Incomplete androgen insensitivity associated with a thermolabile androgen receptor

Mutational Analysis of Androgen Receptor (AR) Gene in 46,XY Patients with Ambiguous Genitalia and Normal Testosterone Secretion: Endocrinological Characteristics of Three Patients with AR Gene Mutations

The prevalence of abnormalities in androgen receptor gene (AR) among patients with ambiguous genitalia is unknown. Moreover, endocrinological data from prepubertal patients with AR mutation are very limited. Thus, the aim of this study was to examine the prevalence of abnormalities in AR among patients with both ambiguous genitalia, which was defined as a combination of two or more genital abnormalities (i.e. hypospadias, microphallus (penile length < 25 mm), hypoplastic scrotum, bifid scrotum, undescended testis) in this study, and normal to elevated T levels. We also compared the endocrinological data of prepubertal patients with AR mutation and ambiguous genitalia with that of those without the AR mutation. We screened 26 Japanese prepubertal 46,XY patients (five from three families were included) with both ambiguous genitalia and normal to elevated T levels. Mutations in AR were found in three (two of the three were related). Among the 23 patients without mutation in AR, the steroid 5-alpha-reductase 2 gene (SRD5A2) was also examined in eight patients with elevated T/dehydrotestosterone ratio after the hCG (>10) or with undervirilized family members. No mutation in SRD5A2 was found. Characteristics of the three patients with mutation in AR were compared with the 23 patients without mutation. In two patients, basal T levels (0.3, 0.2 ng/ml) and peak T levels after the hCG tests (8.3, 8.5 ng/ml) tended to be higher, and the peak LH/ peak FSH ratios after the GnRH tests (4.6, 4.0) were higher than in patients without mutation, at the ages of 1 yr and 9 mo and 3 yr and 8 mo, respectively. In conclusion, an abnormality in either AR or SRD5A2 was not common among patients with ambiguous genitalia and normal testosterone secretion. Elevated peak LH/peak FSH ratio (≥4) after the GnRH test in addition to detectable basal T levels and elevated peak T levels after the hCG test may infer AR abnormality in prepubertal patients with ambiguous genitalia at the age of one and over, although further study is needed, because our data were limited.

Defects of androgen receptor function: from sex reversal to motor neurone disease

The androgen receptor (AR) is a ligand-dependent DNA transcription factor that binds androgens which cause masculinisation of the developing male fetus. Classical abnormalities of receptor function result in the syndrome of androgen resistance, with resultant failure of normal male differentiation. In more recent years, however, mutations in the AR gene have been described in a number of diverse clinical conditions, from male infertility to prostate and breast cancer through to a form of motor neurone disease (Kennedy's disease). This review discusses the various AR gene mutations found in androgen insensitivity syndrome (AIS) and the other conditions described above, and relates how different mutations, or disruption of different functional domains, contributes to the various phenotypes. Mutations that cause complete AIS usually disrupt the DNA or steroid binding ability of the receptor. In partial AIS, mutations generally decrease receptor affinity for ligand, affect thermostability of the protein, or affect the ability of the receptor to activate transcription of responsive genes. Isolated mutations occur in the steroid binding domain of the receptor in prostate cancer, and many cancers have an identical mutation. Similarly, in the two cases of male breast cancer in which AR gene mutations have been described, the mutations in the DNA binding domain of the receptor are alike. In Kennedy's disease a trinucleotide repeat expansion occurs in exon A of the AR gene, which appears to affect ability of the receptor to bind ligand and activate transcription, although the mechanism of neuronal degeneration remains unknown.