A female infant presented at birth with hypotonia, growth retardation, 
distinctive facies, multiple congenital anomalies, and a high-pitched mewing cry 
characteristic of cri du chat syndrome. Chromosome studies from both peripheral 
blood and fibroblasts showed a 46,XX,5p- karyotype. Parental chromosome studies 
revealed that the mother carried an apparently balanced pericentric inversion of 
one chromosome no. 5, 46,XX,inv(5)(p14q35). Meiotic crossing-over in the mother 
within the inverted segment of chromosome 5 gave rise to the unbalanced 
karyotype, 46,XX,rec(5)dup q, inv(5)(p14q35)mat in the infant. A small terminal 
segment of the long arm of chromosome 5 (q35-pter) is duplicated with a deletion 
of the short arm of chromosome 5 (p14-pter), accounting for the features of cri 
du chat syndrome. Fewer than 1 in 200 of cri du chat syndrome cases are due to 
recombination aneusomy arising from a parental inversion of chromosome 5. Some 
of these cases, however, do not have typical cri du chat syndrome, reflecting 
significant duplication of 5q material. These cases are reviewed with the 
present case, and recombination behaviour leading to chromosome imbalance is 
discussed.