| Name: | Description: | Size: | Format: | |
|---|---|---|---|---|
| 1.45 MB | Adobe PDF |
Authors
Abstract(s)
Introdução: A Síndrome de Insensibilidade aos Androgénios (SIA), uma doença rara de
hereditariedade recessiva ligada ao X, é causada por mutações no gene que codifica o recetor
dos androgénios (AR). Esta disfunção leva à resistência dos tecidos-alvo aos androgénios,
impedindo a masculinização e virilização normal num indivíduo com a constituição
cromossómica 46,XY. O diagnóstico pode ser feito in utero ou na infância, mas muitos casos
passam despercebidos até à puberdade, quando a amenorreia primária com desenvolvimento
mamário normal e pêlos púbicos e axilares escassos levam ao estudo dessas jovens. A
presença de uma mutação no gene AR é o principal critério diagnóstico de SIA. O objetivo
deste trabalho foi estudar geneticamente uma paciente adulta de fenótipo feminino e com
cariótipo 46,XY.
Materiais e Métodos: A paciente em estudo apresentava aparência feminina normal, mas com
cariótipo XY e ausência de útero e ovários mas com gónada à esquerda em ecografia. Extraiuse
ADN leucocitário da paciente e amplificaram-se os exões 4-8 do gene AR, que foram
sequenciados. Analisou-se a estrutura do ARN mensageiro do AR através da realização de RTPCR
a partir de ARN leucocitário e sequenciação do produto resultante.
Resultados: Foi encontrada uma mutação c.2173+2T>C, localizada na zona doadora de
splicing do intrão 4, com a substituição de uma timina por uma citosina. A sequenciação do
produto de RT-PCR demonstrou uma deleção de 123 nucleótidos do exão 4, com justaposição
do exão 5 ao restante exão 4. A tradução deste transcrito aberrante produz uma proteína AR
com deleção in-frame de 41 aminoácidos, correspondentes aos resíduos 674-714, do domínio
de ligação da testosterona.
Discussão: Confirmou-se o diagnóstico de síndrome de insensibilidade aos androgénios nesta
paciente. A mutação encontrada é a primeira mutação reportada na posição +2 de um intrão
do gene AR. Esta mutação inativou o local de doação de splicing do intrão 4 e iniciou um
mecanismo de splicing alternativo na posição c.2049 do exão 4, e parte do exão foi
eliminada. No recetor dos androgénios, a região deletada corresponde a grande parte da
hélice 3, cuja presença é crítica para a mudança conformacional do recetor que facilita a
entrada dos androgénios no núcleo. A inexistência da hélice 3 explica a ausência de ligação
fisiológica da testosterona ao seu recetor nesta paciente. Após o diagnóstico de SIA, a
abordagem terapêutica assenta no tratamento da densidade mineral óssea mais baixa, na
exérese cirúrgica das gónadas masculinas, e no apoio psicológico e aconselhamento genético.
Palavras-chave: Síndrome de Insensibilidade aos Androgénios; amenorreia primária;
infertilidade; recetor dos androgénios; genética; mutação; testosterona; endocrinologia
Introduction: Androgen Insensitivity Syndrome (AIS), a rare X-linked recessive disorder, is caused by mutations in the gene coding the androgen receptor (AR). Its dysfunction leads to target-tissue resistance to androgens, preventing a normal masculinization and virilization of a 46,XY individual. Diagnosis can be made in utero or during infancy, but many cases go unnoticed until puberty, when primary amenorrhea with normal breast development and scarce axillary and pubic hair lead to assessment of these girls. Demonstration of a mutation in the AR gene is the main diagnostic criteria for AIS. The aim of this study was to genetically study an adult patient with a female phenotype and 46,XY karyotype. Materials and Methods: The patient presented a normal female appearance, but with an XY karyotype and absence of a uterus and ovaries, but with a gonad on the left, demonstrated by ultrasound. Leukocyte DNA was extracted from the patient and exons 4-8 of the AR gene were amplified and then sequenced. The structure of the messenger RNA was analyzed using RTPCR with leukocyte RNA with subsequent sequencing of the resulting product. Results: A c.2173+2T>C mutation was found, located at the splice donor site of intron 4, with the substitution of a thymine for a cytosine. Sequencing of the RT-PCR product demonstrated a 123-nucleotide deletion in exon 4, with exon 5 being spliced directly to the remaining exon 4. Translation of this aberrant transcript produces an AR protein with an in-frame deletion of 41 aminoacids, corresponding to residues 674-714, in the testosterone-binding domain. Discussion: The diagnosis of AIS was confirmed in this patient. This is the first reported mutation at the +2 position of an intron in the AR gene. This mutation inactivated the donor splice region of intron 4 and initiated an alternative splicing at position c.2049 of exon 4, and part of the exon was deleted. In the androgen receptor, the deleted region corresponds to the majority of helix 3, and its presence is critical to the conformational change of the receptor that enables the entry of androgens into the nucleus. The inexistence of helix 3 explains the absence of physiological binding of testosterone to its receptor in this patient. After the diagnosis of AIS, the therapeutic approach is based on the treatment of the lower bone mineral density, in the surgical removal of the male gonads, and in psychological support and genetic counseling.
Introduction: Androgen Insensitivity Syndrome (AIS), a rare X-linked recessive disorder, is caused by mutations in the gene coding the androgen receptor (AR). Its dysfunction leads to target-tissue resistance to androgens, preventing a normal masculinization and virilization of a 46,XY individual. Diagnosis can be made in utero or during infancy, but many cases go unnoticed until puberty, when primary amenorrhea with normal breast development and scarce axillary and pubic hair lead to assessment of these girls. Demonstration of a mutation in the AR gene is the main diagnostic criteria for AIS. The aim of this study was to genetically study an adult patient with a female phenotype and 46,XY karyotype. Materials and Methods: The patient presented a normal female appearance, but with an XY karyotype and absence of a uterus and ovaries, but with a gonad on the left, demonstrated by ultrasound. Leukocyte DNA was extracted from the patient and exons 4-8 of the AR gene were amplified and then sequenced. The structure of the messenger RNA was analyzed using RTPCR with leukocyte RNA with subsequent sequencing of the resulting product. Results: A c.2173+2T>C mutation was found, located at the splice donor site of intron 4, with the substitution of a thymine for a cytosine. Sequencing of the RT-PCR product demonstrated a 123-nucleotide deletion in exon 4, with exon 5 being spliced directly to the remaining exon 4. Translation of this aberrant transcript produces an AR protein with an in-frame deletion of 41 aminoacids, corresponding to residues 674-714, in the testosterone-binding domain. Discussion: The diagnosis of AIS was confirmed in this patient. This is the first reported mutation at the +2 position of an intron in the AR gene. This mutation inactivated the donor splice region of intron 4 and initiated an alternative splicing at position c.2049 of exon 4, and part of the exon was deleted. In the androgen receptor, the deleted region corresponds to the majority of helix 3, and its presence is critical to the conformational change of the receptor that enables the entry of androgens into the nucleus. The inexistence of helix 3 explains the absence of physiological binding of testosterone to its receptor in this patient. After the diagnosis of AIS, the therapeutic approach is based on the treatment of the lower bone mineral density, in the surgical removal of the male gonads, and in psychological support and genetic counseling.
Description
Keywords
Amenorreia Primária Endocrinologia Genética Infertilidade Mutação Recetor dos Androgénios Síndrome de Insensibilidade Aos Androgénios Testosterona