyte and
thelamina densa is made by thetransmembranous proteins basedon the
external plaque of the hemi-desmosome (collagen XVII andintegrin
a6b4) and by laminin 5,present in the lamina lucida. Theadherence
between the laminadensa and the dermis is promotedby anchorage
fibrils (collagen VII).The plectin is present in the inter-nal
plaque of the hemidesmosome,and its alterations lead to
theintraepidermal separation, belon-ging to the group of the
epidermoly-sis bullosa simplex, as well as thealterations of the
basal cytokeratins.
Figura 3: A aderncia entre oqueratincito basal e a lmina
densa feita pelas protenas trans-membranosas a partir da
placa
externa do hemidesmossoma(colgeno XVII e integrina a6b4) epela
laminina 5, presente na lmi-
na lcida. A aderncia entre almina densa e a derme pro-
movida pelas fibrilas ancorantes(colgeno VII). A plectina est
pre-
sente na placa interna dohemidesmossoma, e suas alter-
aes levam clivagem intra-epidrmica, pertencendo ao
grupo da epidermlise bolhosasimples, assim como as alteraes
das citoqueratinas basais
-
Figure 4: Diagram of thesynthesis of collagen VIIand anchoring
fibrils. After the loss of segmentNC2 the formation ofantiparallel
dimers occurs,which group together andform anchorage fibrils.
Figura 4: Esquema da sntesedo colgeno VII e das
fibrilasancorantes. Aps a perda do
segmento NC2 ocorre a formao dos dmeros
antiparalelos, os quais seagrupam e formam
as fibrilas ancorantes.
524 Almeida Jr.
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2002.
correlaciona com a ausncia tecidual do colgeno XVII.Alguns
autores denominam essa forma, por ter curso bran-do e expectativa
de vida normal, de EBJ no-Herlitz. 21,22
Semelhante s mutaes dos componentes dohemidesmossoma descritas
acima, as mutaes da lamini-na tambm provocam o descolamento da
epiderme. Amaior parte das mutaes dos gens da laminina 5 leva PTC,
provocando ausncia da protena e quadro clnicointenso,23,24
caracterizado por leses disseminadas afetandotambm as mucosas,23
com sobrevida curta em funo dascomplicaes bacterianas, denominadas
EBJ tipo Herlitzou EBJ letal.
As alteraes j foram demonstradas no trs gensque codificam a
laminina5, 25 no havendo diferena fenot-pica de acordo com o
segmento envolvido,26 sugerindo quetodos so importantes para a funo
adesiva da mesma.26,27
Oitenta por cento das mutaes residem no gen LAMB3,22,24,28-30
havendo duas delas recorrentes (R635X e R42X),26,28 asquais
perfazem metade das mutaes no LAMB3.1 Nessegen j foram relatadas 35
mutaes diferentes.22
Existem relatos de mutao da laminina 5 em pacien-tes nos quais a
imuno-histoqumica consegue demonstrardiminuio da laminina 5, e no
ausncia, como na EBJ-Herlitz, e, em decorrncia disso, o quadro
clnico no tograve.31,32 Essas formas tm sido tambm denominadas
EBJno-Herlitz,33 as quais clinicamente so semelhantes s for-mas
decorrentes da mutao do colgeno XVII.33
Todas as formas de EBJ so autossmicas recessivas.23
Epidermlise Bolhosa Distrfica A caracterstica clnica principal
das EBD so as
cicatrizes decorrentes da perda tecidual, pois a clivagemocorre
abaixo da lmina densa.34 Como nos outros grupos,h variantes de
acordo com o quadro clnico; apesar dessasvariantes, o defeito
gentico foi localizado em um nicogen, o COL7A1.35 Esse gen
responsvel pela codificaodo colgeno VII, principal constituinte das
fibrilas ancoran-tes,35 as quais participam da aderncia da lmina
densa coma derme (Figura 3), da tambm a denominao EB dermo-ltica.
Nesse grupo existem formas com herana autossmi-ca dominante e
recessiva.
