Chromosomal abnormalities are problems with one of the 23 pairs of chromosomes. These are the structures within the body’s cells that hold genes. People have 23 pairs. For each of these pairs, one comes from the mother and the other comes from the father. An abnormality can change the number of chromosomes, their structure, or their makeup.

Down Syndrome

Down syndrome, now known as trisomy 21, is when a child has an extra chromosome.

Physical and mental growth is delayed. Babies tend to be quiet and passive with somewhat limp muscles. Most children have a lower than normal IQ. They tend to have a small head, a broad, flat face with slanting eyes and a short nose. The tongue is large and their ears are small and set low in the head. The hands are short and broad, with a single crease across the palm.

This syndrome can be found before birth during an ultrasound. It is confirmed by testing the infant's chromosomes.

Most children survive to become adults. They will live until 45-55 years of age. IQ levels and school/job progress differ from child to child. Many, but not all, have worsening mental skills and get early-onset dementia.

Fragile X Syndrome

Fragile X syndrome is caused by problems in DNA on the X chromosome. Mothers pass down the syndrome to their children.

Many children have normal IQ levels. The syndrome is more common in boys. It results in delayed growth, large ears, a bulging chin and forehead, and, in boys, large testes after puberty. The joints may be extra flexible. There may also be features of autism. Women may have menopause in their mid 30s.

The syndrome can be found by tests before or after birth. .

Klinefelter Syndrome

Klinefelter syndrome is a problem in which male babies are born with an extra X chromosome (XXY). Most boys have normal or slightly low IQ. Many have speech and reading problems and problems with planning. Most also have problems with language skills. This may lead to problems with social skills and behavior. Most boys are tall with long arms.

Puberty happens at the normal time, but the testes stay small. Facial hair growth is minimal and the breasts may get large. Men and boys are infertile.

The syndrome is not suspected until puberty. This is when most of the symptoms start. Chromosome tests will be done.

Klinefelter Syndrome
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Turner Syndrome

In Turner syndrome, girls are born with one of the two X chromosomes partly or completely missing.

Many newborns with Turner syndrome have swelling on the backs of their hands and tops of their feet. Swelling or loose folds of skin are seen on the back of the neck. Many other abnormalities often happen, such as a webbed neck, a low hairline at the back of the neck, a broad chest with wide-spaced nipples, and poorly grown nails.

Girls with Turner syndrome do not have menstrual cycles. The breasts, vagina, and labia stay childlike. The ovaries do not hold eggs. A girl or woman with Turner syndrome is almost always short. Obesity is common.

Many girls have problems with visual and spatial skills. They also have problems with planning and focus. They tend to score poorly on standard tests and in math. They get average or above average scores on verbal tests. Intellectual disability is not common.

Noonan Syndrome

Noonan syndrome may or may not be inherited. Children with the syndrome have normal chromosomal structure. But they have many features that are like Turner syndrome. Both boys and girls can get this. It is caused by a gene change on chromosome 12.

A child may have webbing of the neck, low-set ears, droopy eyelids, short stature, shortened ring fingers, heart and blood vessel abnormalities, and low IQ. Most people are short. Boys may have underdeveloped testes. In girls, the ovaries may not be active or may stop working. Puberty may be delayed. Infertility is likely.

Triple X

Triple X syndrome is the most common chromosomal abnormality in women. It happens when there are three X chromosomes instead of two. Women have mild or no problems. It is believed that there are many people who go undiagnosed. Those with symptoms tend to have slightly lower IQ and problems with verbal skills. They also may have:

  • Tall stature
  • Low muscle tone
  • Seizures
  • Kidney problems

Sometimes the syndrome causes infertility. But some women with triple X syndrome have given birth to healthy children.

Rare cases of babies with four or even five X chromosomes have been found. The more X chromosomes the girl has, the greater the chance of intellectual disability and physical abnormalities.

XYY Syndrome

XYY syndrome is a problem in which a male baby is born with an extra Y chromosome.

Boys tend to be tall and have problems with language. Their IQ tends to be slightly lower. Many have learning problems, attention deficit disorder, and minor behavioral problems.

These are just a few of the health problems from chromosomal abnormalities. Talk to your doctor if you are worried about symptoms in your child.


Chromosome abnormalities. National Human Genome Research Institute website. Available at: Updated January 6, 2016. Accessed July 30, 2018.

Down syndrome. EBSCO DynaMed Plus website. Available at: Updated March 26, 2018. Accessed July 30, 2018.

Learning about Turner syndrome. National Genome Research Institute website. Available at: Updated September 24, 2013. Accessed July 30, 2018.

Tartaglia NR . A review of trisomy X. Orphanet J Rare Dis. 2010;5:8.

Last reviewed May 2018 by EBSCO Medical Review Board Kathleen A. Barry, MD  Last Updated: 7/30/2018