Normal and abnormal sexual differentiation

Abstract

Human sex development follows an orderly sequence of embryological events coordinated by a cascade of gene expression and hormone production in a time- and concentration-dependent manner. Underpinning the entire process of fetal sex development is the simple mantra: sex chromosomes (XX or XY) dictate the gonadotype (ovary or testis), which then dictates the somatotype (female or male phenotype). The constitutive sex in fetal development is female. Disorders of sex development (DSD) can be classified into three broad categories based on the knowledge of the karyotype: sex chromosome abnormality (e.g. X/XY, mixed gonadal dysgenesis); XX DSD (e.g. congenital adrenal hyperplasia); XY DSD (e.g. partial androgen insensitivity syndrome).