| Name | Short description | Estimated numbers |
| Leydig cell hypoplasia (LCH) | The cell in the tested called Leydig cells that usually produce the hormone testosterone are underdeveloped (hypoplasia) or do not develop ('aplasia' or 'agenesis') in a baby in the womb. Children can have a complete and partial form of LCH | Rare |
| STAR/CYP11A1 | 'Steroidogenic acute regulatory protein' (STAR) and CYP11A1 regulate the early stages of steroid production in the testis and sdernal gland. Absence or reduced function of these proteins means that no or less testosterone is produced whilst the baby is in the womb. The child also develops adrenal insufficency, usually in the first few days or weeks of lfe. | Rare |
| 3-Beta or 3β - HSD-2-deficiency | Baby has an absence or reduced function of the 3β -HSD-2 enzyme meaning that less testosterone than usual is produced whilst baby is in the womb | Rare |
| 17alpha hydroxylase | Baby has an absence or reduced function of the 17α hydroxylase enzyme meaning that less testosterone than usual is produced whilst baby is in the womb. This also results in an imbalance in adrenal steroids, which can cause features such as high blood pressure with age. | Rare |
| 17- Beta or 17β - HSD-3 deficiency | Baby has an absence or reduced function of the 17β -HSD-3 enzyme meaning that no or reduced testosterone is produced whilst baby is in the womb. Some young girls with 17-Beta will only be diagnosed in teenage years when they produce testosterone and their body is responding to androgens. | Rare (except in certain geographical areas) |
| 5-alpha or 5α reductase type 2 deficiency | Baby has an absence or reduced function of the 5α reductase enzyme which is usually required to convert testosterone into 'super testosterone' (DHT). Some young girls with 5-alpha will only be diagnosed in teenage years when they produce testosterone and their body is responding to androgens. | Rare (except in certain geographical areas) |
