Laboratory Studies
Conventional cytogenetic studies
The size of the 5p deletion may vary from the entire short arm to only 5p15. A small deletion of 5p may be missed using a conventional cytogenetic technique.
High-resolution cytogenetic studies
These look for a small deletion of 5p.
Fluorescence in situ hybridization (FISH)
Molecular cytogenetic studies using FISH allow the diagnosis to be made in patients with very small deletions. FISH uses genetic markers that have been precisely localized to the area of interest.
The absence of a fluorescent signal from either the maternal or paternal chromosome 5p regions indicates monosomy for that chromosomal region.
Fluorescent in situ hybridization (FISH) study of a patient with cri-du-chat syndrome. FISH photograph shows deletion of a locus-specific probe for the cri-du-chat region. Spectrum orange color represents chromosome 5–specific signal and spectrum green is cri-du-chat locus signal. Absence of a green signal indicates monosomy for that region (left, interphase cell; right, metaphase chromosome spread).
A rare case of cri-du-chat syndrome born to a woman carrying a t(11;22)(q23;q11.2) has been diagnosed using FISH-based preimplantation genetic diagnosis. [18]
Chromosome comparative genomic hybridization (CGH)
Chromosome CGH is capable of screening the entire genome for DNA copy-number alterations in a single hybridization. The resolution is limited to approximately 5-10 Mb. The results cannot be directly mapped onto the genome sequence.
Microarray CGH
Microarray CGH uses array elements made from large-insert genomic clones, such as BACs and phage artificial chromosomes (PACs).
This method has sufficient measurement precision to permit reliable detection of single-copy aberrations affecting individual clones.
SNP-based test
A study by Wapner et al indicated that a single-nucleotide polymorphism (SNP)–based prenatal test can accurately screen prenatally for cri-du-chat syndrome and other microdeletion syndromes. The study, which employed 358 plasma samples from pregnant women and 111 artificial plasma mixtures, used a massively multiplexed polymerase chain reaction and the Next-generation Aneuploidy Test Using SNPs (NATUS) algorithm. The detection rate for cri-du-chat syndrome was 100% (24 out of 24 samples), with a 0.24% false-positive rate. Detection rates were also 100% for Prader-Willi, Angelman, and 1p36 deletion syndromes and 97.8% for 22q11.2 deletion syndrome. [19]
Imaging Studies
Skeletal radiography
Findings include the following:
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Microcephaly, retromicrognathia
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Cranial base malformations (reduced cranial base angle and malformed sella turcica and clivus)
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Disproportionately short third, fourth, and fifth metacarpals and disproportionately long second, third, fourth, and fifth proximal phalanges (common)
MRI
Findings include the following:
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Atrophy of the brainstem, atrophic middle cerebellar peduncles and cerebellar white matter
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Pontine hypoplasia has been described [20]
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Possible hypoplasia of cerebellar vermis with enlargement of the cisterna magna and fourth ventricle
Using magnetic resonance imaging (MRI) analysis, a study by Villa et al indicated isolated pontine hypoplasia to be the most common structural brain anomaly in cri-du-chat syndrome. This was followed by vermian hypoplasia, ventricular anomalies, an abnormal basal angle, widening of the cavum sellae, increased white matter signal, corpus callosum anomalies, and cortical development anomalies. The investigators also demonstrated the presence of polymicrogyria and optic nerve hypoplasia. [21]
Echocardiography
This is used to rule out structural cardiac malformations.
Other Tests
See the list below:
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Swallowing study to assess for feeding difficulty
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Comprehensive evaluation for receptive and expressive language (Most children have better receptive language than expressive language.)
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Developmental testing, referral to early intervention, and appropriate school placement
Procedures
See the list below:
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Gastrostomy in infancy to protect the airway in patients with major feeding difficulties
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Infant with cri-du-chat syndrome. Note the round face with full cheeks, hypertelorism, epicanthal folds, and apparently low-set ears.
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Child with cri-du-chat syndrome. Note the hypertonicity, small and narrow face, dropped jaw, and open-mouth expression secondary to facial laxity.
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Fluorescent in situ hybridization (FISH) study of a patient with cri-du-chat syndrome. FISH photograph shows deletion of a locus-specific probe for the cri-du-chat region. Spectrum orange color represents chromosome 5–specific signal and spectrum green is cri-du-chat locus signal. Absence of a green signal indicates monosomy for that region (left, interphase cell; right, metaphase chromosome spread).
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G-banded karyotype [46,XX,del(5)(p13)].
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G-banded karyotype of a carrier father [46,XY,t(5;17)(p13.3;p13)].
