A group of disorders caused by an extra or missing sex chromosome. This additional or missing genetic information can result in a wide range of developmental and physical differences; however, the characteristics vary greatly from person to person.
What causes sex chromosome aneuploidy?
The average person has 46 chromosomes; males typically have an X and a Y chromosome, while females have two X chromosomes. An individual inherits one chromosome from each parent. An individual with a sex chromosome aneuploidy has an extra or missing sex chromosome. This is usually a mistake that happens at conception by chance and is not inherited.
Types of sex chromosome aneuploidy
Monosomy X (Turner syndrome)
Individuals with monosomy X, or Turner syndrome, are females who are missing an X chromosome. Girls with monosomy X typically look like their parents, but also have a short, thick neck and low ears. They are shorter than other family members. Girls with monosomy X can also have medical health issues including kidney and heart defects. Learning difficulties, motor and language delays are common; however, intelligence is typically in the normal range. Women with monosomy X typically experience delayed puberty and infertility. The type and severity of symptoms varies from one person to another.
In addition to anatomical differences, pregnancies affected with monosomy X often have increased fluid behind the neck (increased nuchal translucency or cystic hygroma) or around the baby (hydrops). This may be identified on first or second trimester ultrasound. These pregnancies are at increased risk for miscarriage and stillbirth. Women carrying these pregnancies may also be at high risk for severe swelling, high blood pressure, and early delivery.
If the pregnancy survives to birth then most girls with monosomy X have a normal life expectancy. Individuals with monosomy X may benefit from extra support in school, hormone therapy, or surgery to correct a birth defect. Genetic testing cannot predict the severity or ultimate level of functioning.
Trisomy X
Individuals with trisomy X (XXX) are females with an extra X chromosome. Individuals with trisomy X look like other family members but are often taller than their siblings. They are not at increased risk for birth defects. Girls with trisomy X are more likely to have developmental delays and learning difficulties; however, intelligence is typically in the normal range. Females with trisomy X usually have typical sexual development and fertility; however, some experience delayed puberty or decreased fertility. Some individuals with trisomy X may have seizures or kidney problems. The type and severity of symptoms varies from one person to another.
Pregnancies affected with trisomy X typically have a normal first and second trimester ultrasound.
Many individuals with trisomy X syndrome do not realize they have the condition. Others may benefit from extra help in school therapies such as speech, occupational, and physical therapies. Genetic testing cannot predict the severity or ultimate level of functioning.
Klinefelter (XXY) syndrome
Individuals with XXY syndrome, or Klinefelter syndrome, are males with an extra X chromosome. Children with Klinefelter syndrome look like other family members but may be taller than their siblings. At birth, infants may have smaller testes. Without treatment, decreased hormone (testosterone) production leads to incomplete puberty, reduced muscle mass, increased breast tissue, and less body and facial hair. Boys with Klinefelter syndrome are more likely to have developmental delays and learning difficulties. Intelligence may be below that of siblings, but within a normal range. Many boys have challenges with social communication or interaction skills and may be diagnosed with autism spectrum disorder. Men with Klinefelter syndrome have incomplete sexual development and infertility. The type and severity of symptoms varies from one person to another. Genetic testing cannot predict the severity or ultimate level of functioning.
Pregnancies affected with Klinefelter syndrome are not at increased risk for birth defects and typically have normal first and second trimester ultrasounds.
Children diagnosed with Klinefelter syndrome may benefit from extra help in school therapies such as speech, occupational, physical therapies, and/or social support. Hormone replacement therapy can enhance puberty and improve bone strength and mood. Many men are not diagnosed until they experience infertility. Sometimes fertility treatment can help men with Klinefelter syndrome to father biological children.
XYY Syndrome
Individuals with XXY syndrome, or Jacobs syndrome, are males with an extra Y chromosome. Children with XYY syndrome look like other family members, but are often taller than their siblings. They are not at increased risk for birth defects. Boys with XYY syndrome are more likely to have developmental delays and learning difficulties; however intelligence is typically in the normal range. Many boys have challenges with social communication or interaction skills and may be diagnosed with autism spectrum disorder. Men with XYY have normal sexual development and fertility. The type and severity of symptoms varies from one person to another.
Pregnancies affected with XYY typically have a normal first and second trimester ultrasound.
Many individuals with XYY syndrome do not realize they have the condition. Others may benefit from extra help in school therapies such as speech, occupational, physical therapies, and/or social support. Genetic testing cannot predict the severity or ultimate level of functioning.
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