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Syndromes of Abnormal Sex Differentiation

I. Introduction

From the Johns Hopkins Children's Center, this booklet is designed to help parents and patients understand intersexuality and the challenges that accompany syndromes of "abnormal" sex differentiation.

Sexual differentiation is a complex process which results in a newborn baby who is either male or female. If errors in development occur, sexual development is abnormal and the sex organs of the baby are malformed. In such cases, individuals may develop both male and female characteristics. This is referred to as intersexuality.

Children born with deviations from normal development of the sex organs can be expected to grow up successfully and to lead enriched lives. However, their problems must be considered carefully. In cases of abnormal sex differentiation, efforts should be made to determine the reason for the abnormality as treatment may vary according to the cause of the disorder. There may also be a need for specific surgical repair and/or hormonal therapy. Finally, it is extremely important for parents and patients to have a good understanding of both the condition of sex differentiation that affects them, as well as possible ways for dealing with the condition. With this approach, patients will be better able to lead a fulfilled life, and to look forward to an education, career, marriage, and parenthood.

This booklet has been prepared to help parents and patients better understand intersexuality and the unique challenges that accompany syndromes of abnormal sex differentiation. We believe that informed individuals are better prepared to face these challenges and are more likely to meet successfully the demands of childhood, adolescence, and adulthood.

First, normal sex differentiation will be described. The understanding of this pattern of development will help patients and their families to understand the problems of ambiguous sex differentiation, which are subsequently outlined. Finally, a glossary of terms and a list of helpful support groups are provided.

II. Normal Sex Differentiation

Human sexual differentiation is a complicated process. In a simple manner, one can describe four major steps which constitute normal sexual differentiation. These four steps are:

  1. Fertilization and determination of genetic sex
  2. Formation of organs common to both sexes
  3. Gonadal differentiation
  4. Differentiation of the internal ducts and external genitalia

Step 1: Fertilization and Determination of Genetic Sex

The first step of sex differentiation takes place at fertilization. An egg from the mother, which contains 23 chromosomes (including an X chromosome), is combined with a sperm from the father, which also contains 23 chromosomes (including either an X or Y chromosome). Therefore, the fertilized egg has either a 46,XX (genetic female) or 46,XY (genetic male) karyotype.

Step 1 in sex differentiation: Determination of genetic sex

Egg (23,X) + Sperm (23,X)=46,XX genetic girl

OR

Egg (23,X) + Sperm (23, Y)=46, XY genetic boy

Step 2: Formation of Organs Common to Both Sexes

The fertilized egg multiplies to form a large number of cells, all of which are similar to each other. However, at specific times during the growth of an embryo, the cells differentiate to form the various organs of the body. Included in this development is the differentiation of the sex organs. At that stage, both 46,XX and 46,XY fetuses have similar sex organs, specifically:

  1. the gonadal ridges
  2. the internal ducts
  3. the external genitalia

a. The gonadal ridges can be easily recognized by 4-5 weeks of gestation. At that time, they already include the undifferentiated germ cells which will later develop into either eggs or sperm. The formation of gonadal ridges similar in both sexes is a prerequisite step to the development of differentiated gonads. This organization of cells into a ridge requires the effects of several genes, such as SF-1, DAX-1, SOX-9, etc. If any one of these genes is non-functional, then there is no formation of a gonadal ridge and therefore no formation of either testes or ovaries.

b. By 6-7 weeks of fetal life, fetuses of both sexes have two sets of internal ducts, the Mullerian (female) ducts and the Wolffian (male) ducts.

c. The external genitalia at 6-7 weeks gestation appear female and include a genital tubercle, the genital folds, urethral folds and a urogenital opening. (see Figure 2)


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Last Updated: 14 March 2016
Reviewed by Harry Croft, MD

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