Para que se entenda acorrelao entre gentipo efentipo na EBD
necessrioque se entenda tambm opapel do colgeno VII na ade-
COL17A,1,21 which correlates with the tissular absence of
colla-gen XVII. Some authors denominate this form non-Herlitz
EBJ,as it presents a mild course and normal life
expectancy.21,22
Similar to the mutations in components of the hemides-mosome
described above, mutations in the laminin also pro-voke dislocation
of the epidermis. Most of the mutations of thegenes of laminin 5
lead to PTC, provoking absence of the pro-tein and intense clinical
picture,23,24 characterized by dissemi-nated lesions also affecting
the mucous membranes,23 with lowsurvival in function of bacterial
complications, denominatedHerlitz syndrome or epidermolysis bullosa
lethalis.
The alterations have already been demonstrated inthe three genes
that codify laminin 5,25 without a phenotypedifference according to
the segment involved,26 suggestingthat all are important for its
adhesion function.26,27 Eightypercent of the mutations reside in
the gene LAMB3,22,24,28-30
two of these are recurrent (R635X and R42X),26,28 whichamount to
half of the mutations in LAMB3.1 In this genealone 35 different
mutations have already been reported.22
There are reports of mutation in laminin 5 amongpatients in
which the immunohistochemistry demonstrateda reduction in laminin
5, but not a complete absence, as inHerlitz Syndrome, and
consequently the clinical picture wasnot so serious.31,32 These
forms have also been denominatednon-Herlitz EBJ,33 which are
clinically similar to the formsarising from mutation of collagen
XVII.33
All forms of EBJ are inherited as an autosomalrecessive
trait.23
Epidermolysis bullosa dystrophica The main clinical
characteristic of EBD is scarring
after tissue loss, since the separation occurs below thelamina
densa.34 As in the other groups, there are variantsreflecting the
clinical picture; in spite of these variants, thegenetic defect is
located in a single gene, COL7A1.35 Thisgene is responsible for
codifying collagen VII, the mainrepresentative of the anchoring
fibrils,35 which participatein the adherence of the lamina densa to
the dermis (Figure3), hence it is also denominated dermolytic EB.
In thisgroup there are forms inherited as autosomal dominant
and
recessive traits. In order to unders-
tand the correlation betweengenotype and phenotype inEBD it is
necessary to also
-
Figura 5: Representaoesquemtica da molcula docolgeno VII. A
maioria das
mutaes da epidermlise bol-hosa distrfica recessiva
Halloupeau-Siemens (EBD-RHS) premature termination codon
(PTC) levando ausncia damolcula no tecido. Na forma
recessiva Mitis (EBD-RM) osdefeitos localizam-se no final
dosegmento colgeno e no NC-2.
Na forma dominante (EBD-D) assubstituies de glicina repre-
sentadas embaixo ocorremgeralmente no segundo segmen-
to colgeno. Cada trao pode rep-resentar mais de uma mutao.
Figure 5: Schematic representa-tion of the molecule of
collagenVII. The majority of mutationsin epidermolysis bullosa
dys-trophica recessive Halloupeau-Siemens (EBD-RHS) are prema-ture
termination codon (PTC)leading to the absence of themolecule in the
tissue. In therecessive mitis form (EBD-RM)the defects are located
at theend of the collagen segment andin NC-2. In the dominant
form(EBD-D) the substitutions ofglycine shown below usuallyoccur in
the second collagensegment. Each line can repre-sent more than one
mutation.
Almeida Jr. 525
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2002.
understand the role of collagen VII in the
dermoepidermaladhesion.
This is produced by the keratinocytes and has a tri-ple helix
configuration of collagen, preceded and followedby non-collagen
segments (NC-1 and NC-2, respectively).36, 37
In the center of the triple helix there is small
non-collagensegment, which probably provides flexibility to the
protein.Later, at the extracellular level, a fusion occurs
betweentwo of these molecules with loss of the NC-2 segment,
for-ming antiparallel dimers. The union of several dimersforms the
anchoring fibrils34,36,37 (Figure 4).
