With decreased serum concentrations of total testosterone or free testosterone level, elevated LH and FSH levels should raise suspicion for a diagnosis of hypergonadotropic hypogonadism (primary hypogonadism), and low or inappropriately normal LH and FSH levels suggest hypogonadotropic hypogonadism (secondary hypogonadism) [186,187]. This evidence concerns the gene PLOD1 and hypogonadotropic hypogonadism.