Complex sentence: If just delayed the testosterone can "kick-start" endogenous puberty, as demonstrated by testicular enlargement, whereas in the case of KS/HH there will be no testicular enlargement while on testosterone therapy alone.
Split into simpler sentences: If just delayed the testosterone can "kick-start" endogenous puberty proved by testicular enlargement. In a case of KS/HH there will be no testicular enlargement while on testosterone therapy alone.