Three subtypes of EBD are well characterized: reces-sive EBD
Halloupeau-Siemens (EBD-RHS), with an intenseclinical picture,
producing acral retractions with synechiaeof the digits and
involvement of the digestive tract;37 recessi-ve EBD mitis
(EBD-RM), in which the clinical picture is muchless intense in
comparison with that of EBD-RHS, with loca-lized lesions in the
areas of greatest trauma, such as theknees and extremities; and the
dominant form (EBD-D), witha similar picture to that of EBD-RM,37
associated to naildystrophy and, in some cases, with white papular
lesions.
Electron microscopy and immunohistochemical cha-racterization
with antibodies against collagen VII showalteration in the
anchoring fibrils to the extent of theirabsence in EBD-RHS and
reduction in the milder forms,EBD-RM and EBD-D.38 In some cases the
immunohistoche-mistry is positive but without anchoring fibrils
revealed byelectron microscopy, which demonstrates the presence
ofpart of the molecule, but with structural alteration.38
The identification of the mutations responsible for EBDhas
brought a greater understanding of this spectrum (Figure 5).
In EBD-RHS the genetic alteration is a PTC, with con-sequent
interruption in the synthesis of collagen VII,39 whichcorrelates
with the intensity of the clinical picture and withthe findings of
electron microscopy and immunohistoche-mistry, in which the
anchoring fibrils are not detected.34,37
In EBD-RM the greater part of the mutations occur atthe end of
the collagen segment and in NC-2, interfering inthe formation of
the antiparallel dimers and altering the
so dermoepidrmica.O mesmo produzido pelos queratincitos e
possui
uma tripla hlice de colgeno, precedida e seguida por seg-mentos
no colgenos (NC-1 e NC-2, respectivamente).36,37
No centro da tripla hlice h pequeno segmento no colge-no, o qual
provavelmente d flexibilidade protena.Posteriormente, no nvel
extracelular, ocorrer com duasdessas molculas uma fuso com perda do
segmento NC-2,formando dmeros antiparalelos. A unio de vrios
dmerosforma as fibrilas ancorantes 34,36,37 (Figura 4).
Trs subtipos da EBD esto bem caracterizados: aEBD recessiva
Halloupeau-Siemens (EBD-RHS), comquadro clnico intenso, produzindo
retraes acrais comsinquia dos dgitos e acometimento do tubo
digestivo;37 aEBD recessiva Mitis (EBD-RM), na qual a intensidade
doquadro clnico bem menor em comparao ao da EBD-RHS, com leses
localizadas nas reas de maior trauma,como joelhos e extremidades; e
a forma dominante (EBD-D), com quadro semelhante ao da EBD-RM,37
associadacom distrofia ungueal e, em alguns casos, com
lesesalbo-papulides.
A microscopia eletrnica e a caracterizao imuno-histoqumica com
anticorpos contra colgeno VII mostramalterao nas fibrilas
ancorantes, indo da ausncia das mes-mas, na EBD-RHS, diminuio nas
formas mais leves,EBD-RM e EBD-D.38 Em alguns casos a
imuno-histoqumica positiva, sem que se observe as fibrilas
ancorantes namicroscopia eletrnica, o que demonstra a presena de
parteda molcula, mas com alterao de sua estrutura.38
A identificao das mutaes responsveis pela EBDtrouxe maior
compreenso a esse espectro (Figura 5).
Na EBD-RHS a alterao gentica uma PTC, comconseqente interrupo na
sntese do colgeno VII,39 o quecorrelaciona com a intensidade do
quadro clnico e com osachados de microscopia eletrnica e
imuno-histoqumica,com os quais no se detectam as fibrilas
ancorantes. 34,37
Na EBD-RM a maior parte das mutaes ocorre nofinal do segmento
colgeno e no NC-2, interferindo na for-mao dos dmeros
antiparalelos, alterando a conformao
-
526 Almeida Jr.
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2002.
