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- How does external genitalia develop?
The development of external genitalia in both gender occurs from the common
genital primordia. Exposure to androgens determines the differentiation toward
a male phenotype, whereas absence of androgens leads to a female phenotype.
The development of external genitalia in both gender is summarized in the table
given below.Structure Male Female
Genital tubercle Glans penis Clitoris
Urethral (urogenital) folds Shaft of the penis Labia minora
Labioscrotal (urogenital) swelling Scrotum Labia majora
Urogenital sinus Prostate Urethra
Prostatic urethra Lower one-third of vagina- What is the difference between hormonal regulation of development of internal
and external genitalia in a male?
Once bipotential gonad develops into testes, the process of sexual differen-
tiation is initiated by secretion of testosterone and anti-Mullerian hormone
(AMH) by testes. AMH is produced by Sertoli cells by seventh week of ges-
tation and acts in a paracrine manner to cause regression of Mullerian ducts.
Testosterone is secreted by Leydig cells from eighth week of gestation and
causes stabilization and development of Wolffi an structures by its paracrine
action. Differentiation of external genitalia starts by ninth week of gestation
and is accomplished by the endocrine action of testosterone. Virilization of
external genitalia requires high concentration of androgens; however, con-
centration of circulating testosterone is too low to virilize the external geni-
talia during embryogenesis. This is overcome by conversion of testosterone
to dihydrotestosterone which has ten times more affi nity for the androgen
receptor. Other DHT-mediated features of virilization include temporal
recession, dense facial and body hair, male torso and hair in the upper pubic
triangle.- How to grade the degree of genital ambiguity in a child with DSD?
The commonly used scores to assess the degree of genital ambiguity in a child
with DSD are Prader staging system and external masculinization score (EMS).
Prader staging was developed to grade the degree of virilization of external
genitalia in a 46,XX individual and comprises of fi ve stages. External mascu-
linization score (EMS) was developed to grade the degree of under- virilization
of external genitalia in an individual with 46,XY DSD. Although both scores
can be used to grade the genital ambiguity, EMS takes into account all physical9 Disorders of Sex Development