Cri du chat syndrome is a rare genetic disorder caused by a genetic mutation where a portion of chromosome 5 is deleted, or missing. The name is a French term that refers to the characteristic high-pitched cry of the affected babies, which sounds like the cry of a cat or “le cri du chat”.
Alright, let’s break this down. Our DNA is packaged up into 46 chromosomes, which contains the genes that are pretty much instructions for making proteins. These proteins control everything from growth and development to the day-to-day functioning of the cells. Each of the 46 chromosomes is actually made up of a pair of chromosomes and you get one from each parent, so 23 pairs. Now, these chromosomes have two rod-shaped arms, one short and one long, hooked together in the middle by a centromere. These two short arms are referred to as p arms from the French term “petit” that means small. In cri du chat syndrome, a part of one of the short arms of chromosome 5 is missing and so cri du chat syndrome is also known as 5p deletion syndrome, or 5p minus.
Okay, so 80-85% of the cases of cri du chat syndrome are the result of de novo deletion, which means they occur on their own without being inherited. However, in 10% of the cases, the deletion is inherited from a parent who has a balanced translocation. Translocation means that a part from one chromosome switches places with a part from another chromosome. and it’s balanced when there is no genetic material gained or lost, so the person doesn’t experience any adverse affect. As an example, let’s say this woman has 23 pairs of normal chromosomes. And here is her boyfriend, and in his karyotype we can see that a part of chromosome 5 has switched places with a part of chromosome 11. But he remains normal because no genetic material is gained or lost. But if these two have a baby, the baby will randomly inherit 2 copies of each chromosome, one from mom and one from dad. Now since both mom and dad have two copies of each chromosome, if the dad passes on the translocated chromosome 5, but the normal chromosome 11, the translocated information from chromosome 5 will be lost. So in this case, the balanced translocation in the father will become unbalanced translocation in the child because some genetic material from chromosome 5 is lost and this baby will have cri du chat syndrome.
Alright now symptoms of cri du chat syndrome vary and depend upon the amount of missing genetic material. The most specific feature is obviously the cat-like cry and it’s due to structural abnormalities of the larynx. Surprisingly, someone can have cri du chat syndrome without having this characteristic “meowing”. Also, they usually have characteristic facies with a small, round face with full cheeks, hypertelorism, or increased distance between the eyes, prominent supraorbital arches, which are the bony ridges above the orbits, and epicanthal folds, or skin folds of the upper eyelids that cover the inner angles of the eyes. In addition, the nose is usually flat with a wide nasal bridge, the ears are low-set, there’s dropped jaw due to increased facial laxity, and dental malocclusion, or misalignment of the teeth. Besides abnormalities in the head and neck, It causes congenital heart defects such as ventricular septal defects. There’s also neurological problems including moderate to severe intellectual disability and slower motor development, leading to delayed walking and clumsiness. Other common characteristics of babies with cri du chat syndrome include failure to thrive and hypotonia, or weak muscle tone, which may become hypertonia later in life. These babies tend to have chronic medical problems include feeding problems because they have difficulty swallowing, constipation, and recurrent infections like otitis media, respiratory infections and urinary tract infections.