Type	Possible causes
Primary (decreased testosterone, increased luteinizing hormone and follicle-stimulating hormone)	Klinefelter syndrome; androgen receptor defects; 5–alpha reductase deficiency; myotonic dystrophy; cryptorchidism; hemochromatosis; mumps orchitis; aging; HIV; AIDS; other chronic diseases
Secondary (decreased testosterone, normal or decreased luteinizing hormone and follicle-stimulating hormone)	Kallmann syndrome; fertile eunuch syndrome; pituitary disorders; HIV; AIDS; other chronic diseases