OBJECTIVETo determine the karyotype of a boy suspected to have Cri du Chat syndrome with severe clinical manifestations, and to assess the recurrence risk for his family.

METHODSHigh-resolution GTG banding was performed to analyze the patient and his parents. Fluorescence in situ hybridization (FISH) with Cri du Chat syndrome region probe as well as subregional probes mapped to 5pter, 5qter, 18pter, 18qter, and whole chromosome painting probe 18 was performed to analyze the patient and his parents. In addition, single nucleotide polymorphism-based arrays (SNP-Array) analysis with Affymetrix GeneChip Genome-wide Human SNP Nsp/Sty 6.0 were also performed to analyze the patient.

RESULTSKaryotype analysis indicated that the patient has carried a terminal deletion in 5p. FISH with Cri du Chat syndrome region probe confirmed that D5S23 and D5S721 loci are deleted. SNP-Array has detected a 15 Mb deletion at 5p and a 2 Mb duplication at 18p. FISH with 5p subtelomeric probes and 18p subtelomeric probe further confirmed that the derivative chromosome 5 has derived from a translocation between 5p and 18p, which has given rise to a 46,XY,der(5)t(5;18)(p15.1;p11.31)dn karyotype.

CONCLUSIONA de novo 5p partial deletion in conjunction with a cryptic 18p duplication has been detected in a boy featuring Cri-du-Chat syndrome. His parents, both with negative findings, have a low recurrence risk. For its ability to detect chromosomal imbalance, SNP-Array has a great value for counseling of similar patients and assessment of recurrence risks.