The 46,XX testicular disorder (or difference) of sexual development (DSD) presents with two X chromosomes in each cell, which is found in genetic females, but these people look like males in every other way. That is, they have a male phenotype. This is also known as 46,XX sex reversal, nonsyndromic 46,XX testicular DSD, XX male syndrome, or XX sex reversal. It occurs in about one in every 20,000 live births.
46,XX testicular DSD people have male genitals, with typically small testes or undescended testes. The urethra may open on the underside of the penis. Some children have ambiguous genitalia that doesn’t look male or female. The majority of children with 46,XX testicular DSD are raised as males and are likely to have a male gender identity.
Why does 46,XX testicular DSD happen?
About 80 per cent of the time, the condition occurs due to the abnormal and random exchange of genetic material between chromosomes. This occurs for no apparent reason as sperm forms in the affected person’s father. The SRY gene is misplaced, but almost always on top of the X chromosome. If the foetus comes from a sperm cell that has an X chromosome belonging to the SRY gene, the child will develop as a male despite having no Y chromosome. This version is called the SRY-positive 46,XX testicular DSD.
The other 20 per cent do not have the SRY gene, which is known as SRY-negative 46,XX testicular DSD. The cause in these cases is unknown, though other genes are known to be involved. Those with SRY-negative are more likely to have ambiguous genitalia than those with the SRY-positive form.
Treatment and management of 46,XX DSD
Treatment and management will start at puberty with testosterone to trigger male sex characteristics to develop like facial hair and a deeper voice. This treatment also prevents breast development. Adults tend to be shorter and are infertile.