Androgen Insensitivity syndrome
Also known as: Androgen Resistance syndrome; Complete Androgen Insensitivity syndrome; Partial Androgen Insensitivity syndrome
Normally, humans have 23 pairs of chromosomes. On fertilisation, the chromosomes combine to give a total of 46 (23 pairs). A female usually has an XX pair of sex chromosomes and a man an XY pair. The female affected by Androgen Insensitivity syndrome (AIS) has an XY pair of sex chromosomes.
Medical text written May 1997 by Dr R Stanhope. Last reviewed August 2010 by Dr R Stanhope, Consultant Paediatric Endocrinologist, The Portland Hospital, London, UK.
An affected infant has no virilisation (development of male sexual characteristics in a female), either during fetal life or during adult life. However, the presence of a testis does not allow the development of any internal female genitalia (no fallopian tubes, uterus or upper two-thirds of the vagina) despite having female external genitalia. The child is born an apparently normal girl. At puberty, the testes produce a large amount of the male hormone testosterone but, in the absence of its receptor, this has no effect. However, testosterone is converted to oestrogen and the girl will have normal breast development, without pubic or axillary hair (under the armpit), and will have no periods (as there is no uterus or vagina). Because the testes are usually found in the abdomen in girls with AIS, there is a risk of them becoming cancerous.
This condition is caused by a genetic defect in the androgen (male hormone) receptor, which enables the male hormone, testosterone, to have its affect.
AIS is not usually diagnosed at birth. The usual presentation is during childhood with a girl who has bilateral inguinal hernias, often containing the testes. Presentation may not be until the middle teenage years, when the girl enters puberty, but has no periods and also no, or minimal, pubic or axillary hair.
The most important part of the management of AIS is the explanation and counselling given to the parents as to what and how to tell the child. This should involve an expert psychologist. Unlike partial androgen insensitivity (see below), the problem is compounded by not being diagnosed at birth. Certainly, full revealment of the diagnosis, including the chromosome abnormality, should be given by the time the child has become an adult.
The testes are usually removed when the diagnosis is made. Puberty should be induced at the normal age and then an accurate assessment of the vaginal size can be made. The assessment of whether to perform a vaginal dilation or a vaginoplasty (an operation to create a vagina) should be made by a gynaecologist who is expert in this field. Certainly, the girl should be counselled not to attempt intercourse until the vagina is an adequate size. There may be longer-term problems such as osteoporosis (see entry Osteoporosis (Juvenile)).
In partial androgen insensitivity, the genetic abnormality in the androgen receptor produces an incomplete block of male hormone action. In this case, the child is usually born with ambiguous genitalia and appears a poorly virilised male (inadequate development of male sexual characteristics). The child may be brought up as either a male or a female and the management very much depends on the severity of the condition in the individual.
This is possible, through chorionic villus sampling at ten to 12 weeks and/or amniocentesis at about 16 weeks, but seldom indicated.
Androgen Insensitivity Syndrome Support Group (AISSG)
AISSG is a peer support group for families and adults affected by androgen insensitivity syndrome and other XY-female conditions. It provides information, holds meetings and runs an online news group. The Group works closely with selected specialist clinicians and researchers to improve the way the conditions are dealt with, medically and psychosocially. It is in touch with several hundred affected families/individuals in the UK and has sister groups in other countries.
Group details last updated January 2016.