AssessmentsCri du chat syndrome
Cri du chat syndrome
USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 3-hour-old female neonate is being evaluated in the newborn nursery for hypotonia. The infant was born via vaginal delivery to a 25-year-old mother, who did not have a perinatal follow-up. Family history is non-contributory. The patient’s birth weight is below the 5th percentile, height at the 6th percentile, and head circumference at the 3rd percentile. On examination, the child appears hypotonic, and her cry is high-pitched and cat-like. In addition, she has a moon face, hypertelorism, a flat nose, and a prominent nasal bridge. Which of the following is most likely responsible for this patient’s condition?
Content Reviewers:Yifan Xiao, MD
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, 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 are shaped like an “X” with two short arms and two long arms hooked together in the middle by a centromere.
These two short arms are also 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 effect.
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.