da protena, estando, porm, presente, decorrendo um qua-dro
clnico mais leve e a presena de fibrilas ancorantes namicroscopia
eletrnica.37,40
Na EBD-D a alterao caracterstica a substituiode uma glicina no
segmento colgeno,41,42 alterando suaestabilidade e talvez
propiciando sua degradao. 36,37,43
Como na EBD-RM, as fibrilas ancorantes esto presentes,mas com
sua funo comprometida. A maior parte dasmutaes localiza-se logo
depois do segmento no colge-no do centro da tripla hlice;42 a mutao
G2043R a maiscomumente descrita.36,41 Tambm j foi demonstrado que
aalterao funcional da fibrila ancorante depende da locali-zao da
substituio da glicina, 34,44 o que, por sua vez, con-tribui para a
variabilidade clnica. No existe explicaoconvincente a respeito de
por que a substituio de glicina herdada de forma dominante.
A maioria dos casos da forma pr-tibial da EBD autossmica
dominante, tendo sido descrita tambm a subs-tituio de glicina.45
Casos recessivos foram igualmentepublicados,45 podendo ser
considerados variantes das for-mas leves de EBD, no se sabendo o
porqu da ocorrncialocalizada das leses.
Cerca de 100 mutaes diferentes j foram descritasna EBD,34 sendo
encontradas em 80% dos casos examina-dos.37 Assim como nas outras
formas de EB, algumas muta-es no se enquadram no esquema acima
exposto, pois,por exemplo, algumas substituies de glicina foram
encon-tradas na EBD-RM;37,40,41 razo de, nesses casos, os
genitoresque apresentam essa substituio de glicina serem normais,ou
seja, a mutao no ser dominante, s se expressando deforma recessiva,
com a herana de dois alelos mutados, eat o momento no pde ser
esclarecida.41
Alguns quadros clnicos intermedirios, de difcil clas-sificao
clnica, j foram tambm descritos com essas muta-es incomuns, como,
por exemplo, EBD recessiva com umaPTC em um alelo e uma substituio
de glicina em outro.46
Discusso Os novos aspectos moleculares, tanto gnico quanto
protico, mostram o quo variado o espectro da EB(Tabela 1). Na
EBS os defeitos genticos das citoqueratinasbasais produzem alterao
histolgica em funo da modi-ficao do citoesqueleto na camada basal
da epiderme,sendo que a alterao da plectina, componente da
placainterna do hemidesmossoma, tambm leva clivagem
intra-epidrmica. Na EBJ vrios gens esto envolvidos, devido
complexidade da zona da membrana basal, mas todoslevam ao
descolamento dos queratincitos basais da lminadensa, ou seja, a
clivagem ocorre na lmina lcida. Por fim,na EBD apenas um gen est
mutado, alterando o colgenoVII, sendo a clivagem abaixo da lmina
densa, mas, mesmo,assim variando fenotipicamente, de acordo com a
conse-qncia da mutao.
Apesar de contribuir com importantes avanos nacompreenso dessas
enfermidades, o seqenciamento gni-
compliance of the protein, though these continue present,giving
rise to a milder clinical picture and the presence ofanchoring
fibrils in the electron microscopy.37,40
In EBD-D, the characteristic alteration is the substi-tution of
a glycine in the collagen segment,41,42 altering itsstability and
maybe propitiating its degradation.36,37,43 As inEBD-RM, the
anchorage fibrils are present, but their func-tion is impaired.
Most of the mutations are located imme-diately after the
non-collagen segment of the center of thetriple helix;42 the G2043R
mutation is the most commonlydescribed.36,41 Likewise it has
already been demonstratedthat the functional alteration of the
anchoring fibrilsdepends on the location in which the glycine is
substitu-ted,34,44 which in turn contributes to the clinical
variability.As yet, there is no convincing explanation as to why
theglycine substitution is an inherited dominant trait.
The majority of cases involving the pretibial form ofEBD are
autosomal dominant and the substitution of glyci-ne has also been
described.45 Recessive cases have beenpublished,45 these could
equally be considered variants ofthe mild forms of EBD, the reason
behind the localizedoccurrence of the lesions is not known.
