Chromosomal Disorders of the Sex Chromosomes
Related to the 23rd Chromosomes:
1. Turner Syndrome (X)
Turner Syndrome is a genetic disorder that affects the development of females. It occurs when an X chromosome is partially or totally missing.
About half of individuals with Turner Syndrome have monosomy X, which means each cell in the individual’s body has only one copy of the X chromosome instead of the usual two sex chromosomes (totally missing).
Turner Syndrome can also occur if one of the sex chromosomes is partially missing or rearranged rather than completely absent. Some women with Turner Syndrome have a chromosomal change in only some of their cells, which is known as mosaicism. Women with Turner Syndrome caused by X chromosome mosaicism are said to have mosaic Turner Syndrome. Often, their signs and symptoms are milder than those of other girls with the condition.
It affects about 1 in every 2,500 girls.
Most cases of Turner Syndrome are not inherited; they are random and caused by nondisjunction.
It can be diagnosed with a special blood test called a karyotype, which counts the number of chromosomes and can identify any that are abnormally shaped or have missing pieces.
Symptoms
(Symptoms can vary because Turner Syndrome is highly variable and can differ dramatically from one person to another):
- Swollen feet and hands
- Short stature
- Heart defects
- Premature ovarian failure
- Infertility
- Normal intelligence
- Learning problems in some subjects
- Kidney problems
- High blood pressure, obesity
- Diabetes mellitus
- Vision problems
- Thyroid problems
- Abnormal bone development
2. XYY Syndrome
This trisomy occurs when males have two copies of the Y chromosome in each of the body’s cells.
Most people with this syndrome have an apparently normal phenotype.
It affects about 1 in every 1,000 boys.
The cause is a random mistake in cellular division.
When the extra chromosome is due to incorrect cell division that takes place early in the development of the embryo, the boy may have a mosaic form of XYY Syndrome. When boys have a mosaic form, they have fewer symptoms.
Symptoms
(Symptoms can vary):
- Tall stature
- Acne
- Learning problems
- Hyperactivity
- Behavior problems
- Very separated eyes
- Lack of muscle tone
- Curved and pink fingers
- Tics
3. Klinefelter Syndrome
Klinefelter Syndrome is a chromosomal condition in boys and men that can affect physical and intellectual development.
Many children with Klinefelter Syndrome, also called XXY Syndrome because they have an extra X chromosome in most of their cells, do not have any signs or symptoms of this disorder, and some do not even know they have it until adulthood.
The XXY chromosomal change, which is the cause of Klinefelter Syndrome, cannot be modified, but medical treatment and work with a therapist can favor the child’s development and help reduce the effects of this syndrome.
Causes
Generally, a person has 46 chromosomes in each cell, divided into 23 pairs, including the pair of sex chromosomes. Chromosomes contain genes, which determine the traits of each individual. Children typically have an X chromosome and a Y chromosome (XY), but children with XXY Syndrome have an extra X chromosome (XXY).
This syndrome is a random error in cell division that occurs when parental reproductive cells are forming.
When a child is born with XXY chromosomes in only some of his cells, he has mosaic Klinefelter Syndrome. Often, boys and men suffering from this form of the syndrome have milder signs and symptoms than those born with XXY chromosomes in all cells.
Symptoms
Babies with Klinefelter Syndrome typically have muscle weakness, reduced muscle strength, and a calm personality.
Children with Klinefelter Syndrome may have some of the following symptoms (or all of them):
- Tall stature and less muscular body
- Wider hips and longer legs and arms
- More developed breasts (a condition called gynecomastia)
- Weaker bones
- Lower energy level
- Smaller testicles and penis
- Delayed puberty or incomplete puberty (some children never get through this stage)
- Less facial and body hair after puberty
Klinefelter Syndrome usually causes the child’s testicles to grow more slowly than in other children. This syndrome prevents the testicles from making normal amounts of sperm and the testosterone hormone.
4. XXX Syndrome
XXX Syndrome, also called Triple X Syndrome or Trisomy X, is a genetic disorder that affects approximately 1 out of 1,000 women.
Women usually have two X chromosomes in all cells (one X chromosome from each parent), but in Trisomy X, women have three X chromosomes.
There is treatment for this syndrome, but it depends on what symptoms are present and their severity.
How This Syndrome Affects Individuals
Not every woman and girl who has this syndrome experiences the same symptoms.
- Many girls and women have no symptoms or only mild symptoms.
- In other cases, the symptoms may be more marked and possibly include developmental delays and learning difficulties.
- Few girls and women with Triple X Syndrome have seizures and renal abnormalities.
If there are significant symptoms, there is an increased risk of:
- Delayed development of speech and language skills
- Learning problems, such as reading difficulties (dyslexia)
- Behavior problems
- Psychological problems, such as anxiety and depression
Causes
As we know, each person has 46 chromosomes organized into 23 pairs, with half from the mother and half from the father.
The pair of sex chromosomes determines the sex of the individual (XX – girl, XY – boy).
Women with Triple X Syndrome have a third X chromosome due to a random error in cell division.
This error can occur before conception or at the beginning of embryo development, resulting in one of these forms of Triple X Syndrome:
- Nondisjunction: In most cases, the mother’s egg cell or the father’s sperm cell splits incorrectly, resulting in an additional X chromosome in the girl. This type of error is called nondisjunction, and all the cells in the girl’s body will have the additional X chromosome.
- Mosaic: Sometimes the additional chromosome is due to incorrect cell division caused by a random event early in the development of the embryo. Women with the mosaic form may have less obvious symptoms.