GNRH1 and obesity due to melanocortin 4 receptor deficiency: Certain mechanisms have been shown to participate in sperm quality due to obesity, including a malfunctioning of the hypothalamic-pituitary-testicular (HPT) axis, low FSH and LH concentrations [75], and alterations in SHBG synthesis [76] that cause an increase of free testosterone, making it available for conversion to E2, a hormone that inhibits GnRH secretion in the hypothalamus [49].