A defect in androgen signalling is most likely due to dysfunction of the androgen receptor (AR) and mutations resulting in a complete lack of function of the AR cause complete androgen insensitivity syndrome (CAIS).48 This presents in the newborn infant as a discordance between a female phenotype and a prenatal karyotype of 46,XY, a postnatal check because of a positive family history, or as inguinal swellings in an otherwise normal girl. The gene discussed is AR; the disease is complete androgen insensitivity syndrome.