Humans have 23 pairs of chromosomes. In each pair, one chromosome is inherited from each parent. One of these pairs is referred to as the sex chromosome pair because it is responsible for sex determination.
Sometimes, abnormalities in the structure or number of chromosomes can cause irregularities in the physical and mental development of affected individuals. A sex chromosome disorder is a condition that occurs due to an abnormality involving one or both sex chromosomes. Examples of sex chromosome disorders include Klinefelter syndrome, Turner syndrome, and triple-X syndrome.
How Do Sex Chromosome Disorders Occur?
There are two sex chromosomes that interact with each other to determine the sex of a child: X and Y. Each parent will pass on one sex chromosome to his/her children. Females Inheriting two copies of an X chromosome will lead to a female child, while inheriting one copy of an X chromosome and one copy of a Y chromosome will result in a male child.
Most sex chromosome disorders are not inherited. Rather, they occur due to a random error in cell division. However, with certain sex chromosome disorders, such as Turner syndrome (characterized by a missing partial or whole X chromosome), there is a small percentage of cases that occurs due to inheriting an abnormal sex chromosome.
What Are the Types of Sex Chromosome Abnormalities?
Errors in sex chromosomes can be either structural or numerical. Examples of structural abnormalities include:
- Translocations (when a portion of one chromosome switches places with a portion of a different chromosome)
- Inversion (when a portion of the chromosome breaks off, gets turned upside down and reattaches.
- Rings (when a portion of the chromosome breaks off and forms a ring)
Numerical abnormalities refer to having fewer or more copies of either the X chromosome or the Y chromosome than usual.
Can Sex Chromosome Disorders Be Diagnosed Before Birth?
Throughout pregnancy, doctors will perform routine prenatal screenings and tests to monitor the health of the child. Sometimes, physical abnormalities associated with sex chromosome disorders can be detected during an ultrasound imaging exam. For example, a fetus with Turner syndrome may have extra fluid located at the back of the neck or a visible heart deformity. If this is the case, the doctor may recommend further prenatal testing.
There is now noninvasive prenatal genetic testing technology allowing scientists to analyze DNA belonging to the fetus. The results of this test help doctors understand the risk that the child has a chromosomal abnormality that could affect his or her health. If results from a noninvasive prenatal genetic test reveal that the risk of a sex chromosomal abnormality is high, diagnostic testing can then be performed to provide a definitive result.
What are the Signs and Symptoms of Sex Chromosome Disorders?
Symptoms of sex chromosome disorders will depend on the chromosomes involved and the severity of the abnormality. Some disorders, like Triple X disorder, do not cause any deformities in growth and development, and individuals with the condition may not even know that there is a discrepancy with their sex chromosomes. Other sex chromosome disorders, like Turner syndrome, can cause sterility and learning disabilities.
Where Can I Learn More About Sex Chromosome Disorders?
For those who would like to learn more about sex chromosome disorders, a good place to start is by making an appointment to speak with a genetic counselor. Genetic counselors are trained healthcare professionals that help couples understand the prevalence of various genetic disorders in addition to their personal risk of giving birth to a child with a genetic disorder. The National Human Genome Research Institute is another resource available for more information about chromosomal abnormalities.