About 100 different mutations have already beendescribed in
EBD,34 and are found in 80% of the cases exa-mined.37 As in other
forms of EB, some mutations are notdefined within the above
described outline, because, for ins-tance, some substitutions of
glycine have been found inEBD-RM;37,40,41 to date, it has yet to be
clarified why in thesecases the progenitors that present such
glycine substitutionmay be normal, or in other words, the mutation
is not domi-nant and is only expressed in a recessive manner, with
theinheritance of two changed alleles.41
Various intermediate clinical pictures, presenting diffi-cult
clinical classification, have already been described withsuch
uncommon mutations, for instance, recessive EBD withPTC in one
allele and a glycine substitution in the other.46
Discussion The new molecular aspects, involving both genes
and proteins, demonstrate just how varied the spectrum ofEB can
be (Table 1). In EBS the genetic defects of the basalcytokeratins
produce a histological alteration due to themodification of the
cytoskeleton in the basal layer of theepidermis, in that alteration
of the plectin, a component ofthe internal plaque of the
hemidesmosome, also leads to theintraepidermal separation. In EBJ
several genes are invol-ved, due to the complexity of the basal
membrane zone, butall lead to the dislocation of the basal
keratinocytes of thelamina densa, in other words, the cleaving
occurs in thelamina lucida. Finally, in EBD only one gene is
modified,altering the collagen VII, cleaving below the lamina
densa,but even so with phenotype variation, according to the
con-sequence of the mutation.
Despite its important contribution to progress in
theunderstanding of these illnesses, gene sequencing should be
-
Almeida Jr. 527
An bras Dermatol, Rio de Janeiro, 77(5):519-532, set./out.
2002.
used together with clinical, histological, electron
microscopyand immunohistochemical findings in the diagnosis of
EB.47
Another important application for molecular gene-tics is in
prenatal diagnosis (PND),2,48 examining fetal DNAobtained from the
chorion rather than the fetal skin. PNDperformed on the basis of
the lesions requires the collectionof a skin specimen, which should
be representative of the ill-ness, in order to avoid a
false-negative result, one shouldwait until the eighteenth or
twentieth week.43 Sequencinghas the advantage that it can be
performed around the tenthweek, which means that a more precocious
decision to ter-minate the gestation can be made in those countries
inwhich this procedure is permitted. Furthermore, complica-tions
arising from fetoscopy with biopsy occur in betweenfour to 7% of
cases compared to 1% in chorionic biopsy.43
Genetic sequencing has already been used in PNDfor all forms of
EB,23,24,43,49-51 and has already been performedbefore
implantation, based on a cell obtained from an embr-yo with a
number of cells varying from five to eight.52
Genetic counseling is another important applicationof this new
information, since it helps to explain the inheri-tance pattern,
especially when dealing with frequent andwell-known mutations. Also
in the case of de novo muta-tions, when the DNA exam of the
progenitors is normal andthe mutation is only found in the patient,
it can be affirmedthat the risk factor for the next gestation is
very low.
