Genetics Behind Cri de Chat
Cri du Chat is a result of the deletion of the end of the short (p) arm in chromosome 5 (5p-). The size of the deletion varies for each infant, but it can be seen that the larger the deletion, the more severe the disabilities and developmental deformities.
Inheritance: For the most part, Cri du chat is not an inherited syndrome and very rarely do you find a history of the disorder in the family. Instead, the deletion most often occurs during the formation of reproductive cells or the early stages of fetal development. The deletion could possibly occur as the chromosome line up at the metaphase plate. If the pairs of chromosones don't line up correctly, or if the chromosome breaks aren't repaired properly then the structure of the chromosome will alter, which could result in the deletion of the p arm on chromosome 5 (Cri du Chat Syndrome). However, about 10 percent of people with cri-du-chat syndrome inherit the chromosome defect from a carrier parent. In this case, the carrier parent has a chromosomal rearrangement called “a balanced translocation,” which means neither genetic material is gained or lost, but a piece of the chromosome changes place with another part of the same, or different, chromosome. For the carrier, this translocation is “balanced” resulting in them being not affected, however once the defect is passed down, the translocation becomes “unbalanced” resulting in a chromosomal rearrangement with extra/ missing genetic material. For Cri du Chat affected individuals, this is a unbalanced translocation of missing genetic material on the short arm of chromosome 5.
Quick facts:
Inheritance: For the most part, Cri du chat is not an inherited syndrome and very rarely do you find a history of the disorder in the family. Instead, the deletion most often occurs during the formation of reproductive cells or the early stages of fetal development. The deletion could possibly occur as the chromosome line up at the metaphase plate. If the pairs of chromosones don't line up correctly, or if the chromosome breaks aren't repaired properly then the structure of the chromosome will alter, which could result in the deletion of the p arm on chromosome 5 (Cri du Chat Syndrome). However, about 10 percent of people with cri-du-chat syndrome inherit the chromosome defect from a carrier parent. In this case, the carrier parent has a chromosomal rearrangement called “a balanced translocation,” which means neither genetic material is gained or lost, but a piece of the chromosome changes place with another part of the same, or different, chromosome. For the carrier, this translocation is “balanced” resulting in them being not affected, however once the defect is passed down, the translocation becomes “unbalanced” resulting in a chromosomal rearrangement with extra/ missing genetic material. For Cri du Chat affected individuals, this is a unbalanced translocation of missing genetic material on the short arm of chromosome 5.
Quick facts:
- It is thought that more girls receive this syndrome than boys
- In 80% of Cri du Chat cases the chromosome carrying the deletion of chromosome 5 is from the father's sperm rather than the mother's egg.
Normal karyotype of chromosomes vs. karyotype of chromosomes with Cri du Chat
Photos taken from: http://www.jax.org/cyto/images/chrs.jpg and
http://learn.genetics.utah.edu/content/disorders/whataregd/cdc/images/criduchat_karyotype.jpg
http://learn.genetics.utah.edu/content/disorders/whataregd/cdc/images/criduchat_karyotype.jpg