Cri-du-Chat Syndrome Cytogenetically Cryptic Recombination Aneusomy of Chromosome 5: Implications in Recurrence Risk Estimation.

Cri-du-chat syndrome is caused by haploinsufficiency of the genes on the distal part of the short arm of chromosome 5, and characteristic features include microcephaly, developmental delays, and a distinctive high-pitched mewing cry. Most cri-du-chat syndrome cases result from a sporadic de novo deletion that is associated with a low recurrence risk. On rare occasions, however, cri-du-chat syndrome with 5p monosomy can be accompanied by 5q trisomy. This combination is virtually always associated with parental large pericentric inversions. Among previously reported cri-du-chat syndrome cases with 5p monosomy accompanied by 5q trisomy, the aneusomy of chromosome 5 in all but one case was cytogenetically visible using G-banding. When an accompanying 5q trisomy is detected, a significant recurrence risk is expected. We here report on a patient with cri-du-chat syndrome phenotype who initially exhibited a normal karyotype on G-banding but in whom molecular analysis using multiplex ligation-dependent probe amplification and array comparative genomic hybridization revealed a 5p deletion accompanied by a 5q duplication. Parental chromosomal testing led to the identification of a very large pericentric inversion, of which breakpoints resided at the terminal regions of 5p15.31 and 5q35.1. This information was vital for counseling the family regarding the significantly high recurrence risk.