co deve ser utilizado em conjunto com a clnica,
histologia,microscopia eletrnica e a imuno-histoqumica no
diagns-tico da EB.47
Outra aplicao importante da gentica molecularocorre no
diagnstico pr-natal (DPN),2,48 examinando-se oDNA fetal obtido do
crion e no a pele fetal. O DPN feitoa partir das leses necessita da
obteno de fragmento dapele, o qual deve ser representativo da
enfermidade, paraevitar resultado falso-negativo, devendo-se
esperar at adcima oitava ou vigsima semana.43 O seqenciamentotem a
vantagem de poder ser feito em torno da dcimasemana, o que permite,
nos pases em que a gestao podeser interrompida nessas situaes,
deciso mais precoce.Alm disso as complicaes da fetoscopia com
bipsiaocorrem entre quatro e 7% dos casos, e na bipsia corini-ca em
1%.43
O seqenciamento gentico j foi utilizado no DPNde todas as formas
de EB,23,24,43,49-51 j tendo sido tambm rea-lizado antes da
implantao, a partir de clula obtida deembrio com nmero de clulas
varivel de cinco a oito.52
Aconselhamento gentico outra aplicao importante des-sas novas
informaes, pois ajuda a esclarecer o padro deherana, principalmente
tratando-se de mutaes freqentese bem conhecidas. Tambm no caso de
mutaes de novo,quando o exame do DNA dos genitores normal e a
muta-
EBS
EBJ
EBD
Dowling-Meara Dowling-Meara
Weber-Cockaine Weber-Cockaine
EBS - distrofia muscular EBS - muscular dystrophy
Herlitz Herlitz
No-Herlitz Non-Herlitz
EBJ - atresia pilrica EBJ - atresia pilori
Halloupeau-Siemens Halloupeau-Siemens
EBD-Recessiva Mitis EBD-Recessive Mitis
EBD-Dominante EBD-Dominant form
Citoqueratina 5 ou 14Cytokeratin 5 or 14
Citoqueratina 5 ou 14Cytokeratin 5 or 14
PlectinaPlectin
Laminina 5Laminin 5
Colgeno XVIICollagen XVII
Integrina alpha6 beta4Integrin alpha6 beta4
Colgeno VIICollagen VII
Colgeno VIICollagen VII
Colgeno VIICollagen VII
KRT5 ou KRT14KRT5 or KRT14
KRT5 ou KRT14KRT5 or KRT14
PLEC1PLEC1
LAMA3, LAMB3 ou LAMC2LAMA3, LAMB3 or LAMC2
COL17A1COL17A1
ITGA6 ou ITGB4ITGA6 or ITGB4
COL7A1COL7A1
COL7A1COL7A1
COL7A1COL7A1
17 ou 1217 or 12
17 ou 1217 or 12
8
18, 1 ou 118. 1 or 1
10
2 ou 172 or 17
3
3
3
Protena alterada Altered protein
Gen envolvido Gene involved
Cromosoma Chromosome
SubtipoSubtype
Tabela 1: Principais tipos de EB, com as protenas, gens e
cromossomas envolvidos.Tabel 1:- Main types of EB, with the
involved proteins, genes and chromosomes.
-
528 Almeida Jr.
An bras Dermatol, Rio de Janeiro, 77(5):519-532, set./out.
2002.
o s encontrada no paciente, pode-se afirmar que o riscopara uma
prxima gestao muito baixo. Com relao prole do paciente, depender do
tipo da mutao encontra-da, dominante ou recessiva,42 ou seja,
presente em um salelo ou em dois.
Em funo dessas recentes informaes sobre a expres-so gnica,53
novas perspectivas teraputicas existem para asEB, embora ainda em
fase experimental. J h relatos da mani-pulao ex vivo de
queratincitos de portadores de EBJ, inca-pazes de produzir a cadeia
3 da laminina 5, os quais, apstransferncia gnica, se mostraram
capazes ainda que transi-toriamente de sintetiz-la, abrindo novas
perspectivas tera-puticas para esse grupo de genodermatoses.54
Modelo animalcom ratos transgnicos, simulando a doena humana,
temacrescentado informaes relevantes na pesquisa das EB. 10,12
Alguns autores consideram que as correlaes entregentipo e
fentipo estejam apenas comeando 34 e que aexpanso dos bancos de
dados sobre as alteraes gnicas sejade extrema importncia, pois
permitir, cada vez mais, que semelhore essa correlao e talvez at se
reclassifique, com baseem aspectos moleculares, parte das
genodermatoses.38 q
Regarding the patient's offspring, this will depend on whe-ther
the type of mutation found, is dominant or recessive,42
present in only one allele or both.In function of this recent
information regarding gene
expression,53 there are new therapeutic perspectives for
EB,although these are still in an experimental phase. Therehave
already been reports of ex vivo manipulation of kera-tinocytes from
patients with EBJ, unable to produce the 3chain of laminin 5,
which, after gene transfer, were demons-trated to be capable albeit
