Cri du Chat Syndrome Pathology
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Direct answer
The mewing cry of a newborn — high-pitched, monochromatic, cat-like — gives cri du chat syndrome its name and its first examination clue: a de novo terminal deletion of the short arm of chromosome 5, with the cry mapped to 5p15.3 and the intellectual disability and dysmorphism to the larger critical region at 5p15.2. Incidence figures between one in 15,000 and one in 50,000 births are quoted across series. The face in infancy is round ("moon face") with hypertelorism, epicanthic folds, down-slanting palpebral fissures and micrognathia; hypotonia gives way to severe developmental and intellectual disability, and congenital heart disease, most often ventricular septal defect, accompanies about a third of cases. Around 10 to 15 per cent arise from a parental balanced translocation, which is why karyotyping the parents changes the recurrence counselling from negligible to substantial.
What you must remember
- The cytogenetics: partial monosomy 5p — terminal deletion with the critical region at 5p15.2; deletions larger than the critical region determine severity, and the cry region sits separately at 5p15.3, a two-region mapping examiners enjoy.
- Incidence and origin: roughly one in 15,000 to one in 50,000 live births; the deletion is de novo in most (about 85 per cent), familial from a parental balanced rearrangement in the remainder.
- The cry: high-pitched, plaintive, cat-like, from laryngeal hypoplasia and softening — it fades with age and is gone by late childhood, so an affected adult no longer shows the sign that named the syndrome.
- Facial gestalt: neonatal round face with full cheeks, hypertelorism, epicanthic folds, down-slanting palpebral fissures, low-set or malformed ears, micrognathia; the face lengthens with age.
- Neurodevelopment: hypotonia in infancy, global developmental delay, severe intellectual disability, speech delay out of proportion to motor delay, hyperactivity and self-injurious or aggressive behaviour in some children.
- Associated malformations: congenital heart disease in about a quarter to a third of cases (ventricular septal defect the classic), plus renal, gastrointestinal and orthopaedic anomalies in a minority.
- Diagnosis: chromosomal microarray is the modern first-line test and defines deletion size; conventional karyotype of the child and both parents identifies translocation carriers; fluorescence in situ hybridisation was the historical tool.
- Counselling: de novo deletion recurrence risk is low (about 1 per cent, allowing for germline mosaicism), while a parental balanced translocation raises recurrence sharply — the number depends on the rearrangement.
Counselling after the deletion is found
A genetics clinic receives a 3-month-old with the cat-like cry, microcephaly and the round facies; microarray confirms a 5p terminal deletion of about 12 megabases. The consultation proceeds in three layers. First, the parents' own chromosomes: karyotypes of both. If neither carries a rearrangement — the common outcome — the deletion was de novo, and the recurrence risk for future pregnancies is near the population baseline, with a small allowance for possible germline mosaicism. If the mother carries a balanced translocation involving 5p, the counselling transforms: each pregnancy carries a substantial risk of an unbalanced outcome, and prenatal diagnosis by chorionic villus sampling or amniocentesis, with the option of preimplantation testing where available in India, enters the conversation.
The third layer is surveillance — echocardiography for the septal defects, renal ultrasound, hearing and vision assessment, and routine Indian immunisation plus genetic-support referral.
Where the exam sets its traps
The first trap is the disappearing cry: examiners ask whether an adult with untreated cri du chat still cries like a cat — no, the laryngeal basis resolves, so the eponym outlives its sign. The second is the inheritance question: candidates answer "always de novo" and lose the translocation minority, which is exactly the group for whom prenatal diagnosis in the next pregnancy matters. The third is regional mapping: the cry and the neurodevelopmental phenotype localize to different sub-bands of 5p15, so a very small deletion can produce the cry with mild disability — the genotype-phenotype correlation the question is fishing for. Finally, distinguish the facial gestalt from Wolf-Hirschhorn (4p): the round face of 5p against the "Greek warrior helmet" profile of 4p is a comparison examiners set deliberately.
Frequently asked questions
Which chromosomal abnormality causes cri du chat syndrome?
A terminal deletion of the short arm of chromosome 5, with the critical region at 5p15.2 for the phenotype and 5p15.3 for the characteristic cry.
Why does the cry disappear with age?
The cat-like cry arises from laryngeal hypoplasia and softening that improve as the larynx grows, so the sign typically vanishes by late childhood.
What proportion of cases follow a parental translocation?
About 10 to 15 per cent result from inheritance of an unbalanced complement from a parent with a balanced translocation, mandating parental karyotyping.
Which congenital heart lesion is most often associated?
Ventricular septal defect is the classic association, with congenital heart disease present in roughly a quarter to a third of patients.
How is the diagnosis confirmed today?
Chromosomal microarray as first line to define the deletion, with conventional karyotyping of the child and parents to detect balanced rearrangements for recurrence-risk counselling.