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- In most populations, the mean ages of onset of puberty are 10.5 years in girls and 11.5 years in boys.
- Girls: The first sign of puberty is most commonly breast development (thelarche), followed by pubic hair (pubarche), and then menarche, which generally occurs 2 to 3 years after thelarche.
- Boys: The first sign is usually testicular enlargement, followed by pubarche and penile growth.
- Precocious puberty has traditionally been defined as physical signs of sexual development before age 8 years in girls and age 9 years in boys (2 to 2.5 standard deviations below the mean age of onset of puberty).
- Guidelines in 1999 by the Pediatric Endocrine Society proposed lowering the age considered to be normal for sexual development in girls to as young as age 6 years in African American girls and age 7 years in Caucasian girls. These guidelines have not been universally adopted.
- When evaluating precocious puberty, the entire clinical picture must be considered, including the rate of pubertal progression and the presence of any neurologic symptoms.
- Occurs in ~1 in 5,000 children
- Up to 10 times more common in girls than boys
- In girls: 80–90% of central precocious puberty is idiopathic.
- In boys: Precocious puberty is more likely to be associated with underlying pathology.
- Only ~50% of boys have idiopathic central precocious puberty.
- Racial differences observed in girls: African American girls may enter puberty 1 year sooner on average than Caucasian girls; racial differences not present in males
- Increased incidence in internationally adopted children and in children born premature or small for gestational age
Genetic causes include the following:
- Familial male precocious puberty (testotoxicosis): sex-limited, autosomal dominant inheritance of luteinizing hormone (LH) receptor activating mutation
- McCune-Albright syndrome: sporadic, postzygotic, somatic mutation in the stimulatory subunit of G-protein receptor; precocious puberty more common in girls
- More recently mutations in kisspeptin (KISS1), kisspeptin receptor (KISS1R), and makorin ring finger protein 3 (MKRN3) genes have been identified as genetic causes of central precocious puberty.
- Central precocious puberty can be associated with central nervous system (CNS) disorders.
- Peripheral precocious puberty
- Arises from peripheral sex hormone sources, including gonadal and adrenal disorders, abdominal or pelvic tumors, or exogenous sex steroids
- Can progress to central precocious puberty due to maturation of the hypothalamic–pituitary axis by sex steroids
- Central precocious puberty (gonadotropin-releasing hormone [GnRH] dependent)
- Associated with gonadotropin (LH and/or follicle-stimulating hormone [FSH]) levels that are elevated beyond the normal prepubertal range; results from activation of hypothalamic–pituitary–gonadal axis
- Physical changes are typically those of normal puberty for a child of that sex.
- Peripheral sex hormone effects (peripheral precocious puberty or GnRH-independent; less common)
- Gonadotropin-independent elevation of sex steroids arising (i) directly from gonads and/or adrenals, (ii) through stimulation of gonads by GnRH-independent mechanism, or (iii) from an exogenous source
- Physical changes reflect predominant excess hormones (estrogenic or androgenic) and are often markedly discordant from normal pubertal development.