transitorily of synthesizing it,thereby opening new therapeutic
perspectives for this groupof genodermatoses.54 Animal models using
transgenic miceto simulate human disease, has been contributing
informa-tion relevant to the research of EB.10,12
Some authors consider that research into the corre-lation
between genotype and phenotype is just at the begin-ning34 and that
the expansion of the databases on gene alte-rations is of extreme
importance, since it will enable anever increasingly improved
correlation and perhaps even areclassification of some
genodermatoses based on molecu-lar aspects.38 q
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BC, Lee KS. Characterization of mutations ofthe type VII collagen
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(M-RDEB) from three Korean patients. JDermatol Sci 2001; 26:
125-32.41. Rouan F, Pulkkinen L, Jonkman MF, et al. Novel and de
novoglycine substitution mutations in the type VII collagen
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292: 159-63.43. Klingberg S, Mortimore R, Parkes J, et al. Prenatal
diagnosisof dominant dystrophic epidermolysis bullosa, by COL7A1
mole-cular analysis. Prenat Diagn 2000; 20: 618-22.44. Murata T,
Masunaga T, Shimizu H, et al. Glycine substitutionmutations by
different amino acids in the same codon of COL7A1lead to
heteregeneous clinical phenotypes of dominant
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477-81.45. Betts CM, Posteraro P, Costa AM, et al. Pretibial
dystrophicepidermolysis bullosa: a recessively inherited COL7A1
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Skranes J, TudermanLB, Dahl TG . Generalized dystrophic
epidermolysis bullosa:identification of a novel, homozygous glycine
substitution,G2031S, in exon 73 of COL7A1 in monozygous triplets.Br
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ENDEREO PARA CORRESPONDNCIA: / MAILING ADDRESS:Prof. Dr. Hiram
Larangeira de Almeida Jr.Departamento de Medicina
EspecializadaFaculdade de Medicina da UFPELAv. Duque de Caxias
250Pelotas RS 96030 002 [email protected]
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1. Qual a herana gentica no grupo da EBS? a) autossmica
dominanteb) autossmica recessivac) ligada a X dominanted) ligada a
X recessivae) polignica
2. Com respeito EBS qual dos achados abaixo NO encontrado?
a) degenerao da camada basal b) clivagem sub-epidrmicac) ausncia
de infiltrado inflamatrio d) ausncia de anticorpos no tecidoe)
citlise
3. Quais das protenas abaixo est alterada no grupo daEBS?
a) citoqueratina 14b) citoqueratina 10c) laminina 5 d) colgeno
XVIIe) colgeno VII
4. Qual manifestao extra-cutnea est descrita na EBS?a) atresia
de pilorob) porfria cutnea tardac) paralisia espsticad) distrofia
muscular tardiae) estenose de esfago
5. Em que parte do gen das citoqueratinas basais localiza-sea
maioria das mutaes da EBS- Weber-Cockayne?
a) no incio do segmento 1A b) no final do segmento 2B c) no
segmento no-helicoidal entre 1B e 2Ad) no incio do segmento 2Be) no
final do segmento 1A
6. Qual a herana gentica no grupo da EBJ? a) autossmica
dominanteb) autossmica recessivac) ligada a X dominanted) ligada a
X recessivae) polignica
7. Em qual das protenas abaixo NO foi ainda descritamutao?
a) plectinab) antgeno do penfigide bolhoso de 180 KDc) antgeno
do penfigide bolhoso de 230 KDd) laminina 5e) integrina a6b4
8. Qual manifestao extra-cutnea est descrita na EBJ?a) atresia
de pilorob) megaclonc) estenose de esfagod) distrofia muscular
tardiae) acloridria
9. Assinale a alternativa falsa.a) As mutaes tipo premature
termination codon (PTC),levam interrupo da sntese proteica com
ausncia da protena no tecido e quadro clnico mais graveb) As mutaes
j foram demonstradas nos trs gens quecodificam a laminina 5, no
havendo diferena fenotpicade acordo com o segmento envolvidoc) O
antgeno do penfigide bolhoso de 180 KD um colgeno transmembranosod)
No grupo da EBJ no ocorrem mutaes recurrentese) A integrina a6b4
uma protena transmembranosa
10. Qual protena est envolvida na EBJ tipo Herlitz ou
EBJLetal?
