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Ancient gender mismatch: How do XX and XY chromosomes determine our gender?
In our biology, gender is more than a simple process of differentiation. Starting from the initial fertilized egg, each person has been given a unique set of genetic blueprints, and the core element of this blueprint is the combination of chromosomes. Typically, women have two X chromosomes (XX), while men have one X chromosome and one Y chromosome (XY). Sometimes, however, this doesn't work as expected, leading to some rare developmental disorders of the reproductive system, one of which is gonadal dysgenesis.
Gonadal dysgenesis is a congenital developmental disorder characterized by the progressive loss of primordial germ cells during embryonic development.
In this case, some babies develop non-functional fibrous tissue called "strip gonads" instead of normal reproductive tissue. Strip gonads are a product of sterilization that are unable to produce necessary sex hormones, leading to delayed sexual development and infertility. The key to the condition lies in a misalignment of genes—the processes that regulate gonadal development are directed by combinations of chromosomes. Under normal circumstances, this process involves a series of genetic, molecular and morphological changes. As the developing gonads form, the hormones produced affect local and distant receptors, driving ongoing physiological changes.
Types of gonadal dysplasia
The disease is mainly divided into three types:
- Pure gonadal agenesis 46,XX (XX gonadal agenesis)
- Pure gonadal agenesis 46,XY (XY gonadal agenesis)
- Mixed gonadal agenesis (partial gonadal agenesis)
Mixed gonadal agenesis is a difference in sexual development associated with sex chromosome aneuploidy and mosaic of Y chromosomes.
Etiology and pathophysiology
46,XX gonadal agenesis is more common in women and involves the formation of strip-shaped ovaries. In these cases, the ovaries contain non-functional tissue that cannot produce estrogen. When estrogen levels decrease, it affects the hypothalamic-pituitary axis (HPG axis), causing the anterior pituitary gland to secrete increased levels of follicle-stimulating hormone (FSH) and luteinizing hormone (LH), further inhibiting the onset of puberty. 46,XY gonadal dysgenesis mainly affects males, which is determined by the SRY gene on the Y chromosome. Loss of function of the SRY gene will hinder the development of the male reproductive system and cause genital abnormalities.
Mixed gonadal agenesis is a more complex condition involving different combinations of sex chromosomes and gonadal development. Specifically, it may exhibit the development of a normal testicle on one side and strip gonads on the other. The detailed mechanism of this condition is not yet fully understood, but is related to partial expression of the Y chromosome.
Turner syndrome
Turner syndrome is another disorder associated with gonadal agenesis, a chromosomal abnormality characterized by partial or complete loss of the second X chromosome. The condition reduces a woman's chromosome number to 45 instead of the normal 46. Clinical symptoms of Turner syndrome include primary amenorrhea, hypergonadotropic hypogonadism, strip gonads, and lack of fertility.
Turner syndrome is usually diagnosed with delayed onset of puberty and is associated with Müllerian duct structures in early childhood.
Diagnosis and Management
The diagnosis of gonadal dysplasia usually needs to be confirmed through genetic testing, hormone level testing, etc. Appropriate management may include hormone replacement therapy as well as surgical intervention as necessary to address the patient's physical and psychological needs.
The history of gonadal agenesis is also fascinating; Turner syndrome was first independently described by Otto Ulrich in 1930, and 46,XX gonadal agenesis was first reported in 1960. Later, 46,XY gonadal agenesis, or Sweyer syndrome, was also proposed in 1955.
Conclusion
As our understanding of gender development improves, gonadal dysplasia provides an excellent example of the interaction of many different factors. This not only involves how genes determine biological sex, but is also closely related to social and ethical aspects. As we think about these complex biological processes, we must ask ourselves, how are the boundaries of gender defined, and what profound impact does the intersection of different genders and identities have on our society and culture?
