Cri du chat is one of those Step 1 genetics syndromes that’s easy to recognize on a vignette—if you know the handful of signature clues and what they’re really testing. This post breaks it down from chromosome to clinic, with the high-yield associations and “why” behind the findings so you can reason through questions instead of memorizing a list.
What is Cri du chat?
Cri du chat syndrome (French for “cry of the cat”) is a chromosomal deletion syndrome caused by loss of genetic material on the short arm of chromosome 5.
- Classic karyotype shorthand: 5p- (deletion of 5p)
- Inheritance pattern: usually sporadic (de novo)
- A minority are due to a parental balanced translocation → recurrence risk higher than “sporadic”
High-yield one-liner: 5p deletion → cat-like cry + microcephaly + developmental delay.
Step 1 pathophysiology: what does deleting 5p do?
Core mechanism
A chromosomal deletion causes haploinsufficiency (one functional copy isn’t enough) of genes important for:
- Brain development → microcephaly, intellectual disability, hypotonia
- Laryngeal development → high-pitched “cat-like” cry
Why the cry sounds like a cat
The famous cry is linked to laryngeal and epiglottic abnormalities (often described as small larynx, abnormal cartilage development). In vignettes, this presents as:
- High-pitched cry in infancy (often at birth)
- Feeding problems and failure to thrive can accompany it
USMLE often tests that the cry is early and may become less prominent with age—but developmental and cognitive issues persist.
Clinical presentation (the vignette checklist)
Key findings (memorize these)
Most high-yield features:
- High-pitched “cat-like” cry (especially in infancy)
- Microcephaly
- Intellectual disability / developmental delay
- Hypotonia
- Growth retardation / failure to thrive
Common facial features (vignette bait)
You may see descriptions like:
- Round face
- Hypertelorism
- Epicanthal folds
- Micrognathia
- Low-set ears (often mentioned across multiple syndromes—don’t over-anchor on this alone)
Congenital anomalies to know
- Congenital heart disease can occur (nonspecific; don’t force a single lesion unless the question gives one)
- Feeding difficulties and aspiration risk may show up in pediatrics-oriented stems
Diagnosis: what test confirms it?
Best confirmatory testing
- Chromosomal microarray (CMA): best for detecting microdeletions and copy number changes
- FISH: can detect known deletions (e.g., targeted probe for 5p) and is classically referenced in older resources/questions
- Karyotype: may detect larger deletions or translocations, but can miss small deletions
High-yield exam move:
If the question is asking about a microdeletion, CMA is the modern “best” answer. If it’s a classic Step 1-style prompt about “detect deletion of 5p,” they may want FISH.
What else to do after diagnosis (Step 2 angle)
- Consider parental karyotypes to assess for a balanced translocation (recurrence risk counseling)
Management: what do you actually do for patients?
There’s no curative therapy for the deletion. Management is supportive and multidisciplinary:
- Early intervention: PT/OT/speech therapy (biggest long-term impact)
- Feeding support: swallow evaluation, nutrition optimization, manage aspiration risk
- Treat congenital anomalies: cardiology evaluation; surgical/medical management as needed
- Developmental and educational support: individualized education plans (IEPs)
- Genetic counseling: especially if a parent carries a balanced rearrangement
Prognosis: varies by deletion size and comorbidities; many survive into adulthood with persistent developmental challenges.
High-yield associations and testable patterns
“Deletion” vs “trisomy” vs “imprinting” (don’t mix them up)
Cri du chat is a deletion syndrome—not aneuploidy and not imprinting.
| Disorder | Genetic mechanism | Classic clue |
|---|---|---|
| Cri du chat | Deletion 5p | Cat-like cry, microcephaly |
| Down syndrome | Trisomy 21 | AV septal defect, duodenal atresia, upslanting palpebral fissures |
| Edwards | Trisomy 18 | Rocker-bottom feet, clenched fists |
| Patau | Trisomy 13 | Holoprosencephaly, polydactyly |
| DiGeorge | 22q11 deletion | CATCH-22, hypocalcemia |
| Williams | 7q11 deletion | “Elfin” facies, hypercalcemia, friendly demeanor |
| Prader-Willi / Angelman | Imprinting / deletions | Hypotonia → hyperphagia (PWS); seizures + laughter (AS) |
Classic Step 1 stem
A newborn with:
- high-pitched cry
- microcephaly
- developmental delay
- facial dysmorphisms
→ pick chromosome 5p deletion.
“Which genetic test?” stem
- Suspected deletion syndrome → chromosomal microarray
- If they explicitly say “use a probe to detect deletion” → FISH
First Aid cross-references (where it fits)
You’ll typically find Cri du chat under Genetics → Chromosomal disorders (often grouped with deletions like DiGeorge and Williams).
First Aid-style anchor:
- Cri du chat = 5p deletion → cat-like cry, microcephaly, intellectual disability
(Exact page numbers vary by edition, so use your edition’s Genetics/Chromosomal Disorders table.)
Common pitfalls (aka how they trick you)
- Confusing the cat-like cry with “abnormal crying” from neonatal abstinence or neurologic injury.
The exam wants the syndrome pattern: cry + microcephaly + dysmorphism + developmental delay. - Choosing karyotype when the question hints “microdeletion.”
Remember: CMA > karyotype for small deletions. - Assuming it’s inherited.
Most cases are de novo, but balanced translocation in a parent is the recurrence-risk twist.
Rapid review (last 20 seconds before you click “Next”)
- Cause: Deletion of short arm of chromosome 5 (5p-)
- Buzzword: cat-like cry (laryngeal abnormality)
- Other findings: microcephaly, developmental delay/intellectual disability, hypotonia, growth retardation, facial dysmorphism
- Dx: chromosomal microarray (best); FISH if targeted classic question
- Tx: supportive (early intervention, manage feeding/heart defects), genetic counseling