Types of Chromosomal Disorders

Chromosome abnormalities usually occur when there is an error in cell division resulting in cells with too few or too many copies of a chromosome. Most chromosome abnormalities originate in the egg or sperm (gametes) but some happen during embryo development or are inherited from a parent.

Cri-du-chat (cat's cry) syndrome, also known as 5p- (5p minus) syndrome, is a chromosomal condition that results when a piece of chromosome 5 is missing. Infants with this condition often have a high-pitched cry that sounds like that of a cat.

Down syndrome is the most common genetic condition in the United States. It was first described in 1866 and is named after John Langdon Down, the doctor who first identified the syndrome. The cause of Down syndrome, also known as trisomy 21, was discovered in 1959.

Jacobsen syndrome is a condition caused by a loss of genetic material from chromosome 11. Because this deletion occurs at the end (terminus) of the long (q) arm of chromosome 11, Jacobsen syndrome is also known as 11q terminal deletion disorder.

Klinefelter syndrome is a chromosomal condition that affects male physical and cognitive development. Its signs and symptoms vary among affected individuals. Affected individuals typically have small testes that do not produce as much testosterone as usual.

Trisomy 13 is a genetic disorder that your baby gets when she has an extra 13th chromosome. In other words, she has three copies of her chromosome 13 when she should have just two. It happens when cells divide abnormally during reproduction, and create extra genetic material on chromosome 13.

A set of chromosomes, as seen under a microscope, is known as a karyotype. Any deviation from the normal karyotype is known as a chromosome abnormality. While some chromosome abnormalities are harmless, some are associated with clinical disorders.

Wolf-Hirschhorn syndrome is caused by a deletion of genetic material near the end of the short (p) arm of chromosome 4. This chromosomal change is sometimes written as 4p-. The size of the deletion varies among affected individuals; studies suggest that larger deletions tend to result in more severe intellectual disability and physical abnormalities than smaller deletions.

Chromosomal genetic disorders occur when chromosomes are partially or completely missing, altered or duplicated. An example of a chromosomal genetic disorder is Down syndrome. Down syndrome is the result of an extra, third copy of chromosome 21 being present in a person.

Trisomy 21, also known as Down syndrome, is the most common chromosomal anomaly in humans and can cause intellectual disabilities and health issues.

Fragile-X syndrome, a chromosomal disorder associated with a fragile site on the end of the X chromosome. The major symptom of the syndrome is diminished mental ability, which may range from mild learning impairment to severe intellectual disability (or mental retardation).

Neurofibromatosis is an inherited disorder of the nervous system in which tumors develop on nerves, leading to a range of complications. Neurofibromas are usually non-cancerous and grow on the nerves of the skin, and sometimes on nerves deeper inside the body. Find out about the different types and treatments.

Prader-Willi syndrome is a genetic condition most known for causing an insatiable appetite. The condition is present at birth and results in physical, intellectual, and behavioral problems in the affected individual.

Rett syndrome is a rare, severe neurological disorder that affects mostly girls. It's usually discovered in the first two years of life, and a child's diagnosis with Rett syndrome can feel overwhelming. Although there's no cure, early identification and treatment may help girls and families who are affected by Rett syndrome.