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Overview of Androgen Insensitivity Syndrome
Androgen Insensitivity Syndrome is a medical condition where there is a failure of the body to recognize, or respond to, the effects of the hormone androgen. And it is mainly due to a chromosomal defect.
Androgen is a male hormone responsible for masculinization, and in the development of the male genitalia such as the scrotum and the penis as well as the production of sperm cells. Together with the mullerian inhibitory hormone, androgens suppress the development of female reproductive organs in the male fetus, thereby allowing the testes to smoothly slide into the scrotum. Depending on the different types of androgen insensitivity syndrome, and their degree of response to androgens, male children usually appear as females.
Children with androgen insensitivity syndrome are genetically male, possessing XY chromosomes. In a normal situation, the X chromosome holds the androgen receptor (AR) gene, which helps the body respond to the effects of androgen. The Y chromosome, on the other hand, is responsible for testicular development and at the same time, suppresses the development of female internal organs such as the fallopian tubes and ovaries. In patients with androgen insensitivity syndrome, the Y chromosome is normal, thus testicular development takes place and the fallopian tubes and ovaries are absent. The problem lies in the X chromosome, where there is an inability to recognize androgen, resulting in undeveloped or underdeveloped male genitalia, and failure of the testes to descend into the scrotum.
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Genetics of Androgen Insensitivity Syndrome
This condition is usually inherited from the mother, through an X-linked recessive pattern of inheritance. Since the defective gene is found in the long arm of chromosome X, female children born to carrier mothers can balance the defect out.
Females carry XX chromosomes, and a defect in one X chromosome may be corrected by another X chromosome which is basically normal. For a male child carrying XY chromosomes, the defective X chromosome remains as it is because the remaining Y chromosome cannot balance the X out. This explains why females are only considered to be carriers of the condition.
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Different Types of Androgen Insensitivity Syndrome
There are different types of androgen insensitivity syndrome, depending on the degree of severity of the defect in the AR gene. More thanh 200 mutations are known.
In complete androgen insensitivity syndrome (CAIS), there is total insensitivity to the effects of androgen, resulting in a male with female external genitals and sterility.
Affected male children present with female external organs with normal looking labia, vagina and clitoris. In partial androgen insensitivity syndrome (PAIS), there is a slight response to androgen and the result is a patient with an ambiguous set of genitalia. For example, males appear slightly feminine with enlarged clitoris, or some could present with small penis size. CAIS and PAIS affected children usually carry the 46,XY karyotype. Patients with mild androgen insensitivity syndrome (MAIS) have male genitals but the sperm production is impaired and there may be the presence of gynecomastia, or the enlargement of male breasts.
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Diagnosis and Treatment
The diagnosis for androgen insensitivity syndrome involves blood tests, determination of hormone levels such as luteinizing hormone and testosterone, and chromosomal analysis. Also, doctors base their diagnosis on the clinical manifestations of the patient. Androgen insensitivity syndrome has no known cure and the management of patients with this particular condition is basically through hormonal replacement, counseling and surgical procedures like orchiectomy and vaginal construction.