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Penile agenesis and testicular agenesis
Penile agenesis is a birth defect in humans, occurring about once in 5–6 million male births, in which a male child is born without a penis.
A partner condition is testicular or gonadal agenesis. This is when a male child is born without gonads and consequently develops no testes. Penile agenesis occurs often as a consequence of Testicular agenesis, but the reverse is never the case. Most patients in both cases have no known family history and usually have an otherwise normal male anatomy.
==Causes==
In an embryo, the conversion of the gonads into testicles in males-to-be and into ovaries in females-to-be is the function of Leydig cells. In testicular agenesis, this process fails. Penile agenesis can be caused by testicular agenesis. Testes are the sole producer of 5-alpha dihydrotestosterone (5aDHT) in the male body. Where the gonads fail to metamorphose into testes, there is no 5aDHT. Therefore, the masculising process that builds the genital tubercle, the precursor to the penis, is stillborn. When this happens, the child is born with both penile and testicular agenesis and is known by the slang term "nullo". This combination of both conditions is estimated to occur in between 20-30 million male births.
Penile agenesis can exist independently after full testicular development; in this case its cause is unknown.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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