Noteworthy, the definitions of POI or POF coined for the adult woman, based on the finding of serum concentrations of FSH >25 or 40 IU/L twice at least 1 month apart, low sex steroid levels and amenorrhoea for at least 4 months in a female aged less than 40 years,7,39,45 cannot be applied in paediatrics: occurrence of low sex steroids and no menstrual cycles reflects the physiological state in prepubertal girls and FSH remains below 25–40 IU/L during most of childhood in girls with primary hypogonadism. This evidence concerns the gene BRD2 and Hypergonadotropic hypogonadism.