The gonads of baby are 'instructed' to develop as testes because of a gene on the Y chromosome, but how do the testes really develop?
Name Short description Estimated numbers
Complete Gonadal Dysgenesis (sometimes called Swyer Syndrome) The gonads of a baby in the womb with CGD remain undeveloped, so most of what is left of the gonads at the time of birth are small pieces of connective tissue. Because there are no testes producing AMH, babies will be born with fallopian tubes, a womb and a vagina (both usually less developed). 1/160 000
Partial Gonadal Dysgenesis (PGD) The gonads of a baby in the womb with PGD may develop partially into testes. Parts of the testes will produce testosterone and AMH, and other parts will remain undeveloped (and not produce any hormone.)

Rare (maybe 1/20 000-

1/40 000)

Steroidogenic factor-1 deficiency (SF1) (also known as NR5A1) SF1 is a protein important for the development of the gonads and the adrenal glands. Reduced SF1 function (this means: when SF1 is not working very well) in a baby in the womb may cause absence or incomplete development of the gonads. This is turn will influence how much testosterone and AMH is produced. SF1 is one known case of gonadal dysgenesis. SF1 may also affect the development of the adrenal glands in some very rare circumstances. Rare (amybe 10% of 46, XY DSD)
DAX1 (Duplication of genetic material on the X chromosome in the region that contains the NR0B1 gene)

A baby in the womb with DAX1 has an extra copy of the NR0B1 gene which prevents the formation of male reproductive tissues. DAX1 is a protein (coordinated by the NR0B1 gene) that acts as an 'anti-testis factor', maybe by acting against the SRY gene.

It means that when SRY kickstarts the development of testes, the extra DAX1 proteins will try to stop this. This means that one or bot testes will not develop fully.

Frasier Syndrome Similar circumstances to partial gonadal dysgeneis- children may have some kidney problems in late childhood that become manifest by loss of small amounts of proteins (caused by changes in the Wilms Tumour/WT1 gene, but less likely to have/result in Wilms Tumour) Rare
Denys-Drash Syndrome Similar circumstances to partial gonadal dysgenesis- children have a high risk of kidney cancer and losing protein in their urine in early life (Wilms Tumour/WT1) Rare