Kohva E, Varimo E, Huopio H, et al. - Researchers examined the effects of treatment of constitutional delay of growth and puberty (CDGP) in boys with aromatase inhibitor letrozole (Lz) vs conventional low-dose testosterone (T) on developing seminiferous epithelium. From a randomized, controlled, open-label trial performed at four pediatric centers in Finland between August 2013 and January 2017, they obtained and analyzed sera of 28 boys with CDGP who participated. Random assignment of the patients was done to receive either Lz (2.5 mg/day) (n = 15) or T (1 mg/kg/month) (n = 13) for 6 months. The 28 patients were at least 14 years of age, presented first signs of puberty, required medical attention for CDGP and were appraised at 0, 3, 6 and 12 months of visits. Both treatment groups exhibited a similar decline in anti-Müllerian hormone (AMH) reassuring safety of developing seminiferous epithelium in both treatment approaches. Differing responses to changes in gonadotrophin milieu were observed in the two Sertoli cell-derived markers (AMH and inhibin B (iB)). Observations suggest that treatment-induced gonadotrophin stimulus was inadequate to limit the androgen-mediated reduction in AMH in early puberty, while changes in iB levels were correlated with alterations in gonadotrophin levels. They identified the induction of variable serum Lz levels with a desired puberty-promoting effect using a fixed dose of Lz in all boys