cri du chat syndrome
Summary
Cri du chat syndrome (5p- syndrome) is caused by a partial deletion of the short arm of chromosome 5 (5p15.2–15.3). It presents with a high-pitched cat-like cry in infancy, microcephaly, intellectual disability, hypotonia, and characteristic facies (round face, hypertelorism, epicanthal folds, low-set ears).
Detail
**Genetics/Pathophysiology:** Terminal or interstitial deletion of 5p (critical regions 5p15.2 and 5p15.3). Most cases (~80-90%) are de novo, usually on the paternal chromosome; ~10-15% result from unbalanced translocation inherited from a carrier parent (balanced translocation or pericentric inversion), so parental karyotype/FISH is indicated for recurrence risk. Incidence ~1 in 15,000-50,000 live births. Diagnosis: chromosomal microarray (first line), FISH, or karyotype. Deletion of the SEMA5A gene is linked to autism features; deletion of the TERT gene (5p15.33) is associated with telomere shortening; the cat-like cry is mapped to 5p15.3 and thought to result from laryngeal hypoplasia/abnormal laryngeal and CNS development; the cry usually disappears by about age 2.
**Clinical features:** - Cat-like, high-pitched cry (mewing) in infancy, the hallmark - Microcephaly, low birth weight, failure to thrive - Severe intellectual disability, developmental and speech delay - Hypotonia (neonatal), later may develop hypertonia - Facies: round (moon) face, hypertelorism, epicanthal folds, downslanting palpebral fissures, micrognathia, low-set ears, broad nasal bridge - Congenital heart defects (VSD, PDA, ASD) in ~15–30% - Other: simian crease, feeding difficulties, hernias, strabismus, renal anomalies, hyperactivity, self-injurious behavior
**Management/Prognosis:** Supportive and multidisciplinary (early intervention, speech/physical/occupational therapy, cardiac and renal evaluation, feeding support). Many survive to adulthood; mortality is mainly in infancy and related to severe congenital anomalies.
**Boards pearls:** - "Cry of the cat" = French name; deletion of chromosome 5 short arm (5p-) - Classic contiguous-gene-style deletion syndrome (a structural chromosomal abnormality), not an aneuploidy - Distinguish from other deletion syndromes: Wolf-Hirschhorn (4p-, "Greek warrior helmet" facies, seizures), Williams (7q11.23, elfin facies, supravalvular aortic stenosis, hypercalcemia), Prader-Willi/Angelman (15q11-13), DiGeorge (22q11.2, CATCH-22) - Prader-Willi (paternal deletion) vs Angelman (maternal deletion) involve imprinting, which is not a feature of cri du chat - Mnemonic: "Cry of a cat = 5 letters in 'chat'/ 5p"; infant with mewing cry and microcephaly → think 5p deletion
Sources
- First Aid for the USMLE Step 1 (Genetics: Autosomal disorders / Chromosomal deletion syndromes)
- Robbins & Cotran Pathologic Basis of Disease (Genetic Disorders)
- Nelson Textbook of Pediatrics (Chromosomal Abnormalities)
- GeneReviews / NCBI: 5p deletion syndrome (Cri-du-Chat)
- Pathoma (Genetic Disorders)
- Lejeune J et al., 1963, Three cases of partial deletion of the short arm of a 5 chromosome (original description)
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