Diagnostic Genetic Testing by David Bourn

Author:David Bourn
Language: eng
Format: epub
ISBN: 9783030855109
Publisher: Springer International Publishing

AIS: Loss of Function Mutations in the AR Gene

AIS is suspected in individuals who have an X and a Y chromosome, but have some combination of atypical development of the external genitalia (which may be seen at birth), abnormal development in puberty, and infertility. The condition covers an entire spectrum from complete AIS where the external genitalia are apparently typically female, though partial AIS with ambiguous genitalia, to mild AIS with typically male external genitalia. The extent of the effect is at least in some families genetically determined, particularly at the complete end of the spectrum. Some mutations lead to a complete loss of function, while with others the function is impaired to varying degrees, which in turn determines the extent to which typical male development is affected: loss of the androgen receptor protein means loss of response to the androgenic hormones such as testosterone. Female (XX) carriers usually do not show any symptoms. This is one of many disorders that can lead to an individual having intermediate sexual characteristics. The AR gene is thus another example of a gene where different types of mutations (in this case gain of function and loss of function) can give rise to entirely different effects (although there is some overlap in that male patients with SBMA do show signs of androgen insensitivity, including reduced fertility, testicular atrophy and swelling of breast tissue). More than 500 different presumed loss of function mutations have been identified in the AR gene, and sequencing of the entire gene by Sanger or next-generation sequencing is the usual diagnostic approach.

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