GNRH1 and central precocious puberty: Precocious puberty can be further subdivided into central precocious puberty (CPP), due to premature maturation of the HPG axis,[25] and peripheral precocious puberty (PPP), independent of GnRH activity and due to excess sex hormone production from the gonads, adrenal glands, ectopic sites, or exogenous sources.[26] Delayed puberty occurs when an adolescent fails to enter puberty by the age of 13 years in girls and 14 years in boys.[27, 28] Given the spectrum of pubertal timing, the inclusion of data from early puberty studies is also relevant to discussions within this review.