GNRH1 and cartilage-hair hypoplasia: We have previously reported that a peak LH to GnRH stimulation of less than 2.8 IU/L, peak 3-day testosterone cut-off of less than 1.04 μg/L (3.6 nmol/L), and a peak 3-week testosterone cut-off of less than 2.75 μg/L (9.5 nmol/L) gave a sensitivity of 88% and a specificity of 100% for the diagnosis of CHH (39).