A 32-year-old woman, gravida 2 para 1, with an uncomplicated prenatal course delivered a 4.1-kg (9-lb) newborn at 39 weeks gestation via spontaneous vaginal delivery. Apgar scores were 8 and 10 at 1 and 5 minutes, respectively. Further evaluation in the newborn nursery shows abnormal sexual differentiation. Karyotype analysis shows a 46,XY genotype. Biopsy of gonadal tissue shows a lack of Sertoli cells but normally functioning Leydig cells. Which of the following phenotypes is most likely to be present?

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11ec160b_3747_db5e_9249_434d5601fcf0_MD0001_00 All early embryos have primitive (undifferentiated) gonads, Wolffian (mesonephric) ducts, and Müllerian (paramesonephric) ducts. The primitive gonads develop from the genital ridges and differentiate into either testes (male) or ovaries (female). This differentiation is a result of the SRY gene on the Y chromosome that codes for testes-determining factor, which allows XY embryos to develop testes from the primitive gonad. In the absence of the Y chromosome, primitive gonads develop into ovaries. The testes contain both Sertoli and Leydig cells: In the absence of Sertoli cells or AMH, the Müllerian ducts develop into the internal female reproductive organs (eg, fallopian tubes, uterus, cervix, upper vagina). Therefore, this infant would develop male internal and external reproductive organs due to the presence of Leydig cells (Choice C). The infant would also have female internal reproductive organs from the lack of Sertoli cells. (Choices A and B) Female internal reproductive organs would develop from a normal XX embryo (or an XY embryo with absence of the SRY gene). The presence of ambiguous or male-type genitalia in genetic females is consistent with androgen excess, as can occur with congenital adrenal hyperplasia due to 21-hydroxylase or 11β-hydroxylase deficiency. (Choice E) The development of only male internal reproductive organs requires normal functioning of both Sertoli and Leydig cells. Ambiguous (undervirilized) genitalia in genetic males can occur with 17-alpha-hydroxylase deficiency. (Choice F) Male internal and external reproductive organs are indicative of normal development of an XY embryo with both Sertoli and Leydig cell function. Educational objective: The SRY gene on the Y chromosome codes for the testes-determining factor, which differentiates the primitive gonads into testes. Sertoli cells produce anti-Müllerian hormone, which causes regression of the Müllerian ducts and suppresses female internal reproductive organ development. Leydig cells produce testosterone, differentiating Wolffian ducts into internal male reproductive organs. Dihydrotestosterone is required for differentiation of the external male genitalia. __________ References: Genetic regulation of mammalian gonad development. (http://www.ncbi.nlm.nih.gov/pubmed/25246082)

A 32-Year-Old Woman, Gravida 2 Para 1, with an Uncomplicated