Cri-du-chat syndrome

Diagnosis and Testing

How do I get tested for Cri-du-chat syndrome?

Cri-du-chat syndrome is caused by having missing genetic information, known as a deletion, on a specific area of chromosome 5. If a person has symptoms that raise the suspicion of Cri-du-chat syndrome, or another chromosome disorder, a medical geneticist or other physician familiar with these conditions may order one or more of a few types of genetic tests, typically done on a blood sample, but also able to be performed on saliva, skin or other tissue.

One genetic test able to diagnosis Cri-du-chat syndrome is called a chromosome analysis, or karyotype. In a karyotype, the chromosomes in a cell are chemically treated in a specific way, and then the chromosomes are visualized, counted and arranged into their pairs. Extra or missing whole chromosomes, or extra or missing pieces of a certain size can be detected by karyotype analysis.

Sometimes the chromosome 5 deletion that causes Cri-du-chat syndrome is smaller than what can be detected by karyotype analysis (similar to degree of resolution of a photograph, with some parts of what was photographed being too small to be seen in detail in the photo). A specialized test known as FISH analysis (fluorescent in situ hybridization) may be used to detect a chromosome deletion too small to be detected by a chromosome analysis. FISH for Cri-du-chat syndrome is a specific test to detect only a deletion in the relevant area of chromosome 5, and so this condition must be suspected clinically in order for this test to be ordered. FISH uses specially prepared colored probes that only attach to a specific area of a chromosome. If the probe specific to the chromosome region that is missing in Cri-du-chat syndrome is added to a sample from an individual with Cri-du-chat, then the probe will only attach to one chromosome 5, not both, since the area the probe would normally attach too is missing on one chromosome 5 in the person with Cri-du-chat syndrome. The colored probes can be visualized and counted under a microscope, and a Cri-di-chat syndrome deletion can be detected by absence of a FISH probe attached to both chromosome number 5s in a cell.

Finally, a test called array comparative genomic hybridization, or chromosome microarray analysis, may also be used to diagnose Cri-du-chat syndrome in an individual. In chromosome microarray analysis, a sample is analyzed for areas of deletions (missing genetic material) and duplications (extra genetic material) all along the 23 pairs of chromosomes found in a cell. If an individual with Cri-du-chat syndrome has a chromosome microarray analysis performed, the deletion that causes Cri-du-chat syndrome would be found.

Karyotype analysis, FISH and chromosome microarray analysis are all available through many hospitals and commercial laboratories across the country. A medical geneticist or another physician familiar with this testing could order the most appropriate genetic test for a given individual/family.

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Is there newborn testing for Cri-du-chat syndrome?

Who else in my family should I test for Cri-du-chat syndrome?

Is there newborn testing for Cri-du-chat syndrome?

No, as 2019, Cri-du-chat syndrome is not a condition that is tested for in routine newborn screening. The genetic testing which would detect Cri-du-chat syndrome is only routinely done in individuals when there is reason to suspect the possibility of a chromosome change, either because of the individual's health or development or family history.

If there is reason to suspect that a baby has Cri-du-chat syndrome or another chromosome change, genetic testing would be an option at any age.

The specific conditions included in the general population newborn screening are determined by individual states. More information about newborn screening, including which disorders are included in the newborn screening panel in a particular state, is available at http://www.babysfirsttest.org.

Who else in my family should I test for Cri-du-chat syndrome?

Since Cri-du-chat syndrome usually occurs for the first time in the affected individual, rather than being inherited from a parent, it may not be necessary to test anyone else in the family to determine if they are affected or not unless other individuals have concerning symptoms. However, approximately 15% of individuals with Cri-du-chat syndrome have a parent with a chromosome rearrangement that may increase the likelihood of Cri-du-chat syndrome or another chromosome rearrangement in that person's children. In order for a family to be given information about the chances of recurrence in another child once one child has been diagnosed with Cri-du-chat syndrome, the parents of a child with Cri-du-chat syndrome should be offered genetic testing, typically through a blood test. This will determine if one of the parents has a rearrangement in their genetic material (translocation) that could make it more likely that a subsequent child might also have Cri-du-chat syndrome.

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