A person’s sex development can vary from typical male or female in terms of chromosomes, anatomy or hormones. This section discusses the genetic causes of the most common variations in sex development and their biological implications, focusing on those that are obvious at birth.


  • Scroll down to read more about:

A word on nomenclature

Classifying variation in sex development

Information provided on this website

  • Use the sidebar to read about different kinds of DSD and other variations in sex.



A word on nomenclature

Terminology in this area of biology remains controversial.

One term that is commonly applied to people with mixed or ambiguous sex organs is “intersex”, a term that arose in the mid-20th century. Many people still prefer to use this term, but others contend that it is not a precise term that distinguishes one of the many conditions from another, and that it does not cater well for those whose biological sex is closely aligned to typical male or female.

In 2005, an international group of doctors, scientists and (a few) patient group representatives met in Chicago to discuss management and possible classifications for this range of conditions. This group suggested a more accurate and inclusive term, “Disorder of Sex Development(DSD). At that meeting, DSDs were defined as congenital conditions in which anatomical, chromosomal or gonadal sex is atypical.

Some welcomed the term DSD. It is considered helpful for those seeking access to insurance and medical assistance, as with other medically defined disorders. Some find it helpful to describe their condition as a legitimate disorder with a defined genetic cause. The term DSD allows the medical and scientific community to refer more specifically, accurately and arguably in a less emotive way to individual conditions (47,XXY DSD, 46,XY DSD and so on).

On the other hand, some contend that variant sex development is not a disorder at all, but simply a reflection of the continuum of sex types that exists, similar to height or eye colour. There is some concern that applying the term “disorder” can have long-lasting negative psychological impacts, and they shun the term DSD. Some groups accept the term DSD, but only to denote “Difference in Sex Development”. Some feel that the Chicago meeting did not include enough lay people to support the development of an inclusive terminology, and reject the term DSD for that reason.

What can scientists add to the debate? For scientists, the term DSD, as a professional term, usefully encompasses a broad variety of genetic conditions. Some of these are adequately covered by “intersex”, but other condiditions are DSDs without being intersex conditions. From a logical standpoint, any variation of human biology or anatomy that causes an individual (or person responsible for their welfare) to seek the help of a doctor could be said to be a disorder. From a genetic standpoint, maleness or femaleness are strongly selected traits, and cellular and hormonal mechanisms have evolved to channel embryonic development towards one or the other outcome—a situation that differs from highly variable traits such as height and eye colour.

Nonetheless, we acknowledge that the use of the term “disorder” may to some people imply an ongoing effect on quality of life that may not be accurate, or may have unintended negative psychological ramifications.

In short, there is currently no single term that is considered acceptable to all groups. On this website, readers will frequently encounter the term DSD, which we have found to be a precise and workable term. However, we also choose to use other terminology (such as atypical sex development, variant sex development, and so on) in many places, particularly when referring to conditions that warrant less medical involvement. We have tended to avoid the term “intersex”, mainly due to the risk of that term being confused with “transgender” and/or “trans-sexual”.


Classifying variation in sex development

Typical and atypical sex development covers a very broad spectrum of situations. How should they be classified, at least for the purposes of presenting them in some logical order on this website?

Scientists might classify sex variations according to the type of gene and the biological process affected, for example disruptions of Sertoli cell differentiation, disruptions of gonad formation, hormonal defects, and so on.

Clinicians might make the distinction between chromosomal anomalies, conditions affecting XX individuals and those affecting XY individuals, or they may classify conditions according to whether reproductive organs form atypically, incompletely, or excessively.

We consider that this section of the website is most likely to be referred to by parents or families of newborns who do not have the typical appearance of males or females. For that reason, we have organised the information based on when the visible signs are usually first noticed, rather than presupposing any knowledge of what the underlying cause might be.


Information provided on this website

To provide information relating to different types of variant sex development in a concise, useful and consistent way, we have addressed the following questions for each:

  • What is it called and what are the signs?
  • What caused it?
  • How common is it?
  • What are the consequences?
  • What is the best way forward?

The material provided reflects a combination of our own research data, published research findings from the international scientific community, and information from other publicly available resources. It is intended as a description of the current state of knowledge, not a source of medical advice. Readers are advised to seek the services of a qualified medical practitioner when considering any diagnostic or treatment options. See Disclaimer.



Last updated: 15 July 2015

Edit history: Author P. Koopman 5/11; revised PK 9/12, 5/13, 10/13, 3/14