Systematization of ambiguous genitalia.

Area of Science:

• Embryology
• Developmental Biology
• Genetics

Background:

• Sex assignment in newborns relies on external genitalia, yet their embryonic origin, particularly the genital tubercle, remains unclear.
• The genital tubercle, precursor to the penis and clitoris, arises from mesenchymal tissue lacking specific androgen receptors, with the initiating signal unknown.

Observation:

• Clinical examination of 114 females with Disorders of Sex Development (DSD) revealed ambiguous genitalia in 73, with 51 undergoing feminizing surgery.
• Intersexuality in 46,XY individuals stems from disruptions in sex steroid hormone pathways or receptors, while in 46,XX females, it's due to excess androgens.

Findings:

• A new hypothesis suggests the genital tubercle derives from 5 sacral somites (sclerotomes, myotomes, angiotomes) during indifferent stages, preceding gonadal and internal organ development.
• The genital tubercle comprises ectodermal (glans), mesodermal (corpora cavernosa), and endodermal (urogenital groove) layers.
• Modified feminizing clitoroplasty preserving neurovascular bundles was performed in females with severe virilization (Prader III-V).

Implications:

• Understanding the genital tubercle's derivation from somites can refine surgical management strategies for intersex disorders.
• This research sheds light on the complex developmental pathways of external genitalia and contributes to the differential diagnosis of DSD.
• Further investigation into the somite-derived origins of the genital tubercle may reveal new therapeutic targets for congenital anomalies.