Disorders of sex development (DSD), are a group of rare congenital conditions. Unlike 46, XX DSD where the cause is usually clear, identification of a cause of XY DSD is often unclear and may be attributed to a disorder of gonadal development, androgen synthesis or androgen action. Reaching a firm diagnosis is challenging and requires expertise within a framework that abides by the highest standards of clinical care. Whilst conditions associated with altered sex development have improved our fundamental understanding of sex and gonadal development, it is debatable whether this improvement in our understanding has improved the lives of people with DSD. Thus, there is a need for more emphasis on showing that a firm diagnosis for conditions associated with DSD is associated with a change in clinical practice that benefits the patient. With the rapid advances in diagnostic technology, there is also a need for clearer guidance on the relative merits of biochemical vs genetic evaluation. The standardization and harmonization of complex genetic and biochemical analyses for rare conditions are issues that require further guidance and it is probably that international networks and registries for rare conditions will facilitate the development of this framework.
Gonadotropin-releasing hormone (GnRH) is essential for the initiation and maintenance of reproductive functions in vertebrates. To date, three distinct paralogue lineages, GnRH1, GnRH2, and GnRH3, have been identified with different functions and regulatory mechanisms. Among them, hypothalamic GnRH1 neurons are classically known as the hypophysiotropic form that is regulated by estrogen feedback. However, the mechanism of action underlying the estrogen-dependent regulation of GnRH1 has been debated, mainly due to the coexpression of low levels of estrogen receptor (ER) genes. In addition, the role of sex steroids in the modulation of GnRH2 and GnRH3 neurons has not been fully elucidated. Using single-cell real-time PCR, we revealed the expression of genes for estrogen, androgen, glucocorticoid, thyroid, and xenobiotic receptors in GnRH1, GnRH2, and GnRH3 neurons in the male Nile tilapia Oreochromis niloticus. We further quantified expression levels of estrogen receptor genes (ERα, ERβ, and ERγ) in three GnRH neuron types in male tilapia of two different social statuses (dominant and subordinate) at the single cell level. In dominant males, GnRH1 mRNA levels were positively proportional to ERγ mRNA levels, while in subordinate males, GnRH2 mRNA levels were positively proportional to ERβ mRNA levels. These results indicate that variations in the expression of nuclear receptors (and possibly steroid sensitivities) among individual GnRH cells may facilitate different physiological processes, such as the promotion of reproductive activities through GnRH1 neurons, and the inhibition of feeding and sexual behaviors through GnRH2 neurons.