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Case Report |
From the * Laboratory for Prenatal Medicine and
Gynecologic Oncology, Department of Medicine, University of Basel, Basel,
Switzerland; the Laboratory for Genetics,
Rasoul Akram Medical Complex, Iran University of Medical Sciences, Tehran,
Iran; and the Department of Urology,
Biomedical Research Center of Medical Sciences University, Tehran, Iran.
| Correspondence to: Ramin Radpour, Laboratory for Prenatal Medicine and Gynecologic Oncology, Women's Hospital/Department of Biomedicine, University of Basel, CH 4031 Basel, Switzerland (e-mail: radpourr{at}uhbs.ch). |
| Received for publication April 2, 2008; accepted for publication November 17, 2008. |
Complete androgen insensitivity syndrome is an X-linked inherited disorder
caused by mutations in the androgen receptor (AR) gene. Using
polymerase chain reaction single-strand DNA conformational polymorphism and
DNA sequencing, we identified a novel nonsense mutation in exon 1 of the
AR gene in 2 Iranian brothers with complete androgen insensitivity
syndrome. Despite a normal 46,XY karyotype, testes, and normal to elevated
plasma levels of testosterone, they were born with female external genitalia
and phenotype. This new mutation, a T-to-A transversion in exon 1, causes
amino acid change of tyrosine (TAT) to ochre stop codon (TAA) at position 514
of the AR polypeptide. The Y514X mutation is located in a region that is
normally important for the formation and function of the hormone receptor
complex. We conclude that the novel Y514X mutation in the androgen receptor is
the cause of complete androgen insensitivity syndrome in this family.
Materials and Methods
Samples—
The study was approved by the institutional review board of Tehran Medical
Sciences University. Blood samples were collected from 2 Iranian brothers with
CAIS. A complete medical history and a physical examination were undertaken.
The genomic DNA samples of all of the subjects were prepared from peripheral
blood lymphocytes according to standard protocols
(Radpour et al, 2007).
AR Gene Mutation Screening— To screen for associated mutations, all exons of the AR gene (1–8) were analyzed by polymerase chain reaction single-strand DNA conformational polymorphism, and results were confirmed by direct sequencing, using previously described conditions (Radpour et al, 2007).
Y Chromosome Microdeletion Analysis— To rule out Y chromosome microdeletions, multiplex polymerase chain reaction was performed to assess Y chromosome microdeletions according to previous studies (Vereb et al, 1997).
Results
After analyzing all exons of the AR gene, we found 1 novel
nonsense mutation in exon 1 of the AR gene.
|
Based on the clinical, hormonal, and karyotype analyses, these patients were diagnosed with CAIS. The patients then underwent laparoscopy, which revealed bilateral testislike structures, each measuring 3.1x2.4x2.1 cm in the 18-year-old, and 2.3x2.0x2.8 cm in the 15-year-old. The gonads were removed. After gonadectomy, hormone substitution therapy was started with estradiol in patches.
These patients were excluded for Y chromosome microdeletions, and all of them had normal karyotype (Figure 1) with a normal ratio of sex hormones (Table). Because CAIS is an X-linked disorder, this new mutation probably is inherited from their mother, but the mother died after the second pregnancy, and we could not determine the origin of this new mutation (Figure 1A).
|
Mutation Screening—
The single-strand DNA conformational polymorphism showed altered mobility
of the fragment corresponding to exon 1 in the 2 patients. Sequence analysis
of these fragments revealed a transversion mutation of 2657T
C in exon 1,
which causes amino acid change of tyrosine (TAT) to ochre stop codon (TAA) at
position 514 of the AR polypeptide (Figure
2). This result was confirmed in the 2 brothers with CAIS. Exons
2–8 of the AR gene had a normal sequence, and exon 1 had 22 CAG
repeats (corresponding to 22 glutamine residues) and 20 GGN repeats
(corresponding to 21 glycine residues).
|
Discussion
The Y514X mutation is located in a region that has the receptor function.
This region is a transcription factor-binding site
(Freedman, 1992), and also is
responsible for binding to the androgen hormone
(McPhaul et al, 1992). This
novel mutation creates a stop codon, leading to the deletion of 405 C-terminus
amino acids of the AR protein, including the end part of exon 1 and all of
exons 2–8. The result of mutation is a truncated nonfunctional protein,
which causes CAIS phenotype in the 2 studied patients.
The Y514X mutation, which is found in the 2 Iranian brothers, is a novel nonconservative substitution (transversion) in a critical region of the AR gene. Our findings suggest that Y514X is responsible for CAIS in this family. Different criteria are used to suggest that a novel mutation is pathogenic: 1) the mutation changes a highly conserved base or disrupts a conserved base pair; 2) the mutation is absent in controls; 3) the mutation has been reported in several pedigrees with similar phenotypes; 4) there is a correlation between the levels of mutated DNA and the severity of symptoms. As previously explained, in this research we studied the first 2 criteria.
In summary, we reported the novel nonsense AR gene mutation in 2 brothers with CAIS and female phenotype.
Acknowledgments
We thank Dr Corina Kohler for her support and comments. We are indebted to the patients for their cooperation.
References
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