a) integrina a6b4b) colgeno XVII c) laminina 5d) plectinae)
colgeno VII
11. Em qual das formas abaixo da EB apenas um gen estmutado?
a) Epidermlise Bolhosa Simplesb) Epidermlise Bolhosa Juncionalc)
Epidermlise Bolhosa Epidermolticad) Epidermlise Bolhosa Distrficae)
Epidermlise Bolhosa Adquirida
12. Qual alterao foi demostrada na EBJ generalizada atr-fica
benigna?
a) PTC no gen COL17A1b) mutao no gen LAMB 3c) mutao nos gens
ITGA6 e ITGB4d) PTC no gen LAMC2e) PTC no gen COL7A1
13. A laminina 5 um:a) heterodmerob) dmero antiparaleloc)
colgeno transmembranosod) heterotrmeroe) componente da placa
interna do hemidesmossoma.
Questes e Resultado das Questes / Questions and Answers to
Questions
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An bras Dermatol, Rio de Janeiro, 77(5):519-532, set./out.
2002.
d) Na EBD-Dominante a alterao encontrada uma substituio de
glicina no segmento colgenoe) A localizao da substituio de glicina
no contribui para a variabilidade clnica na EBD-Dominante
18. Qual das formas de EB no decorrente do defeito deadeso e sim
por citlise?
a) Epidermlise Bolhosa Simples b) Epidermlise Bolhosa
Juncionalc) Epidermlise Bolhosa Distrficad) Epedermlise Bolhosa
Dermolticae) Epidermlise Bolhosa Adquirida
19. Com relao utilizao do sequenciamento gnico apartir do corion
no diagnstico pr-natal, assinale a alterna-tiva falsa.
a) No necessita de bipsia da peleb) As complicaes ocorrem em 1 %
dos casosc) Pode ser realizado ainda antes da implantaod) Pode ser
utilizado em todas as formas de EBe) Deve ser feito na 20a
semana
20. Assinale a alternativa correta.a) Nas mutaes de novo o risco
para a prole do paciente muito baixo
b) A manipulao ex vivo de clulas de portadores de EBno possvelc)
Modelo animal com ratos transgnicos tem ajudado a esclarecer a
patogenia das diversas formas de EBd) Na EB no ocorrem mutaes de
novoe) O sequenciamento gnico substitui outros exames no diagnstico
da EB
14. Na EBD a clivagem ocorre:a) intraepidrmicab) na lmina
lcidac) acima da lmina densad) na placa interna do hemidesmossomae)
abaixo da lmina densa
15. Assinale a alternativa correta com relao EBD.a) Vrias
protenas encontra-se mutadasb) Apenas uma protena est mutada, o que
leva somentea um quadro clnicoc) A herana pode ser autossmica
dominante ou recessivad) As fibrilas ancorantes esto sempre
ausentese) A mutao leva sempre a PTC
16. Com relao EBD recessiva Halloupeau-Siemens qualalternativa
falsa?
a) A microscopia eletrnica mostra ausncia das fibrilas
ancorantesb) A imuno-histoqumica com anticorpos contra o colgeno 7
negativac) Ocorre uma PTC no gen COL7A1 com conseqente interrupo na
sntese do colgeno VIId) O quadro clnico leve com leses nos joelhos
e cotovelose) Ocorre sinquia nas extremidades
17. Assinale a alternativa corretaa) Na EBD-D no so encontradas
mutaes recorrentesb) Na EBD-Dominante a substituio de glicina
esclarecea herana autossmica dominantec) Nas diferentes formas de
EB as mutaes do tipo PTClevam a quadros clnicos mais leves
Gabarito:Eritema Nodoso Hansnico: atualizao clnica
eteraputica.2002;77 (4):389-407
1.e2.e3.a4.d5.b6.c7.d8.e9.b10.e
11.e12.a13.d14.a15.d16.c17.a18.c19.a20.b