Anomalies of human sexual development: clinical aspects and genetic analysis

Disorders of human sex determination result in malformations of the external and internal genitalia. These malformations may vary from sexual ambiguity to complete sex reversal (XY female, XX male). Most of the knowledge of the molecular mechanisms involved in the mammalian sex determination pathway has been derived from the genetic analysis of intersex patients. Clinical management of these conditions critically depends on a precise understanding of their pathophysiology. Until recently, only transcription factors such as SRY, SOX9, DAX1, WT1 and SF1 were known to be responsible for abnormal gonadal development and sexual ambiguity. Gonadal dysgenesis may be isolated, as in the case of SRY mutations, or associated with abnormal development of other organs, such as bone or adrenals, consistent with the spatial expression profile of the disrupted genes (SOX9 or SF1). WNT4 is a new sex-determining signalling molecule. Deletions of Wnt4 were shown to be responsible for the masculinization of XX mouse pups while its duplication and overexpression in humans leads to XY sex reversal. Similarly, duplications of loci containing DAX1 or SOX9 have also been shown to cause sex reversal. These results support the emerging concept that mammalian sex determination is dosage sensitive at multiple steps of its pathway.